Class 10 Biology

Food Chains And Webs

How does the food prepared by green plants or stored in dead matter move in a series of organisms feeding on one another?

Trophic Levels

They are levels in the biotic community at which organisms obtain their food.

1. First Trophic Level (T1). It is the level of food manufacturers or producers which prepare food from inorganic raw materials with the help of solar energy.
2. Second Trophic Level (T2). It is the level of herbivores or primary consumers which directly feed on plants or plant parts.
3. Third Trophic Level (T3). It consists of primary carnivores or secondary consumers which prey upon herbivores.
4. Fourth Trophic Level (T4). It is the level of secondary carnivores or tertiary consumers which feed on primary carnivores.
5. Fifth Trophic Level (T5). It consists of tertiary carnivores which prey upon secondary carnivores.

Food Chains

A food chain is a sequence of trophic levels through which food passes in a biotic community from producers to ultimate carnivores. Here, members of one trophic level become food for members ofthe next trophic level.

Actually food chain is a summary of who eats whom. A food chain may have 3-5 trophic levels. It is rarely more. The various steps of a food chain are producers and various categories of consumers.

1. Producers. They constitute the first trophic level (T1) or base of a food chain. Producers manufacture organic food from inorganic raw materials with the help of solar energy. The major producers are plants in terrestrial ecosystems and phytoplankton in aquatic ecosystems.
2. Herbivores. They constitute the second trophic level (T2). Herbivores feed on plants or plant parts, for Example caterpillars, grasshoppers, deer, rabbits, mouse.
3. Primary Carnivores. They belong to the third trophic level or T3. Primary carnivores or secondary consumers feed on herbivores, Example Frog, Fox.
4. Secondary Carnivores. They are generally large-sized carnivores that belong to the fourth trophic level or T4. They prey upon primary carnivores, Example Hawk. Kingfisher.

Terrestrial Food Chains

1. Three Steps Forest Food Chain
   Plants →Deer →Lion
   (producers) (herbivores) (carnivores)
2. Four Steps Grassland Food Chain
   Grass →Insects →Insectivorous Birds→ Hawk
   (producers) (herbivores) (carnivores 1) (carnivores 2)
3. Five Steps Grassland Food Chain
   Grass→Insects → Frog →Snake→ Hawk
   (producers) (herbivores) (carnivores 1) (carnivores 2) (carnivores 3)

Aquatic Food Chains

1. Four-Step Pond Food Chain

Aquatic →Plants Crustaceans→ Fish →King Fisher
(producers) (herbivores) (carnivores 1) (carnivores 2) (carnivores 3)

2. Five-Step Ocean Food Chain

Phytoplankton →Zooplankton →Small fish →Larger fish →Shark
(producers) (herbivores) (carnivores 1) (carnivores 2) (carnivores 3)

Ecological Pyramids

Ecological pyramids (Elton 1927) arc graphic representations of different ecological parameters like number, biomass, and energy arranged successively with producers at the base, herbivores above them, followed by primary carnivores and top carnivores at the top. The quantity is indicated by the length of the box. It is also written in figures.

Pyramid of Numbers. It is a graphic representation of the number of individuals in a unit area sequence-wise with producer the base, herbivores above them, carnivores L carnivores successfully above them. Only very few top carnivores are supported by a producer population of millions of grassland.

Pyramid of Biomass. It is a graphic representation of biomass or living organic matter present per unit area sequence-wise with producers at the base, herbivores above them followed by carnivores in various categories. Maximum biomass is present in producers. It decreases stepwise with the rise in trophic level.

Pyramid of Energy. It is a graphic representation of energy contained per unit area in various trophic levels with producers at the base, herbivores above them followed by carnivores. Maximum energy is contained in producers with a minimum in the top carnivores.

Flow of Energy and Ten Percent Law

In any ecosystem the flow of energy is unidirectional. Producers obtain energy from sunlight. About 1% of solar energy falling on leaves is changed into organic food. From here the food energy’ passes into herbivores. Herbivores cannot pass back the energy’ to producers nor do the producers pass back energy into the environment.

Lindeman (1942) found that during the transfer of energy from one trophic level to the next higher trophic level only 10% of energy is transferred. 90% of energy is lost in transfer, digestion, respiration, and other body activities. It is lost to the environment. The phenomenon is called the 10% law.

Because ofthe large amount of energy lost at every’ transfer, energy reaching higher trophic levels becomes small. Because the number of top carnivores is always small.

Suppose 1 million Joules of solar energy falls on producers. Producers have 1% efficiency, i.e., they will trap 10,000 Joules of energy in organic food. Herbivores will store 1000 Joules of food energy at 10% efficiency, primary carnivores 100 Joules of food energy while secondary carnivores shall have only 10 Joules of food energy.

Because of the smallness of food energy available at higher trophic levels, both the number of trophic levels as well as members of higher trophic levels will be small.

Biological Magnification (Biomagnification)

What is the phenomenon responsible for the increase in the concentration of persistent chemicals with the rise in trophic levels?

It is an increase in the concentration of persistent soluble chemicals with the rise in trophic levels.

Toxic chemicals are sprayed over crops to protect them from pests and pathogens. They are also sprayed in homes and commercial places to kill insects, mosquitoes, flies, and cockroaches.

Anumberoftoxic chemicals and heavy metals are also released by industries. All these enter waterbodies, soil, groundwater, and then plants. From plants, the persistent chemicals pass into herbivores and from them to carnivores.

Since there is regular entry ofthe chemicals in the food chain, their concentration increases with time in each trophic level. They prove harmful and even fatal to higher trophic-level animals.

Man is also harmed to a great extent as he obtains these chemicals from several sources- water, plant food, milk and meat An example of biomagnification is the study of the concentration of DT in water and the food chain.

Water→Plankton →Small Fish →LargerFish →Fish Eating Birds
0.003pm 0.04 ppm  0.5ppm        2.0ppm                25ppm

The population of fish-eating birds declined in the 1960s due to it. DDT as a pesticide has been banned since then. However, there are several other persistent and toxic chemicals.

Activity 5.5 Pesticide Levels in Food Items and Beverages

Readymade food items and beverages have been found to contain pesticide traces in the past. Many states had to ban the sale of such food items and beverages.

The pesticides are present in the groundwater as well as inside the plant products because they are used to protect the plants from pests.

The sprayed pesticides enter the soil, groundwater as well as water bodies besides the plants and their products. Therefore, beverages and readymade food items prepared from such groundwater as well as plant produce shall contain traces of pesticides.

Farmers must switch over to organic farming where pesticides are not sprayed. Buildings must be provided with double doors. Industries must have safety measures to control pollution.

Food Web

It is a network of several food chains present in an ecosystem where they get interconnected at various trophic levels. It makes each food available to several populations and a population capable of feeding on several foods.

In a food web rabbits can be eaten by foxes, wildcats, wild dogs, jackals, wolves, and hawks. Hawk can feed on snakes, rabbits, and several types of birds. Therefore, in the food web, no consumer is dependent upon a single type of food.

It does not get starved if its favorite food is in short supply. Similarly, if an organism becomes overpopulated, it will be noticed more by predators and therefore, eaten more in number.

On the other hand, an endangered species will not be eaten to a large extent. It will get the opportunity to recover. Thus, the food web is a mechanism for maintaining the stability of an ecosystem.

Question 1. What are trophic levels? Give an example of a food chain and state the different trophic levels init?
Answer: Trophic levels are levels in the biotic community at which organisms obtain their food. The food chain is the sequence of trophic levels through which food passes in a biotic community from producers to ultimate carnivores. A typical grassland food chain consists of the following trophic levels.

Grass →Insects →Insectivorous birds →Hawk
(producers) (herbivores) (carnivores 1) (carnivores 2)

Question 2. What is the role of decomposers in the ecosystem?
Answer: Decomposers are microscopic saprophytes like many bacteria and fungi, which feed on organic remains and organic excretions. They pour digestive enzymes over the organic matter for its simplification and solubilization.

The process releases many inorganic nutrients previously trapped in organic matter. The process is called mineralization. The soluble simple organic substances are picked up by decomposers for their growth. The released minerals become available to plants for their growth and manufacture of food.

Our Environment Multiple-Choice Questions

Question 1. In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form of

1. Heat Energy
2. Chemical energy
3. Mechanical energy
4. Light energy

Answer: 2. Chemical energy

Question 2. Soil fertility is determined by its ability to

1. Decay organic matter
2. Hold organic matter
3. Hold water
4. Support life

Answer: 4. Support life

Question 3. A food web is constituted by

1. Relationship between the organisms and the environment
2. Relationship between plants and animals
3. Various interlinked food chains in an ecosystem
4. Relationship between animals and the environment

Answer: 3. Various interlinked food chains in an ecosystem

Question 4. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

1. 100%
2. 10%
3. 1%
4. 0.1%

Answer: 2. 10%

Our Environment Short Answer Type Questions

Question 1. Construct an aquatic chain showing four trophic levels.
Answer: Algae → Crustaceans → Small Carnivorous Fish → Large Carnivorous Fish.

Question 2. Explain biological magnification with the help of an example.
Answer: Biological magnification or biomagnification is the increase in the concentration of a soluble but persistent chemical per unit weight of an organism with the rise in trophic level. A study on DDT concentration has given the following data.

Water → Plankton → Small Fish → Large Fish → Fish Eating Birds 0.003 ppm 0.04 ppm 0.5 ppm 2.0 ppm 25 ppm

Question 3. Observe the food chain: Plant (1000 J) → Goat → Lion.

1. If autotrophs occupy the first trophic level and are called producers what are herbivores called?
2. How much energy does the Lion get in the above chain?

Answer:

1. Herbivores are primary consumers.
2. As per the 10% law, 1000 J of energy in plants is transferred as 100 J of energy in goats and only 10 J in Lions.

Question 4. The maximum concentration of harmful chemicals accumulates in human beings. State the phenomena involved and justify this statement.
Answer: Biological magnification Human beings are omnivorous. They live at the top of every type of food chain. Harmful chemicals enter the human body through groundwater, plant produce, milk, eggs, and meat. They remain in the human body and continue to accumulate. As a result, the maximum concentration of harmful chemicals occurs in human beings.

Question 5. In the food chain, (Grass → Deer→ Lion), operating in a forest what will happen if all the (a)Lions are removed (b) Deer are removed?
Answer:

Removal of lions will result in a rapid increase in the population of deer. The rise in deer population will ultimately result in the eating of the whole grass and desertification of the area. This will cause the death of deer.

The removal of deer will result in excessive growth of grass but no food for lions. As a result, lions will die.

Question 6. List two reasons to show that the existence of decomposers is essential in an ecosystem.
Answer:

1. Decomposers feed on organic remains and cleanse the earth of the same.
2. They release minerals from organic remains that are utilized by plants for the synthesis of organic matter.

Question 7. A food web is shown as a series of branching lines of food chains. Explain and justify the statement.
Answer: The food web is a network of many food chains that get connected at different trophic levels so that several alternate feeding connections develop amongst the organisms. These alternate feeding connections appear as branching lines of the food chains.

Question 8. Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment.
Answer: Bacteria and fungi are called decomposers as they bring about the degradation of organic remains. For this, they secrete digestive enzymes over the organic remains. The enzymes convert complex substances into simple and soluble substances. The latter are used as food by the decomposers. During this decomposition, the inorganic nutrients forming part of organic matter are released.

Advantages: Decomposers cleanse the earth of organic remains. They bring about the release of inorganic nutrients which become available for recycling.

Question 9. What is an ecosystem? List its main components. We do not clean ponds or lakes but an aquarium needs to be cleaned regularly. Explain.
Answer:

Components of Ecosystem, Biotic components are producers, consumers, and decomposers. Abiotic components are climate, soil, topography, inorganic nutrients, and organic remains.

An aquarium is an incomplete and imbalanced artificial ecosystem that lacks producers, food chains, and decomposers. There is no self-cleaning as occurs in ponds or lakes.

Question 10. “Our food grains such as wheat and rice, vegetables, fruits, and even meat are found to contain varying amounts of pesticide residues.” State the reason to explain how and why it happens.
Answer: Cereals, vegetable, and fruit crops are sprayed with pesticides to protect them from pests. These pesticides not only enter the crop plants but also pass into soil, groundwater, and nearby water bodies. Animals drinking the contaminated water and eating pesticide-containing fodder will also come to have the pesticides. Therefore, green vegetables, fruits, and meat will have varying amounts of pesticides.

Question 11. “Energy flow in a food chain is unidirectional.” Justify this statement.
Explain how the pesticides enter the food chain and subsequently get into our bodies.
Answer:

Energy from the sun enters the food chain at the level of producers. The efficiency is 1%. From producers energy (as food energy) passes to herbivores. The efficiency is 10%. The rest of the energy is dissipated in transfer, digestion, and respiration.

