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UP Board Notes For Class 8 Science Chapter 7 Conservation Of Plants And Animals

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Conservation Of Plants And Animals Chapter In A Nutshell

  • The flora and fauna of a place together form the biodiversity of a place.
  • The cutting down of trees on a large scale for various purposes is called deforestation.
  • Deforestation occurs due to both natural and man-made causes.
  • One of the major causes of deforestation is the use of trees in the paper industry.
  • It takes about 17 full-grown trees to produce one tonne of paper. Thus, we should save, reuse, and recycle paper.
  • Deforestation has various adverse effects on the environment.
  • The restocking of forests by planting new trees is called reforestation.
  • IUCN (International Union for Conservation of Nature and Natural Resources) has created five categories for the conservation of biodiversity. These categories are extinct, endangered, vulnerable, rare, and critically endangered species.
  • Red Data Book is a source that keeps a record of all endangered plants and animals.
  • The government lays down rules, methods, and policies to protect and conserve forests and animals.
  • Various protected areas like sanctuaries, national parks, and biosphere reserves are earmarked for conservation of biodiversity.
  • The Forest Conservation Act, 1927, and Wildlife Protection Act, of 1972 deal with the conservation of forests and wild animals respectively. The main aim of these acts is to preserve and conserve our biodiversity.
  • Migratory birds fly to faraway areas during a particular time of the year because of inhospitable climatic conditions in their habitat.

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Conservation Of Plants And Animals Important Terms And Definitions

Biodiversity: All the living organisms of an ecosystem are together referred to as biodiversity.
Desertification: Desertification is the process by which fertile land loses fertility and gets converted
into desert as a result of deforestation.
Ecosystem: An ecosystem is an interactive system in which all biotic and abiotic components interact
with each other as well as with the environment.
Endangered Species: The species in danger of extinction due to rapid decline in their number and
change in their habitat are called endangered species.
Endemic Species: The species unique to a particular habitat are called endemic species.
Extinct Species: A species is called an extinct species when the last existing member of the species
dies.
Fauna: All the plant species found in a particular habitat are referred to as fauna.
Flora: All the animal species found in a particular habitat are referred to as flora.
Migration: Migration is the regular or systematic movement of a group of organisms in search of
suitable temporary shelter.
Species: A group of a population capable of interbreeding is called a species.

Deforestation

Answer. A major threat to the survival of plants and animals on the Earth is deforestation. Deforestation has adverse effects on the food chains. Deforestation results in increased levels of carbon dioxide in the atmosphere. This results in an increase in the temperature of the Earth and consequently leads to global warming. A decrease in the number of trees and forests results in decreased rainfall. This disturbs the water cycle which leads to drought. Deforestation is also responsible for the change in the physical properties like nutrient content, texture, etc. of the soil. Deforestation exposes the topsoil to agents like wind and water that are responsible for soil erosion. Deforestation also affects the water-holding capacity of the soil.

Human beings are the main cause of deforestation. Forests are cleared to use land for the cultivation of crops, the construction of houses, roads, factories, etc. Forest fire and drought are some natural causes of deforestation.
Hence, reforestation must be practiced to retain the green wealth for future generations.

Conservation Of Plants And Animals Activity 1

Aim: To list the causes of deforestation and classify them as natural and man-made
Observation:

UP Board Notes for Class 8 Science Chapter 7 Conservation Of Plants And Animals Natural Causes Of Deforestation And Man Made Causes Of Deforestation

Conclusion:
Deforestation occurs due to both natural and man-made causes.

Conservation of Plants and Animals Activity 2

Aim: To list various effects of deforestation on animals
Observation: Effects of deforestation on animals are:
1. Loss of habitat
2. Shortage of food
3. Disturbance of food chain
4. Increased risk of natural calamities and hunters

Conservation of Plants and Animals Objective Type Questions

A. State whether the following statements are true or false.

  1. Habitat destruction is a major threat to biodiversity.
  2. Forests are mostly cut for their leaves.
  3. Deforestation ruins the ecology of a region and destroys a large portion of the life forms that live there.
  4. Forests shelter a variety of plants and animals.
  5. Forest conservation is the management of rivers to save the environment.

Answers:

  1. True
  2. False
  3. True
  4. True
  5. False

B. Fill in the blanks.

  1. The large-scale cutting of trees and clearing of forests is called_______
  2. Deforestation reduces the amount of water in the soil and lowers the______
  3. Depletion of forests leads to a decrease in_______fertility.
  4. If all plants in a forest are cut, it will lead to soil______
  5. Establishing a new forest on land that had been deforested earlier is called_____

Answer:

  1. Deforestation
  2. Water table
  3. Soil
  4. Erosion
  5. Afforestation

Conservation Of Plants And Animals Short Answer Type Questions

A. What do you mean by desertification?

Answer. Soil erosion exposes the lower, hard and rocky layers. This soil has less humus and is less fertile. Gradually the fertile land gets converted into deserts. It is called desertification.

Loss of Biodiversity

Answer. The huge variety of flora and fauna on the earth is termed as biodiversity. Some of the major causes of loss of biodiversity are deforestation, land degradation and overexploitation of resources. Some species of plants and animals are found exclusively in a particular geographical area. Such species are called endemic species. The destruction of habitat or introduction of new species may affect the natural habitat of an endemic species IUCN (International Union for Conservation of Nature and Natural resources) evaluates the status of threat to a species based on available information. It has identified five categories of animals and plants that need protection. A Red Data Book is a record of all threatened species of plants and animals.

Conservation Of Plants And Animals Objective Type Questions

A. State whether the following statements are true or false.

  1. The IUCN Red List has information about species that do not exist.
  2. Endangered animals are not seen on the earth anymore.

Answers: 1. False 2. False

B. Fill in the blanks.

  1. Red data book is a list of______species.
  2. The species found only in a particular area is known as______

Answers: 1. Threatened 2. Endemic species

C. Multiple Choice Questions.

1. What are critically endangered species?

  1. Species having an extremely high risk of becoming extinct.
  2. Species with high chances of moving into the endangered category.
  3. Species with huge populations.
  4. Species that do not exist anymore.

Answer: 1. (1) Species having an extremely high risk of becoming extinct

2. The species that exist in small numbers are called_______

  1. Threatened species
  2. Rare species
  3. Endangered species
  4. Critically Endangered

Answer.(2) Rare species

3. Which of the following bird have become extinct?

  1. Dodo
  2. Pigeon
  3. Bat
  4. Gesse

Answer.(1) Dodo

Conservation Of Plants And Animals Short Answer Type Questions

A. What is biodiversity conservation?

Answer. Biodiversity is protection and scientific management of biodiversity so as to maintain it at its optimum level and derive sustainable benefits for present as well as future generations.

Conservation of Forest and Wildlife

Answer. The Government of India has created some protected areas such as national parks, wildlife sanctuaries and biosphere reserves to protect flora and fauna and their habitats.
National parks are protected land areas preserved in natural conditions to provide natural habitat to wildlife. An example of a national park is Jim Corbett national park, Uttarakhand.
Wildlife sanctuary is an area where only animals are protected and their capturing and killing is strictly prohibited. However permission for collection of minor forest products, harvesting of timber and
cultivation is granted.

A biosphere reserve is a large protected area for the conservation of wildlife, plant and animal resources. The main aim of the biosphere reserves is to conserve biodiversity, maintain ecological balance, and maintain the culture of that particular area. A biosphere reserve may contain National Parks and Sanctuaries. For example, Pachmarhi Biosphere Reserve includes Satpura National Park, Bori Sanctuary and Pachmarhi Wildlife Sanctuary.

Zoological park also referred to as a ‘zoo’, is a place where animals are protected by keeping them in special enclosures and cages for public exhibition. Botanical garden is a place where a wide variety of plants are cultivated for scientific, educational, and ornamental purposes. It often includes a library, a herbarium, greenhouses and an arboretum.

Conservation Of Plants And Animals Objective Type Questions

A. State whether the following statements are true or false.

  1. Kanha National Park is in Madhya Pradesh.
  2. A biosphere reserve is an international designation for conservation.

Answers: 1. True 2. False

B. Multiple-Choice Questions

1. Which of the following biosphere reserves is a part of MAB program?

  1. Nokrek
  2. Pachmarhi
  3. Nanda Devi
  4. Bori

Answers. (3) Nanda Devi

2. Wildlife protection act was enacted in which year?

  1. 1967
  2. 1970
  3. 1992
  4. 1972

Answers. (4) 1972

3. Where is Jaldapara Sanctuary located in India?

  1. (West Bengal
  2. Madhya Pradesh
  3. Maharashtra
  4. Andhra Pradesh

Answers: (4) Andhra Pradesh

C. Fill in the blanks.

  1. Jim Corbett National Park is situated in_____
  2. Gir Sanctuary is located in_______ and is famous for_______

Answer: 1. Uttrakhand 2. Gujarat, lion

Conservation Of Plants And Animals Short Answer Type Questions

A. List some important national parks in India.

Some important national parks in India are:

  • Kanha National Park, Madhya Pradesh
  • Betla National Park, Jharkhand
  • Tadoba National Park, Maharashtra
  • Simplipal National Park, Orissa

B. Name at least seven wild animals of Khangchendzonga National Park, which face the danger of extinction.

Answer. Wild animals of Khangchendzonga National Park which face extinction are snow leopard, clouded
leopard, marbled cat, Himalayan black bear, red panda, Tibetian wild ass, blue sheep, serow, goral, takin, musk deer, and green pigeon.

Conservation Of Plants And Animals Textbook Exercises

1. Fill in the blanks.

  1. A place where animals are protected in an artificial habitat is called a______
  2. Species found only in a particular area are known as_______
  3. Migratory birds fly to faraway places because of_______changes.

Answer: (1) Zoo (2) Endemic species (3) Climatic

2. Differentiate between the following:

  1. Wildlife sanctuary and biosphere reserve
  2. Zoo and wildlife sanctuary
  3. Endangered and extinct species
  4. Flora and fauna

(a) Differences between Wildlife sanctuary and Biosphere reserve are:

Wildlife Sanctuary

A wildlife sanctuary is an area where only animals are protected and their capturing and killing is strictly prohibited.

Biosphere Reserve

A biosphere reserve is a large protected area for the conservation of wildlife, plant, and animal resources.

(b) Differences between Zoo and Wildlife sanctuaries are:

Zoo

A zoological park also referred to as a ‘zoo’, is a place where animals are protected by keeping them in special enclosures and cages for public exhibition.

Wildlife Sanctuary

A wildlife sanctuary is an area where only animals are protected and their capturing and killing is strictly prohibited.

(c) Differences between endangered and extinct species are:

Endangered Species

The species in danger of extinction due to rapid decline in their number and change in their habitat are called endangered species.

Extinct Species

A species is called an extinct species when the last existing member of the species dies.

(d) Differences between flora and fauna are:

Flora
All the plant species found in a particular habitat are referred to a flora.

Fauna

All the animal species found in a particular are referred to a flora.

3. Discuss the effect of deforestation on the following.

  1. Wild animals
  2. Environment
  3. Villages (Rural areas)
  4. Cities (Urban areas)
  5. Earth
  6. The next generation

Answer.

  1. Deforestation destroys the natural habitat of wild animals and thus, they can become endangered.
  2. Deforestation decreases the level of oxygen in the atmosphere. The rainfall and fertility of soil also decrease due to deforestation. As a result, there are increased chances of natural calamities like floods and drought.
  3. Most of the agriculture is done in rural areas. Deforestation leads to a change in soil properties, which in turn affects the agriculture.
  4. In cities, there are many factories and automobiles. Deforestation further pollutes the environment and hence, the life in cities will not be healthy for living.
  5. Deforestation leads to an increase in the temperature of the earth causing global warming. Less trees would result in more soil erosion.
  6. Deforestation leads to climatic changes which has a great effect on the next generation. So, the next generation would not be as prosperous as the previous one.

4. What will happen if

  1. we go on cutting trees?
  2. the habitat of an animal is disturbed?
  3. the top layer of soil is exposed?

Answer.

  1. If we go on cutting trees continuously, rainfall and fertility of the soil will decrease. Hence, there are increased chances of natural calamities such as floods and drought. If the habitat of an animal is disturbed, some of the species will not get appropriate food and shelter and with the passage of time, they will come under the category of endangered species.
  2. If the top layer of the soil is exposed, the soil will have less humus and will become less fertile. Gradually, the land will convert into desert. This is called desertification.

5. Answer in brief

  1. Why should we conserve biodiversity?
  2. Protected forests are also not completely safe for wild animals. Why?
  3. Some tribals depend on the jungle. How?
  4. What are the causes and consequences of deforestation?
  5. What is a Red Data Book?
  6. What do you understand by the term migration?

Answer.

  1. We should conserve biodiversity to save flora and fauna from extinction.
  2. Protected forests are also not completely safe for wild animals because people living in the neighbourhood encroach upon them and harm them.
  3. Certain tribes depend on jungle for food, shelter and fuel.
  4. Human beings are the main cause of deforestation. Forests are cleared to use land for the cultivation of crops, construction of houses, roads, factories etc. Forest fire and drought are some natural causes of deforestation. Deforestation has adverse affects on the food chains. Deforestation results in increased levels of carbon dioxide in the atmosphere. This results in the increase in temperature of the Earth and consequently leads to global warming. Decrease in the number of trees and forests results in decreases rainfall. This disturbs the water cycle which leads to drought. Deforestation is also responsible for the change in the physical properties like nutrient content, texture, etc. of the soil. Deforestation exposes the top soil to agents like wind and water that are responsible for soil erosion. Deforestation also affects the water holding capacity of the soil.
  5. Red Data Book is a record of all threatened species of plants and animals. It is published by the International Union for Conservation of Nature and Natural resources (IUCN), which is now known as World Conservation Union (WCU). The red-listing assessment is a simple logical process to determine the status of threat to a species based on available information.
  6. The seasonal, mass movement of animals from one place to another to escape from extreme cold, to breed or to find food is called migration.

6. In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.

Answer. It is not justified to cut trees for such projects.
When trees are cut down, the level of carbon dioxide in the atmosphere goes up, which results in the increase in temperature and consequently leads to global warming. Trees bring rain. So, the decrease in number of trees results in decreasing rainfall. Cutting down of trees is also responsible for the change in physical properties like nutrient content, texture of the soil.

7. How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you.

Answer.

For maintenance of green wealth in our locality, we shoul

  • Grow more and more trees on both sides of the road.
  • Discourage the cutting of trees.
  • Maintain greenery in the parks of our locality.
  • Water the plants in our locality regularly
  • Convince other people to plant new trees.
  • Take out rallies to create awareness among people.
  • Coordinate with local authorities for proper help.

8. Explain how deforestation leads to reduced rainfall.

Answer. Trees lose water by the process of transpiration. This water contributes a lot towards atmospheric moisture. Thus, green plants have major contribution in precipitation and rainfall pattern. So,\ deforestation leads to reduced rainfall.

9. Find out about the national parks in your state. Identify and show their locations in the outline map of India.

Some of the national parks of India are marked on the map

UP Board Notes for Class 8 Science Chapter 7 Conservation Of Plants And Animals Some of the national parks of India are marked in the map

10. Why should paper be saved? Prepare a list of ways by which you can save paper.

Answer. By wasting paper products, we waste forests. The more paper we use, the more trees we need to cut down to feed our insatiable appetite for paper. In order to reduce deforestation, we must learn to recycle used paper, efficiently and economically.

Ways by which paper can be saved are:

  • Collect used paper and recycle it.
  • Use both sides of a paper for writing.
  • Spread awareness about the importance of paper.
  • Use paper intelligently.
  • Old envelopes can also be used for doing the rough work.
  • Schools should encourage online submission of reports and assignments so that papers can be saved.
  • Don’t take a printout unless it is absolutely necessary.

11. Complete the word puzzle.

Down:

  1. Species on the verge of extinction.
  2. A book carrying information about endangered species.
  3. Consequence of deforestation.

Across

  1. Species which have vanished.
  2. Species found only in a particular habitat.
  3. Variety of plants, animals, and micro-organisms found in an area.

UP Board Notes for Class 8 Science Chapter 7 Conservation Of Plants And Animals Cross And Down

Down:
1. Endangered
2. Red data book
5. Deserts
Across:
1. Extinct
3. Endemic
4. Biodiversity

Conservation of Plants and Animals Hots corner

A. People living in hilly areas are cutting down a lot of trees for their daily needs and agricultural purposes. After a few years they face a lot of landslides in their area. What do you think is the reason behind it?

Answer. Cutting down of trees on a large scale is one of the main reasons behind the landslides. The roots of the trees hold the soil. As a result of deforestation, the soil gets loose and runs off during heavy rain resulting in landslides.

B. Suppose in a forest the number of carnivorous animals suddenly increases than the number of herbivore animals. What will be the consequences?

Answer. If the number of carnivorous animals increases as compared to the number of herbivore animals, then there will be a shortage of food for the carnivores and soon they will die due to hunger. There will be a bloom of plants also.

Practice exercise

A. Fill in the blanks.

  1. The Indian Giant Squirrel is_______ fauna.
  2. A species with a very small population on the earth is called_______species
  3. ______ is a protected area where only animals are protected.
  4. Project Tiger was launched in India in the year_______
  5. A_______ is much larger than a national park or a sanctuary.

Answers:

  1. Endemic
  2. Rare
  3. Wildlife Sanctuary
  4. 1973
  5. Biosphere Reserve

B. State whether the following statements are true or false.

  1. Deforestation results in desertification.
  2. Deforestation has disastrous effects on the biodiversity of a place.
  3. Siberian cranes come to India during winter.
  4. Man is not responsible for deforestation.
  5. Climatic changes do not affect biodiversity.

Answer:

  1. True
  2. True
  3. True
  4. False
  5. False

C. Answer the following in one word.

  1. Asiatic lion and pink pigeon belong to which IUCN category?
  2. Which form of wood is used to make paper?
  3. Name an extinct flightless bird.
  4. Which term is used for species that are likely to become endangered shortly?
  5. Which bird covers the longest migration distance?

Answer:

  1. Endangered
  2. Pulp
  3. Dodo
  4. Vulnerable
  5. Arctic tern

Conservation Of Plants And Animals Short Answer Questions

1. Write a short note on biosphere reserve.

Answer. The concept of a Biosphere Reserve has been evolved by the Man and Biosphere (MBA) program of UNESCO. In a biosphere reserve, multiple land use is allowed by designating various zones such as core, buffer zone, and manipulation zone. In a biosphere reserve, wild population, traditional lifestyle of tribals, and varied domesticated plant and animal genetic resources are protected.

 

UP Board Notes For Class 8 Science Chapter 5 Coal And Petroleum Science

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Coal And Petroleum Science Chapter In A Nutshell

  • Resources obtained from nature are known as natural resources, for example, air, soil, minerals, etc.
  • Natural resources can be classified into two types: exhaustible and inexhaustible natural resources. Exhaustible natural resources are present in a limited quantity, cannot be replaced within a reasonable period of time and can be exhausted by human activities. Petroleum, coal, forests, etc., are examples of exhaustible natural resources.
  • Inexhaustible natural resources are present n an unlimited quantity, can be replaced within a reasonable period of time and cannot be exhausted by human activities, for example, air and sunlight
  • Coal is an exhaustible natural resource. It is formed by the decomposition of plants buried under the Earth in conditions of high pressure and extreme temperatures. The process of conversion of dead vegetation into coal is called carbonisation.
  • There are four varieties of coal namely, peat Ignite, bituminous and anthracite.
  • Coal deposits in India are found in Jharkhand, Orissa, Madhya Pradesh and West Bengal.
  • Coal is used as a domestic and industrial fuel, in the manufacturing of synthetic petrol and synthetic natural gas, extraction of metals from their ores, thermal power plants and is
  • Petroleum, another exhaustible natural resource, is formed from the dead bodies of organisms that settled at the bottom of the sea millions of years ago and got covered with layers of sand and clay. In the absence of air and under high pressure and temperature, these dead bodies get converted into petroleum.
  • Oil wells in India are located in Ankleshwar and Kalol in Gujarat; Rudrasagar and Lake in Assam; Bombay High; and deltas of Cauvery, Krishna and Godavari rivers.
  • The process of separating various constituents of petroleum is known as refining and it is done in the petroleum refineries.
  • In India, Petroleum refineries are located at Mumbai, Chennai, Mathura, Barauni. Digboi, Guwahati, Haldia, etc.
  • Petrol and diesel, which are obtained from petroleum, are used as fuel. Petroleum is used for making lubricants, medicines, ointments, metalling roads, etc.
  • natural Gas, another exhaustible natural resource, is formed by the decomposition of vegetable matter lying underwater in the conditions of high temperature, high pressure and absence of oxygen.
  • Natu-‘al gas is used as a domestic and industrial fuel, in fertiliser industry and as fuel for the transport industry.
    natural gas is a clean fuel and produces less pollution. It has high calorific value.
  • Many useful substances, known as petrochemicals, are obtained from petroleum and natural gas. They are used in the manufacturing of detergents, man-made fibres, plastics, etc.
    Since fossil fuels are exhaustible sources of energy, we should not waste and misuse fossil fuels. One should move towards the alternative or renewable sources of energy such as solar, wind and biomass energy.

Read and Learn More UP Board Notes for Class 8 Science

Coal And Petroleum Science Important Terms And Definitions

Fuels: A substance that can be used to produce neat at a reasonable cost is called a fuel.
Fossil fuels: Fuels formed from the dead remains of plants and animals, w hich remained buried deep under the Earth for millions of years. Coal, petroleum and natural gas are fossil fuels.
Coal: It is a hard, black or brownish-black sedimentary rock containing more than 50% of carbon by weight. Along with carbon, it contains hydrogen, oxygen, nitrogen, sulphur, etc.
Crude oil: It is a mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and other particles.
Petroleum: It is a fossil fuel, which is dark, viscous, oily, strong smelling and known as black gold. Petrol and diesel are obtained from petroleum.
Natural gas: It is a very important fossil fuel, which mainly consists of methane and occurs deep under the cost of the Earth either alone or along with crude oil. It is stored under high pressure and is hence, called Compressed Natural Gas or CNG.
Coal gas: It s obtained during the process of making coke from coal. Coal gas is a mixture of hydrogen, methane, carbon monoxide and other gases.
Coal tar: It is a thick, black, opaque fluid, which is obtained as a by-product of the process of manufacturing coke.
Coke: It is a hard, dry fuel produced by heating coal to a very high temperature in the absence of air. It has very high carbon content and is used as a fuel.

Types of Natural Resources

Resources obtained from nature are known as natural resources, for example, air, water, minerals, etc. Natural resources are of two types: exhaustible and inexhaustible natural resources. Petroleum, coal, forests, etc. are examples of exhaustible natural resources and air and sunlight are inexhaustible naturals! resources.

