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NCERT Class 11 Biology Chapter 19 Excretory System
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Excretory System
Chapter: 19
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Define Glomerular Filtration Rate (GFR).
Ans. The amount of the filtrate formed by kidneys per minute is called glomerular filtration rate. In the normal person, the glomerular filtration rate is 125 ml per minute or 180 liters per day. Juxtaglomerular apparatus regulates GFR.
Q.2. Explain the auto regulatory mechanism of GFR.
Ans. Juxtaglomerular apparatus regulates GFR. Fall in GFR stimulates Juxtaglomerular cells to secrete renin which stimulates renal blood flow and GFR.
Q.3. Indicate whether the following statements are true or false:
(a) Micturition is carried out by a reflex.
Ans. True.
(b) ADH helps in water elimination, making the urine hypotonic.
Ans. False.
(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.
Ans. True.
(d) Henle’s loop plays an important role in concentrating the urine.
Ans. True.
(e) Glucose is actively reabsorbed in the proximal convoluted tubule.
Ans. True.
Q.4. Give a brief account of the counter current mechanism.
Ans. COUNTERCURRENT MECHANISM-
(i) It is the mechanism for concentrating the urine in kidneys.
(ii) This mechanism depends on the loops of Henle, vasa recta, collecting ducts and interstitial fluid.
(iii) The flow of filtrate in the two limbs of loop of Henle is in opposite directions and thus forms a counter current.
(iv) The flow of blood in the ascending capillary and descending capillary of vasa recta is also in opposite direction and form a counter current.
(v) The proximity between loops of Henle & vasa recta along with counter current in them is responsible for the increasing osmolality towards the medulla: 300 mOsmo/L in cortex to 1200 mOsmol/L in inner medulla. This gradient is mainly caused by NaCI and urea.
(vi) The counter current mechanism maintains a concentration gradient in the medullary interstitial fluid which helps in absorption of water from the filtrate in the collecting duct.
(vii) Concentration of filtrate is increased and hypertonic urine is produced in human beings.
Q.5. Describe the role of liver, lungs and skin in excretion.
Ans. Liver secretes bile and helps in the excretion of cholesterol, steroid hormones, vitamins, drugs, and other waste materials through bile. Ammonia is changed into urea in the liver and eliminated from the body. Lungs remove carbon dioxide from the body.
Skin has sweat and sebaceous glands. Sweat glands secrete sweat which excretes salt and water from the body. Sebaceous glands secrete an oily secretion called sebum.
Q.6. Explain micturition.
Ans. MICTURITION:
(i) The expulsion of urine from the urinary bladder is called micturition.
(ii) It is a reflex process subject to voluntary control.
(iii) Urine fills the urinary bladder and stretches the urinary bladder wall.
(iv) Stretch receptors in the bladder walls send signals to CNS.
(v) CNS signals the contraction of smooth muscles of bladder and relaxation of urethral sphincter causing the release of urine. This process of release of urine from urinary bladder is called micturition.
Q.7. Match the items of column I with those of column II:
| Column I | Column II |
| (a) Ammonotelism | (i) Birds |
| (b) Bowman’s capsule | (ii) Water reabsorption |
| (c) Micturition | (iii) Bony fish |
| (d) Uricotelism | (iv) Urinary bladder |
| (e) ADH | (v) Renal tubule |
Ans.
| Column I | Column II |
| (a) Ammonotelism | (iii) Bony fish |
| (b) Bowman’s capsule | (v) Renal tubule |
| (c) Micturition | (iv) Urinary bladder |
| (d) Uricotelism | (i) Birds |
| (e) ADH | (ii) Water reabsorption |
Q.8. What is meant by the term osmoregulation?
Ans. Osmoregulation is regulation of water and solute in the body fluids by the kidney.
Q.9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?
Ans. Terrestrial animals are either ureotelic or uricotelic and not ammonotelic G because ammonia is the most toxic form and requires large amount of water for its elimination while Uric acid is the least toxic and can be removed with minimum loss of water.
Q.10. What is the significance of juxtaglomerular apparatus (JGA) in kidney function?
Ans. JUXTAGLOMERULAR CELLS:
(i) These are swollen smooth muscle cells of both the afferent and efferent arterioles which contain dark granules containing renin.
(ii) Renin is secreted by Juxtaglomerular cells.
(iii) Renin converts angiotensinogen into angiotensin.
(iv) Angiotensin increase blood pressure.
(v) Angiotensin also stimulates the secretion of aldosterone by the adrenal cortex, influencing the reabsorption of sodium ions by the distal convoluted tubule and of water through the collecting duct.
Q.11. Name the following:
(a) A chordate animal having flame cells as excretory structures.
Ans. Amphioxus.
(b) Cortical portions projecting between the medullary pyramids in the human kidney.
Ans. Columns of Bertini.
(c) A loop of capillary running parallel to the Henle’s loop.
Ans. Vasa rectae.
Q.12. Fill in the gaps:
(a) Ascending limb of Henle’s loop is _____________ to water whereas the descending limb is ____________ to it.
Ans. Ascending limb of Henle’s loop is impermeable to water, whereas the descending limb is permeable to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone _____________.
Ans. Reabsorption of water from distal parts of the tubules is facilitated by the Hormone vasopressin.
(c) Dialysis fluid contains all the constituents as in plasma except ____________.
Ans. Dialysis fluid contains all the constituents as in plasma, except the nitrogenous waste.
(d) A healthy adult human excretes (on an average) ____________ gm of urea/day.
Ans. A healthy adult human excretes (on an average) 25 – 30 gm of urea/day.