Primary carnivores similarly can retain only 10% of the energy obtained from herbivores. Because ofthe regular dissipation of energy at every step and decrease of energy with the rise in trophic level, energy cannot flow back. Thus, its flow is unidirectional from

Sun→producers → herbivores → primary carnivores→ secondary carnivores.

Pesticides are sprayed over crops to protect them from pests. They enter the plants, soil, vegetation, groundwater, and water bodies and hence all types of food chains and from there to humans as man is a consumer of water, crop products, milk, eggs, meat, etc. all of which get contaminated with pesticides.

Question 12. How do pesticides spray over crops and fruit plants enter our bodies and accumulate? Name the phenomenon by which their concentration increases in our body.
Answer: Pesticides sprayed over plants enter their bodies and reach their edible parts. They also seep into the ground and contaminate groundwater. Groundwater also enters plants and further contaminates them.

From vegetables, fruits, other edibles, and groundwater pesticides regularly enter the human body and accumulate. They also enter the food chains which pass the same to human beings. Accumulated pesticides become highly toxic and cause harm to vital organs.

The increase in the concentration of non-biodegradable substances with time and with the rise in trophic levels is called biomagnification.

Question 13. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.
Answer: Ecosystem. It is a self-sustained segment of nature that has a biotic community and abiotic components of the environment both interacting and exchanging materials between them.

Question 14. Define a food chain. Design a food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies. What is the phenomenon called?
Answer: Food Chain. It is a sequence of trophic levels through which food passes in the biotic community from producers to ultimate consumers. It is also called the series of eating and being eaten.

Maximum Concentration of Pollutant. Members of the highest trophic level have the maximum concentration of pollutants. The phenomenon of a rise in the concentration of nonbiodegradable pollutants with the rise in trophic levels is called biomagnification.

Question 15.

1. Construct a terrestrial food chain comprising four trophic levels.
2. What will happen if we kill all the organisms at one trophic level?
3. Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the organisms at the second trophic level is 2000 J.

Answer:

1. Grass → Insects → Frog → Snake.
2. If all the organisms of one trophic are killed (/) The animals of higher trophic levels will starve and die Organisms of the lower trophic level will increase.
3. 2nd Trophic level → 3rd Trophic level → Fourth Trophic Level

⇒ \(2000 \mathrm{~J}{10 \%} 200 \mathrm{~J} {10 \%} 20 \mathrm{~J} .\)

Question 16. What are decomposers? List two consequences of their absence in the ecosystem. 
Answer: Decomposers. They are microscopic organisms like many bacteria and fungi that break down complex components of organic remains and excretions into simpler forms releasing minerals in the process.

Consequences of Their Absence. Organic remains and excretions will pile up (it) There will be no recycling of minerals and other nutrients in nature.

Question 17.

1. From the following group of organisms, create a food chain that is the most advantageous for human beings in terms of energy Hawk, Rat, Cereal plant, Goat, Snake, Human beings
2. State the possible disadvantage if the cereal plant is growing in soil rich in pesticides.
3. Construct a food web using the organisms mentioned above.

Answer:

1. Cereal Plants→ Human Beings.
2. Pesticides enter the cereal plants and undergo accumulation with the rise of trophic levels as they are non-biodegradable. The phenomenon is called biomagnification.

Question 18.

1. Define ecosystem.
2. Autotrophs are at the first level of the food chain. Give reason.
3. In a food chain of frogs, grass, insects and snakes assign trophic levels to frogs. To which category of consumers do they belong?

Answer:

• Only autotrophs can manufacture food and transfer this food and its energy to the next level of the food chain.
• Grass→Insects→Frogs→Snakes
• Primary consumer Secondary consumer Tertiary consumer

Question 19.

1. State the reason for the consequence of the decrease in the number of carnivores in an ecosystem.
2. In a food chain, state the trophic level at which the concentration of harmful chemicals is maximum.
3. Why is it so?

Answer: (cr) Decrease in carnivores will increase the number of herbivores being their prey.

Top carnivores. The harmful chemicals are non-biodegradable. They accumulate in higher qua rise in trophic level.

Question 20. What is meant by trophic level in a food chain? The energy flow in a food chain is
Answer: Trophic Level. It is the level in the biotic community at which a particular group of organisms obtain Energy flow.

Question 21. Complete the following flow chart based on the ecosystem and its components

Answer:

1. Aquatic,
2. Abiotic
3. Air, water, soil, temperature, light.
4. Plants and animals.

Question 22.

1. Create a food chain of insects, hawks, Grass, snakes, and frogs.
2. Name the organism at the third trophic level.
3. Which organism will have the highest concentration of non-biodegradable chemicals?
4. Name the phenomenon associated.
5. If 10,000 joules of energy are available to frogs, how much energy will be available to snakes

Answer:

1. Grass Insect Nake Hawk.
2. Frog,
3. Hawk
4. Biomagnification
5. 1000 joules (10,000/10).

Question 23. What is an ecosystem? List any two natural ecosystems.
We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Why
Answer: Pond ecosystem, Forest ecosystem.

Question 24. In the following food chain, only 2J of energy was available to peacocks. How energy would have been present in the grass? Justify your answer. Grass→Grasshopper→ Frog → Snake→Peacock
Answer: Transfer of energy from the lower to the next higher trophic level follows the 10% law. 2 J energy in a peacock ha from 20 J energy of a snake. 20 J energy of the snake has been obtained from the 200 J energy of the frog.

Frog gets this much energy from the 2000 J (200 x 10) energy of a grasshopper. 2000 J energy of grasshopper has come from 20,000 J (2000 x 10) energy of grass.

Question 25.

1. What is meant by garbage? List two classes into which garbage is classified.
2. What do we mean when we say that the “enzymes are specific in their action”?

Answer: Garbage is rubbish formed of mostly household waste and similar waste from vegetable and fruit markets as well as food industries, Example food left-over, spoiled food, vegetable and fruit peels, tea leaves, milk powder, polythene bags, wrappers, broken crockery, paper waste clothes, waste plastic and metallic articles.

Garbage consists of two types of waste, biodegradable and non-biodegradable. Biodegradable Garbage.

It is garbage that gets decomposed naturally by microbes, for Example, vegetable and fruit peels, food leftovers, paper, etc. Nonbiodegradable Garbage. It is garbage that cannot be disposed of by microbes, for example, broken crockery, plastic, and metallic wastes.

Enzymes are specific for various substrates. They require a particular pH temperature for their activity.

Question 26.

1. Human beings are most adversely affected by biological magnification. State the reason.
2. Why can ordinary washing of edibles (fruits and vegetables) not reduce the effect of biological magnification?

Answer: Biological magnification is the increase in the concentration of non-biodegradable or persistent chemicals with the rise in trophic level.

As human beings occupy the top position in various food chains, they receive the maximum concentration of these chemicals. Being long-lived, the harmful chemicals accumulate in the human body and cause toxic effects.

Washing vegetables and fruits can remove harmful chemicals from their surface. However, it cannot remove nonbiodegradable chemicals as they occur inside the food items.

Question 27.

1. What are trophic levels in a food chain?
2. Explain the flow of energy through the food chain.
3. Write a four-trophic level food chain.

Answer:

1. Trophic Levels. They are levels in the biotic community at which organisms obtain their food. Producers constitute the first trophic level (T1), herbivores the second trophic level (T2), primary carnivores the third trophic level (T3), and so on.
2. Flow of Energy Through Food Chain.
3. Grass →Insect →Insectivorous bird→Hawk.

How Do Our Activities Affect The Environment Questions

India today is facing the problem of overuse of resources, contamination of water and soil, and lack of methods of processing waste. The time has come for the world to say goodbye to “single-use plastics”.

Steps must be undertaken to develop environment-friendly substitutes, effective plastic waste collection, and methods of disposal. Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques.

Bioremediation involves introducing microbes into landfills to naturally ‘break’ it down. Biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component.

The city managed to chip away 15 lakh metric tonnes of waste at the cost of around < 10 crore. A similar experiment was successfully carried out in Ahmedabad also.

Question 1. What is ozone and how does it affect any ecosystem?
Answer: Ozone is a molecule formed by three atoms of oxygen O3. Normal oxygen is 02 or formed of two atoms. Ozone is toxic if present in the lower atmosphere or troposphere.

It destroys the photosynthetic cells of plants and causes injury to mucous membranes, eye irritation, and internal hemorrhage. However, ozone present in the stratosphere is highly useful.

It protects the ecosystem from harmful UV radiations (UVC 100 – 280 nm, UVB 280 – 320 nm) by dissipating their energy. In case of ozone depletion, there would be a rise in skin cancers, cataracts, photobombing, a decrease in immunity, a fall in photosynthetic efficiency, and death of larvae.

Question 2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: The following two methods can help in reducing the problem of waste disposal:

1. Recyclable Waste. It should be separated from the rest ofthe garbage. Recyclable waste includes paper, cardboard, polythene, plastic, glass, metallic cans, etc. They are picked up by rag pickers for selling them to factories for recycling.
2. Nonrecyclable Biodegradable Waste. It includes stale food, leftover food, vegetable peelings, fruit peelings, used tea leaves, prunings of the kitchen garden, etc. It can be converted into compost for your kitchen garden, or school garden or handed over to municipal waste disposal workers.

How Do Our Activities Affect The Environment Short Answer Type Questions

Question 1. What is ozone? How does it protect the organisms on the earth?
Answer: Ozone is a triatomic molecule that is formed by three atoms of oxygen, 03. Ozone present in the stratosphere filters out harmful high-energy UV radiations and thus protects the organisms on the earth from them.

Question 2. We often observe domestic waste decomposing in the by-lanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment
Answer: Domestic waste is often thrown outside each home or at one corner of the street. This attracts pigs, stray cattle, and dogs who scatter the waste that starts decomposing and emitting a foul smell. The practice is unhygienic. Domestic waste must be segregated and the segregated waste must be lifted by municipal staff.

Question 3. Explain how ozone is formed in the atmosphere. How does it protect living beings from harmful radiations of the sun?
Answer: Ozone is formed in the stratosphere from O₂ by the action of energy UV radiations.

⇒ \(\begin{gathered}
\mathrm{O}_2 \xrightarrow{\mathrm{UV}}[\mathrm{O}]+[\mathrm{O}] \\
\mathrm{O}_2+[\mathrm{O}] \longrightarrow \mathrm{O}_3 \text { (ozone) }
\end{gathered}\)

Ozone present in the stratosphere also dissipates the energy of harmful UV radiation. The latter, therefore, do not reach the earth.

Question 4. Why is the Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment.
Answer: Polythene is non-biodegradable. Discarded polythene bags choke drains, kill animals feeding on garbage, and pile up. They are being replaced by cloth/jute and paper bags. Cloth/jute bags can be used again and again. Along with paper bags, they are biodegradable.

Question 5. Recycling of paper, metal, plastic, and e-waste is done in most places. Mention the positive impact of this recycling process on the environment.
Answer: There will be less exploitation of resources in forming newer articles.

There will be less pollution as the recyclable articles are picked up as soon as they are discarded.

Question 6. It is said that there is a need to put a complete ban on the products containing aerosols. What are aerosols? Why is there a demand to ban them?
Answer: Aerosols are propellant gases that are used to release substances such as a fine spray, for Example perfumes, and deodorants. The gases used to be chlorofluorocarbons. Since they have strong ozone-depleting properties, there clamor for banning them. Chlorofluorocarbons have now been replaced by isobutene or methyl propane.

Question 7. In order anto individual so ? can contribute by becoming environmentally friendly. What practice
Answer:

1. Use repeatedly reusable cloth bags instead of polythene bags.
2. At home separation of biodegradable and nonbiodegradable wastes.
3. Employment of containers used in packing at home, instead of throwing them after taking out the contained edibles.

Question 8. Damage to the ozone layer is a cause of concern.” Justify the statement. Suggest any two steps to limit this damage.
Answer: The ozone layer present in the stratosphere has thinned out by more than 8%. It has resulted in a 15-20% increased penetration of harmful UVB radiations reaching the earth.

They are causing increased skin cancers, snow blindness, cataracts, a fall in immunity, reduced photosynthesis, and a higher number of mutations.

Steps to Limit Damage:

1. Stoppage of the use of chlorofluorocarbons.
2. Stoppage of the use of halons.
3. Replacing the ODS with safer chemicals.

Question 9. List 2/3 changes in habits that people must adopt to dispose of non-biodegradable waste to save the environment.
Answer:

1. Use of cotton and jute bags for shopping.
2. Segregation of household waste into biodegradable and non-biodegradable and placing them in separate bins.
3. Adoption of three ‘Reduce, reuse, and recycle.

Question 10. Suggest two measures to manage the garbage we produce.  =As an individual what can be done to generate the least garbage? Give two points.
Answer:

Management of Garbage.

1. Separation of garbage into biodegradable and nonbiodegradable, recyclable, and nonrecyclable portions.
2. Handing over the recyclable garbage to rag pickers, and others to waste collectors.

Generate No Garbage.

1. Use cloth bags or jute bags for shopping. Say no to polythene or plastic bags.
2. Reuse glass and metallic containers instead of throwing them.