Coal And Petroleum Science Activity 2

Aim: To show that as the number of consumers increases, the quantity of resources available decreases.
Procedure:
1. Fill a few containers with popcorn, peanuts, roasted gram and toffees.
2. Divide students into groups of seven each.
3. Further divide each group into three sub-groups containing 1,2 and 4 students.
4. Label these sub-groups as first, second and third generations respectively.
5. Put one full container for each group on a table.
6. Ask students or consumers of the first geneation to eat from the containers.
7. Next, ask students or consumers of the second generation to eat from the containers.
8. Next, ask students or consumers of the third generation to eat from the containers.

Observation: The quantity’ of the food available dwindled with each generation of students or consumers.
Conclusion: With each generation, the number of consumers increase and the quantity of resources available becomes less.

Coal And Petroleum Science Objective Type Questions

A. State whether the following statements are true or false.

1. Fossil fuels are formed from dead remains of plants and animals.
2. Forests are inexhaustible natural resources.
3. Exhaustible natural resources can be replenished within a reasonable amourt of time.
4. Coal is an exhaustible natural resource.
5. CNG is a man-made fuel.

Answers: 1. True 2. False 3. False 4. True 5. False

B. Fill in the blanks.

1. A substance that can be used to produce heat energy at a reasonable cost is known as a____
2._____and are exhaustible natural resources.
3. ____ is formed by the decomposition of plants buried under the Earth in conditions of high Dressure and extreme temperatures.
4.____natural resources are present in a limited quantity and can be exhausted by human activities.

Answers: 1. Fuel 2. Petroleum, coal, forests 3. Coal 4. Exhaustible

Coal

Answers. Coal is a hard, black or brownish-black sedimentary rock containing more than 50% carbon by weight Coal comes in four varieties — peat lignite, bituminous and anthracite. Plants that remain buried under the Earth in conditions of high pressure and extreme temperatures over millions of years converts into coal. This process is called carbonisation. Coal is used as a domestic and industrial fuel. It is processed to form coal gas, coal tar and coke. Coal gas is obtained during the process of making coke from coal.

Coal And Petroleum Science Objective Type Questions

A. State whether the following statements are true or false.

1. Coal contains more than 50% of carbon by weight.
2. Coal tar is formed from petroleum.
3. Bituminous is a variety of coal.
4. Coal is processed to form coal tar.

Answers: 1. True 2. False 3. True 4. True

B. Fill in the blanks.

1. Coal is formed over millions of years by decomposition of plants buried under the Earth in conditions of high____ and____
2.______is obtained during the process of making coke from coal.
3.Coal is used as a_____ and____ fuel.

Coal And Petroleum Science Short Answer Type Questions

A. What is coal tar used for?

Answers. Coal tar is a mixture of about 200 substances. It is used for metalling roads and in the manufacturing of synthetic dyes, perfumes, explosives, photographic materials, plastics, paints, roofing materials, naphthalene balls, etc.

B What is carbonisation?

Answers. The Process of formation of coal by the decomposition of plants buried under the each in conditions of high pressure and extreme temperatures is called carbonisation.

Coal And Petroleum Science Long Answer Type Questions

A. Give few uses of coal.

Answers. Coal is used as a fuel in homes and in industries to run steam engines and to produce electricity in thermal power plants. Products obtained from coal are coke, coal gas and coal tar. Coke is used in the manufacture of steel and extraction of metals. Coal gas is used as a fuel and more than 200 products are obtained from coal tar. These products are used for manufacturing synthetic dyes, paints, perfumes, naphthalene balls, photographic materials, etc.

Petroleum

Answers. Petroleum is a dark, viscous, oily, strong-smelling liquid, which is also known as black gold. Petrol and diesel are obtained from petroleum. Petroleum is formed from the organisms whose dead bodies settled at the bottom of seas or oceans and got covered with layers of sand and clay. In the absence of air and under high pressure and temperature, these dead bsdies got converted into petroleum. The process of separating various constituents of petroleum is known as refining and t is done in petroleum refineries.

UP Board Notes For Class 8 Science Chapter 5 Coal And Petroleum Science constituents petroleum and their uses

Coal And Petroleum Science Objective Type Questions

A. State whether the following statements are true or false.

1. Petrol and diesel are obtained from petroleum.
2. Petroleum is formed in the absence of air over millions of years.
3. There are no petroleum refineries in India.
4. Paraffin wax is obtained from coal.
5. The process of separating the various constituents of petroleum is known as refining.

Answers: 1. True 2. True 3. False 4. False 5. True

B. Match the items in column A with those in column B.

UP Board Notes For Class 8 Science Chapter 5 Coal And Petroleum Science Match the items in column A with those in column B

Coal And Petroleum Science Short Answer Type Questions

A. How are various constituents of petroleum obtained?

Answers. Various constituents or fractions of petroleum are separated in a Process known as refining of petroleum and it is done in petroleum refineries.

B. List the various constituents of petroleum.

Answers. The constituents of petroleum are LPG, petrol, diesel, kerosene, lubricating oil, paraffin wax and bitumen.

Coal And Petroleum Science Long Answer Type Questions

A. State the uses of at least three constituents of petroleum.

Answers.

Petrol, paraffin wax and diesel are the three constituents of petroleum.
1. Petrol is used as a motor fuel. It is also used for dry cleaning.
2. Paraffin wax is used for making ointments, candles, Vaseline etc.
3. Diesel is used as a fuel for heavy motor vehicles and electric generators.

Natural Gas

Answers. Natural gas is a very important fossil fuel. It mainly consists of methane and occurs deep under the crust; of the Earth either alone or along with the crude oil It is stored under high pressure and is hence, called! Compressed Natural Gas or CNG. Natural gas is formed by the decomposition of vegetable matter lying underwater in conditions of high temperature, pressure and in the absence of oxygen. Natural gas; is used as a domestic and industrial fuel, in fertiliser industry and as fuel for the transport industry. It is a clean fuel and produces less pollution. Since fossil fuels are exhaustible sources of energy, we should not; waste and misuse fossil fuels. One should move towards the alternative or renewable sources of energy! such as solar, wind and biomass energy.

Coal And Petroleum Science Objective Type Questions

A. State whether the following statements are true or false.

1. Natural gas is always found alone.
2. Natural gas mainly consists of methane and is stored under high pressure.
3. Petrochemicals are used for manufacturing detergents, plastics, etc.
4. Solar, wind and biomass energy are exhaust ble natural resources.

Answers: 1. False 2. True 3. True 4. False

B. Fill in the blanks.

1. Natural gas is formed in the absence of____
2. We should not_____or____fossil fuels.
3. _____is used in the fertiliser industry
4. Natural gas is a_____ fuel.

Answers: 1. Oxygen 2. Waste, misuse 3. Natural gas 4. Clean

Coal And Petroleum Science Short AnswerType Questions

A. Why natural gas is considered a clean fuel?

Answers. Natural gas bums with a smokeless flame and does not produce harmful gases such as carbon- monoxide. It has a high calorific value. Hence, natural gas is called a clean fuel.

B. What are renewable sources of energy and why are they called so?

Answers. Air, wind, water and biomass are examples of renewable sources of energy. They are present in unlimited quantity or replenish themselves quickly through natural processes. Hence, they will not be exhausted by human activities. Such resources are therefore called renewable sources of energy.

Coal And Petroleum Science Long Answer Type Questions

A. Discuss the various types of gaseous fuels.

Answers.

Different types of gaseous fuels are:
1. Natural gas is found either alone or along with petroleum deep under the Earth’s crust It mainly contains methane.
2. Water gas is prepared by passing steam over red-hot carbon fuel such as coke. It contains carbon monoxide and hydrogen.
3. Coal gas is obtained as a by-product during the making of coke from coal. It is a mixture of hydrogen, methane, carbon monoxide and other gases.
4. LPG is liquefied and compressed before being filled in cylinders and hence, it is called liquefied Petroleum gas. It is an odourless gas but a chemical known as ethyl mercaptan, which has a foul smell, is added to it to assist n detecting leakages from cylinders.
5. CNG or compressed natural gas is a substitute for gasoline or diesel fuel. It is made by compressing methane extracted from natural gas.

Coal And Petroleum Science Textbook Exercises

Question 1. What are the characteristics of CNG and LPG as fuels?

Answers.

The characteristics of LPG and CNG are:

  • LPG and CNG have high calorific values.
  • (LPG burns with a smokeless flame and does not cause pollution. CNG also does not cause pollution. They do not produce any poisonous gases on burning.
  • They are easy to handle and convenient to store.
  • They undergo complete combustion.
  • They are both clean and environment-friendly fuels.

Question 2. Name the petroleum product used for surfacing roads.

Answers. Bitumen is the petroleum product used for surfacing roads.

Question 3. Describe how coal is formed from dead vegetation. What is this process called?

Answers. About 300 million years ago, forests got buried under the soil. They were compressed by soil deposits and their temperature raised as they sank deeper and deeper. Due to the high temperature and pressure, gradually the dead vegetation changed into coal and this process is known as carbonisation.

Question 4. Fill in the blanks.

  1. Fossil fuels are ____ ______and_____
  2. Process of separation of different constituents from petroleum is called_____
  3. Least polluting fuel for vehicles is______

Answers: (1) Coal, petroleum, natural gas (2) Refining (3) CNG (Compressed Natural Gas)

Question 5. Tick True/False against the following statements.

Answers.

  1. Fossil fuels can be made in the laboratory.
  2. CNG is a more polluting fuel than petrol.
  3. Coke is almost a pure form of carbon.
  4. CNG (Compressed Natural Gas)
  5. Coal tar is a mixture of various substances.
  6. Kerosene is not a fossil fuel.

Answers: (1) False (2) False (3) True (4)True (5) False

Question 6. Explain why fossil fuels are exhaustible natural resources.

Answers. Fossil fuels are formed from the remains of dead plants and animals. It takes millions of years for this process to take place. The known reserves of these fuels are limited and herce, these are exhaustible fuels.

Question 7. Describe the characteristics and uses of coke.

Answers. Coke is a pure form of carbon. It is tough, porous and black. Coke is used to manufacture artificial graphite, which is used in the manufacturing of calcium carbide, required for manufacturing acetylene gas. Acetylene gas is the basic raw material for manufacturing acetic acid and PVC. Acetylene is used for manufacturing water gas and producer gas, which are used as fuel. It is used to extract metals from their ores. Since coke does not produce any smoke, hence it is used as a household fuel.

Question 8. Explain the process of the formation of petroleum. 

Answers. Petroleum is formed from the bacterial decomposition of the remains of animals and plants, which got buried under the sea millions of years ago. When these organisms died, they sank to the bottom of the seas and oceans and got covered by sand and clay. Over a period of millions of years, in the absence of air. these organisms got converted into petroleum due to excessive heat and pressure. The hydrocarbons formed were trapped by impervious rocks forming an oil trap. Natural gas is usually found along with petroleum.

Question 9. The following table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.

UP Board Notes For Class 8 Science Chapter 5 Coal And Petroleum Science the total power shortage in India from 1991-1997

Coal And Petroleum Science Hotscorner

A. Which property of petroleum causes it to form a layer over water?

Answers. A liquid less dense than water will always float on water. Petroleum is less dense than water and hence, it forms a layer over water.

B. Why is petrol used in lightweight vehicles but diesel is used in heavy trucks?

Answers. Petrol has low ignition temperature and calorific value as compared to diesel. Thus, burning of diesel produces a large amount of energy. Hence, diesel is used as a fuel in heavy vehicles.

Coal And Petroleum Science Practice exercises
Objective Type Questions

A. Fill in the blanks.

1.______is usually found along with petroleum in the reservoirs under the ground.
2. Various useful products are separated from petroleum by_____
3. Petrol has a low______and____as compared to diesel.

Answers: 1. Natural gas 2. Refining 3. Ignition temperature, calorific value

B. Circle the odd one out.

1. Coal, petroleum, natural gas, cow dung cakes, kerosene
2. Jharkhand, Orissa, Ankleshwar, Madhya Pradesh, West Bengal
3. Cotton, detergents, polyester, nylon, plastics

Answers: 1. Cow dung cakes 2. Ankleshwar 3. Cotton

C. State whether the following statements are true or false

1. ‘When heated in air, coal burns and produces mainly carbon dioxide.
2. Coke is used in the extraction of steel.
3. Petrol is a mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and other particles.
4. Coal tar is a thick, black, opaque fluid, which is obtained as a by-product of the process of manufacturing coke.

Answers: 1. True 2. True 3. False 4. True

D. Multiple Choice Questions.

Question 1. Which fuel is used in jet aircraft?

  1. Petrol
  2. Kerosene
  3. CNG
  4. Coal
    Answers. Kerosene

Question 2. ‘Which of the following is a non-polluting fuel for vehicles?

  1. Coal
  2. CNG
  3. Kerosene
  4. DieselAnswers. 1) CNG

Question 3. Which petroleum product is used for surfing roads?

  1. Coal Tar
  2. Paraffin wax
  3. Bitumen
  4. PetrochemicalsAnswers. 3)Bitumen

Question 4. Which of the following is the best variety of coal?

  1. Anthracite
  2. Peat
  3. Lignite
  4. BituminousAnswers. 1)Anthracite

Question 5.  Which of the following forms of energy is obtained from the Sun?

  1.  Wind energy
  2. Geothermal energy
  3. Chemical energy
  4. Solar energyAnswers. 4)Solar energy’ Short

Coal And Petroleum Science Answer Type Questions

A. What is petroleum?

Answers: Petroleum is a dark, oily liquid with a strong smell. It is a mixture of petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.

B. Why do we need to be judicious while using fossil fuels?

Answers: Fossil fuels are formed over millions of years and hence, if not used judiciously, they will run out soon. Also, burning of fossil fuels releases carbon dioxide and other gases, which are the main cause of air pollution.

UP Board Notes For Class 8 Science Chapter 6 Combustion And Flame Science

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Combustion And Flame Chapter In A Nutshell

  • Fuels of different varieties are used for various purposes in homes, industries, automobiles, etc.
  • Cowdung, wood, coal, charcoal, petrol, diesel, natural gas, L.P.G., etc., are various types of fuels.
  • Some fuels bum with a flame while some fuels do not give flame on burn ng.
  • Combustion is a chemical process in which a substance bums in the presence of oxygen to give off heat and light.
  • Fuels are combustible substances that may exist as solids, liquids or gases.
  • The presence of oxygen is essential for the process of combustion.
  • A combustible substance starts burning when it attains its ignition temperature.
  • Substances which have very high ignition temperature do not catch fire easily while substances like sodium and phosphorus which have low ignition temperature catch fire when exposed to air.
  • The ignition temperature of inflammable substances is very low. They catch fire rapidly and burn with fame.
  • Three important requirements essential to initiate a fire are the presence of oxygen, the Presence of a combustible substance arid heat supply to attain the ignition temperature of the combustible substance.
  • Fires can be controlled by – cutting off the supply of air bringing down the ignition temperature or removing the combustible substance.
  • Water is used to extinguish fire as it cools the combustible substance below its ignition temperature. In addition, the water vapours formed, surround the combustible substance and cut off the air supply. Water works as a fire extinguisher only when things like wood, paper, etc. catch fire.
  • The fire caused by to burning of oil or petrol cannot be controlled by water as water is heavier than oil. It settles down below the oil and oil continues to bum.
  • Water is not used in case of fires caused by electrical equipment as water is a good conductor of electricity and can thus cause electrocution.
  • Sand or carbon dioxide is used to control fires caused by the burning of liquid fuels or electricity.
  • Carbon dioxide is stored in cylinders in liquid form under high pressure.
  • Combustion can be classified as rapid combustion, spontaneous combustion and explosion.
  • The substances which vaporise on burning, give out flames. For example, kerosene oil.
  • The flame of a candle is divided into three zones – the innermost zone (dark zone), the middle zone (luminous zone) and the outermost zone (non-luminous zone).
  • The non-luminous zone is the hottest part of the flame.
  • The luminous zone of flame usually contains unburnt particles of carbon in it
  • A good fuel is readily available, cheap, bums easily in air, produces large amounts of heat and does not leave any unwanted substance behind.
  • The efficiency of a fuel is determined by its calorific value. The higher the calorific value of a fuel, the better the fuel.
  • The unit of calorific value is kilojoules per kg (KJ/kg).
  • Burning of fuels causes air pollution, health hazards, global warming, acid rain, etc.
  • Global warming results in the melting of polar glaciers which leads to a rise in the sea level. This may cause floods in the coastal areas.
  • Nitrogen and sulphur oxides are produced by the burning of fossil fuels. These oxides dissolve in rainwater to produce acid rain.
  • Acid rain is harmful to plants, buildings, statues, soil, etc.
  • CNG (Compressed Natural Gas) is a clean fuel as it causes no air pollution.

Read and Learn More UP Board Notes for Class 8 Science

Combustion And Flame Important Terms And Definitions

Combustible substances: The substances which bum easily in the presence of oxygen to give heat; and light are called combustible substances.
Non-combustible substances: The substances which do not bum in the presence of oxygen are
called non-combustible substances.
Ignition temperature: The minimum temperature at which a substance catches fire or starts burning; is called its ignition temperature.
Inflammable substances: Substances which have very low ignition temperature and quickly- catch fire are called inflammable substances.
Rapid combustion: The type of combustion in which a substance burns quickly to produce heat and light is known as rapid combustion.
Spontaneous combustion: The type of combustion in which a substance bursts into flames on its own is called spontaneous combustion.
Explosion: The type of combustion in which a substance bumps very rapidly with the evolution of tremendous amounts of heat, light and sound energy is called an explosion.
Flame: The gaseous light-emitting part of a fire is called a flame.
Calorific Value: The amount of heat energy released by the complete combustion of I kg of a fuel is: called its calorific value.
Global warming: Global warming is the slow rise in the temperature of the Earth’s atmosphere due to increased concentration of carbon dioxide.

Combustion

Combustion is a chemical process in which a substance burns in the presence of oxygen to give off heat and light. The minimum temperature at which a substance catches fire or starts burning is called its ignition temperature.
Inflammable substances like petrol, alcohol, and LPG (Liquefied Petroleum Gas) catch fire easily as these substances have very low ignition temperatures. Fires can be controlled by cutting off the air supply, removing the combustible substance, or bringing down the ignition temperature using fire extinguishers.
Combustion can be classified as rapid combustion, spontaneous combustion and explosion.

Combustion And Flame Activity 1

Aim: To identify combustible and non-combustible substances Procedure:
1. Take the materials given in the observation -.able.
2. Bum each of these materials one by one.
3. Note down the observations in the observation table.

Observation:

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustible And Non Combustible products

Conclusion: Wood, paper, kerosene oil, straw, charcoal, and matchsticks are combustible substances while iron nails, stone pieces, and glass are non-combustible substances.

Combustion And Flame Activity 2

Aim: To investigate the conditions necessary for combustion Procedure:
1. Case (a) Fix a candle on a table and put a glass chimney over it
2. Rest the candle on a few wooden blocks such that air can enter the chimney.
3. Observe the flame of the candle.
4. Case (b) – Remove the wooden block and ‘est the chimney on the table.
5. Observe the flame of the candle again.
6. Case (c) – Put a glass plate over the chimney and observe the flame.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion and Flame Activity 2

Experiment to show that air is necessary for burning

Observation:

1. The candle burns freely in case (a) when air can enter the chimney from below.
2. The flame of the candle flickers and produces smoke in case (b) when air does not enter the chimney from below.
3. The flame of the candle goes off in case (c) when air is not available.

Conclusion: Air is necessary for the process of combustion to take place

Combustion And Flame Activity 3

Aim: To show that combustion takes place in the presence of air
Procedure:
1. Place a piece of burning wood or charcoal on an iron plate or tawa.
2. Cover it with a glass jar or tumbler, or a transparent plastic jar.
3. Observe the burning wood or charcoal.

Observation: The wood or charcoal stops burning after some time.
Conclusion: Air is necessary for the process of combustion to take place.

Combustion And Flame Activity 4

Aim: To show that a substance starts burning at its ignition temperature
Procedure:

1. Make two paper cups from paper.
2. Pour about 50 ml of water in one of the cups.
3. Carefully, heat both the cups separately with a candle and observe them.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion And Flame Activity 4

heating paper cups

Observation:

1. The temperature of the empty paper cup reaches its ignition temperature and starts burning.
2. The heat supplied to the paper cup filled with water is transferred to water by conduction. Thus, in the presence of water, the ignition temperature of paper is not reached and it does not burn.
Conclusion: A substance catches fire at its ignition temperature.

Combustion And Flame Objective-Type Questions

A. State whether the following statements are true or false.

1. Substances which burn easily are called non-combustible substances.
2. Water can be used to extinguish fires caused by to burning of { kerosene oil.
3. A good fuel should be safe to handle.
4 All fuels have the same ignition temperature.

Answers: 1. False 2. False 3. True 4. False

B. Answer the following in one word.

1. Name a gas which is a supporter of combustion.
2. Give an example of an inflammable substance.
3. Which type of combustion produces a tremendous amount of heat, light and sound energy?

Answers: 1. Oxygen 2. Kerosene oil 3. explosion

Combustion And Flame Long Answer Type Questions

A. What are the different types of combustion? Give an example of each.

Answers. The different types of combustion are rapid combustion, spontaneous combustion and explosion. Example of rapid combustion – When a burning matchstick is brought near a gas burner, the gas starts burning immediately with the evolution of heat and light
Example of spontaneous combustion – Sodium and phosphorus bums spontaneously when exposed to air. Example of an explosion – When crackers are ignited, heat, sound and light energy are produced.

Flame

Answers. The substances which vaporise during burning, give out flames. For example, when we bum a candle wick, the wax around it melts and vaporises upward through the wick. These vapours bum in the air and; produce a flame.
The flame of a candle is divided into three zones – the innermost zone (dark zone), the middle; zone (luminous zone) and the outermost zone (non-luminous zone). No combustion takes place! the innermost zone of the flame while complete combustion takes place in the outermost zone of the flame.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion And Flame

different zones of a candle flame

Combustion And Flame Activity 5(a)

Aim: To show that substances that vaporise during burning, give flame Procedure:
1. Light a candle.
2. Hold a glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame.
3. Bring a burning matchstick near the other end of the glass tube.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion And Flame Activity 5a

Observation: The molten wax of the candle rises through the wick and vaporises which gives a flame near the other end of the glass tube.
Conclusion: Substances that vaporise during burning, give flame.

Combustion And Flame Activity 5(b)

Aim: To show that unbumt carbon particles are present in the luminous zone of the flame Procedure:
1. Light a candle.
2. Hold a clean glass plate or a glass slide into *. he luminous zone of the flame for 10 minutes.
3. Remove the glass plate and observe it.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion And Flame Activity 5(b)

Observation: A blackish ring is formed on the glass plate or slide.
Conclusion: Unbumt carbon particles are present in the luminous zone of the flame.

Combustion And Flame Activity 5(c)

Aim: To show that the non-luminous zone is the hottest part of the flame. Procedure:
1. Light a candle.
2. Hold a clean thin long copper wire inside the flame for some time.
3. Observe the copper wire just outside the flame.

