Class 10 Biology Life Process Notes For Excretion

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.