Question 11. How is ozone formed in the upper atmosphere? State its importance. What synthetic chemicals are responsible for the drop in the amount of ozone in the upper atmosphere? How can the use of these chemicals be reduced? Write one harmful effect of ozone depletion. Why did the amount of ozone in the atmosphere drop sharply in the 1980s?
Answer: Ozone is formed in the upper atmosphere or stratosphere from 02 by the action of high energy UV radiations

⇒ \(\begin{aligned}
& \mathrm{O}_2 \xrightarrow{\mathrm{UV}}[\mathrm{O}]+[\mathrm{O}] \\
& \mathrm{O}_2+[\mathrm{O}] \longrightarrow \mathrm{O}_3 \text { (ozone) }
\end{aligned}\)

Ozone present in the stratosphere dissipates the energy of harmful UV radiations ( 1 00-320 nm). The latter, therefore, do not reach the earth.

However, certain synthetic and other chemicals destroy the same, for example chlorofluorocarbons, and halons. They are called ozone-depleting substances (ODS). To the ozone layer, the use of ODS has to be reduced and leakage of these substances prevented.

Alternative chemicals that do not harm the ozone are being searched to replace the ODS. Cb) Release of ozone-depleting substances like CFCs from refrigerators, air conditioners, foam manufacturing industry, fire extinguishers, and aerosols. Harmful Effect of Ozone Depletion. Skin Cancer, Snow blindness.

Question 12. Complete the following table

Answer:

1. O₂
2. O₃.
3. Breathing
4. Absorbs harmful UV radiations.

Question 13. Kulhads (disposable cups made of clay) and disposable paper cups, both are used as alternatives to disposable plastic cups. Which one of these can be considered a better alternative to plastic cups and why?
Answer: Disposable paper cups are a better choice as they are biodegradable and do not harm the ecology. Kulhads which are made of clay deprive the fields of their fertile topsoil.

Question 14. Why is the ozone layer getting depleted at the higher levels of the atmosphere? Mention harmful effects caused by its depletion.
Answer: The ozone layer present in the upper atmosphere has been getting depleted due to synthetic chemicals emanating from the earth, viz. chlorofluorocarbons (used in refrigeration) and halons used in fire extinguishers). They release chlorine which reacts with ozone breaking it into oxygen. Harmful Effect. More UV radiation reaches the earth. They cause skin cancer.

Question 15 What are decomposers? State the role of decomposers in the natural replenishment of the soil. Why are decomposers not helpful in decomposing plastic waste?
Answer: Decomposers do not possess enzymes for digestion on the breakdown of plastics

Question 16. State two methods of effective plastic waste collection in your school.
Answer: Use separate bins for recyclable waste, plastic waste, and biodegradable waste.

Question 17. Name any two uses of “single-use plastic” in daily life.
Answer:

• Packaging of water, milk, food, biscuits, etc.
• Formation of disposable articles like bowls, tumblers, plates, forks, spoons, etc.

Question 18. If we discontinue the use of plastic, how can an environmentally friendly substitute be provided?
Answer: Use thick glazed paper, jute or cloth, cardboard, metallic utensils, and earthen pots.

Question 19. Do you think microbes will work similarly in landfill sites as they work in the laboratory? Justify your answer.
Answer: Yes, microbes will work similarly in laboratory and waste dumps provided the conditions of the two are similar.

How Do Our Activities Affect The Environment Long Answer Type Questions

Question 1.

1. What is ozone? How is it formed in the atmosphere? Explain with equations.
2. How is the ozone layer useful?
3. Name the substances responsible for the depletion of the ozone layer.

Answer: Chlorofluorocarbons (CFCs), halon, carbon tetrachloride, methyl; chloroform, methyl bromide, bromochloromethane.

Control And Coordination

Control is the faculty to regulate an activity, start it, slow down it, expedite it, or stop it. Coordination is the orderly working of different parts to smoothly carry out an activity.

• For example, during the eating of food, the nose smells it, saliva moistens the food, teeth masticate it and the tongue tastes it as well as moves it for mastication and swallowing.
• However, if the nose is blocked due to a bad cold, the food will appear bland or tasteless showing the requirement of coordination between smell and taste.
• Major controls and coordination are achieved through movements. Movements or changes in position are of two types-growth movements and nongrowth movements.
• Growth movements mostly occur in plants, for example., sprouting of seed to form seedlings. Animals perform mostly nongrowth movements, for example., running, playing, buffalo chewing cud, and shouting.
• Plants also perform many non-growth movements for example., folding and drooping of leaves in Sensitive Plant on being touched.
• Movements usually occur in response to changes in the external or internal environment. They are carefully controlled and coordinated. For example, while talking to your classmates in the class you whisper. In the playground, you shout at your classmates.
• In multicellular organisms, control and coordination are achieved using specialized tissues and organs. In animals, this is performed by nervous tissue and muscular tissue.

Additional control and coordination are achieved through the endocrine system. In plants, only the endocrine system operates in control and coordination.

Animals Nervous System

What is the system to detect information from the environment? What are receptors?

The nervous system is a system of nervous organs, nerves, and a network of electrically conducting neurons that runs throughout the body of the animal for controlling and coordinating body activities. Body activities are performed in response to internal and external stimuli.

• Stimulus is a detectable change in environment, factor, agent, or chemical that brings about a response in the organism.
• The response is the specific reaction of an organism to a specific stimulus.
• Receptors are cellular structures that are capable of receiving specific stimuli and generating impulses to be picked up by sensory or afferent nerves.
• An impulse is an electrical signal that travels along the length of nerve fiber for the passage of information.
• Effectors are muscles, glands, cells, tissues, or organs that respond to a stimulus received through nerve impulses. The message to effectors is sent through motor or efferent nerves.
• Sense and Sense Organ. The faculty by which an organism perceives the change in external or internal environment is called sense, for example., smell, hearing, touch.
  • The organ which contains sensory receptors for obtaining information about the environment is called a sense organ, for example., the eye, or ear.
  • In humans and higher animals, there is the brain that functions as a super center for the control and coordination of various activities. The basic unit of the nervous system is neurons or nerve cells.

Neuron or Nerve Cell

A neuron or nerve cell is the structural and functional unit of the nervous system. It can receive, conduct, and transmit impulses. Neurons appear like miniature branched trees.

It can reach a length of 90-100 cm. A neuron has three parts body, dendrites, and axon. Dendrites and axons are collectively called neurites.

1. Cell Body (Cyton). It is the widest part of neuron which is polygonal with a stellate outline. There is a prominent centrally located nucleus, various cell organelles (except centrosome), and two special structures, Nissl granules and neurofibrils. Nissl granules are ribosomes containing particles. Neurofibrils are cytoskeletal fibrils (microtubules, microfilaments, and neurofilaments).
2. Dendrites. They are short, fine, branched, protoplasmic outgrowths of the cell body. Nissl granules and neurofibrils are present. Dendrites pick up sensations and transmit the same to the cell body.
3. Axon. It is a long fiber-like process of the cell body that is specialized to carry impulses away from the cell body. It contains neurofibrils but lacks Nissl granules. Axon is branched terminally to form knobbed ends called boutons. They are meant for transmission of impulses to another neuron, cell, gland, muscle, or organ.

Axon is covered by one or two sheaths. The ensheathed axon is known as a nerve fiber. The single or the outer sheath is called neurilemma (= neurolemma).

• It is made up of Schwann cells. When two layers are present, the inner layer is made of lipid or myelin. Such nerve fibers are called myelinated or medullated.
• At intervals, nonmyelinated areas occur. They are called nodes of Ranvier. Myelinated or medullated nerve fibers are more efficient in the transmission of impulses than nonmedullated ones.

Types Of Neurons

• Depending upon the Impulne enameled motor or Inlerneuron, Scnnory or account lemon picks up Nenmny Impulse iVom lorcplt^i or sense organ and immimilii llm same towards brain or spinal cord.
• Motor or efferent neuron carries a message from the brain or spinal cord to muscle, gland, organ, or other effector.

Nerves

What is a nerve? Name different types of nerves.

• They are elongated thread-like structures of the nervous system which are formed by grouping and regrouping of nerve fibers inside the sheath of connective tissue.
• Connective tissue sheaths keep the nerve fibers insulated from one another. Like neurons, based on their functioning, nerves are of three types -sensory, motor, and mixed. Mixed nerves contain both sensory and motor fibers.

Differences between Sensory and Motor Nerve Fibres

Transmission of Nerve Impulse

Define impulse. Name the chemical that helps in the transmission of impulses.

An impulse is a self-propagated electrical signal that travels along the length of the neuron for the passage of a message. At rest, a neuron is polarized with a positively charged exterior and a negatively charged interior.

• As soon as it receives a stimulus, the neuron region undergoes depolarisation with the outer surface becoming negatively charged and the inner surface becoming positively charged. This happens due to the opening of ion channels causing entry of Na+ ions inside the nerve.
• The depolarized region functions as a local current or stimulus which depolarises the next part of the nerve while itself becoming polarised. The process continues till the impulse reaches the end of the neuron.
• From here impulse jumps to the next neuron, muscle, or other ‘target organ with the help of chemicals (for example.,. acetylcholine) called neurotransmitters.

Synapse

It is a narrow communicating junction between two neurons. The axon terminal of one neuron forms a presynaptic Knob. The dendrite tip of the next neuron is expanded but depressed to form postsynaptic depression.

• The narrow space between the two is called the synaptic cleft. The presynaptic knob possessed a number of neurotransmitters containing synaptic vesicles.
• The remembrance of the postsynaptic depression possesses several chemoreceptor sites.

As the impulse reaches the presynaptic knob, it activates the synaptic vesicles. They reach the presynaptic membrane and burst open. Ncurotransmittcr (for example., acetylcholine) is released.

Neurotransmitter molecules come in contact with chemoreceptor sites of the postsynaptic membrane.

The latter becomes depolarized to generate an electric current or impulse. The impulse travels across the synapse only in one direction from the axon terminal to the dendrite tip.

Neuromuscular Junction

What is a neuromuscular junction? Give its function.

It occurs at the junction between the muscle (or some other effector organ) and the axon end of the motor neuron. The axon end bears a motor end plate of knobbed branches.

• A knob or bouton of the motor end plate comes in near contact with depression called a sole plate on the surface of the muscle fiber. As the motor impulse reaches the synaptic knob, it activates the synaptic vesicles.
• They come to the surface and burst releasing neurotransmitters (for example., acetylcholine). The neurotransmitter coming in contact with the sole plate receptors brings about excitation that causes the muscle to contract.

Activity 2.1

Taste Vs Smell

Put some sugar in your mouth. It tastes sweet. Rinse mouth with water. Block your nose with your thumb and index finger. Put some sugar again in your mouth. There is very little sweetness indicating that our taste is largely governed by smell.

Nerve Actions

There are three types of nerve actions, involuntary and reflex, Voluntary nerve action is under the control or command of the brain, for example., talking, and writing.

• Involuntary nerve action operates without the command of the brain as per the requirement of sensation generated in internal organs, for example., peristalsis.
• Reflex action is nerve-mediated automatic mechanical and immediate response to a stimulus for protection and functional efficiency, eg., closing of eyes when strong light is flashed over them, pulling of hand from a hot surface before the brain feels the pain.

Control And Coordination Long Answer Type Questions

Question 2. Mention the part of the brain involved in the following:

1. Walking in a straight line.
2. Picking up a pencil.
3. Blood pressure.
4. A question is asked by the teacher in the class.
5. Change in size of the pupil in response to the intensity of light.

Answer:

1. Walking in a straight line. Cerebellum.
2. Picking up a pencil. Cerebrum and cerebellum.
3. Blood Pressure. Medulla oblongata.
4. The question being asked by the teacher. Temporal lobe and frontal lobe of the cerebrum.
5. Changing pupil. Superior corpora quadrigemina of midbrain.

Question 5.

1. Define nerve impulse. Name the structure that helps to conduct a nerve impulse
   1. Towards cell body
   2. Away from the cell body.
2. Why have organisms adapted to use electrical impulses to transmit messages? State two limitations of the use of electrical impulses.

Answer:

1. Nerve Impulse. It is a progressive electrochemical wave that develops in response to stimulus and travels along a nerve fiber to stimulate or inhibit the action of another nerve, muscle, or gland.
   1. Dendrite
   2. Axon.
2. Electrochemical impulses are very fast. There is no chance of spillover or after-effects. This allows the animal body to use the same nerve time and again.

Impulse Limitations.

1. Electrochemical impulse is unidirectional.
2. It is short-acting, also in the presence of stimulus only,
3. It does not reach every cell of the body,
4. After the generation and transmission of an electrical impulse, the nerve cell will take some time to receive and transmit a fresh electrochemical impulse.

Coordination In Plants

What are movements? How do they differ from locomotion? What are tropic movements?

Plants are devoid of nerves and muscles. They are fixed. Even then they show movements though locomotion is absent. These movements may be directional (tropic) or nondirectional (nastic), growth, or turgor-based.