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Combustion And Flame Activity 5(c)

Observation: The copper wire just outside the flame becomes red-hot
Conclusion: The non-luminous zone is the hottest part of the flame.

Combustion And Flame Objective-Type Questions

A. State whether the following statements are true or false.

  1.  Kerosene oil vaporises while burning.
  2. A substance which does not vaporise during burning gives flame.
  3.  Camphor bums with a flame.

Answers: 1. True 2. False 3. True

B. Fill in the blanks.

  1. _____ zone is the hottest part of the flame.
  2. The innermost zone of a flame is also known as______zone.
  3. ____ zone of the flame contains unbumt carbon particles.

Answers: 1. Non-luminous 2. Dark 3. Luminous

Combustion And Flame Short Answer Type Questions

A. Why middle zone of a flame is yellowish in colour?

Answers. Partial combustion of the combustible substance takes place in the middle zone of a flame due to an insufficient supply of oxygen in this region. The middle zone consists of unburnt carbon particles which become red hot and impart a yellow colour to the flame.

Fuels

Answers. Fuels are the substances which burn to produce heat and light energy. The efficiency of a fuel is determined by its calorific value. The higher the calorific value of a fuel, the better the fuel. Hydrogen has the highest calorific value.
Burning of carbon-containing fuels like wood, coal, etc. releases unburnt carbon particles into the environment Incomplete combustion of carbon-containing *fuels like petrol, kerosene, etc. produces carbon monoxide. Burning of coal in factories and power plants produces gases like sulphur dioxide and nitrogen dioxide. Carbon-containing fuels also release carbon dioxide which is a greenhouse gas and causes global warming.

Combustion And Flame Objective-Type Questions

A. State whether the following statements are true or false.

Acid rain is harmful to plants, buildings, statues, soil, etc.

  1. CNG produces a high amount of pollutants.
  2.  A good fuel should have low calorific value.

Answers: 1. True 2. False 3. False

B. Fill in the blanks.

  1. Fuels burn to produce_____and energy.
  2. Incomplete combustion of carbon-containing fuels produces______ gas.
  3. _____ results in the melting of polar glaciers.

Answers: 1. Heat, light 2. Carbon monoxide 3. Global warming

Combustion And Flame Long Answer Type Questions

A. List the harmful effects of burning carbon-containing fuels.

Answers.

Some of the harmful effects of burning carbon-containing fuels are:
1. Burning of fuels like wood, coal, etc. releases unburnt carbon particles which cause respiratory problems such as asthma and bronchitis.
2 Incomplete combustion of fuels like petrol, kerosene, etc. produces carbon monoxide which is a highly poisonous gas. If a person is exposed to carbon monoxide for a long time, it may prove fatal and he may even die.
3. Burning of coal in factories and power plants produces gases like sulphur dioxide and nitrogen d oxide which dissolve in rainwater to form acid rain.
4. Carbon-containing fuels also release carbon dioxide which can trap heat. This increases the temperature of the atmosphere and causes global warming.

Combustion And Flame Textbook Exercises

Question 1. List the conditions under which combustion can take place.

Answers.

The three important requirements for combustion to take place are:

  1. The presence of a supporter of combustion live, oxygen
  2. Presence of a combustible substance
  3. Heat supply to attain the ignition temperature of the combustible substance

Question 2. Fill in the blanks:

  1. Burning of wood and coal causes_______ of air.
  2. A liquid fuel, used in homes is______.
  3. Fuel must be heated to its______ ______ before it starts burning
  4. The fire produced by oil cannot be controlled by——

Answers:

  1. Pollution
  2. Kerosene oil before it starts burning
  3. Ignition temperature
  4. (Water

Question 3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Answers. CNG (Compressed Natural Gas) is a clean gaseous fuel. It has a high calorific value. It burns completely in the air and does not produce any harmful gases. It does not leave any residue after burning. So, pollution is reduced by the use of CNG in automobiles in our cities. of air.

Question 4. Compare LPG and wood as fuels. 

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Compare LPG and wood as fuels.

Question 5. Give reasons:

1)Water is not used to control fires involving electrical equipment
2)LPG is a better domestic fuel than wood.
3)Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not

Answers.

(1) Water is not used to control fires involving electrical equipment because water is a good conductor of electricity. Thus, it can cause electrocution.
(2) LPG is a better domestic fuel than wood because it is a cleaner fuel than wood. It neither produces smoke nor does it leave any residue after burning. It has a high calorific value. While wood produces a lot of smoke on burning and leaves behind ashes on burning. Wood has a low calorific value.
(3) When paper wrapped around an aluminium pipe is brought near a flame, it does not bum because the heat given to the paper gets transferred to the aluminium pipe and the ignition temperature of the paper is not attained.

Question 6. Different Zones of a Candle Flame

UP Board Notes for Class 8 Science Chapter 5 Combustion And Flame Science Different Zones of a Candle Flame

different zones of a candle flame

Question 7. Name the unit in which the calorific value of a fuel is expressed.

Answers. The unit in which the calorific value of a fuel is expressed in kilojoules per kilogram (KJ/kg).

Question 8. Explain how C02 can control fires.

Answers. Carbon dioxide is heavier than oxygen and covers the combustible substance like a blanket Thus, carbon dioxide cuts off the contact between the combustible substance and air. This extinguishes the fire.

Question 9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Answers. Green leaves have a lot of moisture in them which increases their ignition temperature. The dr)’ leaves do not contain moisture arid thus, their ignition temperature is low. Therefore, a heap of green leaves do not bum easily but the dr)’ leaves catch fire easily.

Question 10. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Answers. Goldsmiths usually use the outermost layer.e., the non-luminous zone of the flame for melting gold and silver because it is the hottest part of the flame.

Question 11. In an experiment, 4.5 kg of fuel was completely burnt. The heat produced was measured to be 180,000 KJ. Calculate the calorific value of the fuel.

Answers. Mass of the fuel = 4.5 <g Heat produced = 180,000 KJ
We know the calorific value = Heat produced by burning I kg of the fuel
Therefore, Calorific value = _ 4Q(000 kl/kg
4.5 kg

Question 12. Can the process of rusting be called combustion? Discuss.

Answers. Yes, the process of rusting can be called combustion.
Combustion is a chemical process in which a substance reacts with oxygen and gives off heat and light Rusting of iron is also a chemical process in which iron reacts with oxygen at a very slow rate and gives off heat. So, rusting can be termed as a slow combustion process.

Question 13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

Answers. Ramesh’s beaker will get heated in a shorter time because the outermost part of the flame is the hottest.

Combustion and Flame Hots corner

A. Why a person should not run when his clothes are on fire?

Answers. A person, whose clothes are on fire, should not run because running provides more oxygen to the flames. As oxygen is a supporter of combustion, this will increase the fire and cause more burns to the person.

B. Why is a matchstick lighted by rubbing it on the rough surface provided on the side of the matchbox?

Answers. When we rub a match stick on the rough surface of the matchbox, it produces heat due to friction. This heat raises the temperature of the chemical present on the matchstick head to its ignition temperature. Therefore, the chemical substance catches fire and the matchstick starts burning.

Combustion And Flame Practice Exercises

A. Encircle the correct option in the following sentences:

1. Hydrogen/LPG has the highest calorific value.
2. Not much air is available in the innermost zone/middle zone of a candle flame.
3. The higher/Lower the calorific value of a fuel, the better the fuel.
4. A good fuel should be cheap/expensive.
5. The outermost zone of a candle flame is the coolest/hottest

Answers: 1. Hydrogen 2. Middle zone 3. Higher 4. Cheap 5. Hottest

B. Fill in the blanks.

1. Materials such as glass, metals, ceramics, etc., are known as
2. The outermost zone of a flame is known as
3. A clean fuel does not produce
4. The gaseous light-emitting part of a fire is called

Answers: 1. Non-combustible while burning. 2. Non-luminous zone 3. Smoke materials. 4. Flame

Combustion And Flame Short Answer Type Questions

Question 1. Why water cannot be used to put off fires caused by oil?

Answers. Water cannot be used to put off fires caused by the oil because:
A)oil is lighter than water and keeps floating on it. Thus, the fire keeps on burning.

Question 2. Why is it dangerous to burn coal in a closed room? It is dangerous to burn coal in a closed room because:

Answers.

1) Burning of coal releases unburnt carbon particles into the environment. These are very fine particles that can cause respiratory problems such as asthma and bronchitis.
2) Incomplete combustion of coal produces carbon monoxide which is a highly poisonous gas. If a person is exposed to carbon monoxide for a long time, it may prove fatal and he may even die.

Question 3. How is a flame produced when a candle wick is burnt?

Answers. When a candle wick is burnt, the wax around it melts and vaporises. The vaporised molten wax moves upward through the wick. These vapours burn in the air and produce a flame.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions

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Cell Structure And Functions Chapter Objectives

  • Cells are the building blocks of all living organisms. Therefore, a cell is the smallest basic structural unit of life.
  • The shape and size of a cell depend on its functions.
  • The size of a cell is measured in micrometers (um) or microns.
  • Most cells are microscopic and can only be seen when enlarged or magnified under a microscope.
  • The size of the cell is not related to the size of the organism. An organism with billions of cells begins life as a single cell.
  • Organisms made up of only one cell are called unicellular organisms such as Amoeba, Paramecium, Euglena, bacteria, etc.
  • Organisms made up of more than one cell are called multicellular organisms.
  • A typical cell consists of three parts namely- cell membrane, cytoplasm, and nucleus. The cell membrane of plant cells is surrounded by an additional outer thick layer known as their cell wall.
  • Cell wall supports and safeguards the plants’ cells against temperature changes, high wind speed, moisture, etc.
  • Cytoplasm is a thick, jelly-like substance present inside the cell.
  • Different cell organelles present in the cytoplasm are mitochondria, plastids, Golgi bodies, endoplasmic reticulum, vacuoles, lysosomes, ribosomes, and centrosomes.
  • Plastids and vacuoles are present only in plant cells.
  • The centrosome is present only in animal cells.
  • Non-living substances such as water, sugar, minerals, proteins, lipids, etc. are also present in the cytoplasm.
  • The nucleus is the most important part of a cell. It is located within the cytoplasm at the center of the cell.
  • The nucleus consists of the nuclear membrane, nucleoplasm, nucleolus, and chromosomes.
  • The nuclear membrane is the thin semi-permeable membrane that separates the nucleus from the cytoplasm.
  • The nucleolus is a small spherical body present within the nucleus. The main function of nucleolus is to synthesize ribosomes.
  • Chromosomes possess genes or the units of heredity of living organisms.

Read and Learn More UP Board Notes for Class 8 Science

Cell Structure And Functions Important Terms And Definitions

Tissue: It is a group of similar cells that perform various specific functions.
Organ: It is a group of similar types of tissues to perform a particular function.
Organelles: These are the smaller components of the cell that perform various functions in the cell.
Gene: These are the carriers of hereditary characters from one generation to another.
Pseudopodia: The false foot present in the amoeba that performs locomotion and helps to trap the food particles called pseudopodia.
Cell inclusions: Non-living constituents of the cell are known as cell inclusions.
Prokaryotic cells: The cells without well-organized nuclear material are called prokaryotic cells.
Prokaryotes: The organisms having prokaryotic cells are called prokaryotes. For example, bacteria and blue-green algae.
Eukaryotic cells: The cells which have a well-organized nucleus along with the nucleus membrane are called eukaryotic cells.
Eukaryotes: The organisms having eukaryotic cells are called eukaryotes. For example, onion cells, human cheek cells, etc.

Cells: The Basic Unit of Life

  • Cells are the basic structural and functional unit of a living organism. Cells are complex living structures. Robert Hooke discovered the cell in 1665.
  • Organisms made of a single cell are known as unicellular organisms, for example, Amoeba, Paramecium, Euglena, etc. Organisms made of several cells are called multicellular organisms.
  • Cells can be spherical, spindle, or long branched like in red blood cells, muscle cells, and nerve cells respectively. Generally, cells are microscopic and are not visible to the unaided eye. By using a microscope they can be magnified or enlarged.
  • A group of specialized cells together form the tissues. Tissues are in turn grouped to form specified structures called organs.

Cell Structure And Functions Objective Type Questions

A. State whether the following statements are true or false.

  1. Organisms made of more than one cell are called multi-cellular organisms.
  2. Cells are complex non-living structures.
  3. Most cells can be seen by unaided eyes.
  4. Cells are the basic structural unit of all living organisms.
  5. Pseudopodia helps Amoeba in moving and capturing food.

Answers:

  1. True
  2. False
  3. False
  4. True
  5. True

B. Multiple Choice Questions.

1. Which one of the following is a unicellular organism?

  1. Elephant
  2. Rat
  3. Humans
  4. ParameciumAnswers. (4)Paramecium

2. In which one of the following organisms is aispseudopodia found?

  1. Paramecium
  2. Amoeba
  3. Bacteria
  4. None of these
    Answers.     (2)Amoeba

3. Who discovered cells?

  1. Theodor Schwann
  2. Albert Einstein
  3. Robert Hooke
  4. Matthis jakkob

Answers: (3)c)Robert Hooke

Parts of the Cell

The basic structure of all cells comprises three main parts: the cell membrane or plasma membrane, cytoplasm, and nucleus. The cell membrane also known as the plasma membrane is a thin, delicate layer that protects the cells, gives them a definite shape, and separates one cell from the other. It surrounds the cytoplasm and the nucleus.
Cytoplasm is a thick, jelly-like substance present between the cell membrane and the nucleus. It contains different cell organelles and other nonliving substances.
The nucleus controls all the activities of the cell and regulates its growth. A thin membrane called the nuclear membrane separates the nucleus from the cytoplasm. A small round-shaped body called na nucleolus is present within the nucleus. Thread-like structures called chromosomes are also present in the nucleolus, which carry genes.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Part Of Cells

Cell Structure and Functions Activity 3

Aim: To observe the basic components of the cells.
Procedure:

  1. Peel off the dry pink covering of the onion bulb using forceps or your hand.
  2. Separate the thin layers of onion peel from inside the onion bulb using forceps.
  3. Cut the separated onion peel into smaller pieces with the help of forceps.
  4. Put a drop of water on the glass slide and place the onion peel.
  5. Put a drop of methylene blue solution on the onion peel and cover with overslip.
  6. Place the slide under the microscope and observe it.

Observation:

Several cells can be seen lying side-by-side bound by the cell membrane and an additional layer called the cell wall. A spherical-shaped nucleus is present in the center of each cell.

Conclusion:

The basic components of all cells are the cell membrane, nucleus , and cytoplasm. The cell wall is an additional layer present in plant cells.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Part Of Cell Membrane

Cells observed in an onion peel

Cell Structure And Functions Activity 4

Aim: To study the human cheek cells
Procedure:

  1. Break the tip of a clean toothpick or matchstick and use it to scratch the inside of your cheek gently.
  2. Put a drop of water on the glass slide and place the scraping on it.
  3. Add a drop of iodine or a few drops of methylene blue solution to it.
  4. Place the slide under the microscope and observe it.

Observation:

The cells do not have any definite shape and are enclosed within a thin cell membrane. The cell wall is not seen around the cells.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Activty 4

Conclusion:
The basic components of all cells are the cell membrane, nucleus, and cytoplasm. The cell wall is not present in animal cells.

Cell Structure and Functions Objective Type Questions

A. State whether the following statements are true or false.

  1. The nucleus is located in the center of the cell.
  2. Cytoplasm separates the cells from their surroundings.
  3. Animal cells have cell walls
  4. The nuclear membrane separates the nucleus from the cytoplasm.

Answers:

  1. True
  2. False
  3. False
  4. True

B. Multiple-Choice Questions

1. Which of the following cell organelles is present within the nucleus?

  1. Lysosomes
  2. Ribosomes
  3. Chromosomes
  4. Centrosome

Answers. 3) Chromosomes

2. Which of the following cell organelle is referred to as the ‘powerhouse of the cells?

  1. Mitochondria
  2. Protoplasm
  3. Plastids
  4. Ribosomes

Answers. 1) Mitochondria

3. Where does protein synthesis take place in a cell?

  1. Golgi bodies
  2. Endoplasmic Reticulum
  3. Vacuoles
  4. Ribosomes

Answers. 2) Endoplasmic Reticulum

Cell Structure And Functions Short Answer Type Questions

A. Why is the plasma membrane also called an electively permeable membrane?

A plasma membrane allows only certain substances such as water and minerals to flow in and out of the cell hence, it is also called a selectively permeable membrane.

B. What is the function of genes?

Genes transfer hereditary features from parents to their offspring.

Comparison of Plant and Animal Cell

Cell organelles present in animal cells are the same as those in plant cells; however, some cell organelles are present only in plant cells. In plant cells, the cell membrane is surrounded by an additional outer thick layer known as the cell wall which gives rigidity and shape to these cells. Plant cells contain some colored cell organelles, these are called plastids. Plastids that contain green colored pigment chlorophyll are called chloroplasts. Cells also contain certain blank-looking structures in the cytoplasm. These structures are called vacuoles. Vacuoles are large and common in plant cells and much smaller in animal cells.

Cell Structure And Functions Objective Type Questions

A. Fill in the blanks.

  1. Chlorophyll present in leaves is essential for______
  2. Colored pigments present in the cells of the leaves are called_______

Answers: 1. Photosynthesis 2. Plastids

B. State whether the following statements are true or false.

  1. The membrane of an animal cell is surrounded by an additional layer.
  2. Vacuoles are more prominent in plant cells.

Answers: I. False 2. True

Cell Structure And Functions Short Answer Type Questions

A. What are the differences between cell walls and cell membranes

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Difference Between Cell Membrane And Cell Wall

Differences between cell wall and cell membrane are:

Cell Structure and Functions Textbook exercises

1. Indicate whether the following statements are True (T) or False (F).

  1. (Unicellular organisms have one-celled body.
  2. Muscle cells are branched.
  3. The basic living unit of an organism is an organ.
  4. Amoeba has an irregular shape.

Answer:

  1. True
  2. False
  3. False
  4. True

2. Sketch the human nerve cell. What functions do nerve cells perform?

The nerve cells receive and transfer messages as well as control and coordinate the functioning of different parts of the body.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions The human nerve cell

A human nerve cell

3. Write short notes on the following.

(a) Cytoplasm (b) Nucleus of a cell

(a) Cytoplasm is a thick, jelly-like substance present between the cell membrane and the nucleus. Various cell organelles such as mitochondria, ribosomes, plastids, etc. are present in the cytoplasm. It also contains non-living substances such as water, sugar, minerals, lipids, proteins, etc.

(b) The nucleus controls all the activities of the cell and regulates its growth. A thin membrane called the nuclear membrane separates the nucleus from the cytoplasm. A small round-shaped body called a nuclear Eolus is present within the nucleus. Thread-like structures called chromosomes are also present in the nucleolus, which carries genies or the hereditary unit of living organisms.

4. Which part of the cell contains organelles?

Cytoplasm present between the cell membrane and the nucleus contains the various cell organelles.

5. Make sketches of plant and animal cells. State three differences between them.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Plant Cells And Animal Cells

6. State the difference between eukaryotes and prokaryotes.

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Eukaryotes vs prokaryotes

7. Where are chromosomes found in a cell? State their function.

Chromosomes are found in the nucleus of a cell. Chromosomes carry genes and help in the inheritance i.e. transfer of characteristics from the parents to the offspring.

8. ‘Cells are the basic structural unit of living organisms. Explain.

As bricks are put together to construct a building, similarly, the body of a living organism is formed of cells. All the basic life functions of an organism occur in the cell. A group of cells forms a tissue that performs a specific function. Different tissues combine to form an organ and different organs together form organ systems which in turn form an organism. Hence, cells are referred to as the basic structural unit of life.

9. Explain why chloroplasts are found only in plant cells. Chloroplasts are green-colored plastids. They are green in color due to the presence of chlorophyll in them. Chlorophyll is vital for photosynthesis as it traps solar energy and uses it to produce food for the plant.

10. Complete the crossword with the help of the clues given below:

UP Board Notes for Class 8 Science Chapter 8 Cell Structure and Functions Cross And Down

Across:

  1. This is necessary for photosynthesis.
  2. Term for the component present in the cytoplasm.
  3. The living substance in the cell.
  4. units of inheritance present on the chromosomes.

Down:

  1. Green plastids.
  2. Formed by a collection of tissues.
  3. It separates the contents of the cell from the surrounding medium.
  4. Empty structure in the cytoplasm.
  5. A group of cells.

Across:

  1. Chlorophy
  2. Organelles
  3. Protoplasm
  4. Genes

Down:

  1. Chloroplasts
  2. Organ
  3. Membrane
  4. Vacuole
  5. Tissue

Cell Structure and Functions Hotscorner

A. If you are given two slides, one with an animal cell and the other with a plant cell, how will you differentiate between the animal and the plant cell?

When two slides are observed under a microscope, the cell which shows a well-defined cell wall is a plant cell and the one which does not have a defined cell wall is an animal cell.
The cells with a large number of vacuoles and chloroplasts are plant cells and the cells that lack chloroplast and have a less number of vacuoles are animal cells.

B. Do rats and elephants have nerve cells of different sizes? Give reasons for your answer.

Nerve cells in both rats and elephants are long and branched as they both perform the function of receiving and transmitting messages. This is because the size of a cell depends upon its function and not on the size of the body of the living organism.

Cell Structure and Functions Practice exercise

Objective Type Questions

A. Give one word for the following.

  1. The living part of the cytoplasm.
  2. The thread-like structures within the nucleus.
  3. The most important part of a cell.
  4. The site of protein synthesis.
  5. The measurement unit of the size of the cell.

Answers:

  1. Protoplasm
  2. Chromosomes
  3. Nucleus
  4. Ribosomes
  5. Micron

B. Fill in the blanks.

  1. The powerhouse of the cell is______
  2. ______are referred to as the suicidal bags of cells.
  3. _______synthesize, store, and secrete enzymes and proteins.
  4. Organisms made of more than one cell are called______

Answer:

  1. Mitochondria
  2. Lysosomes
  3. Golgi bodies
  4. Multicellular

C. State whether the following statements are true or false.

  1. The size of the cell is not related to the size of the organism.
  2. Amoeba do not have a definite shape as pseudopodia keep appearing and disappearing.
  3. Cells are visible to the naked human eye.
  4. Lysosomes help in protein synthesis.
  5. Plastids are present in both animal and plant cells.