• The movements are quite slow in most of the cases. It may take a few days to notice the change in position or movement. However, some turgor-based movements are quite fast and easily discernible.

Turgor-Based Plant Movements

• The plants have certain areas that have special cells that can shrink or swell with the loss or gain of water. They show reversible movements, for example., opening or closing of stomata, sleep movements of legume leaves, and drought-induced rolling of some grass leaves.
• Sleep movements of legume leaves are called nyctinasty. Drought-related rolling of grass leaves is called hydronasty.

Immediate Response To Stimulus

If you happen to touch a pinnule of Mimosa pudica (Sensitive Plant, Touch-me-not Plant, Shame Plant, Shy Plant) all the pinnules fold upwardly, the pinnae come together, and the whole leaf droops down.

• The place of stimulus is away from the area of movement. Further, it goes beyond the area of sensitization to other pinnae as well as to the whole leaf. Naturally, the stimulus travels from the area of contact to the area of response.
• This passage must be cell-to-cell like an electrical-chemical impulse or a chemical called turgorin. The differential movements are due to special cells at the base of pinnules, pinnae, and petiole that shrink on activation and later recover after about 10 minutes.
• As the movement in Mimosa is nondirectional, it is called nastic movement. The movement is due to touch or shock. It is, therefore, known as haptonasty or seismonasty.

Growth Based Plant Movements

What are growth movements? Name its two types.

They are plant movements caused by differential growth or unequal growth in different parts of the organ. This results in bending and other types of movements. Growth movements are of two types, nastic and tropic.

• Nastic movements are non-directional. They are determined by the structure of the organ and not the direction of the stimulus, for example., the opening of flowers due to greater growth or epinasty on the upper surface of sepals and petals.
• Tropic movements occur in cylindrical organs. The direction of movement is related to the direction of the stimulus. Tropic movements are also called curvature movements.

Differences Between Nastic And Tropic Movements

Depending upon the stimulus, tropic movements are of many types—phototropism, geotropism, hydrotropism, chemotropism, and thigmotropism.

1. Phototropism. It is tropic movement in response to uni-directional exposure to light. Stems generally bend towards the source of light.

• They are called positively phototropic. Leaves lie at right angles to the direction of light. They are diaphototropic. Roots are either neutral or negatively phototropic.
• In the stem, the stimulus of light is received by the stem apex. Leaves are essential for it. The region of response is a zone of elongation present below the apex. Blue light is effective in causing phototropism. The photoreceptor is a chemical called phototropin.
• The movement is caused by decreased availability of auxin on the illuminated side and more on the shaded side. The shaded side grows more resulting in bending movement.
• In the root where negative phototropic movement is observed, more auxin on the shaded side causes inhibition of growth (opposite to that of the stem).

Sunflower heads perform suntracking due to positive phototropism while plants growing in the open do not show bending movements as auxin diffuses uniformly in the growing region.

Activity 2.2

Demonstration Of Phototropism

Fix a wire mesh over the mouth of a conical flask full of water. Place one or two freshly germinated bean seeds on the mesh. Take a large cardboard open on one side.

• Place the flask in the cardboard kept near a window so that the seedling receives light from one side only. Observe after 2-3 days.
• The shoot has bent towards the source of light while the root has bent away from it. It shows that the stem is positively phototropic while the root is negatively phototropic.
• Now rotate the flask by 180° and observe after 3-4 days. The shoot and the root have developed curvatures and a new direction of bending by the young shoot towards the light and the young root away from light.

2. Geotropism. It is tropic movement or growth movement of curvature that occurs in response to the vector of gravity. Stems are generally negatively geotropic while roots are positively geotropic.

• Their branches are plagiogeotropic or lie at an angle to the direction of gravity. Stimulus of gravity is perceived by the stem apex, stem nodes, and root cap.
• It is because of the negative geotropic nature of the stem and the presence of receptor regions in the nodes that the lodged shoots become vertical.
• Negative geotropism helps shoots to properly expose themselves to sunlight.

Positive geotropism of roots helps them to fix the plant in the soil and absorb water as well as minerals from the same.

Activity 2.3

Demonstration Of Geotropism

• Place a potted plant horizontally on the ground. Provide support to the pot to prevent rolling. Regularly water the plant. Observe after a week.
• The apical part of the shoot has bent upwardly while the roots have bent downwardly. It shows that the stem is negatively geotropic while the root is positively geotropic.

3. Hydrotropism. It is tropic or directional growth movement of curvature that develops due to unilateral exposure to water. Hydrotropism is mostly seen in roots which are positively hydrotropic. Positive hydrotropic movement of roots is stronger and even overcomes their positive geotropic response.

Activity 2.4

Demonstration Of Hydrotropism

Take a sieve. Fill it with moist sawdust and support it on the sides over wooden blocks. Place a few soaked germinating seeds in the sawdust. Sprinkle water over the sawdust.

• Within 1-2 days radicles will be seen coming down from the pores of the sieve and hanging in the air.
• However, within a few hours, the radicle will be found to bend back and enter the wet sawdust showing that the positive hydrotropism of roots is stronger than that of their positive geotropism.

4. Thigmotropism. It is tropic or growth movement of curvature that occurs in tendrils and twiners in response to the stimulus of contact.

• As a tendril or twiner comes in contact with a support, it encircles the same. The reason is less growth in the region of contact and more growth on the free side.
• Here, contact causes less auxin production and hence less growth.

5. Cliemotropism. It is tropic or growth movement of curvature that occurs in plants in response to a chemical stimulus.

• The best example is the passage of the pollen tube through the style and inside the ovary towards the ovule where synergids are sending out chemical signals.

Chemicals Coordination in Plants

What arc phytohormoncs? Why they are called plant growth regulators?

Plants do not have nerves and muscles to coordinate their activities. Instead, they have chemical messengers or hormones.

• Plant hormones or phytohormones are non-nutrient diffusible chemical substances that can control various activities of plants like growth, differentiation, movements, development, and other physiological processes.
• For this, the target or effector cells possess receptors for picking up the hormones. Plant hormones are also called plant growth regulators (PGRs) as they function by promoting or inhibiting growth.
• Major plant hormones are auxins, gibberellins, cytokinins (growth promoters), abscisic acid (growth inhibitor), and ethylene (both promotion and inhibition).

Auxins

They are weakly acidic organic substances having unsaturated ring structures that promote cell enlargement of shoots in the concentration range of 10-100 ppm, which is inhibitory to the growth of roots.

• Natural auxin is indole 3-acetic acid or IAA. Some other examples are IBA, NAA, 2,4-D, 2,4,5-T. 1AA is synthesized inside shoot tips, young developing leaves, and seeds.

Auxins Functions

1. Cell Enlargement. Auxin promotes cell growth at a concentration of 10 ppm in the stem and 0.0001 ppm in the root.
2. Apical Dominance. Axillary buds do not sprout near the apical bud due to the secretion of auxin by it.
3. Prevention of Abscission. Auxin prevents the premature falling of leaves and fruits.
4. Movements. Phototropic, geotropic, and other plant movements are caused by differential distribution of auxin.
5. Root Formation. Root formation on stem cuttings is stimulated by auxins like NAA and IBA.
6. Tissue Culture. Auxin promotes callus formation in tissue culture. Along with cytokinin, it promotes the differentiation of callus into plantlets.
7. Fruit Growth. Auxin promotes fruit growth, sweetening of fruit, and even parthenocarpic development of fruit.
8.  Weedicides. In higher concentrations 2,4-D and 2,4,5-T are used as weedicides.

Gibberellins

They are mildly acidic tetracyclic organic substances that bring about cell elongation of leaves, stems, and fruits in intact plants. They are formed by the young leaves of buds, root tips, and developing seeds.

Gibberellins Functions

1. Growth. Gibberellin promotes growth in leaves, stems, internodes, and fruits. They are used to increase the yield of fruits and sugar in sugarcane.
2. Overcoming Dormancy. Dormant buds and seeds sprout in the presence of gibberellins.
3. Flowering. They can replace cold and long-day requirements for flowering in some plants.
4. Parthenocarpy. Like auxin gibberellin can induce the formation of seedless fruits.
5. Overcoming Dwarfism. Genetically dwarf plants grow to normal size on the application of gibberellins.

Cytokinins

They are mildly alkaline aminopurine or adenine derivatives that promote cell division in plants, for example., zeatin (natural), and kinetin (synthetic). Cytokinins are synthesized in the root tip and endosperm of developing seeds.

Cytokinins Functions

1. Cell Division, Differentiation and Morphogenesis. Cytokinins are essential for cell division, cell differentiation, and morphogenesis.
2. Prevention of Senescence. Aging of leaves, marketed vegetables, fruits, and cut flowers can be prevented by the application of cytokinin.
3. Accumulation of Nutrients. Cytokinins improve the yield and quality of fruits by stimulating nutrient flow into them.
4. Resistance. They enhance the resistance of plants to environmental stresses and diseases.
5. Apical Dominance. Application of cytokinins overcomes apical dominance. The nearby axillary buds sprout.

Abscisic Acid (ABA)

It is a mildly acidic organic substance that functions as a general growth inhibitor.

• Abscisic acid can counter the growth-promoting activity of auxins, gibberellins, and cytokinins.
• It helps the plant to overcome stress conditions mostly through induction of dormancy. Therefore, it is known as a stress hormone as well as dormant.

Abscisic Acid Functions

1. Controlled Growth. By counteracting the effect of other hormones, abscisic acid or ABA controls growth.
2. Wilting. Under conditions of stress, it causes wilting and senescence of leaves.
3. Abscission. It promotes the abscission of flowers and fruits.
4. Dormancy. Abscisic acid causes dormancy of buds and seeds.
5. Transpiration. It checks transpiration by causing the closure of the stomata. Because of this, abscisic acid can also be used as an antitranspirant.

Coordination In Plants Long Answer Type Questions

Question 1.

1. Mention the role of
   1. Auxin
   2. Abscisic acid.
2. How do plants respond to external stimuli?

Answer:

1. Auxin. It promotes cell growth, and apical dominance, and prevents premature leaf and fruit fall while differential distribution causes tropic movements.
   1. Abscisic Acid. It moderates growth promotion by auxin and gibberellins, prepares the plant for stress tolerance, and induces dormancy of buds and seeds.
2. Plant Response to External Stimuli. Plants respond to external stimuli by the two types of movements- turgor movements and growth moments.

Turgor Movements. They are caused by changes in the size and shape of cells through loss and gain of water, for example., opening and closing of stomata, haptonasty in Mimosa pudica, and hydronasty in many grasses.

Growth Movements. They are movements caused by unequal growth. Growth movements can be nondirectional or directional. The non-directional movements are called nastic movements.

• They are not related to the direction of stimulus but to the structure of the responding organ, for example., the opening and closing of flowers.
• The directional movements are called tropic movements. They mostly occur in cylindrical organs. The direction of this growth movement is related to the direction of stimulus, for example., phototropism.

Question 1. Why are some substances biodegradable and some non-biodegradable?
Answer: There are two types of substances, biological origin and man-made. Biological origin waste articles can be degraded by decomposer organisms because they have enzymes to do so, for example, garbage, livestock waste, agricultural waste, paper, etc.

They are called biodegradable substances. Most man-made articles cannot be degraded by decomposers because they do not have enzymes to do so, for Example plastic, glass, crockery, and metallic cans. Such articles are called non-biodegradable substances.

Question 2. Give any two ways in which biodegradable substances would affect the environment.
Answer:

1. Foul Smell. Biodegradable substances begin to stink after a few hours. They emit a foul smell.
2. Pathogens and Pests. Pathogens and pests multiply rapidly in the heap. They spread diseases through flies, mosquitoes, cockroaches, and rats.

Question 3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer:

Dumping Area. It becomes a source of pollution to groundwater and the emission of foul gases. There is a limit to the creation of new dumping areas as it makes the land barren and an eye sore.

Biological Magnification. Soluble persistent pesticides like DDT, and heavy metals (For example lead, cadmium, nickel, mercury) enter the food chain through soil, groundwater, and plants. They change and increase in concentration at higher trophic levels. Several diseases are caused by them.

Our Environment Paragraph-Based Question

The human body is made up of five important components of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields.

These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants.

As these chemicals are not biodegradable, they accumulate progressively at each trophic level. The maximum concentration ofthese chemicals gets accumulates in our bodies and greatly affects the health of our mind and body.

Question 1. Why is the maximum concentration of pesticides found in human beings?
Answer: Human beings belong to lie lot of food chain

Question 2. Give one method that could be applied to reduce our intake of pesticides through food to some extent.
Answer: Organic farming of Biopesticides/through the washing of vegetables, fruit; and grains

Question 3. Various steps in a food chain represent

1. Food Web
2. Trophic Level
3. Ecosystem
4. Biomagnification

Answer: 2. Trophic Level

Question 4. About various food chains operating in an ecosystem, man is a

1. Consumer
2. Producer
3. Producer And Consumer
4. Producer And Decomposer

Answer: 1. Consumer

Our Environment Short Answer Type Questions

Question 1. Mention the basis of classifying substances as biodegradable and non-biodegradable. Give two examples
Answer: Putersxibility or the (lie ability to get decomposed or not. Biodegradable substances are decomposed by saprophytes, for example; food leftovers used leaves leaves.