Answer:

  1. True
  2. True
  3. False
  4. False
  5. False

D. Multiple Choice Questions.

1. Which of the following selectively permeable membranes is present around the cells?

  1. Nuclear membrane
  2. Cell membrane
  3. Nucleosome
  4. Cell wall

Answers. 2) Cell membrane

2. Which of the following cell organelle is also called the control center of the cell?

  1. Mitochondria
  2. Nucleus
  3. Cell membrane
  4. Cytoplasm

Answer. 2) Nucleus

3. Which of the following are referred to as the ‘kitchen of the cell’?

  1. Ribosomes
  2. Centrosome
  3. Leucoplasts
  4. chloroplasts

Answer. 4) chloroplasts

4. Which of the following are colorless plastids?

  1. Chloroplasts
  2. Leucoplasts
  3. Chloroplast
  4. None of these

Answer. 2) Leucoplasts

5. Which of the following is a multicellular organism?

  1. bacteria
  2. Amoeba
  3. Euglena
  4. Fungi

Answer. 4) Fungi

6. Which of the following organelles is not found in an animal cell?

  1. Lysosomes
  2. Ribosomes
  3. Endoplasmic Reticulum
  4. Chloroplasts

Answer: 4) Chioroplats

Also Read

UP Board Notes For Class 8 Science Chapter 4 Materials Metal And Non Metals Science

by

Materials Metal and Non-Metals Chapter In a Nutshell

  • Materials can be classified as metals and non-metals.
  • Metals differ from non-metals in physical and chemical properties.
  • Metals are usually solids except for mercury, which is liquid at room temperature.
  • Metals are hard materials except sodium and potassium which are soft metals that can be easily cut by a knife.
  • Metals are lustrous, sonorous, malleable arid ductile. They conduct heat and electricity.
  • Metals have high melting points except gallium which melts in the hand i.e., at body temperature.
  • Non-metals exist in all three states — solid, liquid and gas. They are brittle, non-lustrous, non-sonorous, poor conductors of heat and electricity.
  • Metals usually combine with oxygen to form metallic oxides, which are basic. These oxides react with water to form bases.
  • Sodium and potassium are the most reactive metals which react readily with oxygen, even at room temperature. That is why they are stored in kerosene oil.
  • Copper reacts with atmospheric oxygen and acquires a green coating of a mixture of copper hydroxide (Cu(OH)j) and copper carbonate (CuCOj) on its surface.
  • Non-metals combine with oxygen and form non-metallic oxides, which are also known as acidic oxides. These oxides react with water to form acids.
  • Phosphorus rapidly bums in the air at room temperature to form phosphorus oxide. It is thus stored in water to avoid its contact with the atmospheric oxygen.
  • Metals react with water depending upon their reactivity to form oxides or hydroxides and hydrogen gas. Non-metals do not react with water.
  • Some very reactive metals like sodium and potassium react violently with cold water.
  • Metals like gold, silver and platinum do rot react even with steam. They are called noble metals.
  • Iron reacts with moisture in the air to form iron oxide. Iron oxide is brownish-red in colour and is called rust
  • Metals react with acids to form corresponding salts with the evolution of hydrogen gas. Non-metals do not react with acids.
  • Most of the metals generally do not react with bases at room temperature. Metals like aluminium and zinc react with strong bases like sodium hydroxide to form complex compounds with the evolution of hydrogen gas.
  • Some of the metals in their increasing order of reactivity are Gold, Silver, Copper, Iron, Zinc, Aluminium, Magnesium, Sodium and Potassium.
  • A reaction in which a more reactive metal displaces a less reactive metal from its solution is called a displacement reaction.
  • Metals and non-metals are used in the industries, kitchens, household items, transport, etc.

Read and Learn More UP Board Notes for Class 8 Science

Materials Metal And Non-Metals Important Terms And Definitions

Malleability: The property of metals by the virtue of which they can be hammered or beaten into thin sheets is known as malleability.
Ductility: The property of metals by the virtue of which they can be drawn to thin wires is known as ductility.
Sonorous: The property of metals to produce a ringing sound when struck by an object is known as sonorous.
Metallic lustre: The property of metals by the virtue of which they shine is called metallic lustre. Metalloids: Materials that show the properties cf both metals and non-metals are called metalloids.

Physical Properties of Metals and Non-Metals

Materials are of two types – metals and non-metals. Metals usually exist in the solid state. They are hard, lustrous, sonorous, malleable, ductile and good conductors of heat and electricity. Metals have high; density and high melting points. Examples of metals are Aluminium, gold, silver, copper, sodium, etc.

Non-metals exist in all three states, liquid and gas. They are soft, brittle, non-lustrous, non-sonorous and poor conductors of heat and electricity. They are neither ductile nor malleable. Examples of non-metals are sulphur, oxygen, bromine, carbon, etc.

Materials Metal and Non-Metals Activity 1

Aim: To show that metals are malleable while non-metals are non-malleable
Procedure:
1. Take a small iron nail, a piece of coal, a piece of thick aluminium wire and a pencil.
2. Hit hard all the materials one by one with a hammer.
3. Note down the observations in the observation table.

Observation:

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Activity 1

Conclusion: Iron and aluminium are malleable while coal and pencil lead are non-malleable materials. This shows that metals are malleable i.e., they can be beaten into thin sheets. Non-metals are non-malleable.

Materials Metal and Non-Metals Activity 2

Aim: To show that metals are good conductors of electricity while non-metals are poor conductors of electricity
Procedure:
1. Make an electric circuit as shown below.
2. Connect the circuits one by one with an iron nail, a piece of sulphur, a piece of coal and a copper wire.
3. Note down your observations in the observation table.

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Activity 2

An electric circuit

Observation:

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Activity 2.

Conclusion: Metals are good conductors of electricity-‘ while non-metals are poor conductors of electricity.

Materials Metal and Non-Metals Objective Type Questions

A. State whether the following statements are true or false.

1. Metal and non-metals have the same physical properties.
2. All non-metals possess lustre.
3. Cooking utensils are made of metals because they/ are good conductors of heat.
4. Mercury is a non-metal found in the solid state.

Answers: 1. False 2. False 3. True 4. False

Materials Metal and Non-Metals Short Answer Type Questions

A. What do you understand by the ductility and malleability of a metal? Give examples of two metals which are both ductile and malleable.

Answer. Ductility is the property of metals by which they can be drawn into thin wires. Examples of ductile metals are copper, silver, etc.
Malleability is the property of metals which means that they can be hammered into thin sheets or foils. Examples of malleable metals are gold, silver, etc.

B. Why aluminium and copper are used for making electrical wires?

Answer. Aluminium and copper are metals. They are duct le and good conductors of electricity. Therefore, aluminium and copper are used for making electrical wires.

Chemical Properties of Metals and Non-Metals

Reaction with oxygen – Metals react with oxygen to form metallic oxides which are basic. Non¬metals react with oxygen to form non-metallic oxides which are acidic.
Reaction with water – Metals react with water to form either oxides or hydroxides and hydrogen gas. Most of the non-metals do not react with water.
Reaction with acids and bases – Metals react with acids to form corresponding salts with the evolution of hydrogen gas. Metals usually do riot react with bases. Most of the iron metals do not react with acids; and bases.
A more reactive metal tends to displace a less reactive metal from its solution. Such a reaction; is known as a displacement reaction.

Materials Metal and Non-Metals Activity 3

Aim: To show that metallic oxides are basic in nature
Procedure:
1. Take a spoonful of rust and dissolve it in a small amount of water.
2. Shake the mixture well and test the solutior with red and blue litmus papers.
3. Observe the colour change of the Irtmus paaer.

Observation: The solution of rust and water changes the colour of red litmus paper to blue. The colour of blue litmus paper does not change.
Conclusion: Metallic oxides are basic in nature.

Materials Metal and Non-Metals Activity 4

Aim: To show that non-metallic oxides are acidic in nature AM Procedure:
1. Take a small amount of sulphur powder in a deflagrating spoon and heat it.
2. As sulphur starts burning introduce the spoon into the gas jar or glass tumbler.
3. Cover the lid and ensure that the gas produced does not escape from the jar.
4. Add a small amount of water it the jar and cover the jar with the lid quickly.
5. Shake the tumbler well and test the solution with red and blue litmus papers.
Observation: When sulphur bums in oxygen, it produces sulphur dioxide. On dissolving this sulphur dioxide in water, sulphurous acid is formed.
so2 +H2O > H2SO,
SJafr.rD’-xde Sjiphjrojt *od
Sulphurous acid changes the colour of blue litmus Daperto red.
Conclusion: Non-metals react with oxygen to form non-metallic oxides. These oxides are acidic in nature. These oxides dissolve in water to form acid.

Materials Metal and Non-Metals Activity 5

Aim: To show the reaction of sodium metal with water
Precaution: The size of the sodium metal should be nearly the size of a wheat grain. A pair of tongs must be used to handle the piece of sodium metal.
Procedure:
1. Take a 250 ml beaker or a glass tumbler and fill it half with water.
2. Cut a small piece of sodium metal carefully.
3. Dry the piece of sodium metal and wrap it in a small piece of cotton.
4. Put the wrapped sodium piece into the bea<er containing water and observe carefully.
5. Touch the beaker after the reaction.
6. Test the solution with red arid blue litmus paper

Observation: Sodium metal reacts vigorously with water and catches fire. The beaker becomes hot during the reaction. The solution turns red Irtmus blue.
Conclusion: Metals like sodium are very reactive. They react vigorously with water ana release a large amount of heat.

Materials Metal and Non-Metals Activity 6

Aim: To show the reaction of metals and non-metals with acids
Precaution: Use a test tube holder to hold the test tube and keep the mouth of the test tube away from your face.
Procedure:
1. Take samples of metals and non-metals as given in the observation table.
2. Put them in separate test tubes and label them as A, B, C, D, E and F.
3. Add 5 ml of dilute hydrochloric acid in each test tube with a dropper.
4. Observe the reaction in the test tubes.
5. If the reaction does not occur in cold solution, warm the test tube.
6. Bring a burning matchstick near the mouth of the test t Jbe.
7. Repeat the activity using dilute sulphuric acid and note the observations in the observation table.

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Activity 6

Conclusion: Metals react with acids to liberate hydrogen gas. The rate of this reaction increases as the temperature of the acid increases. Non-metals do not react with acids.

Materials Metal and Non-Metals Activity 7

Aim: To show the reaction of metals with strong bases
Precaution: Use a plastic spatula to handle the pellets of sodium hydroxide
Procedure:
1. Dissolve 3-4 pellets of sodium hydroxide in 5 ml of water in a test tube.
2. Drop a piece of aluminium foil into the test tube.
3. Bring a burning matchstick near the mouth of the test, tube and observe.

Observation: The burning matchstick extinguishes with a pop sound.
Conclusion: Metals like aluminium react with strong bases to produce hydrogen gas.

Materials Metal and Non-Metals Activity 8

Aim: To show that a more reactive metal can replace a less reactive metal from its solution Procedure:
1. Take five 100 ml beakers and label them as A, B, C, D and E
2. Take 50 ml of water in each beaker and dissolve a teaspoonful of:
Beaker A: Copper Sulphate (CuSO^ and Z’rc granules (Zn)
Beaker B: Copper Sulphate (CuSOJ and Iron nail (Fe)
Beaker C: Zinc Sulphate (ZnSOJ and Copper turnings (Cu)
Beaker D: Iron Sulphate (FeSOJ and Copper turnings (Cu)
Beaker E: Zinc Sulphate (ZnS04) and Iron nail (Fe)
3. Keep the beakers undisturbed for some time and observe the changes in them.

Observation: Beaker A: Zinc replaces copper from the copper sulphate solution and the blue colour of the copper sulphate solution fades. A red powder)’ mass of copper settles at the bottom of the beaker.
Copper Su I phate (C JS04 )+Zi nc (Zn) > Zi nc Sulphate (ZnS04)+Copper (Cu)
CcJou’ets
Beaker B: Iron replaces copper from copper sulphate solution to form iron sulphate. A red powdery mass of copper settles at the bottom of the beaker.
Copper Sulphate (CuS04)+lron(Fe)  iron Sulphate (FeS04) + Copper (Cu)
Bu* colour Rfo
Beaker C: No change is observed in the beaker.
Beaker D: No change is observed in the beaker.
Beaker E: No change is observed in the beaker.
Conclusion: A more reactive metal displaces a less reactive metal from its solution. Such a reaction is called a displacement reaction.

Materials Metal and Non-Metals Objective Type Questions

A. State whether the following statements are true or false.

1. Non-metals vigorously react with water.
2. Metal oxides are basic:n nature.
3. Phosphorus is a non-metal which is stored in water.
4. Hydrogen gas bums with a pop sound.

Answers: 1. False 2. True 3. True 4. True

B. Fill in the blanks.

1. _______and_____are stored in kerosene oil.
2. Iron reacts with oxygen to form____
3. Metals like gold and platinum do not even react with steam. These metals are called____
metals.

Answers: 1. Sodium, potassium 2. Iron oxide 3. Noble

Materials Metal and Non-Metals Short Answer Type Questions

A. Why potassium is not stored in the water?

Answer. Potassium is a reactive metal. It reacts violently with water at room temperature and catches fire. Hence, it is not stored in water but kept in the kerosene oil.

B. Why gold ornaments look new even after several years of use?

Answer. Gold is a non-reactive metal. It does not tarnish. It is unaffected by air, water and acids. Thus, gold ornaments look new even after several years of use.

Uses of Metals and Non-Metals

Answer. Metals like aluminium and copper are used to make electrical wires, iron is used to construct buildings and bridges, aluminium, iron and copper are used in utensils, tools and machinery, gold and platinum are used to make jewellery, magnesium is used to make fireworks, etc.
Non-metals like oxygen is essential for respiration in living beings, hydrogen is used as a fuel, diamond is a form of carbon used as a gemstone, iodine is used as an antiseptic, nitrogen is used to preserve food, chlorine is used for water purification, etc.

Materials Metal and Non-Metals Objective Type Questions

A. Fill in the blanks.

1. _____is a form of carbon used as a gemstone.
2. Food is wrapped in foils made up of______
3.______ is a non-metal used in the purification of water.

Answers: 1. Diamond 2. Aluminium 3. Chlorine

Materials Metal and Non-Metals Long Answer Type Questions

A. List two uses of metals and non-metals.

Two uses of metals are:
1. Metals like iron are used in the construction of buildings and bridges.
2. Metals like gold and platinum are used for making jewellery.
Two uses of non-metals are:
1. Oxygen is essential for respiration in living beings.
2. Nitrogen is used to preserve food. It is a nutrient required by the plants to grow.

Materials Metal and Non-Metals Textbook Exercises

Question 1. Which of the following can be beaten into thin sheets?

  1. Zinc
  2. Phosphorus
  3. SulphurAnswers. The material which can be beaten into thin sheets is (1) Zinc

Question 2. Which of the following statements is correct?

  1. All metals are ductile.
  2. All non-metals are ductile.
  3. Generally, metals are ductile.
  4. Some non-metals are ductile.

Answers. The correct statement is (3) Generally, metals are ductile.

Question 3. Fill in the blanks.

  1. Phosphorus is a very____ non-metal
  2. Metals are_____conductors of heat and
  3. Iron is_____reactive than copper.
  4. Metals react with acids to produce_______gas.

Answers: (1) Reactive (1) Good, electricity (3) More (4) Hydrogen

Question 4. Mark if the statement is true and ‘P if it is false.

  1. (Generally, non-metals react with acids.
  2. Sodium is a very reactive metal.
  3. Copper displaces zinc from the zinc sulphate solution.
  4. Coal can be drawn into wires.

Answers: (1) F (2) T (3) F (4) F

Question 5. Some properties are listed in the following Table. Distinguish between metals and non-metals based on these properties.

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Metals And Non-metals

Question 6. Give reasons for the following.

  1. Aluminium foils are used to wrap food items.
  2. Immersion rods for heating liquids are made up of metallic substances.
  3. Copper cannot displace zinc from its salt solution.
  4. (Sodium and potassium are stored in kerosene.

Answers.

  1. Aluminium foils are used to wrap food items because aluminium is malleable and less reactive to air and water.
  2. Immersion rods used for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity.
  3. Only a more reactive metal can displace a less reactive metal from its solution. Copper is a less reactive metal than zinc. Therefore, copper cannot displace zinc from its salt solution.
  4. Sodium and potassium are very reactive metals. They react vigorously with water to form oxides or hydroxides. Therefore, they are stored in kerosene oil.

Question 7. Can you store lemon pickles in an aluminium utensil? Explain.

Answer. No, lemon pickles cannot be stored in an aluminium utensil because lemon contains citric acid which reacts with aluminium to produce a salt of aluminium and hydrogen gas. This will spoil the food and make it unfit for eating.

Question 8. Match the substances given in Column A with their

UP Board Notes For Class 8 Science Chapter 4 Materials Metals ANd Non-Metals Science Match The Columns

Question 9. What happens when
(a) Dilute sulphuric acid is poured on a copper plate.
(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.

Answers.

  1. When sulphuric acid is poured on a copper plate, copper reacts with the acid and produces copper sulphate and hydrogen gas.
    Copper + Sulphuric Acid » Copper Sulphate + Hydrogen Gas
  2. Iron is a more reactive metal than copper. When iron nails are placed in the copper sulphate solution, iron displaces copper and forms iron sulphate. This reaction fades the blue colour of the copper sulphate solution and a brown deposit of copper is seen at the bottom of the beaker.
    Iron + Copper Sulphate > Iron Sulphate + Copper


Question 10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
(b) Write down word equations of all the reactions taking place in this process.

Answers.

  1. Saloni can find the nature of the gas by adding few drops of water in the test tube and testing the solution with a red and a blue litmus paper. The blue litmus paper will turn red while the red litmus paper will show no change. This shows that the gas is acidic in nature.
  2. ‘When a charcoal is burnt, it reacts with oxygen to form an acidic oxide called carbon dioxide.
    Charcoal + Oxygen –» Carbon Dioxide
    Carbon dioxide released on burning charcoal reacts with water to form carbonic acid.
    Carbon Dioxide + Wa: er –»Carbonic Acid

Question 11. One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Answers. Jewellers usually use a strong acidic solution to polish the gold jewellery. When the gold is dipped in the acidic solution, it reacts with the acid. A small amount of the gold dissolves in the acid from the outer layer of the jewellery. Thus, there is a slight loss in the weight of the jeweller)

Materials Metal and Non-Metals Hots corner

A. based on the reactions given below, indicate the most reactive metal and the least reactive metal out of zinc, copper and iron.
                   Copper Sulphate + Iron⇒ Iron Sulphate + Copper
                        Iron Sulphate + Zinc ⇒ Zinc Sulphate + Iron

Answers. In the first reaction, iron displaces copper from the copper sulphate solution, therefore, iron is more reactive than copper. In the second reaction, zinc displaces iron from iron sulphate solution, therefore, zinc is more reactive than iron. Therefore, zinc is the most reactive metal and copper is the least reactive metal.

B.Why is graphite not used for making electrical wires?

Answers. Graphite is a form of a carbon which is a non-metal. It is brittle and non-ductile. It is a poor conductor of heat and electricity. Therefore, it can not be used for making electrical wires.

Materials Metal and Non-Metals Practice Exercises

Objective Type Questions

A. Fill in the blanks.

1. Metals exist in _____state.
2. ______foils are used to decorate sweets.
3. Metals produce a ringing sound when struck by something. This shows that metals are_____
4. _______is a non-metal used in the pencil lead.
5. Non-metallic oxides are_______ in nature.

Answers: I. Solid 2. Silver 3. Sonorous 4. Graphite 5. Acidic

B. Answer the following questions in one word.

1. Name a metal that can be cut by using a knife.
2. Name a metal which melts at body temperature.
3. Name a metal which is liquid at room temperature.
4. Name a metal which does not react with water, air or acid.
5. Name a non-metal used for making antiseptics.
6. Name a non-metal which is found in the gaseous state.

Answers: 1. Sodium 2. Gallium 3. Mercury 4. Gold 5. Iodine 6. Oxygen

Materials Metal and Non-Metals Short Answer Type Questions

A. Why phosphorus is stored in water?

Answers. Phosphorus reacts rapidly with oxygen present n air and catches f re. It is, therefore, stored in water to avoid its contact with the atmospheric oxygen.

B. What is the difference in the reaction of oxygen with metals and non-metals? Write their word equation.

Answers.

Metals react with oxygen to form metallic oxides which are basic in nature. These oxides dissolve in water to form bases.
Metals + Oxygen > Metallic Oxide
Non-Metals react with oxygen to form non-metallic oxides which are acidic in nature. These oxides dissolve in water to form acids.
Non-metals + Oxygen » Non-Metalic Oxide

Materials Metal and Non-Metals Long Answer Type Questions

A. Magnesium ribbon burns with a dazzling white flame and forms a white powdered ash. This ash is dissolved in water and tested with a red and blue litmus paper.
Answer the following questions:

  1. What is the white ash formed after burning the magnesium ribbon?
  2. Write the word equation of the reaction that takes place when magnesium ribbon is burnt.
  3. What happens when the white ash is dissolved in water? Give the word equation.
  4. (Give one use of magnesium.

Answers.

  1. The white ash formed after burning the magnesium ribbon is magnesium oxide.
  2. Magnesium + Oxygen » Magnesium Oxide
  3. When the white ash is dissolved in water, magnesium hydroxide is formed.
    Magnesium Oxide + Water > Magnesium Hydroxide
  4. Magnesium is used in fireworks.

 

Also Read

UP Board Notes For Class 8 Science Chapter 9 Reproduction In Animals

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Reproduction In Animals Chapter Objectives

  • Reproduction is essential for the continuation of a species.
  • Gametes are the reproductive cells produced by the sex organs.
  • The male reproductive system in animals includes a pair of testes, a pair of sperm ducts, and a penis.
  • Testes produce sperm or the male gametes.
  • A sperm is a very small, single-celled structure with all the usual cell components. It consists of a head, a middle piece, and a tail.
  • The female reproductive system in animals consists of a pair of ovaries, oviducts or fallopian tubes, uterus and vagina.
  • Each ovary produces one mature ovum or egg every month and discharges it into the oviduct.
  • The uterus is a hollow. muscular, pear-shaped organ in which the embryo develops.
  • Asexual and sexual reproduction are the two modes of reproduction in animals.
  • In asexual reproduction, a new individual is formed from the cell of a single parent.
  • Binary fission and budding are the two methods of asexual reproduction.
  • In binary fission, a fully-grown cell divides to produce two new cells. Amoeba reproduces by binary fission.
  • In budding new individuals are formed as an outgrowth from a single parent. These extensions are called buds.
  • A fully matured bud detaches itself from the parent body and becomes a new individual capable of existing independently.
  • Sexual reproduction involves the fusion of male and female gametes. Human beings and other
    mammals reproduce sexually.
  • Fertilisation is the fusion of sperm and ovum to form a fertilised egg or zygote. It is the first step in the process of reproduction.
  • When male and female gametes fuse inside the female’s body as in human beings, dogs, cats, etc, the fertilisation is referred to as internal fertilisation.
  • External fertilisation occurs when male and female gametes combine outside the female’s body.
  • Viviparous animals give birth to young ones. Human beings, dogs, cats, etc., are viviparous animals.
  • Oviparous animals lay eggs, which later develop into young ones. Frogs, birds, etc., are examples of oviparous animals
  • Metamorphosis is the transformation of a larva into an adult through a series of changes.
  • Larva is an animal’s early form having features, different from the adult.

Read and Learn More UP Board Notes for Class 8 Science

Reproduction In Animals Important Terms and Definitions

Cloning: It is the process of production of an exact copy of an organism.
Foetus: It is that stage of the embryo in which all the body parts can be identified.
In vitro fertilization (IVF): It is a technique in which the egg is fertilised outside the body of the female.
It is used when women are not able to conceive due to blockage of oviducts.

Reproductive Organs

Answers: The male reproductive organs consist of a pair of testes, a pair of sperm ducts and a penis. Testes produce nearly millions of sperm. The male gamete or the sperm is single-celled and has a head, a middle piece and a tail. Ovaries, oviducts or fallopian tubes, a uterus and vagina are the main female reproductive organs. The female gamete or the ovum is produced by the ovaries. When a male gamete fertilises a female gamete, it results in the formation of a zygote.

Reproduction In Animals Objective Type Questions

A. State whether the following statements are true or false.

  1. The embryo gets embedded in the fallopian tube.
  2. Sperms are single-celled.
  3. The male reproductive system consists of a pair of testes, two sperm ducts and a penis.
  4. The zygote divides repeatedly to form a ball of cells.
  5. The egg of a human female contains a large amount of yolk.

Answers:

  1. False
  2. True
  3. True
  4. True
  5. False

B. Multiple Choice Questions.

1. Which of the following is not a male reproductive organ?

  1. Penis
  2. Testes
  3. Sperm ducts
  4. Fallopian tubes

Answers: 4) Fallopian tubes

2. Which of the following is referred to as the beginning of an individual?

  1. Sperm
  2. Male gametes
  3. Zygote
  4. Embryo

Answers: 3) Zygote

3. Which of the following statements is true for fertilisation?

  1. Meeting of an egg and a sperm cell
  2. Fusion of the male and female gametes
  3. Results in carrying of inherited characters to the next generation
  4. All of these

Answers: 4) All of these

4. Which one of the following is known as a sex cell?

  1. Zygote
  2. Gamete
  3. Embryo
  4. Foetus

Answers: 2) Gamete

C. Fill in the Blanks.

  1. A male gamete is known as a/an______ and a female gamete is known as a/an
  2. The stage of a developing embryo at which all body parts become identifiable is known as a______
  3. A multicellular animal starts its life as a single cell known as a_______
  4. In human beings, the embryo develops inside the________of the female.
  5. In human beings, fertilisation takes place in the

Answers:

  1. Sperm, ovum
  2. Foetus
  3. Zygote
  4. Uterus
  5.  Fallopian tubes

Reproduction In Animals Short Answer Type Questions

A. Describe the female reproductive system in brief.

Answers: The female reproductive system consists of ovaries, oviducts or fallopian tubes and the uterus. The female gametes called the ova or eggs, are produced by the ovaries. The ovaries discharge one mature, single-celled egg into the oviduct of human females every month.

B. What organs in human beings produce gametes?

Answers: In human beings, the male gamete or the sperm is produced by a pair of testes and the female
gamete or the ovum is produced by a pair of ovaries.

Modes of Reproduction

Answers: Animals have two modes of reproduction: sexual and asexual. When male and female gametes combine to form a zygote, it is known as sexual reproduction. The zygote divides repeatedly to form an embryo, which embeds itself in the wall of the uterus and develops into a foetus. The different stages of a frog starting from the egg to the adult are:
Egg → Larva →→ Adult
When organisms are reproduced by a single parent, it is known as asexual reproduction. The two methods of asexual reproduction are budding and binary fission. Hydra reproduces through budding. Single-celled organisms such as Amoeba reproduce asexually through binary fission.

Reproduction In Animals Activity 1

Aim: To observe the colour and size of frog’s eggs
Procedure:
1. Visit a pond during the rainy or spring season.
2. Notice the things floating in it.
Observation: Dull-white, bunches of frog eggs can be seen floating on the surface of the water.
Conclusion:
1. Frogs move to ponds in the rainy or spring season and female frogs lay hundreds of eggs in water.
2. These eggs are dull white, are not covered by a shell and are held together by a layer of jelly which also protects them.

Reproduction In Animals Activity 2

Aim: To observe the eggs of frogs, lizards, butterflies moths, hens crows or any other bird
Procedure:
1. Visit a garden near your home or school.
2. Look for the eggs of frogs, butterflies, lizards and crows.
3. Visit a local shop to look at the eggs of a hen.
4. Observe the eggs and note down the differences among them.
5. Note the size, colour and shape of each type of egg.
6. Make drawings of these eggs in your notebook.

Observation: The eggs of each organism are different in shape and size.
Conclusion:
1. Animals such as hens, frogs, etc., lay eggs outside their bodies. Such animals are called oviparous
animals.
2. Animals such as cows, dogs, etc., do not lay eggs but give birth to young ones. Such animals are called viviparous animals.

Reproduction In Animals Activity 3

Aim: To study budding in Hydra
Material Required: Permanent slides of Hydra and a microscope
Procedure:
1. Observe the permanent slides of Hydra under the microscope.
2. Observe them first under the low-power lens and then under the high-power.
3. Look for bulb-like projections from the parent body and count them.
4. Observe the size of different projections or buds.
5. Draw a rough sketch of what you observe.

UP Board Notes For Class 8 Science Chapter 9 Cell Structure And Functions Reproduction In Animals Activty 3

Observation: Each Hydra has one or more than one bud.
A bud is an outgrowth, which develops as cells divide constantly at a particular location.
A fully matured bud detaches itself from the parent body and becomes a new individual capable of
existing independently.
Conclusion: Hydra reproduces asexually through budding.

Reproduction In Animals Objective Type Questions

A. State whether the following statements are true or false.

Answers:

  1. In sexual reproduction, male and female gametes combine to form a zygote.
  2. All animals reproduce through sexual reproduction.
  3. Out of the millions of sperm produced, only one of the sperm fuses with the egg.
  4. Fertilisation occurs inside the body of a cow.
  5. Amoeba reproduces asexually through budding.
  6. Cows and dogs are viviparous animals.

Answers:

  1. True
  2. False
  3. True
  4. True
  5. False
  6. True

B. Multiple Choice Questions.

Question 1. Which of the following animals reproduces through budding?

  1. Rat
  2. Elephant
  3. Human beings
  4. HydraAnswers. 4) Hydra

Question 2. What is the process of formation of an adult frog from the larva called?

  1. Internal fertilisation
  2. External fertilisation
  3. Sexual reproduction
  4. MetamorphosisAnswers. 4) Metamorphosis

Question 3. What is the stage between the egg and the larva in a butterfly called?

  1. Pupa
  2. Adult
  3. Caterpillar
  4. None of these answers. 1) Pupa

Question 4. By which stage are the parts of an embryo identifiable?

  1. Adult
  2. Larva
  3. Pupa
  4. FoetusAnswers. 4)Foetus

Question 5. What term is given to an organism that has both the male and the female sex organs?

  1. Unisexual
  2. Multisexual
  3. Hermaphrodite
  4. Asexual

Answers: 3) Hermaphrodite

C. Fill in the blanks.

  1. Amoeba reproduces asexually through____
  2. Budding is a form of______reproduction.
  3. External fertilisation occurs in_______
  4. Gametes are produced in_____reproduction

Answer: 1. Binary fission 2. Asexual

Reproduction In Animals Short Answer Type Questions

A. What is binary fission?

Answers: It is a method of asexual reproduction and is common in single-celled organisms such as Amoeba. In this method, a fully grown parent cell divides itself to produce two daughter cells. Each daughter cell gives rise to a new individual.

B. What is the difference between unisexual organisms and hermaphrodites?

Answers: Unisexual organisms are those in which male and female gametes are produced by separate individuals Hermaphrodites are organisms in which the same individual produces both the male and female gametes.

C. How are chicks born?

Answers: Internal fertilisation takes place in hens but they do not give birth to young ones. The zygote moves down the oviducts and protective layers are formed around it. One of these protective layers is the hard shell. The hen lays the eggs once this hard shell is formed and sits on them to provide them with warmth. In three weeks, the embryo within this shell develops into a chick. Once the chick is fully developed it breaks open the eggshell and comes out.

Reproduction In Animals Textbook exercises

Question 1. Explain the importance of reproduction in organisms.

Answers: Reproduction is an important biological process because it ensures the existence and continuity of a species. It also helps in the transmission of heredity from one generation to another.

Question 2. Describe the process of fertilisation in human beings.

Answers: The first step in the process of reproduction in human beings is the fusion of a sperm and an ovum or egg. Millions of sperm are released into the female’s body out of which only one of the sperm may fuse with the egg. Such fusion of the egg and the sperm is called fertilisation. During fertilisation, the nucleus of the sperm and the egg fuse to form a single nucleus. The zygote thus formed is the beginning of a new individual.

Question 3. Choose the most appropriate answer.

(a) Internal fertilisation occurs

  1. in the female body
  2. outside the female body
  3. in the male body
  4. outside the male body

Answer: (1) in the female body

(b) A tadpole develops into an adult frog by the process of

  1. Fertilisation
  2. Metamorphosis
  3. Embedding
  4. Budding

Answer: (2) Metamorphosis

(c) The number of nuclei present in a zygote is

  1. None
  2. One
  3. Two
  4. Four

Answer: (2) One

Question 4. Indicate whether the following statements are True (T) or False (F).

Answers:

  1. Oviparous animals give birth to young ones.
  2. Each sperm is a single cell.
  3.  External fertilisation takes place in frogs.
  4. A new human individual develops from a cell called a gamete.
  5. An egg laid after fertilisation is made up of a single cell.
  6. Amoeba reproduces by budding.
  7. Fertilisation is necessary even in asexual reproduction.
  8. Binary fission is a method of asexual reproduction.
  9. A zygote is formed as a result of fertilisation.
  10. An embryo is made up of a single cell.

Answers:

  1. (a) False
  2. (g) False
  3. (b) True
  4. (h) True
  5. (d) False
  6. (i) False
  7. (iv) Budding
  8. (iv) Four
  9. (e) True
  10. (f) False

Question 5. Give two differences between a zygote and a foetus. It is unicellular.

Zygote

It is formed by the fusion of the male and female gametes.

Foetus

It is formed by the repeated divisions of the zygote. It is multicellular.

Question 6. Define asexual reproduction. Describe two methods of asexual reproduction in animals.

Answers: The type of reproduction in which only a single parent is involved is called asexual reproduction.
Following are the two methods of asexual reproduction in animals:

  1. Binary fission: Binary fission involves almost an equal division of the parent cell into two daughter cells, each of which grows into a new individual. This method of reproduction occurs regularly among protozoa like Amoeba, Paramecium, etc.
  2. (Budding: Budding is the form of asexual reproduction in which a new individual arises from a bud. The bud develops on the parent body, gets detached and grows into a separate individual, for example as in Hydra.

UP Board Notes For Class 8 Science Chapter 9 Cell Structure And Functions Two Methods Of Asexual Reproduction In Animals.

Question 7. In which female reproductive organ does the embryo get embedded?

The embryo gets embedded in the walls of the uterus.

8. What is metamorphosis? Give examples.

Metamorphosis is the drastic change that takes place during the development of an animal from the larval to the adult stage.

UP Board Notes For Class 8 Science Chapter 9 Cell Structure And Functions What Is Metamorphosis

The above figure shows three stages in the development of a frog. egg, tadpole or larva and the adult frog.
The tadpole or larva is different from its adult form. Tadpole has gills for respiration because it lives in water. During metamorphosis, the body of the tadpole changes to become an adult frog. For example, the gills are replaced by the lungs. Another animal in which metamorphosis takes
place is the silkworm.

Question 9. Differentiate between internal fertilisation and external fertilisation.

UP Board Notes For Class 8 Science Chapter 9 Cell Structure And Functions Differentiate between internal fertilisation and external fertilisation.

Question 10. Complete the crossword puzzle using the hints given below.

Across:

  1. The process of fusion of gametes.
  2. The type of fertilisation in hens.
  3. The term is used for bulges observed on the sides of the body of Hydra.
  4. Eggs are produced here.

Down:

  1. Sperms are produced in these male reproductive organs.
  2. Another term for the fertilised egg.
  3. These animals lay eggs.
  4. A type of fission in Amoeba.

Across:

  1. Fertilisation
  2. Internal
  3. Buds
  4. Ovary

Down:

  1. Testis
  2. Zygote
  3. Oviparous
  4. Binary

External Fertilisation
The fusion of male and female gametes takes
place outside the female body.
Both the males and females discharge their
gametes in water.
Development of embryo occurs outside the
female body.
A few examples are frogs, fish, starfish, etc.

Reproduction In Animals Hots corner

A. Why do aquatic animals like frogs and fish that undergo external fertilisation produce a large number of sperm and eggs?

Answers: The eggs and sperm of aquatic animals get exposed to water movement, wind and rainfall. There are other animals present in water, which feed upon these eggs. All these factors reduce the chances of fertilisation of the eggs. Thus, the production of a large number of eggs and sperm is necessary to ensure the fertilisation of at least a few of them.

Reproduction In Animals Practice Exercise Objective Type Questions

A. Circle the odd one out.

  1. Ovary, Oviducts, Uterus, Testes
  2. Testes, Sperm ducts, Penis, Vagina
  3. Fertilisation, Embryo development, Metamorphosis, Budding

Answers: 1. Testes 2. Vagina 3. Budding

B. Give one word for the following.

  1. The process by which a tadpole develops into an adult frog
  2. The animals that lay eggs
  3. Mode of reproduction in which both parents are needed
  4. The cell formed due to the fusion of male and female gametes
  5. Animals which lay eggs

Answers:

  1. Metamorphosis
  2. Oviparous
  3. Sexual
  4. Zygote
  5. Oviparous

C. State whether the following statements are true or false.

  1. Viviparous animals give birth to young ones.
  2. Foetus is another name for the unfertilised egg.
  3. The first mammal to be cloned was a cow.
  4. Reproductive cells produced by the male sex organs are called ova.

Answers:

  1. True
  2. False
  3. False
  4. False

Reproduction In Animals Short Answer Type Questions

A. What is a zygote?

Answers: Zygote is formed from the fusion of the male and the female gametes. It is the first cell of the organism and hence, is also referred to as the beginning of an individual.

B. Sometimes identical twins are born to human beings. What do you think is the reason behind this?

Answers: At times, the fertilised egg or the zygote splits into two and each of these develops into two individuals. The two resulting offspring are identical twins.

C. Why do several animals like dogs, cats, etc., always produce so many young ones at a time?

Answers: In animals like dogs, cats, etc., instead of one egg several eggs are fertilised. Each fertilised egg develops into a zygote. Hence, many young ones are produced at a time.

Also Read

UP Board Notes for Class 8 Science Chapter 15 Some Natural Phenomena

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Some Natural Phenomena Chapter Objectives

  • Two objects can be electrically charged by rubbing them with one another.
  • American scientist, Benjamin Franklin, showed that clouds have electrical charges on them.
  • Electrical charges are of two types Positive charges and Negative charges.
  • Like electrical charges repel each other while unlike electrical charges attract each other.
  • A charged object can transfer its charge to another object through a metal conductor.
  • Earthing protects us from electric shocks that may take place due to leakage of electric current.
  • Natural phenomena like lightning, earthquakes, etc. cause large-scale destruction of human life and property.
  • Lightning occurs due to electric discharge between the clouds and the Earth or between different clouds.
  • The lightning conductor is installed at the highest point of a building to protect them from the damaging effects of lightning.
  • During lightning and thunderstorm, we must find a safe place for ourselves.
  • During the thunderstorm, we must not travel in open vehicles or try to be in open fields or parks.
  • The sudden shaking or trembling of the Earth due to a disturbance caused deep inside the Earth’s crust is known as an earthquake.
  • Other reasons of earthquakes are volcanic eruptions, meteor hits or an underground nuclear explosion.
  • The outermost layer of the earth is fragmented and each fragment is called a plate.
  • Earthquakes generally occur at the boundaries of the Earth’s plates. These boundaries are known as seismic or fault zones.
  • A seismograph is used to measure the intensity of an earthquake.
  • The power of an earthquake is measured on the Richter scale. An earthquake of intensity 7 or more can cause severe destruction of life and property on the Earth.
  • Necessary precautions must be taken to protect ourselves from the earthquakes.

Read and Learn More UP Board Notes for Class 8 Science

Some Natural Phenomena Important terms and definitions

Static charges: Electrical charges produced when two objects are rubbed with one another are known as static charges.
Electroscope: A device used to detect the presence of charge on an object is known as
electroscope.
Earthing: The process of transferring charge of a charged object to the Earth is called earthing.
Seismic waves: The waves produced on the Earth’s surface due to the tremors of the earthquake are known as seismic waves.
Seismograph: An instrument used to record the intensity of the earthquake is called seismograph.

Electrical Charges

Two objects acquire static electrical charge when they are rubbed with one another. Static charges do not move by themselves. There are mainly two types of electrical charges positive charges and negative charges. The presence of charge on an object can be detected by an electroscope.

The process of transferring charge of a charged object to the Earth is known as earthing. It is
provided in a tall buildings to protect us from electric shocks that may take place due to the leakage of electric current.

Some Natural Phenomena Activity 1

Aim: To show that objects get electrically charged by rubbing them with other objects
Precaution: Do not touch the rubbed end of the refill with your hand or with a metallic object.
Procedure:

  1. Take a used ball pen refill and rub it vigorously with a piece of polythene.
  2. Bring the refill close to small pieces of paper.
  3. Repeat this activity with small pieces of dry leaf, husk, and mustard seeds. Record your observations.

Observation: After rubbing the plastic refill with a piece of polythene, the refill attracts bits of paper.
Conclusion: An object can be charged by rubbing it with another object.

Some Natural Phenomena Activity 2

Aim: To charge objects by rubbing them with other objects
Procedure:

  1. Collect different objects or materials as given in the observation table.
  2. Try to charge each material by rubbing it with other materials.
  3. Record your observations in the table.

Observation:

Conclusion: Objects acquire a charge when they are rubbed with other objects.

Some Natural Phenomena Activity 3

Aim: To show that like charges repel each other whereas unlike charges attract each other
Procedure:

  1. Inflate two balloons and hang them such that they do not touch each other.
  2. Rub both the balloons with a woolen cloth and release them.
  3. Observe them carefully.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Activity 3

  1. Interaction between like charges
  2. Now, take a used pen refill and rub it with polythene.
  3.  Place this refill carefully in a glass tumbler.
  4. Rub another refill with polythene and bring it close to the charged refill.
  5. Observe the refills.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Activity 3.

Interaction between like charges

8. Now, rub a refill and place it gently in a glass tumbler. Bring an inflated charged balloon near the refill and observe it.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Activity 3..

Interaction between unlike charges

Observations:

  1. The charged balloon repelled the other charged balloon.
  2. The charged refill repelled the other charged refill.
  3. However, the charged balloon attracted the charged refill.

Conclusion: Like charges attract each other whereas unlike charges repel each other.

Some Natural Phenomena Activity 4

Aim: To show that electrical charge can be transferred from a charged object to another object through a metal conductor

Procedure:

  1. Take an empty jam bottle and a piece of cardboard slightly bigger than the mouth of the bottle.
  2. Pierce a hole in the cardboard and insert a metal paper clip in it.
  3. Now, open the paper clip as shown below.
  4. Cut two strips of aluminum foil of size about 4 cm x 1 cm each.
  5. Hang these aluminum foil strips on the paper clip.
  6. Insert the paper clip in the cardboard lid such that, it is perpendicular to it.
  7. Charge a refill and touch it with the end of the paper clip.
  8. Observe aluminum strips carefully.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Activity 4

A simple electroscope

Observations: The strips acquire the same charge from the charged refill and repel each other. They become wide open.
Conclusion: Electrical charge can be transferred from a charged object to another object through a metal conductor.

Some Natural Phenomena Objective Type Questions

A. State whether the following statements are true or false.

  1. Objects made up of the same materials acquire different electrical charges.
  2. The negative charge is acquired by a glass rod when it is rubbed with silk.
  3. Positive charges will always attract negative charges.
  4. The motion of electrical charges constitutes an electric current.

Answers:

  1. False
  2. False
  3. True
  4. True

B. Multiple Choice Questions.

Question 1. Which of the following will charge an object?

  1. Rubbing with another object
  2. Wetting with water
  3. Drying the object in the Sun
  4. All of these

Answers: 1) Rubbing with another object

Question 2. Which of these instruments is used to test whether an object is carrying charge or not?

  1. Kaleidoscope
  2. Microscope
  3. Telescope
  4. Electroscope

Answers: 4) Electroscope

C. Fill in the blanks.

  1. A body or an object possessing charge is said to be a______ object.
  2. The electrical charges generated by rubbing are________in nature.
  3. Electrical charge can be transferred from a charged object to another object through a____ conductor.
  4. ______is the process of transferring of charge from a charged object to the earth.

Answers:

  1. Charged
  2. Static
  3. Metal
  4. Earthing

Some Natural Phenomena Short Answer Type Questions

A. What do you mean by ‘static charge’?

Answers: The electrical charges that are generated by rubbing two objects with one another are known as static charges. This means that these charges do not move by themselves.

B. When you rub an air-filled balloon with your dry hair and press it against the wall, it sticks to the wall. Explain why?

Answers: When an air-filled balloon is rubbed with dry hair, it gets charged. Therefore, the presence of electrical charge on the surface of the balloon makes it stick to the wall.

C. What are the two types of electrical charges? What happens when a glass rod is rubbed with silk?

The two types of electrical charges are positive charges and negative charges. When a glass rod is rubbed with silk, it gets electrically charged. The glass rod acquires a positive charge on it.

Lightning: Causes, Effects, and Safety Measures

Lightning occurs due to the electric discharge between the clouds and the Ear or between different clouds. During the lightning and thunderstorms, it is recommended to rush to a safer place like a building, a car with closed windows, etc. If no shelter is available, we must stay far away from all the trees and squat down on our knees with our heads between our hands. Inside the house, the electrical appliances like computers, TVs, etc., should be unplugged. Taking a shower or bath must be avoided.

Lightning conductors protect buildings from the damaging effects of lightning. The lightning conductor consists of a metallic rod at the top of the building connected to an aluminum or copper cable. The cable connects to a copper plate buried in the Earth. The metallic rod acts as a medium to easily transfer electric charge to the ground.

Some Natural Phenomena Objective Type Questions

A. State whether the following statements are true or false.

  1. You should avoid taking a bath during a thunderstorm.
  2. It is advised to use an umbrella during lightning.
  3. The phenomenon of lightning takes place due to the accumulation of electrical charges in the clouds.

Answers:

  1. true
  2. False
  3. True

B. Multiple-Choice Questions

Question 1. The process of electric discharge can occur between which of the following?

  1. Two or more clouds
  2. A building and a tree
  3. Two buildings on the Earth
  4. Either a) or b)

Answers: 1) Two or more clouds

Question 2. Which of these should be done during a thunderstorm?