Non-biodegradable substances are not decomposed by saprophytes as they do not have enzymes for them, for example, milk pouches, and aluminum foil.

Question 2. If nil the wastes we generate are biodegradable, what effect will this have on the environment? Write two virtues that will be imbibed if the people are made to understand that the generation of waste should be restricted to biodegradable only.
Answer: There will be no pilling up of waste, nor there will be pressure to acquire Jand for their disposal.

Biodegradable waste gets decomposed by saprophytes within 2 to 3 months producing manure, compost, biogas, etc. There will be recycling of nutrients. Decomposers release nutrients from biodegradable wastes.

The same arc is picked up by plants for their nutrition and growth. Virtues. Many diseases will disappear, and Earth will remain clean. Manure and compost will be available for crops, Biogas shall be available for energy and lighting. CM.

Question 3. Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags. List any two practices that can be followed to dispose of the waste produced in our homes.
Answer: Harmful Effects, Plastic is non-biodegradable. Therefore, waste plastic bags cause pollution of land and water bodies, Waste plastic bags thrown indiscriminately block the drainage system, and They harm or even kill stray animals, Burning of waste plastic releases toxic gases. Alternatives. Use of jute or cloth bags, paper bags (if) Use of washable or biodegradable containers.

Separation of recyclable articles for rag pickers. Separation of biodegradable and non-biodegradable wastes in separate bins. Use of container bottles for storing articles in kitchens Composting of kitchen wastes for the kitchen garden.

Our Environment Long Answer Type Questions

Question 1. Distinguish between biodegradable and nonbiodegradable substances. List two effects of each of them in our environment
Answer:

• Foul Smell. Biodegradable substances begin to stink after a few hours. They emit a foul smell.
• Pathogens and Pests. Pathogens and pests multiply rapidly in the heap. They spread diseases through flies, mosquitoes, cockroaches, and rats.
• Dumping Area. It becomes a source of pollution to groundwater and the emission of foul gases. There is a limit to the creation of new dumping areas as it makes the land barren and an eye sore.
• Biological Magnification. Soluble persistent pesticides like DDT, and heavy metals (For example lead, cadmium, nickel, mercury) enter the food chain through soil, groundwater, and plants. They change and increase in concentration at higher trophic levels. Several diseases are caused by them.

Heredity

Why do individuals produced after the sexual process, have similar designs?

• Heredity is the study of the transmission of genetic characteristics from parents to offspring and the laws governing such a transmission.
• Along with genetic characteristics, variations also appear during the transmission.
• The branch of biology that deals with the study of heredity and variations is called genetics. The term was coined by Bateson (1906).

Inherited Traits

Inherited traits are features that an organism receives from its parents through their genes, for example, free ear lobes, attached ear lobes, roller tongue, non-roller tongue, black hair, blonde hair, blue eyes, dimpled and non-dimpled cheeks, and thick and thin lips. The varied expression of so many trials is the reason for such a large number of variations in the same population.

Attached and Free Ear Lobes

Observe The Ear Lobes Of Your Classmates. Note That The Majority Of Them Have Free Ear Lobes. Classmates With Attached Ear Lobes Are Fewer In Number. Record The Ear Lobes Of The Parents Of Your Classmates. Again More Parents Have Free Ear Lobes.

If Both Parents Have Attached Ear Lobes, Their Child Will Also Have Attached Ear Lobes. In Other Cases, Inheritance Depends Upon The Genetic Nature Of The Parents And The Dominance Of Free Ear Lobes Over The Traits Of Attached Ear Lobes.

Rules For The Inheritance Of Traits—Mendel’s Contributions A

What will be the trait seen in a child, when both the father and mother contribute an equal amount of genetic material (DNA)?

As found out in the inheritance of the trait of ear lobes, both mother and father contribute an equal amount of genetic material to the child.

It means that the child receives two versions of the trait, one from each parent. The expression of the trait in the child depends upon the nature of the traits contributed by the parents. The rules of such inheritance were worked out by Mendel in the 19th century.

Mendel—The Father Of Genetics

Gregor Johann Mendel (1822-1884) found out the mechanism of the passage of traits from one generation to the next and so on. Because of this discovery, he is known as the father of genetics.

• Mendel was born to a farmer’s family in the village of Silesian (now part of the Czech Republic). After graduating he joined a monastery in Brunn (then Austria now Bruno of the Czech Republic) in 1843. He became a priest there in 1847.
• In 1851 Mendel went to Vienna to study science and mathematics. He returned as a substitute teacher as he failed to clear the certificate course for teaching.
• In 1856, Mendel became interested in hybridization experiments on Garden Pea (Pisum sativum) which had several contrasting traits.
• He first raised pure breeding plants and then selected seven characters that had two alternate traits for breeding.
• He read out the results of his experiments in two sittings of Natural History of Brunn in 1865. The same was published as “Experiments on Plant Hybridization” in the proceeding of the society in 1866.

However, Mendel’s work remained unnoticed till similar results were obtained by three scientists independently in 1900—de Vries of Holland, Carl Correns of Germany, and Tschermak Seysenegg of Austria. Mendel’s original paper was found out and republished in Florida in 1901.

Mendel’s Experimental Material

Mendel selected Pea Plant (Pisum sativum) as experimental material because :

• It occupies a small space.
• It has a short life span and annual nature.
• Presence of easily detectable contrasting traits.
• Formation of a large number of seeds.
• It has a flower structure that enables cross-pollination but is normally self-pollinated.
• The plant requires little aftercare.

Seven Characters with Contrasting Limits Selected by Mendel

Mendel’S Experiments

Mendel made reciprocal crosses between plants having alternate traits like tall and dwarf, round seeded and wrinkled seeded.

He emasculated (removed anthers) of 50% of the plants of each type and used them as female parents. Pollen for other traits was collected and dusted over their stigmas. Flowers were kept covered with paper and thus obtained were hybrid and constitute tblS CF0SS Were collected and sown next year.

The plants thus obtained were hybrid and F₁ or first filial generation. The hybrids were not intermediate between the traits but belonged to one of them. The expressed trait is called dominant while the other unexpressed one is called recessive.

Mendel allowed the F₁ plants to self-breed. He obtained F₂ generation which had both types of plants, dominant 75% and recessive 25%. Mendel further self-bred F₂ plants and obtained F₃ generation.

The recessive trait individuals produced recessive trait offspring. One-third of the dominant trait plants formed only dominant offspring while 2/3 behaved like the hybrids giving rise to both dominant and recessive trait offspring in the ratio of 3: 1.

Such a ratio comes to 1 pure dominant, 2 hybrid dominant, and 1 pure recessive. It is called the genotypic ratio.

Monohybrid Cross: Mendel studied the inheritance of two traits of a character at one time through cross-breeding and then self-breeding. It is called a monohybrid cross.

In a cross between pure tall and pure dwarf Pea plants, Mendel obtained only tall plants in the F₁ generation. On self-pollination of F₁ plants, the F₂ generation had both tall and dwarf plants in the ratio of 3: 1.

It is called the monohybrid ratio. The occurrence of dwarf plants in the F₂ generation is possible only if the trait of dwarfness is present in the F₁ generation but remains unexpressed due to its recessiveness.

Mendel, therefore, proposed that each individual carried two factors for a character. They separate randomly at the time of gamete formation and come together randomly at the time of fertilization.

Work out the Dominant and Recessive Trait 

It is a cross between purple-flowered plants with white-flowered plants. The hybrid or F₁ plant is purple-flowered though it has received the factor for white flowers as well.

This is proved by the plants of F₂ generation where both purple and white flowered ratio of 3: 1. This dominant over the trait of white flower colour as plants occur in the also indicates that the trait for purple colour is the latter remains Ft” Self Fertilisation unexpressed in F1 generation.

Dihybrid Cross: It is a cross between two individuals for studying the inheritance of traits of two different characters. Mendel crossed a pure breeding round green-seeded (RRyy) plant with the pure breeding wrinkled yellow-seeded plant (RR).

F₁ plants or hybrids were all round and yellow-seeded (RrYy). On self-breeding the F₁ plants Mendel obtained four types of plants—round yellow (315/556 or 9/16), round green (108/556 or 3/16), wrinkled yellow (101/556 or 3/16) and wrinkled green (32/556 or 1/16).

Here, round yellow and wrinkled green are new combinations of traits. This is possible only if there is an independent assortment of traits of the two characters. The ratio is called the dihybrid ratio.

Important Terms :

Character: It is a distinct feature of an organism like the flower colour, or height of a plant.

Trait: It is the alternate expression of a character, for example, tallness for height.

Gene: It is a linear segment of DNA or chromosome that functions as a unit of inheritance.

Alleles: Genes occurring in homologous chromosomes at the same locus are called alleles or allelomorphic pairs.

Being particulate they are also called factors or units ofinheritance. They may express the same trait or different traits of character, for example, TT, Tt, tt, RR, Rr, rr. Here, the capital letter represents the dominant factor (T for tallness) while the small letter signifies the recessive factor (t for dwartness).

Homozygous:  It is an organism with identical alleles, for Example, TT, RR, r r, 1 1. Homozygous individuals are generally genetically purebred.

Heterozygous: It is an organism which possesses contrasting (both dominant and recessive) traits of character, Example Tt, Rr.

Dominant Factor: It is an allele or factor that expresses its effect in both homozygous and heterozygous states, Example TT, Tt.

Recessive Factor: It is an allele or factor that is unable to express its effect in the heterozygous state. Recessive factor expresses its effect only in the homozygous state, Example tt.

Differences Between Dominant And Recessive Factors

F1 Generation (First Filial Generation). It is a generation of hybrids that are formed from a cross between two genetically different pure-breeding individuals.

F2 Generation (Second Filial Generation). It is a generation that is formed through inbreeding amongst members of the Fj generation.

True Breeding (Pure Line): It is a lineage of homozygous or genetically pure individuals that produce similar genetically pure offspring.

Monohybrid Ratio: The ratio of types of individuals produced in the F2 generation, when the inheritance of a single character is studied, is called the monohybrid ratio. The phenotypic ratio is 3: 1 while the genotypic ratio is 1 : 2: 1.

Dihybrid Ratio: The ratio of types of individuals produced in F2 generation when the inheritance of two characters is studied is called the dihybrid ratio. Its phenotypic ratio is 9: 3 : 3: 1 while the genotypic ratio is 1: 2: 2: 4: 1: 2: 1: 2: 1.

Phenotype: It is the morphologically expressed character of an individual, for Example round seeded, wrinkled seeded. the  In case of a recessive trait, the phenotype and genotype are the same. In the case of a dominant trait, the phenotype is genetically of two types, pure (Homozygous) and hybrid (Heterozygous).

Genotype: It is the genetic complement of an individual about one or more characters whether or not their factors find expression in the phenotype. example the le, genotype of tall pea plants can be TT or Tt. In Tt, the factors for tallness (T) find expression while the factor for dwarfhess remains (t) unexpressed.

Differences Between Phenotype And Genotype

Mentalism

(Mendel’s Laws of Inheritance)

Principles or laws of inheritance as discovered by Mendel (1866) are collectively called Mendelism. They are three in number —the law of dominance, the law of segregation and the law of independent assortment.

Law of Dominance: Out of the two alleles or factors in hybrid, | Parents| only one expresses its effect. The other allele remains unexpressed. The allele which finds expression in the hybrid is called the dominant allele or factor while the unexpressed allele is known as the recessive allele or factor.

• The dominant allele is designated by a capital (Example T) letter while the recessive allele is designated by a small letter (t) of the alphabet.
• Cross a pure tall (TT) plant of Pea with a pure dwarf (tt) plant. Fj plants are all tall though they have also received an allele for dwarfness.
• This shows that the factor or allele of tallness is dominant over the allele of dwarfness.

Law of Segregation: The two alleles or factors of a character particulate entities which remain distinct in an individual whether or not any of them expresses its effect. Both the factors separate or segregate at the time of gamete formation. A gamete receives only one of the two factors for the character. It is, therefore, always pure. The law of segregation is, therefore, also known as the law of purity of gametes. The double nature of factors is restored after fertilization.

Select pure tall (TT) and pure dwarf (tt) Peas plants as parents. Cross the two. The hybrid or plants of the F₁ generation are all tall despite their having received a factor for dwarfness as well.

F₁ plants are allowed to self-breed and produce F₂ generation. In the F₂ generation, both tall and dwarf plants appear in the ratio of 3: 1. It is possible only if the factor for dwarfness was present in the F₁ generation. It separates from the factor of tallness during the formation of gametes. On fusion of two gametes each carrying the factor for dwarfness will produce an offspring with the recessive character of dwarfness.