  1. Taking a bath
  2. Staying inside a building
  3. Using wired phones
  4. Standing under the trees

Answers: 2) Staying inside a building

C. Fill in the blanks.

  1. During the development of a thunderstorm, the air currents move_____while the water droplets move_____
  2. When the negative charges of the clouds and the positive charges of the earth meet, they produce
    streaks of bright light in the form of_____

Answers:

  1. Upwards, downwards
  2. Lightning

Some Natural Phenomena Short Answer Type Questions

A. Which places are safe for taking shelter during a thunderstorm?

Covered vehicles like cars and buses (with windows and doors closed), buildings, and houses are safe places for taking shelter during a thunderstorm.

B. Which position is recommended during a thunderstorm – lying on the ground or squatting?

Squatting is a safer position during a thunderstorm. While squatting, place your hands on your knees with your head between your hands.

Some Natural Phenomena Long Answer Type Questions

A. Explain how lightning occurs between two clouds during a storm.

Answers: During a thunderstorm, the air currents move upward while the drops of water move downwards. These movements cause the separation of charges such that the positive charges are collected near the upper surface of the clouds and the negative charges are collected near the lower surface of the

cloud. At the same time, a positive charge is accumulated near the ground. When the accumulated charges become large in magnitude, the positive and negative charges meet and produce lightning.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Accumulation of charges leading to lightning

Accumulation of charges leading to lightning

Earthquakes: Causes, Effects, and Protective Measures

Earthquakes cause huge damage to life and property. Earthquake occurs due to the motion of Earth’s plates. The Earth’s plates collide and move past one another or slide over one another.

UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Movement of earth's plates

Movement of earth’s plates

A seismograph records the seismic waves produced due to the tremors of the earthquake on the Richter scale. A seismograph consists of a vibrating rod or a pendulum, which vibrates when the tremors of an earthquake occur. The pen attached to the vibrating system records the seismic waves on the paper moving under it.

Necessary precautions must be taken to protect ourselves from earthquakes. We should avoid the use of heavy construction materials in the highly earthquake-prone areas. The buildings constructed must be ‘Quake Safe’. If we are inside the house, we must take shelter under a table and stay away from heavy objects. If we are outside the house, we must move to a clear spot.

Some Natural Phenomena Objective Type Questions

A. State whether the following statements are true or false.

  1. 1Earthquakes can also cause floods, landslides, and tsunamis.
  2. The fault zones are the most susceptible regions to earthquakes.
  3. An earthquake measuring 8 on the Richter scale is mild and quite harmless.

Answers:

  1. True
  2. True
  3. False

B. Multiple-Choice Questions

Question 1. Which of the following instruments is used to record seismic waves during an earthquake?

  1. Seismograph
  2. Richter scale
  3. Electroscope
  4. Barometer

Answers: 1)Seismograph

Question 2. Most earthquakes are caused by disturbances in which of these parts of the earth?

  1. Crust
  2. Mantle
  3. Inner core
  4. All of these

Answers: 1)Crust

C. Fill in the blanks.

  1. Each fragment of the Earth’s crust is called a____
  2. The outermost layer of the Earth is known as_____

Answers:

  1. Plate
  2. Crust

Some Natural Phenomena Short Answer Type Questions

A. How does a seismograph work?

Answers: A seismograph consists of a vibrating rod or a pendulum, which vibrates when tremors occur. The pen attached to the vibrating system records the seismic waves on the paper moving under it. Scientists construct a complete map of the earthquake by studying these waves.

Some Natural Phenomena Long Answer Type Questions

A. What is an earthquake? How is the magnitude of an earthquake expressed?

Answers: The sudden shaking or trembling of the Earth due to a disturbance caused deep inside the Earth’s crust is known as an earthquake. The magnitude of an earthquake is expressed in the Richter scale. The earthquakes measuring up to 3 on the Richter scale are said to be mild and do not cause any damage. On the other hand, earthquakes measuring 7 or more on the Richter scale are very severe and can destroy the entire area where they occur.

Some Natural Phenomena Textbook Exercises

Select the correct option in Questions 1 and 2.

Question 1. Which of the following cannot be charged easily by friction?

  1. A plastic scale
  2. A copper rod
  3. An inflated balloon
  4. A woollen cloth

Answers: (2) A copper rod

Question 2. When a glass rod is rubbed with a piece of silk cloth the rod

  1. and the cloth both acquire a positive charge.
  2. becomes positively charged while the cloth has a negative charge.
  3. and the cloth both acquire a negative charge.
  4. becomes negatively charged while the cloth has a positive charge.

Answers: (2) becomes positively charged while the cloth has a negative charge.

Question 3. Write T against true and F against false in the following statements:

  1. Like charges attract each other.
  2. A charged glass rod attracts a charged plastic straw.
  3. Lightning conductors cannot protect a building from lightning.
  4. Earthquakes can be predicted in advance.

Answers:

  1. F
  2. T
  3. F
  4. F

Question 4. Sometimes, a crackling sound is heard while taking off sweaters during winter. Explain.

Answers: Woolen clothes get charged when they get rubbed with the human body. When these clothes are taken off, the electric discharge takes place between the sweater and the body. This electric discharge produces a crackling sound.

Question 5. Explain why a charged body loses its charge if we touch it with our hand.

The human body is a conductor of electricity. When we touch a charged body with our hand, the charge of the charged body passes to the Earth through our body. Thus, the charged body loses its charge.

Question 6. Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

Answers: The destructive energy of an earthquake is measured in the Richter scale. Yes, an earthquake that measures 3 on the Richter scale will be recorded by a seismograph. Such an earthquake is mild and does not cause any damage to life and property.

Question 7. Suggest three measures to protect ourselves from lightning.

Answers:

Three safety measures to protect ourselves from lightning during a thunderstorm are:

  • Stay indoors or under a covered area
  • Do not take a shower or bath
  • Do not use electrical appliances or wired phones at home

Question 8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon.

Answers: The same materials get the same charges on rubbing and the same charges to repel each other. Therefore, balloons on rubbing are similarly charged and they repel each other. The charged and the uncharged balloons do have the same charges on them. Therefore, they attract each other.

Question 9. Describe with the help of a diagram an instrument that can be used to detect a charged body.

Answers: An electroscope can be used to detect if a body is charged or not. When a charged body touches the metal conductor, the metal strips repel each other and open wide. This proves that the body is charged.
UP Board Notes For Class 8 Science Chapter 15 Some Natural Phenomena Activity 4

A simple electroscope

Question 10. List three states in India where earthquakes are more likely to strike.

Answers: In India, the earthquake-prone areas are Kashmir, Gujarat, and Rajasthan.

Question 11. Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?

Answers: During an earthquake, if we are outside the home, we should find a clear spot, away from buildings, trees, and overhead power lines. If in a car or a bus, we should not come out and ask the driver to drive slowly to a clear spot.

Question 12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Answers: Carrying an umbrella is not a good idea during a thunderstorm because it has metal wires and a metal rod in it which can provide an easy path for the electric discharge from the clouds. Hence, it increases the risk of electrocution in case of lightning strikes.

Some Natural Phenomena Hots corner

A. A glass rod can be charged by rubbing when held in hand. However, an iron rod cannot be charged in the same way. Can you explain why?

Answers: A glass rod is an insulator. Hence, it does not transfer the electric charge produced on its surface through our hand and the body to the Earth. However, an iron rod is a good conductor of electricity. As soon as it gets charged by rubbing, the electric charges produced on its surface flow through our hand and body into the Earth. Therefore, the iron rod remains uncharged.

Some Natural Phenomena Practice Exercises

Objective Type Questions

A. Circle the odd one out.

  1. Polythene, silk, woolen cloth, wet hair
  2. Seismic zone, safe zone, fault zone, weak zone
  3. Plastic refill, glass rod, balloon, metal rod

Answers:

  1. Wet hair
  2. Safe zone
  3. Metal rod

B. Give one word for the following.

  1. The device is used to protect buildings from the damaging effects of lightning.
  2. The device is used for detecting the presence of charge on an object.
  3. The sudden shaking or trembling of the Earth.
  4. Waves are produced during an earthquake.

Answers:

  1. Lightning conductor
  2. Electroscope
  3. Earthquake
  4. Seismic waves

C. State whether the following statements are true or false.

  1. If you are indoors during an earthquake, it is best to rush outside immediately.
  2. We should go to the roof of tall buildings when it is lightning.
  3. During an earthquake, the Earth’s plates collide with each other.

Answers:

1. True
2. False
3. True

D. Fill in the blanks.

  1. Earthquakes tend to occur at the_____of the Earth’s plates.
  2. _____is the rapid flow of charge through air between the two oppositely charged clouds.
  3. Lightning occurs when____and_____ charges meet.
  4. Two charged plastic refills will_____each other.

Answers:

  1. Boundaries
  2. Electric discharge
  3. Positive, negative
  4. Repel

Some Natural Phenomena Short Answer Type Questions

A. Give two common examples of static electricity from your daily life.

Answers:

Two common examples of static electricity are:

  1. When the television sets are turned on for a long time a layer of charge develops on their screens. This is due to the presence of static electricity.
  2. When we brush our hair, they start getting attracted to the hairbrush. This is because they have acquired charge in the form of static electricity.

B. Which regions of the Earth are more prone to earthquakes?

Answers: The regions that fall on the boundaries of the Earth’s plates are weak or dangerous zones. Earthquakes are more likely to occur in these zones. These weak zones are also called seismic or fault zones.

C. Do earthquakes bring some changes to the Earth’s surface? Explain.

Answers: Yes, earthquakes can bring some geographical changes to the Earth’s surface. During an earthquake, the Earth starts shaking. Sometimes, deep and large slits appear on the Earth’s surface. Earthquakes with high intensity are so strong that new islands and coral beaches may be formed. Some freshwater springs have also been formed due to earthquakes.

Also Read

UP Board Notes For Class 8 Science Chapter 10 Reaching The Of Adolescence

by

Reaching The Of Adolescence Chapter Objectives

  • Adolescence is the period of transition from childhood to adulthood during which the human body undergoes changes leading to reproductive maturity. It starts from the age of II and continues till 18 or 19 years of age.
  • Sweat and sebaceous glands become more active during adolescence causing acne and pimples on the face of boys and girls during this period.
  • Reproductive organs become fully functional during adolescence. In boys, testes start producing sperm and in girls, ovaries enlarge and start releasing eggs.
  • Larynx is the voice-producing area present in the throat. Puberty leads to change in the voice of boys and girls. Boys; voice becomes deep and those of girls become high-pitched.
  • Hormones produced by endocrine glands control the changes that take place during adolescence.
  • Endocrine glands secrete hormones directly into the bloodstream. Hence, they are also known as ductless glands.
  • Testosterone, the male hormone, is released by the testes. It helps in sperm production.
  • Estrogen, the female hormone, is released by the ovaries and it enables eggs to mature in the ovaries. Testosterone and estrogen are known as sex hormones. They also help in the development of secondary sexual characters.
  • Thyroid gland, located in the throat region, produces thyroxine.
  • Thyroxine controls the rate of metabolism, growth, and respiration.
  • Goitre, a disease of the thyroid gland, occurs due to the deficiency of iodine in diet.
  • Adrenalin, produced by adrenal glands, helps the body to adapt to stress, anger, embarrassment, or worry.
  • All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are sex chromosomes.

Read and Learn More UP Board Notes for Class 8 Science

Reaching The Of Adolescence  Important Terms And Definitions

Adam’s apple: The protruding part of the throat in boys is referred to as the Adam’s apple.
Secondary Sexual Characters: Features that help to distinguish males from females such as facial and chest hair in males and breasts in females are known as secondary sexual characters.
Ovulation: The release of a mature egg from one of the ovaries after every 28 to 30 days is called ovulation.
Menstruation: It is the bleeding that occurs in females every month and continues for 3-5 days.
Menarche: It the first menstrual flow that occurs at puberty.

Adolescence and Puberty

Adolescence is the period during which the human body undergoes changes leading to reproductive
maturity. Adolescence starts at age of II and continues till 18 or 19 years of age. Puberty refers to the process of physical changes that happens to child’s body leading to sexual maturity. The child changes into an adult capable of sexual reproduction.

Reaching The Adolescence Activity 2

Aim: To observe the increase in the height of boys and girls with age
Procedure:
1. Use the data given in Activity I and draw a graph.
2. Mark age (in years) on the X-axis and percentage of full height on the Y-axis.
3. Highlight the point that represents your age.
4. Calculate the percentage of height you have already reached.
5. Calculate the height you might eventually reach. Tally your graph with the one shown below.

UP Board Notes for Class 8 Science Chapter 10 Reaching The Of Adolescence Activity 1

Conclusion: The rate of growth in height varies in different individuals.

Reaching The Of Adolescence Objective Type Questions

A. State whether the following statements are true or false.

  1. Boys have high-pitched voices.
  2. Genes inherited from parents influence the height of an individual.
  3. Acne in teens is caused due to the increased activity of sweat and oil glands.
  4. Testes in males, start producing sperm during puberty.
  5. Ovaries of a girl start releasing ovum soon after birth.
  6. During adolescence, the body’s muscles grow more prominently in boys than in girls.

Answers:

  1. False
  2. True
  3. True
  4. True
  5. False
  6. True

B. Multiple Choice Questions.

Question 1. At what age do boys and girls attain their maximum height?

  1. 15 years
  2. 20 years
  3. 18 years
  4. 16 yearsAnswers:  3) 18 years

Question 2. What is the protruding part of throat in boys called?

  1. An apple
  2. Adam’s apple
  3. Adam’s box
  4. None of theseAnswers: 2) Adam’s apple

Question3. Due to which of the following reasons does the voice of boys change during puberty?

  1. Increased activity of oil glands
  2. Development of sex organs
  3. Brain’s increased capacity for learning
  4. Growth of voice boxAnswers: 4) Growth of voice box

Question 4. What other name is given to adolescents?

  1. Adults
  2. Teenagers
  3. Newborn babies
  4. None of these Answers: 2)Teenagers

Question C. Fill in the blanks.

  1. Changes in the human body during adolescence mark the onset of______
  2. The period between childhood and adulthood is known as_______
  3. On an average, girls reach puberty at the age of______years.
  4. ________and sebaceous glands become more active during puberty.

Answers:

  1. Puberty
  2. Adolescence
  3. 11-13
  4. Sweat

Reaching The Of Adolescence Short Answer Type Questions

A. Is the adolescence and puberty the same?

Answers: Adolescence and puberty are not the same. Puberty is the process of physical changes by which adolescents reach sexual maturity, while adolescence is the period of psychological and social transition from childhood to adulthood.

Hormones and their Role in Reproduction

Answers: Hormones are chemical substances which control the changes that take place in human beings during adolescence. The testes in males secrete testosterone or the male hormone at the onset of puberty. It helps in the production of sperm in testes. In females, the ovaries release estrogen or the female hormone which makes the breasts develop.

Activity 3

Aim: To identify the importance of consuming iodised salt
Procedure:
Collect information regarding the importance of consuming iodised salt from doctors, magazines and the internet.
Observation: Thyroid gland needs iodine to produce thyroxine, which regulates the metabolic activities of the body.
Conclusion: lodine is essential for the production of thyroxine hormone, which regulates body’s metabolic activities. lodine deficiency causes a disease known as goitre.

Reaching The Of Adolescence Objective Type Questions

A. State whether the following statements are true or false.

  1. Hormones are released by endocrine glands.
  2. Thyroxine is a sex hormone.
  3. Both males and females develop hair under arms and in the pubic region.
  4. The male hormone testosterone is secreted by the pituitary gland.

Answers:

  1. True
  2. False
  3. True
  4. False

B. Multiple Choice Questions.

Question 1. Which hormone helps in the production of sperms?

  1. Estrogen
  2. Testosterone
  3. Thyroxine
  4. AdrenalinAnswers: 2) Testosterone

Question 2. Which of the following is the female hormone?

  1. Estrogen
  2. Testosterone
  3. Thyroxine
  4. AdrenalinAnswers: 1) Estrogen

Question 3. Which of the following are the milk-secreting glands that develop inside breasts?

  1. Endocrine glands
  2. Pituitary gland
  3. Thyroid
  4. Mammary glandsAnswers: 4) Mammary glands

Question 4. What is the role of adrenalin?

  1. Maintains blood sugar level
  2. Maintains body temperature
  3. Maintains the salt balance in the blood
  4. Maintains reproductive healthAnswers:  3) Maintains the salt balance in the blood

Question 5. Which element is essential for the formation of thyroxine hormone?

  1. Sodium
  2. lodine
  3. Bromine
  4. MagnesiumAnswers: 2) lodine

C. Fill in the blanks

  1. Adolescence lasts up to_____ years of age.
  2. The specific body part to which a hormone reaches and the body part reacts to the hormone is called the_______
  3. _____is also called the voice box.
  4. Growth hormone is produced by the_____gland.
  5. Hormones are the secretions of the_____gland.

Answers:

  1. 19
  2. target site
  3. larynx
  4. pituitary
  5. endocrine

Reaching The Of Adolescence Short Answer Type Questions

A. Why endocrine glands are called ductless glands?

Answers: Endocrine glands are known as ductless glands because they release their hormones directly into the bloodstream. Thyroid and pituitary glands are examples of endocrine glands.

B. Why iodine is important for us?

Answers: lodine is important for the production of thyroxine hormone, which regulates the metabolism of our body. Deficiency of iodine causes a disease called goitre.

C. Write the main characteristics of hormones.

Main characteristics of hormones are:

  1. Hormones are secreted by the endocrine glands.
  2. They have specific functions and hence, they affect specific organs only.
  3. Hormones are required in very little quantity.

D. Give the names of hormones secreted by the following endocrine glands.

1. Thyroid gland   2. Adrenal gland   3. Pancreas

  1. Thyroid gland secretes thyroxine
  2. Adrenal gland secrets adrenalin
  3. Pancreas secretes insulin and glucagon

Phases of Reproduction in Human Beings

In females, at the onset of puberty, ovaries mature and start releasing an egg every 28 to 30 days. Pregnancy occurs when an egg gets fertilised by a sperm.

Reaching The Of Adolescence Activity 4

Aim: To identify food items which are responsible for growth and development during adolescence
Note: This answer may vary from one student to another. Here is what a sample answer may look like.
Procedure:

  1. Create a group and note down the food items which you had taken on the previous day.
  2. Identify the items that enable proper growth.

UP Board Notes for Class 8 Science Chapter 10 Reaching The Of Adolescence Activity 4

Conclusion:

  1. A balanced diet includes carbohydrates, fats, vitamins, proteins, minerals, water and fibers in appropriate quantities.
  2. Food items such as burgers, chips, tinned snacks are not good for health and should be consumed only occasionally.

Reaching The Of Adolescence Activity 5

Aim: To spread awareness about the benefits of a balanced diet
Procedure:

  1. Prepare posters, charts depicting items that make-up a balanced diet.
  2. Display these charts and posters in your class.

Conclusion:
A balanced diet consists of all the nutrients, carbohydrates and fats, vitamins, water, minerals, and fibers, in the proper proportion. It is needed to provide energy to the body, to facilitate the formation of blood, bones, and teeth, to regulate body functions, to initiate chemical reactions in the body, and to have a healthy digestive system.

Reaching The Of Adolescence Activity 6

Aim: To prepare a report on the advantages of regular exercise
Procedure:

  1. Find out how many of your classmates exercise regularly and how many don’t.
  2. Observe and note down the difference in their fitness level.

Observation:

  1. The classmates who exercise regularly are energetic, more alert and have a better immune system.
  2. The classmates who do not exercise are lethargic, lack focus and are often unwell. Conclusion: Physical exercises such as walking, running and playing outdoor games increase physical and mental health.

Reaching The Of Adolescence Objective Type Questions

A. State whether the following statements are true or false.

  1. Females attain reproductive maturity between the ages of 10 to 12 years.
  2. Menopause occurs around the age of 30 to 40 years.
  3. Testosterone is a female hormone.
  4. Sex chromosome in human males consists of two X chromosomes.
  5. Reproductive life of a woman lasts till menopause.

Answers:

  1. True
  2. False
  3. False
  4. False
  5. True

Reaching The Of Adolescence Multiple Choice Questions.

Question 1. Which of the following is the process wherein one of the ovaries produces an egg or ovum, after it matures, in every 28 to 30 days?

  1. Menstruation
  2. Ovulation
  3. Menarche
  4. Menopause

Answers: 2)Ovulation

Question 2. Which of the following is not included in the menstrual cycle?

  1. Release of egg
  2. Maturing of egg
  3. Fertilisation
  4. dShedding of uterus wall

Answers: 3)Fertilisation

Question 3. How many pairs of sex chromosomes are present in human beings?

  1. One
  2. Two
  3. Three
  4. Four

Answers: 1) One

Question 4. Where does fertilisation in human beings take place?

  1. Fallopian tube
  2. Uterus
  3. Vagina
  4. All of these

Answers: 1) Fallopian tube

C. Fill in the blanks.

  1. ________is the first menstrual flow.
  2. The bleeding that occurs in females after every 28 to 30 days is called_______
  3. Insulin is secreted by the_______
  4. Human beings have_________pairs of chromosomes.
  5. The male hormone testosterone is secreted by_______
  6. In human beings, the_______is responsible for determining the sex of the child.

Answers:

  1. Menarche
  2. Menstruation
  3. Pancreas
  4. 23
  5. Testes
  6. Sex chromosome

Reaching The Of Adolescence Short Answer Type Questions

A. Why is adolescent pregnancy harmful?

Answers: It is harmful because a teenage mother is neither mentally nor physically capable of taking the responsibility of motherhood and coping with its challenges. Early motherhood leads to health problems in both the mother and the child.

B. What is the meaning of reproductive health?

Answers: According to the World Health Organization (WHO), reproductive health means a total well being in all aspects of reproduction, i.e., physical, emotional, behavioural and social health.

Textbook Exercises

Question 1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?

Answers: Hormones

Question 2. Define adolescence.

Answers: The period during which the human body undergoes changes leading to reproductive maturity is called
adolescence. It begins at the age of 11 years and ends between the age of 18 to 19 years.

Question 3. What is menstruation? Explain.

Answers: In females, an ovum matures and is released by one of the ovaries once in about every 28 to 30 days. If the egg is not fertilized by a sperm, it is released out from the body along with the thickened lining of the uterus. This causes monthly bleeding in women and is called menstruation.

Question 4. List changes in the body that take place at puberty.

Answers:

The following changes take place in the body at puberty:

  • The most noticeable change is the increase in the height of adolescents.
  • The voice box or the larynx grows during puberty resulting in a change in voices of both the boys
    and girls.
  • The increased activity of sweat and sebaceous glands during puberty results in acne and pimples
    on the face.
  • The male sex organs (testes and penis) develop fully during this period and testes start producing
    sperms. In girls, the ovaries expand, eggs mature and ovaries start releasing matured eggs.

Question 5. Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.

UP Board Notes for Class 8 Science Chapter 10 Reaching The Of Adolescence Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them

Question 6. What are sex hormones? Why are they named so? State their functions.