Law of Independent Assortment: The two factors or alleles of a character separate independent of factors of another character at the time of gametogenesis. They also come together independently of one another during fertilization. As a result of independent assortment, fertilization produces a new combination of traits or factors. They are called recombinations.

Select pure-breeding tall round-seeded and pure-breeding dwarf wrinkled-seeded Pea plants as parents. Cross the two. Plants of the F₁ generation or hybrids are all tall and round-seeded because of the dominant nature of alleles of tallness and round-seededness. Raise F₂ generation by allowing the F₁ plants to self-breed.

F₂ generation has four types of plants-tall and round seeded (9/16), tall and wrinkled seeded, (3/16), dwarf and round seeded (3/16) and dwarf and wrinkled seeded (1/16). Only two of these (tall rounded and dwarf wrinkled) are parental types. The other two types (tall wrinkled and dwarf rounded) are new combinations. New combinations can appear only if the factors for the two characters separate and come together independently of one another.

Contribution By The Parents

Each parent has two sets of genes or chromosomes. A gamete receives only one set of genes or chromosomes. When the gametes fuse during fertilization, the double set or diploid number of genes or chromosomes is restored.

Therefore, in sexual reproduction, each parent contributes half of the genetic material. Thus, both parents contribute equally. Of course, there is reshuffling of chromosomes during gametogenesis and fertilization that results in variations and independent assortment.

In asexual reproduction, there is no halving of genetic material, nor doubling of halved material. Instead, the full gene complement or genetic material of the parent is transferred to the daughters through mitotic divisions.

How Do The Traits Get Expressed

How does the mechanism of cellular DNA (gene) work in the production of hormone enzymes?

Traits are morphological or physiological expressions of factors or genes. Genes are segments of DNA. They operate through the formation of wRNA which then forms structural or enzymatic proteins. A dominant factor produces a fully functional protein.

• A recessive factor does not form a fully functional protein. Therefore, while a dominant factor can express its effect even in the heterozygous state, a recessive factor cannot do so. It shows its effect only when it is present in the homozygous state.
• The character of height in Pea is controlled by growth hormones. They are synthesized through enzymes produced by proteins formed by growth factors. The dominant factor for tallness (T) synthesises a protein that efficiently gives rise to growth hormones.
• Therefore, the plant becomes tall. In the case of the recessive factor for dwarfness (t) less efficient protein is formed when it is present in the homozygous state. As a result growth hormones are formed and the plant remains dwarfed.

Sex Determination

How is the sex of a newborn individual determined? Does it depend on the inheritance of X and Y chromosomes?

Sex determination is the establishment of maleness and femaleness of the individuals through the formation of their sex organs. In some animals, sex is determined environmentally while in the majority of animals and humans, it is controlled genetically.

In turtle Chrysema picta, females are formed if the eggs are incubated at a temperature of about 33°C. A temperature below 28°C forms male animals.

In the lizard Agama agama, males are formed at higher temperatures.

Annelid Ophryotrocha changes sex from male to female as it grows old. Similar sex changes also occur in some snails.

Sex Determination in Humans: Genetic control of sex determination is carried out by chromosomes. There are two types of chromosomes, autosomes and allosomes.

Autosomes control various functions of the body other than sex. Allosomes (=heterosomes) determine sex along with other functions. They are called sex chromosomes.

Human beings possess 23 pairs of chromosomes. 22 pairs are autosomes. One pair of chromosomes are sex chromosomes or allosomes. The two allosomes are similar in females.

They are XX chromosomes. The two allosomes of males are different. One is X-chromosome while the other is smaller and called Y-chromosome.

Human Females are 44 + XX while human males are 44 + XY. Because of the similar nature of X-chromosomes the sex chromosomes of females are called homomorphic. They are heteromorphic m males. The Emma endosperm forms one type of egg, 22 + X.

The males are heterogametic. They form two types of sperm, (22 + Y) and gymnosperms (22 + X). The two types of sperms are produced in equal numbers.

1 n + x and 22 + Y chance factor which depends upon whether an angiosperm fuse with the egg and forms male is 50: 50 or 44 + XY) or a gymnosperm fuse with the egg to produce a female baby (22 + X and 22 + X or 44 )ÿ chance of the birth of a boy or girl.

Heredity Questions And Answers

Question 1. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:

Mendel’s crosses between plants having visible contrasting traits proved that traits may be dominant or recessive. He crossed a pure tall Pea plant with a pure dwarf Pea plant.

• All the plants of the F₁ generation were tall and none J with medium height or dwarfnature.
• On self-breeding of F₁ plants, Mendel obtained two types of plants, tall: and dwarf in the ratio of 3: 1. It means that the factor of dwarfness was present in Fj plants.
• It did not express its effect because it is recessive while the factor for tallness is dominant as it can express its effect and suppress that of the factor for dwarfness.

Question 2. How do Mendel’s experiments show that traits are inherited independently?
Answer:

The traits of different characters are not linked. The traits of one character are inherited independently of the traits of, another character. Mendel performed a dihybrid cross between rounded green-seeded plants (RRyy) and wrinkled yellow-seeded plants (rrYY).

• In the F1 generation, he obtained round yellow-seeded plants. On self-breeding F₁ plants, Mendel obtained a progeny of F₂ generation of four types of plants—round yellow seeded (9/16), round green seeded (3/16), wrinkled yellow seeded (3/16) and wrinkled green seeded (1/16).
• In this progeny, there are two parental types and two new combinations or recombinations. Recombination of traits can occur only if they are inherited independently of one another.

Question 3. A man with blood group A marries a woman with blood group 0 and their daughter has blood group O. Is this information enough to tell you which of the traits, blood group A or O, is dominant? Why or why not?
Answer:

No, The appearance of a recessive trait can occur only when its factors are in the homozygous state. The appearance of a dominant trait can occur both in homozygous and heterozygous states.

• In this particular cross, both A and 0 blood groups can be dominant as well as recessive. Possibility 1. Blood group A is dominant. Father with blood group A can be I AIA or IA 1°. The mother with blood group 0 must be I°I°.
• The daughter can be genetically IAI° or I°I°, that is of blood group A or 0. Possibility 2. Blood group 0 is dominant. Mothers with blood group 0 can be I°I° or 1° IA. Father with blood A should be I I only. The daughter would be of blood group 0 or A.

Question 4. How is the sex of the child determined in human beings?
Answer:

The sex of the child is determined by the chromosome complement of the gametes that fuse during fertilization. In human beings, females are homogametic. They produce only one type of ova, i.e., 22 + X.

• Males are heterogametic. They produce two types of sperm, angiosperms with 22 + Y chromosome complement and gymnosperms with 22 + X chromosome complement Sex of the child will depend upon the type of sperm that fuses with the ovum.
• It will be male if fusion has occurred with endosperm (44 + XY) and female if fusion has occurred with a gymnosperm (44 + XX).

 

Excretion

What is excretion? What are the excretory products?

• Excretion is the removal of metabolic wastes from the body.
• Metabolic wastes are not only unwanted by-products but are often toxic, For Example, urea, uric acid, ammonia, creatinine, excess salts, drugs, vitamins, etc.
• The excretory system is a system of organs and tissues that take part in the separation, collection, and elimination of waste products.
• Elimination of waste products maintains a favorable internal environment in the body. Different organisms have different mechanisms to eliminate their waste products.
• Excretion in Unicellular Organisms An excretory system is absent, However, waste products are regularly produced during their metabolism, For Example., ammonia, and carbon dioxide. They pass out into the surrounding water through diffusion, (For Example., Amoeba) from the surface of the body.
• Excretion in Multicellular Organisms In sponges and coelenterates excretion occurs through diffusion into the surrounding aquatic medium.
• Excretory structures developed in Platyhelminthes (flame cells), annelids (nephridia), crustaceans (green glands), insects (Malpighian tubules), mollusks (kidneys), and chordates (kidneys).
• Excretion or elimination of metabolic waste is accomplished through the urinary or excretory system. In humans, the excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

 

Micturition

What Is The Need For Micturition?

The urge for micturition or voiding of urine begins to appear when the urinary bladder is nearly half-filled. However, one can overcome this urge till the urinary bladder is nearly full.

At this time the stretched urinary bladder sends a reflex for contraction. However, voluntary micturition can be undertaken at any time. The total urine produced per day under normal conditions is 1.6 – 1.8 liters.

Urine. It is a transparent fluid of amber color. Urine is 96% water, 2.5% organic substances (urea, uric acid, creatine, creatinine, oxalates, vitamins, hormones), and 1.5% inorganic solutes (sodium, chloride, sulfate, magnesium, calcium, phosphate).

Functions Of The Urinary System

1. Elimination of Metabolic Wastes. The urinary system eliminates both nitrogenous and non-nitrogenous metabolic wastes from the body.
2. Extra Materials. Kidneys flush out extra salts, pigments, drugs, and toxic substances from the body.
3.  Water Balance. It regulates the blood volume of the body through the control of fluid loss in urine.
4. Regulation of Blood Pressure. Kidneys secrete hormones (renin, erythropoietin) for regulating blood pressure in the body.
5. Other Functions. The urinary system regulates the salt balance of the body and the pH of the body fluids.

Haemodialysis (Artificial Kidney)

What is Haemodialysis? Where is it needed?

• Kidney functioning may be impaired due to injury, infection, or reduced blood supply. This leads to the accumulation of urea and other waste products. Uremia can lead to death.
• In such a situation accumulated waste products are eliminated from the body by means of artificial kidneys. It works on the principle of dialysis and is called hemodialysis.
• An artificial kidney or dialysis machine consists of a number of semipermeable cellophane tubes immersed in a tank of dialyzing fluid. The dialyzing fluid has the same osmotic concentration as that of blood but is without nitrogen waste products, sulfate, and phosphate. Instead, it has more glucose.
• Blood from an artery (even vein also) is pumped out, mixed with heparin, and cooled to 0°C and then passed into cellophane tubes of the artificial kidney. Nitrogen wastes, sulfate, phosphate, and other wastes pass into dialyzing fluid.
• On purification, at the end of cellophane tubes, blood is taken to a warming machine, mixed with anti-heparin, and passed back into a vein. Hemodialysis is completed in 3-4 hours.
• After dialysis, a patient can resume normal working. However, if the kidney damage is severe, dialysis has to be repeated at intervals till a compatible kidney donor is found and a normal kidney is transplanted.

Organ Donation

1. It is the process of giving an organ or tissue by a person (organ donor) to a person (organ recipient) through surgical removal from the donor and transplantation of the same in the recipient. Organ donation is of two types, living donation and deceased donation.
2. In living donation, one of the two similar organs (For Example., kidney), a piece of organ (For Example., liver, lung, bone marrow) is given by a donor for restoring body function. In deceased donation, the organs of a dead person are taken out for transplantation.
3. For this, the person must have pledged to donate the organs or the family members agree to the same. A dead person can help ten persons to lead a normal life. Some common forms of deceased donation are heart, cornea, lung, liver, pancreas, intestine, trachea, skin, heart valves, and blood vessels.
4. Organ donation is a noble gesture and the public should be made aware of it so that more and more persons with life-threatening debility can come out of it.

Excretion in Plants

Plants produce waste products like other organisms. However, they have different mechanisms for their disposal. Carbon dioxide is produced as waste during the night, oxygen is produced as waste during the daytime and excess water absorbed from soil is passed out into the atmosphere through diffusion. Roofs, also produce exudates having different types of wastes.

The main wastes of plants are secondary metabolites like alkaloids, organic acids, (For Example., oxalic acid), tannins (by-products of aromatic compounds), latex, gums (degradation products of cell walls), resins (oxidation products of aromatic compounds) and some inorganic salts.

These wastes are disposed of as follows :

1. Old Leaves. Waste products collect in old leaves which fall off.
2. Bark. Tannins, gums, and resins collect in the bark which is periodically peeled off.
3.  Old Xylem. Most waste products are collected in old nonfunctional xylems like heartwood.
4. Central Vacuole. Excess salts and waste products get stored in the central vacuole of the cells. They are not able to harm the living cytoplasm due to the presence of tonoplast over the vacuole.
5. Idioblasts. They are isolated plant cells that are specialized to store excretory materials, pigments, minerals, tannins, resin, gum, oil, latex, etc.
6. Root Exudates.

Excretion Question And Answers

Question 1. Describe the structure and function of the nephron.
Answer:

• The nephron is the structural and functional unit of the kidney. A nephron is about 3 cm long and 20-60 cm in diameter. It has two components, renal capsule and renal tubule. The renal or Malpighian capsule has two parts, Bowman’s capsule and glomerulus.
• Bowman’s capsule is a blind broad cup-shaped end of a nephron. It encloses a bunch of capillaries called glomerulus. The glomerulus develops from a slightly broader afferent arteriole and passes into a slightly narrow efferent arteriole.
• The renal tubule has three parts proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). It is surrounded by peritubular capillaries formed by the efferent arteriole.

Function. Nephron takes part in urine formation. It has four components ultrafiltration, reabsorption, tubular secretion, and concentration.

1. Ultrafiltration. In the glomerulus, blood is under pressure due to the narrowness of the efferent arteriole. All small-sized solutes and a good part of water pass into Bowman’s capsule and then the proximal convoluted tubule as primary urine.
2. Reabsorption. The peritubular capillaries around PCT reabsorb useful substances present in the primary urine including some 75% of water.
3. Tubular Secretion. Peritubular capillaries actively secrete waste products remaining in their blood into the distal convoluted tubule. Waste-free blood passes into venules formed from the peritubular capillaries,
4. Concentration. Some 10% of water is passed out of the filtrate in the region of the loop of Henle by exosmosis. The remaining concentration occurs in collecting tubules under the effect of antidiuretic hormone or ADH (= Vasopressin).

Question 2. What are the methods used by plants to get rid of excretory products?
Answer:

1.  Carbon dioxide during the night, oxygen, and excess water during the daytime are got rid of through diffusion.
2. Roots get rid of many waste materials in the soil as exudate from their surface.
3. Deposition in the bark which is periodically peeled off.
4. Deposition in old leaves which fall off.
5. Deposition in old xylem which becomes functionless in conduction of sap.
6. Deposition in idioblasts and inside central vacuoles of cells.

• The amount of urine production is regulated by two phenomena—amount of blood and ADH or vasopressin. If there is an excess intake of water, the volume of blood will increase. It increases glomerular pressure and hence formation of more primary urine.
• Some water is absorbed from it in PCT and the loop of Henle. However, there is no secretion of antidiuretic hormone (= vasopressin) so dilute urine is passed out from the kidneys. Its amount is higher than the normal.
• When the body is deficient in water (as during summer due to sweating) there will be a lesser amount of blood being filtered and hence lesser amount of primary urine.
• ADH or vasopressin is secreted by the pituitary. It helps in withdrawing water from the urine. This produces a smaller and more concentrated amount of urine.

Excretion Multiple Choice Question

Question. In the excretory system of human beings, some substances in the initial filtrate such as glucose, amino acids, salts, and water are selectively reabsorbed in

1. Urethra
2. Nephron
3. Ureter
4. Urinary bladder.

Answer: 2. Nephron

Excretion Short Answer Type Questions

Question 1. What is excretion? How do unicellular organism remove their wastes?
Answer:

Excretion is the elimination of metabolic wastes, toxins, and excess salts from the body. In unicellular organisms, excretion is carried out through diffusion from the surface.

Question 2. A major amount of water is selectively reabsorbed in the tubular part of the nephron. What are the factors on which the amount of water reabsorbed depends?
Answer:

• Amount of excess water present in the filtrate.
• Amount of waste to be eliminated
• Length of the loop of Henle.

Question 3. 1. Name any two substances that are selectively reabsorbed as the urine flows along the tube,

2. Name the part of the excretory system In which mine is stored for some time.
Answer:

1. Glucose, amino adds.
2. Urinary bladder,

Question 4. “About 180 liters of renal filtrate is produced each day blit only 1.5 liters of urine Is excreted out”. Justify the statement.
Answer:

The renal filtrate contains all the small size/volume solutes and most of the water from the blood. Therefore, the volume of renal filtrate is higher. Most of the useful solutes and over 75% of water are reabsorbed by blood capillaries from the renal filtrate.

As a result, the volume of the filtrate decreases. Further, loss of water occurs in the loop of Henle and collecting tubules. Therefore, the final urine formed is quite small as compared to the original glomerular filtrate.

Question 5. Define excretion. Write any two vital functions of the kidney.
Answer:

Excretion. It is the removal of metabolic wastes, toxins, and excess salt from the body.

Vital Functions of Kidney. (1) Separation and elimination of metabolic waste products. (2) Maintenance of blood pressure and water balance of the body.

Question 6. 1. Name one nitrogenous waste present in urine.

 2. What is the basic unit of the kidney called?

3. How the amount of urine produced is regulated?
Answer:

1. Nitrogenous Waste. Urea (most common).
2. Basic Unit of Kidney. Nephron.
3.  Regulation of Amount of Urine. It is carried out by antidiuretic hormone (ADH) or vasopressin. It is secreted in good amounts if water is to be conserved.

• • Then only concentrated urine is passed out. If the amount of water is in excess, very little ADH is produced and dilute urine is allowed to pass out.

 

Respiration

What Is Respiration? Define Respiratory Substrate.

Respiration is a multistep enzymatic breakdown of organic compounds like glucose that releases small packets of energy at various steps. Glucose that is commonly broken down in respiration is called respiratory substrate. In the aerobic type of respiration, oxygen is used as a terminal oxidant. Besides energy, carbon dioxide is released.

Respiration Experiment

Carbon Dioxide Is Released During Respiration

Take two test tubes. Half-fill them with freshly prepared lime water. Blow air into one test tube by means of a tube. Note the time taken by lime water to turn milky. Now, blow fresh air into the second test tube by means of a syringe (or Pichkari). Repeatedly do it till lime water turns milky. Note the time taken. Compare the two time periods.

Lime water turns milky only when it reacts with carbon dioxide. Air blown out of the mouth is the one which has come out from the lungs. As it turns lime water milky very soon, it is clear that respiration releases carbon dioxide. ‘Atmospheric air contains comparatively very low concentrations of carbon dioxide as it takes a long time to change lime water milky.

Cellular Respiration

What Is Cellular Respiration?

Break-down of respiratory substances occurs only inside living cells. It is, therefore, called cellular respiration. Oxygen used in cellular respiration and carbon dioxide produced by it are called respirators or metabolic gases.

Complex animals have three more steps for respiration—breathing, external respirator’ exchange and internal respiratory exchange. There is a direct respiratory exchange of gases in simple animals and most plants.

Release Of Energy ATP

How Much Energy Is Released By Breakdown Of One Molecule Of Glucose?

Respiration releases energy in small steps. A part of this energy is dissipated as heat while another part is used in the formation of adenosine triphosphate (ATP).

About 50% of the released energy is used in the formation of ATP from ADP and inorganic phosphate (Pi or P)

ADP + Pi or (P) + Energy ↔ ATP or ADP ∼ (P)

About 30.5 kJ or 7.3 kcal of energy is used in the synthesis of one molecule of ATP from ADP and Pi. The same energy is released whenever energy is required for any activity of the cell. ATP functions as the energy currency of the cell.

The energy is used in various functions of the cell (just as a batter) and can be used to provide electricity for diverse activities) for example, muscle contraction, nerve conduction, membrane permeability, active absorption, cyclosis or cytoplasmic streaming, working of genetic system, biosynthesis, etc.

Respiration And Photosynthesis

What Is The Difference Between Respiration And Photosynthesis?

Respiration is a breakdown or catabolic process which releases energy stored in chemical bonds of the respiratory substrate. Photosynthesis is a build-up or anabolic process which traps solar energy and uses the same in the formation of chemical bonds in organic compounds. The two processes are complementary as the products of one are used as raw materials for the other.

Photosynthesis occurs only during the daytime in green cells. Respiration occurs all the time in all the living cells. However, the rate of photosynthesis is several times the rate of respiration, so a lot of food gets stored in plants after meeting their respiratory requirement.

Differences Between Respiration And Photosynthesis

Types Of Respiration

Respiration is of two types: anaerobic and anaerobic.

Aerobic Respiration. It is a mode of respiration in which the respiratory substrate is completely oxidised to form carbon dioxide and water. It is the common mode of respiration since it yields the maximum energy contained in the respiratory substrate.

A part of the liberated energy is stored in some 38 ATP molecules. The rest is dissipated.

Aerobic respiration occurs in two steps, cytoplasmic and mitochondrial.

1. In cytoplasm glucose is broken into two molecules of 3-carbon compound pyruvic acid. Two ATP and two NADH₂ are also formed. This cytoplasmic step is called glycolysis.

2. In mitochondria one pyruvic acid undergoes decarboxylation and dehydrogenation to form 4NADH₂, one FADH₂; one ATP and 3 molecules of carbon dioxide.

The mitochondrial step is called the Krebs cycle after the scientist who discovered it in 1940. Both NADH₂ and FADH₂, are used in mitochondria to form ATP molecules through a process called oxidative phosphorylation. One NADH-, produces 3 ATP molecules while one FADH₂ forms two ATP molecules.

Total NADH₂ formed in aerobic respiration = Glycolysis – 2NADH₂

Kreb’s cycle — 4 NADH₂ x 2 = 8NADH₂

Total FADH₂ formed in aerobic respiration = 1 FADH₂ x 2 = 2FADH₂

Direct ATP formed = Glycolysis – 2ATP = Kreb’s cycle – 1 ATP x 2 = 2ATP

From 10 NADH₂, 10 x 3 = 30, From FADH₂ 2 x 2 = 4, Direct ATP = Glycolysis — 2, Krebs’ cycle — 2.

Total 30 + 4 + 4 = 38 ATP

Anaerobic Respiration

What Is Anaerobic Respiration? Why It Is Uncommon?

It is a breakdown of the respiratory substrate without using oxygen. A complete breakdown into inorganic products is absent At least one product of anaerobic respiration is an organic substance. Anaerobic respiration occurs in the cytoplasm only. It has two components, glycolysis and reduction of pyruvic acid produced in glycolysis.

Anaerobic respiration occurs in many bacteria, yeast and some other microorganisms. In yeast, the most common products are ethyl alcohol (C₂H₅OH) and carbon dioxide. Anaerobic respiration also occurs in striated muscles during heavy exercise. Here pyruvate is reduced to form lactic acid. Lactic acid causes pain in the muscles and forces the athlete to stop further exercise.

Fermentation. It is an anaerobic breakdown of sugars by microorganisms that is usually accompanied by effervescence or bubbling out of waste gases and the formation of a variety of products like alcohol and organic acids.

The fermentation activity of yeast is used in the baking industry and brewing industries. The formation of yoghurt, curd, idli and dosa is also the fermentation activities of specific bacteria. Acids produced through fermentation include vinegar, citric acid, lactic acid and butyric acid.

Fermentation Experiment

In Fermentation, Yeast Produces Alcohol And Carbon Dioxide.

Take a test tube. Fill 5/6 of it with 10% glucose solution or some fresh fruit juice. Add half a spoonful of yeast to it. Pour a drop of non-drying oil over the surface of the solution to exclude oxygen. Fit a one-holed cork having a delivery tube into the mouth of the tube.

Dip the free end of the delivery tube in a tube having freshly prepared lime water. Note bubbles of gas coming out of the sugar solution. They pass into lime water. Lime water turns milky indicating that yeast is producing carbon dioxide. Remove the cork and smell the solution. It smells of alcohol. Yeast, therefore, produces alcohol and carbon dioxide during fermentation or anaerobic respiration.

Differences Between Anaerobic And Aerobic Respiration

Exchange Of Gases In Plants

Higher plants respire aerobically. The rate of respiration is different in different parts. Growing points of both stem and roots, cambial cells, floral buds, growing fruits and germinating seeds respire more actively than other parts.

Most parts respire slowly because being fixed, plants have a lower requirement of energy. Plants also do not have any transport system for gases. Instead, they have a well-connected network of intercellular spaces for the diffusion of gases. Even then every part of the plant has its own system of exchange of gases.

Leaves And Young Stems. They possess stomata for gaseous exchange. During day time carbon dioxide is consumed in photosynthesis and oxygen evolves. Stomata help in the inward diffusion of carbon dioxide and the outward diffusion of oxygen. The oxygen required for respiration is generated internally. Similarly, carbon dioxide produced in respiration is consumed in photosynthesis.

At night, plants also require oxygen for respiration. They may also release carbon dioxide. The exchange occurs through some partially opened stomata as well as gases stored in intercellular spaces during the daytime.

Older Stems And Roots. They possess permanently open pores called lenticels. A lenticel has a number of loosely arranged complementary cells. Their interspaces connect atmospheric air with air present in the intercellular spaces.

Young Roots. Epiblema cells and root hairs of young roots are permeable to metabolic gases. They are in contact with small spaces present in between soil particles. Oxygen from soil diffuses into roots while carbon dioxide comes out of the roots into air spaces. Soil air spaces are in contact with soil pores present on the surface of the soil.

However, in waterlogged soil, the soil aerating system disappears. In the absence of oxygen, young roots stop growth and fail to undertake active transport. Cell membranes lose permeability. As a result, the plant devoid of root aeration, withers and may die.

Respiration Multiple Choice Questions And Answers

Question 1. Anaerobic process

1. Takes place in yeast during fermentation
2. Takes place in the presence of oxygen
3. Produces energy only in the muscles of human beings
4. Produces ethanol, oxygen and energy.