Answers: Testosterone and estrogen are called sex hormones. Testosterone is the male hormone secreted by testes at the start of puberty. Estrogen is the female hormone secreted by ovaries. It makes the egg mature. These hormones help in the development of secondary sexual characters and hence are called sex hormones.

Question 7. Choose the correct option.

(a) Adolescents should be careful about what they eat, because:

  1. Proper diet develops their brains.
  2. Proper diet is needed for the rapid growth taking place in their body.
  3. Adolescents feel hungry all the time.
  4. Taste buds are well-developed in teenagers.

Answers:  (2) Proper diet is needed for the rapid growth taking place in their body

b)Reproductive age in women starts when their:

  1. Menstruation starts
  2. Breasts start developing
  3. Body weight increases
  4. Height increases

Answers: (1) Menstruation starts

(c) The right meal for adolescents consists of:

  1. Chips, noodles, coke
  2. Chapatti, dal, vegetables
  3. Rice, noodles and burger
  4. Vegetable cutlets, chips and lemon drink

Answers:  (2) Chapatti, dal, vegetables

Question 8. Write notes on:

  1. Adam’s apple
  2. Secondary sexual characters
  3. Sex determination in the unborn baby

Answers:

  1. Adam’s Apple: The protruding part of the throat in boys is the growing voice box. It is called the Adam’s apple.
  2. Secondary sexual characters: Features which help in distinguishing a man from a woman are called secondary sexual characters. In males, the secondary sexual characters are growth of hair on face, chest, under arms, and pubic region. In females, the development of breasts and growth of hair in the under arm and pubic regions are the secondary sexual characters.
  3. Sex determination in the unborn baby: The sex of an unborn child depends on whether the zygote has XX or XY chromosomes. If the zygote has one X and one Y chromosome, it develops into a male child. On the other hand, if the zygote has two X chromosomes, it develops into a female child.

Question 9. Word game: Use the clues to work out the words.

Across:

  1. Protruding voice box in boys
  2. Glands without ducts
  3. Endocrine gland attached to brain
  4. Secretion of endocrine glands
  5. Pancreatic hormone
  6. Female hormone

Down:

  1. Male hormone
  2. Secretes thyroxine
  3. Another term for teenage
  4. Hormone reaches here through bloodstream
  5. Voice box
  6. Term for changes at adolescence

UP Board Notes for Class 8 Science Chapter 10 Reaching The Of Adolescence Across And Down

Across:

  1. Adam’s apple
  2. Endocrine
  3. Pituitary
  4. Hormone
  5. Insulin
  6. Estrogen

Down:

  1. Testosterone
  2. Thyroid
  3. Adolscence
  4. Target site
  5. Larynx
  6. Puberty

Question 10. The table given below shows the data on the likely height of boys and girls as they grow in age. Draw graphs showing the height and age of both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

The graph is given below:

UP Board Notes for Class 8 Science Chapter 10 Reaching The Of Adolescence Age And Height

It can be seen from the graph that girls at the age of 12 are generally taller than boys. At 16 years, the height of both is the same but eventually boys gain height and become taller than girls.

Reaching The Of Adolescence Hots corner

A. How will a human body be affected if the thyroid gland is removed from the body?

Answers: Thyroid gland releases thyroxine, which regulates metabolism, maturation and growth.. If it is removed, the growth and metabolic activities of human beings will be adversely affected.

Reaching The Of Adolescence Practice exercises

Objective Answer Type Questions

A. Select the odd one out

  1. Endocrine gland, Pituitary gland, Adrenals, Oil gland
  2. Testosterone, Estrogen, Insulin, Ovaries
  3. AIDS, Goitre, Diabetes, Menstruation

Answers:

  1. Oil gland
  2. Ovaries
  3. Menstruation

B. Give one word for the following.

  1. The master gland in our body.
  2. The milk secreting gland in human females.
  3. The hormone secreted by the adrenals.
  4. The process in which mature ovum is released from the ovary.

Answers:

  1. Pituitary gland
  2. Mammary Glands
  3. Adrenalin
  4. Ovulation

C. State whether the followire true or falseng statements a.

  1. During puberty, the voice box grows more in boys than in girls.
  2. Goitre is caused due to the lack of thyroxine.
  3. Mother’s chromosomes are responsible for the sex of the child.
  4. The adrenals are responsible for causing acne in teenagers.

Answers:

  1. True
  2. True
  3. False
  4. False

D. Fill in the blanks.

  1. ______is a female hormone_____
  2. _____is a male hormone.
  3. Salivary gland is a type of_____ gland.

Answer:

  1. Estrogen
  2. Testosterone
  3. Exocrine

Reaching The Of Adolescence Short Answer Type Questions

A. It is assumed that an 8-years old child will attain about 72% of his or her full height at the end of the growth period. If the child is 108 cm tall now, what would his or her height at the end of the growth period?

Answers:

Current age of child = 8 years
Current height of child = 108 cm
According to the formulas
Full height of the child =
current height of child
% of full height
108
= .*100=
12
-x100
150 cms.

Also Read

UP Board Notes for Class 8 Science Chapter 18 Pollution Of Air And Water

by

Pollution Of Air And Water Abstract

  • The force that opposes the relative motion between two objects in contact with each other is called friction.
  • Air is a mixture of gases. About 78% of this mixture is nitrogen and 21% is oxygen. Rest 1% is formed by the gases like carbon dioxide, argon, methane, ozone and water vapour.
  • Any undesirable change in the physical, chemical or biological characteristics of air is called air pollution.
  • Vehicles produce harmful gases, such as carbon monoxide, nitrogen oxides, carbon dioxide and sulphur dioxide, which pollute the air.
  • Smog is a thick fog-like layer in the atmosphere formed especially during winter. It causes breathing problems such as asthma, cough and wheezing in children.
  • Chlorofluorocarbons (CFCs) used in refrigerators, air conditioners and aerosol sprays cause depletion of the ozone layer. The ozone layer protects us from the harmful ultraviolet rays of the Sun.
  • The Supreme Court of India has ordered industries to switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas).
  • Contamination of water by harmful substances such as sewage, toxic chemicals, silt, etc., is known as water pollution.
  • An ambitious plan called the Ganga Action Plan was launched in 1985 to save River Ganga from water pollution.
  • It is important to conserve water because it is a precious natural resource. Hence, we should follow the scheme of reduce, reuse and recycle.

Read and Learn More UP Board Notes for Class 8 Science

Pollution Of Air And Water  Important Terms And Definitions

Pollutants: Substances which cause pollution are called pollutants.
Greenhouse effect: The trapping of Sun’s radiation by the Earth’s atmosphere due to the increasing level of gases such as carbon dioxide, methane, nitrous oxide and water vapour in the atmosphere is called greenhouse effect. These gases are called greenhouse gases.
Global warming: The increase in the average temperature of the Earth’s atmosphere due to the increasing levels of greenhouse gases is known as global warming.
Potable water: Water which is purified and fit for drinking is known as potable water.
Chemical contamination: Discharge of harmful chemicals into rivers and streams causing pollution of water is known as chemical contamination.
Eutrophication: Gradual increase in the concentration of phosphorus, nitrogen and other plant nutrients due to excessive fertiliser runoff into an aquatic ecosystem such as a lake is known as Eutrophication.

Air Pollution: Causes, Effects and Ways to Control it

Air is essential for the survival of all living things. The combustion of fuels in automobiles, trucks and jet planes is the major source of air pollution. Air pollution can be reduced to a great extent by using clean fuels like CNG (Compressed Natural Gas) and unleaded petrol.

Pollution Of Air And Water Activity 1

Aim: To compare the quality of air in a park and a busy road; a residential area and an industrial area; a busy traffic intersection at different times of the day for example early morning, afternoon and evening; and a village and a town

Procedure:

  1. Visit the places listed above and notice the quality of air at these places.
  2. Note down your observations.

Observations:

  1. A park is full of fresh air, whereas a busy road is much polluted because of fumes, smoke, dust and sound.
  2. A residential area is polluted but compared to an industrial area its pollution level is negligible.
  3. Early in the morning, the traffic intersection is relatively free from any pollutants. However, in the afternoon, it becomes much polluted due to vehicular smoke. In the evening, the air at a traffic intersection becomes extremely polluted.
  4. A village is usually not polluted, whereas the air in a town is polluted.

Conclusion: Air quality varies from place to place. It gets affected by the presence of undesirable substances such as vehicular emissions. The contamination of air by unwanted substances that have a harmful effect on both the living and the non-living objects is known as air pollution.

Pollution Of Air And Water Activity 3

Aim: To prepare a list of air pollutants, their sources and effects
Observation:

UP Board Notes For Class 8 Science Chapter 18 Pollution Of Air And Water Activcity 3

Conclusion:

  1. 1Excessive amount of carbon dioxide in the air leads to respiratory problems.
  2. Carbon dioxide is a greenhouse gas. Excessive amount of carbon dioxide in the Earth’s atmosphere results in trapping more than required amount of Sun’s radiation and leads to a rise in the average temperature of the atmosphere. This is called the greenhouse effect and it leads to global warming.
  3. Carbon monoxide is a poisonous gas. Inhaling it can prove to be fatal.
  4. CFCs damage the protective ozone layer of the atmosphere.

Pollution Of Air And Water Objective Type Questions

A. State whether the following statements are true or false.

  1. Air pollution is caused by natural sources only.
  2. The quality of air in villages is generally better than in big cities.
  3. Particulate matter consists of tiny particles suspended in air.
  4. Deforestation leads to a decrease in the amount of CO₂ in the air.
  5. Carbon dioxide is the main gas responsible for greenhouse effect.

Answers:

  1. False
  2. True
  3. True
  4. False
  5. True

B. Multiple-Choice Questions

Question 1. greenhouse effect leads to which of the following?

  1. Melting of glaciers
  2. Decrease in the Earth’s average temperature
  3. Depletion of the ozone layer
  4. Forest fire

Answers: 1) Melting of glaciers

Question 2. Which of the following gases mixes with blood and prevents it from carrying oxygen?

  1. Nitrogen
  2. Oxygen
  3. Carbon monoxide
  4. Carbon dioxide

Answers: 3)Carbon monoxide

Question 3. Which of these damages the ozone layer?

  1. Methane
  2. Chlorofluorocarbons
  3. Carbon monoxide
  4. Oxygen

Answers: 2) Chlorofluorocarbons

Question 4. Which of these may be caused because of air pollution?

  1. Bronchitis
  2. Asthma
  3. Irritation in eyes
  4. All of these

Answers: 4) All of these

C. Fill in the blanks.

  1. Deforestation results in______amount of CO₂ in the air.
  2. In the context of air pollution, SPM stands for_______
  3. ______ diseases are caused by air pollution.
  4. _____ is produced from incomplete burning of fuels such as petrol and diesel.
  5. The rain that becomes unusually acidic due to the presence of acidic gases is called_______

Answers:

  1. Increased
  2. Suspended Particulate Matter
  3. Respiratory
  4. Carbon monoxide
  5. Acid rain

Pollution Of Air And Water Short Answer Type Questions

A. How does carbon monoxide act on human beings?

Answers: Carbon monoxide combines with the haemoglobin in the blood and cuts off the supply of oxygen to the cells. This results in headache, drowsiness, coma and even death.

B. List ways to minimise air pollution caused by the use of petrol and diesel.

Answers:

Ways to minimise air pollution caused by the use of petrol and diesel are:

  1. Supplying sufficient air so that partially burned carbon particles and carbon monoxide are almost absent.
  2. Using platinum as a catalyst assists complete oxidation of carbon particles and harmful gases.

Water Pollution: Causes, Effects, Ways to Control it

Answers: Contamination of water bodies by unwanted substances is called water pollution. Waste materials like chemicals, drugs and paints from different industries are discharged into nearby water bodies. Boiling the water kills the disease-causing microorganisms that are present in it. We must learn ways to control water pollution and conserve water, which is a precious natural resource.

Pollution Of Air And Water Activity 5

Aim: To compare the smell, acidity and colour of different water samples

Procedure:

  1. Collect samples of water from a tap, pond, river, well and lake.
  2. Pour each sample into separate glass containers.
  3. Compare these samples for smell, acidity and colour.

Observation:

 

UP Board Notes For Class 8 Science Chapter 18 Pollution Of Air And Water Activcity 5

Conclusion: Water gets polluted when substances such as sewage, toxic chemicals, salts, etc. get mixed with IT.

Pollution Of Air And Water Activity 7

Aim: To construct a water filter with simple, everyday materials
Procedure:

  1. Take a plastic bottle and cut it into two halves from the middle. Use the upper half as a funnel by putting it upside down in the lower half.
  2. Make layers in the lower portion of the bottle with paper napkins or a fine cloth followed by cotton, sand and then gravel.
  3. Now, pour dirty water through the filter and observe the filtered water.

Observations: The filtered water was clean and free from odour.

Pollution Of Air And Water Objective Type Questions

A. State whether the following statements are true or false.

  1. Clean water may not always be safe for drinking.
  2. Boiling water kills most of the germs present in it.
  3. Disease-causing microorganisms present in water bodies are good for human beings.
  4. Oil spills have a positive effect on aquatic life.
  5. Eutrophication reduces the level of oxygen in water bodies.

Answers:

  1. True
  2. True
  3. False
  4. False
  5. True

B. Multiple Choice Questions.

Question 1. Which of these is a waterborne disease?

  1. Cancer
  2. Measles
  3. Typhoid
  4. Cataract

Answers: 3) Typhoid

Question 2. Which of the following is most harmful to aquatic animals?

  1. Heavy metal ions
  2. Sodium ions
  3. Potassium ions
  4. Chloride ions

Answers: 1) Heavy metal ions

Question 3. Water containing high salt concentration can be purified by which

  1. Boiling
  2. UV irradiation
  3. Filtration
  4. Reverse osmosis

Answers: 4) Reverse osmosis

Question 4._______ is a common chemical method to purify water.

  1. Boiling
  2. Filtering
  3. Chlorination
  4. All of these

Answers: 3) Chlorination

C. Fill in the blanks.

  1. The Ganga Action Plan was launched in______.
  2. Substances that pollute water are called_____.
  3. Excessive quantities of fertilisers that run off into water bodies act as______for algae.

Answers:

  1. 1985
  2. Water pollutants
  3. Nutrients

Pollution Of Air And Water Short Answer Type Questions

A. Define the term ‘chlorination’.

Answers: Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the polluted water.

B. How can water pollution be controlled?

Answers:

Water pollution can be controlled by:

  1. Making sure that industries treat polluted water before it is discharged into rivers and lakes
  2. Minimising fertiliser run-off into water bodies
  3. Making sure that domestic sewage is not released into water bodies without being treated first

C. Hot water can also be a pollutant. Explain how?

Answers: Hot water is discharged into rivers by power plants and industries. As a result the temperature of the water body increases. This adversely affects aquatic plants and animals and disrupts the natural ecosystems that exist in the water bodies..

Pollution Of Air And Water Textbook Exercises

Question 1. What are the different ways in which water gets contaminated?

Answers: Water gets contaminated in various ways, such as by sewage, silt, washing, bathing or other household activities. Additionally, toxic chemicals from industries, garbage and dead bodies of animals and human beings, run-off fertilisers, insecticides, pesticides, etc., also contaminate water.

Question 2. At an individual level, how can you help reduce air pollution?

Answers:

At an individual level, the following steps can be taken to reduce air pollution:

  1.  Reduce the use of automobiles; use unleaded petrol or diesel in the automobiles
  2. Plant trees or vegetation around residential areas
  3. Use public transport or carpools
  4. Enforce laws to make sure that industrial and vehicular emissions are treated before being released into the air

Question 3. Clear, transparent water is always fit for drinking. Comment.

Answers: This statement is incorrect. Clear, transparent water may appear clean but it may not necessarily be safe or fit for drinking. There may be dissolved impurities and disease-causing microorganisms present in the clear water.

Question 4. You are a member of the municipal body of your town. Make a list of the measures that would help your town to ensure the supply of clean water to all its residents.

Answers:

To obtain clean water:

  1. Industrial waste must be properly treated before being released into water resources.
  2. Sewage must be treated by physical and chemical methods before it is dumped into water bodies.
  3. Use of fertilisers should be minimised to reduce its run-off into water bodies.
  4. Dumping of wastes into water bodies, washing clothes or giving baths to animals on the banks of rivers and disposal of household sewage into water bodies without treating it first should be stopped.

Question 5. Explain the difference between pure air and polluted air.

UP Board Notes For Class 8 Science Chapter 18 Pollution Of Air And Water The Difference Between Pure Air And Polluted air
Question 6. Explain the circumstances leading to acid rain. How does acid rain affect us?

Answers: Some pollutants like sulphur dioxide, nitrogen dioxide, etc. react with the water vapour present in the atmosphere to form sulphuric and nitric acids respectively. The acid mixes in the rainwater and thus makes it acidic. Acid rain destroys crops, wild plants, steel rail tracks, monuments, and electrical equipment. It irritates the eyes, nose and throat and adversely affects water bodies.

Question 7. Which of the following is not a greenhouse gas?

  1. Carbon dioxide
  2. Sulphur dioxide
  3. Methane
  4. Nitrogen

Answer: 4) Nitrogen

Question 8. Describe the ‘Greenhouse Effect’ in your own words.

Answers: The heating of the Earth’s atmosphere due to trapped infrared radiations of the Sun is called the greenhouse effect. There are four gases which can trap infrared radiations: carbon dioxide (CO₂), ozone (03) and methane (CH₂).

Question 9. Prepare a brief speech on global warming. You have to deliver the speech in your class.

Answers: When the Sun’s rays reach the Earth’s surface, some of them are reflected back and the rest are absorbed by greenhouse gases, which include water vapour, carbon dioxide, methane and ozone. The absorbed energy maintains the temperature of the Earth. Increased concentration of greenhouse gases in the atmosphere is leading to global warming, which is the increase in the average temperature of Earth. The increase in temperature is leading to melting of polar ice caps and an increase in the water level in the sea. This poses a danger for the people living in coastal areas.

Question 10. Describe the threat to the beauty of the Taj Mahal.

Answers: Taj Mahal is made up of white marble. The whiteness of the marble used in the monument is at threat owing to air pollution. Industrial establishments around the Taj Mahal emit many harmful gases such as sulphur dioxide, nitrogen oxides, etc. These gases react with the water vapour present in the atmosphere to form sulphuric and nitric acids. These acids come down as acid rain and corrode the marble of the monument.

Question 11. Why does the increased level of nutrients in water affect the survival of aquatic organisms?

Answers: Excessive quantities of chemicals like nitrates and phosphates present in the fertilisers act as nutrients for algae to flourish. When these algae die, decomposers such as bacteria use the oxygen present in the water to decompose the algae. Thus, there is a reduction in the oxygen level of the water, which adversely affects the survival of aquatic organisms.

Pollution Of Air And Water Hots corner

A. Carbon dioxide is used by plants. Then why is it considered a pollutant?

Answers: Carbon dioxide is a natural component of the atmosphere and also a by-product of the process of respiration. However, excessive amount of carbon dioxide in the atmosphere is very harmful as it is a greenhouse gas and traps the infrared radiations of the Sun. This raises the temperature of the Earth’s atmosphere and thus excessive amount of carbon dioxide is considered a pollutant.

Pollution Of Air And Water Practice exercise

Objective Type Questions

A. Give one word for the following.

  1. IA gas which protects the Earth from the harmful ultraviolet radiations of the Sun.
  2. Commonly used chemical method for purifying water
  3. Substances which contaminate air and water
  4. Purified water that is suitable for drinking

Answers:

  1. Ozone
  2. Chlorination
  3. Pollutants
  4. Potable water

B. State whether the following statements are true or false.

  1. Sewage is a major source of water pollution.
  2. Greenhouse effect leads to depletion of the ozone layer.

Answers:

  1. True
  2. False

C. Circle the odd one out.

  1. Unleaded petrol, LPG, CNG, CFC
  2. Dust storms, Automobile exhausts, Volcanic eruptions, Pollen floating in air

Answers:

  1. CFC
  2. Automobile exhausts

D. Fill in the blanks.

  1. A combination of smoke and fog is called_____
  2. Unpolluted air contains 78%______and 21%______
  3. The stratosphere layer of the atmosphere protects us from_______

Answers:

  1. Smog
  2. Nitrogen, oxygen
  3. Ultraviolet radiations.

Pollution Of Air And Water Short Answer Type Questions

A. What is the ozone hole? What could be its possible effect?

Answers: Ozone hole refers to the region in the ozone layer of the atmosphere where the ozone gas is either absent or present in very low concentrations. This region cannot absorb the harmful ultraviolet radiations of the Sun. The UV rays are the leading cause of skin cancer, cataract and damage to the immune system.

B. Why sewage water is called polluted water?

Answers: Sewage water contains human urine and faeces, wastewater from the kitchen, bathing, washing of clothes and industrial wastes. This water is totally unfit for drinking, washing and for other purposes. It emits a foul smell and contains microorganisms that spread diseases. Hence, sewage water is called polluted water.

C How can air pollution be controlled?

Answers:

We can control air pollution by:

  • Minimising the use of aerosols
  • Using compressed natural gas (CNG) as fuel
  • Stopping deforestation and planting more trees
  • Putting a ban on the use of CFCs
  • Using clean fuels or alternative sources of energy in vehicles and factories

Also Read

UP Boar Notes For Class 8 Science Chapter 16 Light

by

Light Abstract

  • All the objects or surfaces reflect light.
  • When light from an object enters our eyes, we can see that object. The light may have been emitted by the object or reflected by it.
  • The ray of light which strikes a surface is called the incident ray. The ray of light which comes back after reflection from the surface is known as the reflected ray.
  • The point at which the incident ray strikes the surface is called the point of incidence.
  • The perpendicular drawn to the reflecting surface at the point of incidence is called the normal.
  • The angle between the normal and the incident ray is called the angle of incidence. It is denoted by Zi.
  • The angle between the normal and the reflected ray is known as the angle of reflection. It is denoted by Zr.
  • Reflection from a smooth surface such as a mirror is called regular reflection.
    When the rays reflected from a surface are not parallel, the reflection is known as diffused or irregular reflection. It takes place on rough surfaces.
  • The splitting of white light into its constituent colors is known as the dispersion of light.
  • Important parts of an eye are the cornea, iris, pupil, lens, retina, and optic nerves.
  • Light enters the eye through the cornea. It helps protect the eye and focus the light.
  • The amount of light entering into the eye is controlled by the iris. It is the iris that gives distinctive color to the eyes.
  • The size of the pupil increases or decreases depending on the brightness of the light falling on the eye.
  • The lens in our eyes forms images of the objects on a layer called the retina. The impression of an image persists on the retina for about 1/16th of a second.
  • The retina contains many nerve cells. These cells are of two types: cones and rods.
  • Sensory cells are not present at the junction of the optic nerve and the retina. Thus, no vision is possible at that spot. This spot is called the blind spot.
  • Myopia or short-sightedness is an eye defect in which people can see near objects clearly but cannot see distant objects so clearly.
  • Hypermetropia or long-sightedness is an eye defect in which people cannot see near objects
    clearly but they can see distant objects quite well.
  • A cataract is an eye defect that occurs particularly during old age. The eyesight becomes foggy during a cataract because the eye lens becomes cloudy.
  • The Braille system enables visually challenged people to read and write. This system uses patterns of raised dots to represent letters and numerals.

Read and Learn More UP Board Notes for Class 8 Science

Laws of Reflection

We can see objects because of the light that falls on them. When the light from an object enters our eyes, we see that object. The bouncing back of light rays from the surface of an object is called the reflection of light. The two laws of reflection are:

  • The angle of incidence is equal to the angle of reflection.
  • The incident ray, the reflected ray, and the normal drawn at the point of incidence, all lie in the same plane.

Light Activity 1

Aim: To verify the first law of reflection i.e. the angle of incidence is equal to the angle of reflection
Procedure:

  1. Fix a white sheet of paper on a drawing board or a table.
  2. Take a comb and close all its openings, except one in the middle. You can use a strip of black paper for this purpose.
  3. Hold the comb perpendicular to the sheet of paper.
  4. Throw light from a torch through the opening of the comb from one side. With a slight adjustment of the torch and the comb, you will see a ray of light along the paper on the other side of the comb.
  5. Keep the comb and the torch steady.
  6. Place a strip of plane mirror in the path of the light ray. Notice that after striking the mirror, the ray of light is reflected in another direction.
  7. Draw lines showing the position of the plane mirror, the incident ray and the reflected ray on the paper with the help of your friends.
  8. Remove the mirror and the comb. Draw a line making an angle of 90° to the line representing the mirror at the point where the incident ray strikes the mirror.
  9. Measure the angle of incidence and the angle of reflection. Repeat the activity several times by changing the angle of incidence.
  10. Note the observations in the observation table.

UP Board Notes For Class 8 Science Chapter 16 Light Activity 1

(a) Arrangement for showing reflection

UP Board Notes For Class 8 Science Chapter 16 Light Activity 1.

 

(b) Drawing the normal

UP Board Notes For Class 8 Science Chapter 16 Light Activity 1..

 

(c) Angle of incidence and the angle of reflection

Observation:

UP Board Notes For Class 8 Science Chapter 16 Light Activity 1...

Conclusion: The angle of incidence is always equal to the angle of reflection.

Light Activity 2

Aim: To verify the second law of reflection, i.e. the incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane
Procedure:

  1. Fix a white sheet of paper on a drawing board in such a way that a small portion of it protrudes a little beyond the edge of the drawing board.
  2. Place the plane mirror strip on the sheet of paper and hold it vertically with a mirror stand.
  3. Throw a ray of light on the mirror using a torch.
  4. Look at the reflected ray. Make sure that the reflected ray extends to the projected portion of the paper.
  5. Bend that part of the projected portion on which the reflected ray falls.
  6. Now, bring the projected portion of the paper back to its original position and observe.

UP Board Notes For Class 8 Science Chapter 16 Light Activity 2

 

Incident ray, reflected ray, and the normal at the point of incidence lie in the same plane

Observation: When the paper is bent, the reflected ray is not seen.
The entire sheet fixed on the drawing board represents a plane. The bent paper represents a new plane in which the incident ray and the normal lie.

Conclusion: The incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane.

Light Activity 3

Aim: To show the image formed by a plane mirror
Procedure:

  1. Place a source of light O in front of a plane mirror PQ such that two rays OA and OC are incident on it.
  2. Draw normal to the surface of the mirror PQ at points A and C.
  3. Now, draw the reflected rays at points A and C. Label the reflected rays as AB and CD, respectively.
  4. Extend them further. The reflected ray on the extension will appear to meet at point I.

UP Board Notes For Class 8 Science Chapter 16 Light Two Mirrior Meet At Right Angles

Observation: Since the reflected rays do not actually meet at I, but only appear to do so, we say that a virtual
image of the point O is formed at I. Such an image cannot be obtained on a screen.
Conclusion: The image formed by a plane mirror is virtual.

Light Objective Type Questions

A. State whether the following statements are true or false.

  1. It is only when light from an object enters our eyes that we see the object.
  2. The angle of reflection is the angle between the normal and the reflected ray.
  3. The angle of incidence is always greater than the angle of reflection.

Answers:

  1. ITrue
  2. True
  3. False

B. Multiple Choice Questions

Question 1. If the angle of incidence is 45°, what will be the angle of reflection?

  1. 30°
  2. 45°
  3. 55⁰
  4. 90°

Answers: 2) 45°

Question 2. Which of these phenomena enables us to see objects?

  1. Circulation of light
  2. Absorption of light
  3. Reflection of light
  4. None of these

Answers: 3) Reflection of light

C. Fill in the blanks.

  1. The light ray, which strikes any surface, is called the_____ray.
  2. The angle of incidence is the angle between_______and the____ray.

Answers:

  1. Incident
  2. Normal, incident

Light Short Answer Type Questions

A. How do we see objects?

We see various objects due to the reflection of light. All the objects reflect light falling on them. The reflected light reaches our eyes and we can see the object.

B. State the characteristics of the image formed by a plane mirror.

The image formed by a plane mirror is always:

  1.  virtual and erect,
  2. of the same size as the object, and
  3. laterally inverted

C. What is meant by lateral inversion?

In the image formed by a plane mirror, the left side of the object appears on the right and the right side appears on the left. This is known as lateral inversion.

Types of Reflection: Regular and Diffused

Objects which shine in the light of the other objects are called illuminated objects, for example, the Moon. Objects which emit their light are known as luminous objects, for example, the Sun.
Reflection from a smooth surface such as a mirror is called regular reflection. When the rays reflected from a surface are not parallel, the reflection is known as diffused or irregular reflection. When two mirrors are inclined to each other, they give multiple images. Beautiful patterns are formed in a kaleidoscope because of multiple reflections.

Light Activity 4

Aim: To show the reflection of light rays by an irregular surface
Procedure:

  1. Imagine that parallel rays are incident on an irregular surface as shown in the figure.
  2. Use the laws of reflection to construct the reflected rays at various points.
  3. Observe whether the reflected rays are parallel to each other or not.

(a) Parallel rays incident on an irregular surface

UP Board Notes For Class 8 Science Chapter 16 Light Activity 4

(b) Rays reflected from irregular surface

Observation: The rays are reflected in different directions.
Conclusion: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as diffused or irregular reflection. Reflection from a smooth surface such as a mirror is called a regular reflection.

Light Activity 5

Aim: To study the formation of multiple images
Procedure:

  1. 1Take two plane mirrors. Set them at right angles to each other with their edges touching and hinge them using adhesive tape.
  2. Place a coin in between the mirrors and notice the number of images of the coin formed.
  3. Now, hinge the mirrors using the adhesive tape at different angles, say 45°, 60°, 120°, 180°, etc. Place an object (say, a candle) in between them.
  4. Note down the number of images of the object in each case.
  5. Finally, set the two mirrors parallel to each other and then find out how many images of the candle placed between them are formed.

Observations:

  1. Three images are formed by the two mirrors placed at right angles to each other.
  2. The number of images varies depending on the angle of inclination between the two mirrors.
  3. When the two mirrors are placed parallel to each other and an object is placed between them, infinite images are formed.

Conclusion: Multiple images are formed when two or more mirrors are used in combination.

Light Activity 6

Aim: To make a kaleidoscope
Procedure:

  1. Take three rectangular mirror strips, each about 15 cm long and 4 cm wide.
  2. Join them together to form a prism as shown in the figure ‘a’. Fix them in a circular cardboard tube or the tube of a thick chart paper. Make sure that the tube is slightly longer than the mirror strips.
  3. Close one end of the tube with a cardboard disc having a hole in the center, through which you can see as shown in Figure ‘b’. To make the disc durable, paste a piece of transparent plastic sheet under the cardboard disc.
  4. At the other end, touching the mirrors, fix a circular plane glass plate as shown in Figure ‘c’. Place on this glass plate several small pieces of colored glass (broken pieces of colored bangles). Close this end of the tube with a ground glass plate.
  5. Allow enough space for the color pieces to move around.

UP Board Notes For Class 8 Science Chapter 16 Light Activity 6

Making a kaleidoscope

Observation: When you peep through the hole of a kaleidoscope, you will be able to see a variety of patterns in the tube.
Conclusion: A kaleidoscope is based on the idea of multiple images formed by using two or more mirrors placed at certain angles to one another.

Light Activity 7

Aim: To show the dispersion of light
Procedure:

  1. Take a plane mirror of suitable size and place it in a bowl (Katori).
  2. Fill the bowl with water and place this arrangement near a window such that direct sunlight falls on the mirror.
  3. Adjust the position of the bowl such that the reflected light from the mirror falls on a wall. If the wall is not white, fix a sheet of white paper on it.
  4. Observe the reflected light.

Observation: The reflected light splits into its constituent colors.

Conclusion: The sunlight, also called white light, consists of seven colors. The mirror and water form a prism. This breaks up the light into its constituent colors. Such splitting of white light into its constituent colors is known as dispersion of light.

Light Objective Type Questions

A. State whether the following statements are true or false.

  1. A reflected ray of light cannot be reflected again.
  2. Regular reflection takes place from uneven or rough surfaces.
  3. When two mirrors are placed parallel to each other and an object is placed between them, an infinite number of images of the object are formed.

Answers:

  1. False
  2. False
  3. True

B. Fill in the blanks.

  1. The sunlight, also known as white light, consists of_____colours.
  2. Working of a kaleidoscope is based on the concept of_____

Answers:

  1. Seven
  2. Multiple reflections

Light Short Answer Type Questions

A. ‘Reflection from two mirrors enables you to see objects which are not visible directly. Give two examples of this.

Example 1: After a haircut, a hairdresser places a mirror at the back of the head to show the haircut.
Example 2: Periscopes are used in submarines or tanks and also by soldiers in bunkers to see the things that are outside or above the level of observation.

B. Reflection depends on the nature of the surface on which the light falls. Explain.

When parallel rays fall on a plane surface, all the reflected rays are parallel. But if the reflecting surface is irregular (uneven), all the rays reflected from the surface are not parallel. So, the reflection depends on the nature of the surface on which the light falls.

The Human Eye: Structure, Working, Defects, and Care

The important parts of the eye are the cornea, iris, pupil, lens, retina, and optic nerve.

UP Board Notes For Class 8 Science Chapter 16 Light The Human Eye

Human eye

The transparent, front part of the white outer coat of the eye is called the cornea. The dark muscular structure behind the cornea is called the iris. The small opening in the iris is called the pupil. Its size is controlled by the iris. Behind the pupil, there is a lens that is thicker in the middle. The muscles that hold the lens in place are called ciliary muscles. The lens focuses light on a layer at the back of the eye called the retina. It contains several nerve cells.

Sensations felt by the nerve cells are transmitted to the brain through the optic nerve. The nerve cells which are sensitive to the bright light are called cones. The nerve cells which are sensitive to the dim light are called rods.

Light Activity 8

Aim: To observe the change in the size of the pupil with a change in the amount of light falling on the pupil.
Precaution: Never use a laser torch for this activity.
Procedure:

  1. Look into your friend’s eye and observe the size of the pupil.
  2. Throw light on his/her eye with a torch and observe the pupil again.
  3. Switch off the torch and observe his/her pupil once again.

Observation: When the light from the torch falls on the pupil, its size becomes smaller. When the light falling on the pupil is dim, the size of the pupil gets bigger.
Conclusion: The iris controls the amount of light entering the eye by changing the size of the pupil. When the light from the torch falls on the pupil, its size becomes smaller so that less amount of light can enter into the retina. When the light is dim, its size gets bigger so that more amount of light can enter into the retina.

Light Activity 9

Aim: To demonstrate the presence of blind spot
Procedure:

  1. Make a round mark and a cross on a sheet of white paper about 6 – 8 cm apart.
  2. Hold the sheet of paper at arm’s length from the eye.
  3. Close your left eye and look continuously at the cross.
  4. Move the sheet slowly towards you, keeping your eye on the cross.
  5. Now, close your right eye look at the round mark, and repeat the activity.

Observation: The round mark or the cross disappears at some point. The disappearance of the mark shows that there is a point on the retina that cannot send messages to the brain when light falls on it.
Conclusion: The blind spot is a region on the retina that does not have any rods and cones. Hence, the images falling on this part of the retina cannot be seen.

Light Activity 10

Aim: To show that the impression of an image persists for about 1/16th of a second on the retina even after we stop looking at the object
Procedure:

  1. Take a square piece of cardboard with sides 6 – 8 cm.
  2. Make two holes on it as shown in the figure.
  3. Thread a string through the two holes.
  4. Draw or paste a cage on one side of the cardboard and a bird on the other side.
  5. Twist the string and make the card twirl rapidly.

 

UP Board Notes For Class 8 Science Chapter 16 Light Activity 10
Observation: When the card twirls rapidly, the bird seems to be inside the cage.
Conclusion: When still images of a moving object are flashed at a rate faster than 1/16th of a second, the eye perceives this object as moving.

Light Objective Type Questions

A. State whether the following statements are true or false.

  1. Cones and rods are the light-sensitive cells.
  2. The color of the human eye is determined by the cornea.
  3. A normal eye can see nearby and distant objects.

Answers:

  1. True
  2. False
  3. True

B. Multiple Choice Questions

Question 1. Which part of the human eye controls the size of the pupil?

  1. Cornea
  2. Lens
  3. Retina
  4. IrisAnswers: 4) Iris

Question 2. Which of the following holds the lens of the eye in its place?

  1. Cones
  2. Optic muscles
  3. Ciliary muscles
  4. Rods

Answers: 2) Ciliary muscles

C. Fill in the blanks.

  1. Sensations felt by the nerve cells are transmitted to the brain through the_____
  2. Short-sightedness is also known as_____

Answers:

  1. Optic nerve
  2. Myopia

Light Short Answer Type Questions

A. What is cataract? Can it be corrected?

Answers: Cataract is a common defect of the eye wherein vision becomes foggy. It occurs particularly in old age. However, it is possible to treat this defect. The opaque lens is removed and a new artificial lens is inserted. Modern technology has made this procedure simpler and safer.

B. What is the range of normal vision of the human eye?

Answers: The minimum distance at which the human eye can see objects distinctly varies with age.
However, the range of vision of a normal human eye is from infinity to about 25 cm.

C. Explain how the human eye works.

Answers: Light enters our eye through the cornea. The amount of light entering the eye is controlled by the iris. The lens focuses the image of the object on the retina, which converts these optical images into optical pulses. These pulses are sent to the brain through the optical nerves.

Light Textbook Exercises

Question 1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

Answers: We see things only when light reflected by them enters our eyes. Since no light is reflected from the surface of the objects in a dark room, we are not able to see them. However, outside the room, where light is available, objects can reflect light and thus, we can see them.

Question 2. Differentiate between regular and diffused reflection. Does diffuse reflection mean the failure of the laws of reflection?

The key differences between regular and diffused reflection are:

UP Board Notes For Class 8 Science Chapter 16 Light Difference Between Regular And Diffuses Reflection

No. Diffused reflection does not mean the failure of the laws of reflection because the irregularities in the reflecting surface cause it.

Question 3. Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

  1. Polished wooden table
  2. Chalk powder
  3. Cardboard surface
  4. Marble floor with water spread over it
  5. Mirror
  6. Piece of paper

Answers:

  1. A polished wooden table will have regular reflection because its surface is smooth.
  2. A chalk powder will give a diffused reflection because the chalk powder particles are not smooth.
  3. The cardboard surface has minute irregularities on it, so it will have a diffused reflection.
  4. Marble stone with water spread over it will have regular reflection if the water is stable. However, if waves are formed, diffused reflection will take place.
  5. Any mirror has a shiny and smooth surface. Therefore, regular reflection will be observed.
  6. A piece of paper has a rough surface. Therefore, the diffused reflection will be observed.

Question 4. State the laws of reflection.

The laws of reflection are as follows:

(a) The angle of incidence is always equal to the angle of reflection.
(b) The incident ray, the normal at the point of incidence, and the reflected ray, all lie in the same plane.

Question 5. Describe an activity to show that the incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.

Procedure:

  1. Fix a white sheet of paper on a drawing board in such a way that a small portion of it projects a little beyond the edge of the drawing board.
  2. Place a plane mirror strip on the sheet of paper and hold it vertically with a mirror stand.
  3. Throw a ray of light on the mirror using a torch. Look at the reflected ray. Make sure that the reflected ray extends to the projected portion of the paper.
  4. Bend the part of the projected portion on which the reflected ray falls. Now, bring the projected portion of the paper back to its original position and observe.

Observation: The entire sheet fixed onto the drawing board represents a plane. When the paper is
bent, a new plane is formed which is different from the plane in which the incident ray and the normal lie. So the reflected ray is not seen.
Conclusion: The incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane.

Question 6. Fill in the blanks in the following:

  1. A person I’m in front of a plane mirror seems to be from his image.
  2. If you touch your_____ ear with the right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with the_____ hand.
  3. The size of the pupil becomes______when you see in dim light
  4. Night birds have______ cones than rods in their eyes.

Answers:

  1. I
  2. Left, left
  3. Larger
  4. Lesser

Choose the correct option in Questions

Question 7. The angle of incidence is

  1. Always
  2. Sometimes
  3. Under special conditions
  4. Never

Answer: (1) Always

Question 8. An image formed by a plane mirror is

  1. (virtual, behind the mirror, and enlarged
  2. virtual, behind the mirror, and of the same size as the object
  3. real at the surface of the mirror and enlarged
  4. real, behind the mirror, and of the same size as the object.

Answer: (2) virtual, behind the mirror, and of the same size as the object

Question 9. Describe the construction of a kaleidoscope.
Answer: A kaleidoscope is made up of three narrow strips of plane mirrors inclined at 60° to each other and enclosed in a tube. A ground glass plate on its inner side closes one end of the tube. The space between the mirrors is filled with colored pieces of glass or broken bangles. Cardboard with a hole in the center is fixed on the other end of the tube through which different patterns formed by the mirrors are seen.

Question 10. Draw a labeled sketch of the human eye.

UP Board Notes For Class 8 Science Chapter 16 Light The Human Eye

 

Question 11. Gurmit wanted to perform an activity to see the change in the size of the pupil by throwing light into the eyes using a laser torch. Her teacher advised her not to do so. Can you explain the basis of her teacher’s advice?

Answers: Gurmit’s teacher advised her not to do so because laser light is harmful to the eyes. It can cause permanent damage when flashed directly in the eyes.

Question 12. Explain how you can take care of your eyes.

The following precautionary measures should be taken to care for eyes:

  1. We should wash our eyes frequently with cold water.
  2. We should not rub our eyes or touch them with dirty hands. If dust particles enter our eyes, we should wash our eyes with clean water.
  3. We must not look at the Sun or a powerful light directly.
  4. We should eat a sufficient quantity of vitamin A-enriched food like raw carrots, green vegetables, papaya, mango, eggs, milk, etc.
  5. We should maintain a suitable distance while reading or watching TV.
  6. An eye specialist should be consulted in case of any irritation or redness in the eyes.

Question 13. What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

If Zi= angle of incidence, and Zr= angle of reflection
Then, Zi + <r = 90° (given)
But Zi = Zr (according to the laws of reflection)
:: Zi+Zi= 90°
(186
or, 22i = 90°
or, <r = Zi = 45°
Therefore, the angle of incidence of the ray will be 45°.

Question 14. How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

Infinite images of the candle will be formed if it is placed between two parallel plane mirrors.

Question 15. Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the figure below. Draw the reflected ray from the second mirror.
Answer:

UP Board Notes For Class 8 Science Chapter 16 Light Two Mirrior Meet At Right Angles

Question 16. Bhoojo stands at A just on the side of a plane mirror as shown in the figure below. Can he see himself in the mirror? Also, can he see the image of objects situated at P, Q, and R?
Answer: Bhoojo cannot see his image. However, he can see images of objects P but not Q and R.

UP Board Notes For Class 8 Science Chapter 16 Light Bhoojo light

Question 17. (a) Find out the position of the image of an object situated at A in the plane mirror (Figure given below).

  1. (Can Paheli at B see this image?
  2. Can Bhoojo at C see this image?
  3. When Paheli moves from B to C, where does the image of A move?

Answer:

  1. The image of A in the mirror will be as far behind as the object in front of the mirror.
  2. Yes, Paheli can see the image.
  3. Yes, Bhoojho can see this image.
  4. When Paheli moves from B to C, the image of A will not move.

Light Hots corner

A. If all the objects around us were to reflect light in a regular way, what possible problems might we face?

Answers: When the rays of light fall on an object with a smooth surface, they are reflected in one direction only. On the other hand, when the rays of light fall on an object with an uneven surface, they get reflected in different directions. It is due to the irregular reflection that we can see objects from every direction. Further, irregular reflection of the sunlight by the objects around us enables our room to have light during the day even if sunlight does not fall directly.
However, if all the objects around us were to reflect light regularly, we would not be able to see the objects (1) from different directions and (2) during the daytime even when light is not falling on them directly.

Light Practice Exercise Objective Type Questions

A. Circle the odd one out.

  1. Cornea, Iris, Retina, Cataract
  2. Kaleidoscope, Telescope, Microscope, Binoculars
  3. Crow, Kite, Eagle, Owl

Answers:

  1. Cataract
  2. Kaleidoscope
  3. Owl

B. Give one word for the following.

  1. The splitting of light into its constituent colors
  2. The dark muscular structure behind the cornea gives the eye its distinct color
  3. The ray of light which returns after striking the surface

Answers:

  1. Dispersion
  2. Iris
  3. Reflected ray

C. State whether the following statements are true or false.

  1. An owl has a larger number of rods and a lesser number of cones.
  2. Rods are sensitive to bright light.
  3. A plane mirror forms an image of an object as far behind the mirror as the object in front of it.

Answers:

  1. True
  2. False
  3. True

D. Fill in the blanks.

  1. The image formed by a plane mirror is called_______image.
  2. In cataracts, the lens of the eye becomes______.
  3. There are______types of nerve cells found in the retina

Answers:

  1. Virtual
  2. Foggy
  3. Two

Light Short Answer Type Questions

A. What is a blind spot?

Answers: At the junction of the optic nerve and the retina, there are no sensory cells. Hence, no vision is possible at that spot. This is called the blind spot.

B. Why is it difficult to see objects in a room when you come from outside on a bright sunny day?

Answers: In bright sunlight, the iris causes the pupil to become smaller so that only a small amount of light enters the eye. However, when a person enters into a room, it takes time to increase the diameter of the pupil so that more amount of light can enter into the eyes to see the object. This is why, it is difficult to see objects in a room when we come from outside on a bright sunny day.

C. Explain how the Braille system enables visually challenged people to read and write.

Answers: The Braille system has 63 dot patterns or characters. Each character represents a letter, a combination of letters, a common word or a grammatical sign. Dots are arranged in cells of two vertical rows of three dots each. The patterns of dots when embossed on Braille sheets help visually challenged people to recognize words by touching them.

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