Answer: 1. Takes place in yeast during fermentation

Respiration Long Answer Type Questions

Question 1. Explain how the exchange of gases occurs in plants across the surface of stem, root and leaves.
Answer:

1. Young Stems and Leaves. Through stomata between the atmosphere and intercellular spaces present in leaves and young stems. During daytime oxygen is passed out of them and carbon dioxide is absorbed. During night the reverse exchange of gases occurs.
2. Young Roots. There are no pores or stomata. The epiblema and root hairs are permeable to gases so the exchange of gases occurs between intercellular spaces of roots and the soil interspaces.
3. Old Stems and Old Roots. Lenticels or permanently open pores occur over the surface of old stems and roots. They are connected internally to intercellular spaces.
   • The exchange of gases occurs between the atmosphere and plant interior through the lenticels which have loosely held complementary cells.

Transportation

What is transportation? What is its importance?

It is the carrying of materials from one part to another of the body. Materials are carried from the region of their availability to the region of their consumption, storage or elimination.

Transportation Importance

1. Food. Every cell of the body requires food. It is passed on from the area of synthesis (in plants) or availability (alimentary canal in animals) to all parts of the body through the transport system.
2. Oxygen. In animals, oxygen becomes available from the respiratory surface. It is passed on to various parts through transportation.
3. Carbon Dioxide. It is produced during respiration. It is carried to the respiratory surface by a transport system for elimination.
4. Waste Materials. Metabolic wastes like urea, uric acid and others are first taken to the kidneys for separation and then stored temporarily for elimination through transportation.
5. Water. It circulates in the body through a transportation system.
6. Hormones. They are poured into the transport system for passage to the area of use.
7. Minerals. They are passed from the region of availability to all the parts for utilisation.
8. Other Functions. The transportation system has an accessory function of defence against pathogens and plugging the place of injury.

Transportation in Human Beings

Human beings have a circulatory system for transportation. It consists of a pumping heart, circulatory fluids blood and lymph and tubes. Depending upon the fluid being circulated, the circulatory system is of two types, blood blood-vascular system and the lymphatic system. The blood-vascular system comprises blood, blood vessels and the heart.

 

Heart Beat

What is Heartbeat? How pulse is different from a heartbeat?

It is a rhythmic contraction (systole) and expansion (diastole) of the heart. The rate is 70-72/ minute for adult human males and about 80/minute for adult females. Heartbeat is listened to by an instrument called a stethoscope.

Heartbeat has a low-pitched sound of a longer duration called lubb and a high-pitched shorter duration sound called dup. Lubb represents the simultaneous closure of auriculo-ventricular valve while dup is due to the simultaneous closure of semilunar valves.

Pulse. It is a rhythmic throb felt by a finger over a superficially placed artery (e.g., radial artery below the base of the thumb). Its value is equal to the heartbeat.

Types of Blood Circulation

What is double circulation? Give one importance.

Fishes possess a single blood circulation— venous blood → heart → Gills → Body → Venous blood. An incomplete circulation occurs in amphibians and lizards where mixed blood passes into the body for supply as well as lungs for oxygenation. A complete double circulation occurs in birds and mammals including human beings.

Double Circulation. It is a passage of the same blood twice through the heart, once in a deoxygenated form on the right side and then on the left side in an oxygenated state. The two components of double circulation are pulmonary circulation and systematic circulation.

1. Pulmonary Circulation. It is a short distance blood circulation from the heart to the lungs and back. Deoxygenated blood collects in the right auricle, is pumped into the right ventricle and from there to the pulmonary trunk.

The latter forms two pulmonary arteries which go to the lungs. In the lungs, the blood is oxygenated. Oxygenated blood flows to the left auricle by means of two pairs of pulmonary veins.

2. Systemic Circulation. It is a long-distance circulation of blood from the heart to all parts of the body except the lungs. The blood circulated by it is oxygenated. This blood becomes deoxygenated in the body tissues.

• From there the deoxygenated blood is carried by veins to the right atrium of the heart through a recall, a postcard and a coronary sinus. Nutrients, waste products and other materials are also transported in the process.
• Importance of Double Circulation. Double circulation, as found in birds and mammals, is the most efficient pathway of blood circulation. It provides 100% oxygenated blood to various body parts. The deoxygenated blood is sent by pulmonary circulation to the lungs for complete oxygenation.
• This is helpful for the thermoregulation of the body and the availability of maximum energy for body activities. Animals with incomplete double circulation (amphibians and reptiles) are unable to regulate the temperature of their body.
• Fishes with single circulation use partially oxygenated blood in most parts of their body. They are also unable to regulate their body temperature.

The Tubes: Blood Vessels

Human blood flows only inside closed blood vessels. The latter are of three types-arteries, veins and capillaries.

Arteries. They carry blood coming from the heart to various parts of the body. They are thus distributing blood vessels. Since the blood is coming from the heart, it flows rapidly but with jerks due to alternate expansions.

• The wall is thick and elastic due to the thickening of the middle tunica media. The lumen is narrow. Valves are absent. Most arteries are deep-seated except a few like radial where pulse can be felt. Except for pulmonary arteries, all other arteries cany oxygenated blood. Empty arteries do not collapse.

Veins. They carry blood from various parts of the body towards the heart. They are, therefore, collecting blood vessels. Blood flow is slow but smooth. Internal valves prevent the backflow of blood.

• The wall is moderately thickened as tunica media is a little thickened. The lumen is wide. The empty veins collapse. Most veins are superficial. They carry deoxygenated blood except in pulmonary veins.
• Capillaries. They are narrow (4-10 pm) blood vessels having a single-layered wall which occur in contact with tissues inside all body organs. They are meant for the exchange of materials between blood and body cells.

• For this blood capillaries have fine pores from which some plasma, dissolved substances and even some WBCs come out. It is called a capillary exchange. The reverse flow from cells also occurs.
• The capillary formation is a device to help in the exchange of materials. An artery branches to form arterioles while each arteriole gives rise to several capillaries. The capillaries reunite to produce venules which join to form veins.

Blood Pressure

What is blood pressure? Define systolic and diastolic pressure.

The pressure exerted by blood on the wall of an artery is called blood pressure. The instrument used in measuring blood pressure is called a sphygmomanometer. It has a mercury manometer, an inflatable cuff, and a compressible rubber bulb with a screw for pumping and releasing air.

A stethoscope is required. The rubber cuff is wrapped around the upper arm just above the elbow. It is inflated. The diaphragm of the stethoscope is placed over the brachial artery in the fold of the elbow. Air is very slowly released. The first sound of blood flowing in the brachial artery gives systolic pressure.

With the further release of air, a point is reached when the sound of flowing blood disappears. It is diastolic pressure. For a normal young person, the two values are 120 mm Hg (systolic) and 80 mm Hg (diastolic).

A higher value, say 140/90 mm Hg is hypertension (high blood pressure) while a lower value, say 110/70 mm Hg, is hypotension (low blood pressure).

Maintenance By Platelets

How do the platelets minimise the leakage of blood from an injured blood tube?

• At the place of injury, the injured blood vessel begins to spill blood. Besides loss of blood, there is a fall of blood pressure which is harmful to the working of the body. Blood platelets (thrombocytes) help in sealing the place of injury.
• On exposure, the platelets release thromboplastin. In the presence of calcium, thromboplastin acts on the prothrombin of blood to form a proteolytic enzyme called thrombin.
• Thrombin acts on blood protein fibrinogen to form insoluble fibrin monomers. Fibrin monomers undergo polymerization. They form long fibres which give rise to a fine network at the place of injury.

• It entraps blood corpuscles. A jelly-like mass called a blood clot is formed. The clot contracts brings the injured walls together and seals the area. A liquid called serum is released during the solidification of the clot.
• It is straw coloured second transport fluid of the body. Lymph is derived from tissue fluid. It is picked up by lymph capillaries which join to form larger lymph vessels. Tissue fluid continues to increase in quantity due to pressure filtering in the blood capillaries.
• Excess of tissue fluid passes out as lymph. Lymph is devoid of red blood corpuscles and blood platelets. It has a small number of leucocytes. Protein content is also less. Lymphocytes (a type of leucocytes) are in good numbers.
• They actually mature in special areas attached to lymph vessels which are called lymph nodes and lymph-containing organs. Lymph-containing organs are adenoids, tonsils, thymus and spleen.
• Lymph capillaries are more permeable than blood capillaries. Therefore, most of the organs pour their secretions into the lymph. In the intestine, lymph vessels called lacteals are involved in the absorption of fat Lymph vessels join to form larger ducts which open into right and left subclavian veins.
• Like veins, movement of lymph in lymph vessels occurs through the milking action of surrounding muscles. Lymph vessels also possess valves, like veins, to prevent backflow of lymph.

Lymph Functions

Blood Volume. Lymph maintains the blood volume of the body which has a tendency to decrease due to plasma filtration in tissues,

1. Middleman. Lymph acts as a middleman between tissues/glands and blood,
2. Fat. Digested fat is collected by lymph for passing into blood.
3. Lymphocytes. They mature in lymph nodes,
4. Germs. Lymph capillaries and lymph nodes attract and destroy germs.

Transportation Multiple Choice Question

Which one of the following statements is correct about the human circulatory system?

1. Blood transports only oxygen and not carbon dioxide
2. The human heart has five chambers
3. Valves ensure that the blood does not flow backwards
4. Both oxygen-rich and oxygen-deficient blood get mixed up in the heart.

Answer: 3. Valves ensure that the blood does not flow backwards

Heredity

Individuals of a species appear similar because they have a common body design. Careful observation shows that they have subtle differences. These differences or variations are quite small and fewer in the case of asexually reproducing organisms. They are quite abundant in sexually reproducing organisms. In sugarcane fields multiplied by vegetative propagation, all the plants look similar except for minor differences. This is because in asexual reproduction variations develop only due to errors in DNA replication.

In sexually reproducing organisms, variations are so abundant that we can easily recognize one individual from another.

1. There is a regular reshuffling of variations as well as the addition of new variations due to
2. Separation of homologous chromosomes during gametogenesis.
3. Chance coming together of individual chromosomes in gametes.
4. I am crossing over during meiosis.
5. Chance coming together of homologous chromosomes during fertilization.
6. Change in genetic material due to error of DNA copying and faulty distribution of chromosomes.

Accumulation Of Variation During Reproduction

Why with each generation, does inheritance provide a common basic body design, along with differences from the previous generation?

Variations appear during reproduction, whether it is asexual or sexual. Each new generation inherits two things from the parent generation.

• A common body design and subtle changes are present in that generation. The new generation develops its variations in addition to variations received from the parents.
• The process of accumulation of variations goes on. Of course, there are fewer in asexually reproducing organisms like bacteria and numerous in sexually reproducing organisms.
• However, all the variations do not survive. Harmful variations are eliminated with the death of the individuals. Useful variations survive as they increase the adaptability and competence of the individuals.
• Neutral variations may persist or get eliminated. Some of them can help the individuals in pre-adaptation like surviving during heat waves in temperate areas or resisting a new insecticide and antibiotic.

Therefore, environmental factors determine the usefulness and accumulation of variations. The variants form the basis for the evolution of new types.

Heredity Short Question And Answers

Question 1. If trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the same species, which trait is likely to have arisen earlier?
Answer:

A trait that is present in a larger number of individuals must have developed earlier than the one that is present in a smaller number of individuals. Therefore, trait B present in 60% population must have developed earlier than trait A found in 10% population.

Question 2. How does the creation of variations in a species promote survival?
Answer:

All types of variations do not promote survival.

Two types of variations promote survival.

• Useful variations that help the individuals to better adapt to the environment and enhance competitiveness in the struggle for existence.
• Preadaptation or those neutral variations become useful in the changing environment.

For example, bacteria can tolerate higher temperatures if a heat wave sweeps a temperate region.

Question 3. State the two advantages of variations.
Answer:

They help in the struggle for existence and natural selection.

Some variations function as preadaptation to changing environments and adverse conditions.

Question 4. Variations that confer an advantage to an individual organism only will survive in a population. Justify.
Answer:

Survival of an individual depends upon its ability to tolerate stressful conditions of the environment, compete with other individuals, and obtain proper food, shelter, and mate.

• It results in differential reproduction and transfer of useful variations to the next generation.
• Under stressful conditions, variations that function as pre-adaptations will be useful and help some individuals to survive while others remain weak and die.

Question 5. Explain how organisms create an exact copy of themselves.
Answer:

Organisms create exact copies of themselves through reproduction. In reproduction, whether asexual or sexual, the genetic traits of the parents are transferred to the individuals of the new generation. Hence, the exact copy. Of course, some small variations do occur due to errors in DNA copying and shuffling of chromosomes.

Question 6. Define the term variation. Why is variation beneficial to a species? List two reasons for the appearance of variations among the progeny formed by sexual reproduction
Answer:

Variation: It is the difference in structure, physiology, or behavior among individuals of the same species. Advantages. See SAQ 1.

Reasons: Separation of two chromosomes of each type during meiosis

• Crossing over
• Chance coming together of chromosomes during fertilization
• Errors in DNA copying and mutations.