CBSE/NCERT/Exercises/Class_11_Biology
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
NCERT Biology Exercises for Class 11 Biology - Chapter 16 Excretory Products and their Elimination - Class_11_Biology
1. Define Glomerular Filtration Rate (GFR) Answer: Glomerular Filtration Rate (GFR) is the amount of filtrate formed by the kidneys per minute. In a healthy individual, it is approximately 125 ml/minute, which amounts to about 180 litres per day.
2. Explain the autoregulatory mechanism of GFR. Answer: The kidneys have a built-in mechanism for the regulation of GFR, primarily through the Juxta Glomerular Apparatus (JGA). JGA is a specialized sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at their contact point. A fall in GFR activates the JG cells to release renin, which stimulates glomerular blood flow and brings the GFR back to normal.
3. Indicate whether the following statements are true or false: (a) Micturition is carried out by a reflex. (True) (b) ADH helps in water elimination, making the urine hypotonic. (False - ADH facilitates water reabsorption, making urine hypertonic) (c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule. (True) (d) Henle’s loop plays an important role in concentrating the urine. (True) (e) Glucose is actively reabsorbed in the proximal convoluted tubule. (True)
4. Give a brief account of the counter current mechanism. Answer: The counter current mechanism operates between the two limbs of Henle’s loop and the vasa recta to maintain an increasing osmolarity towards the inner medullary interstitium (from 300 mOsmolL⁻¹ to 1200 mOsmolL⁻¹). This gradient is mainly caused by NaCl and urea. NaCl is transported by the ascending limb of Henle’s loop and exchanged with the descending limb of vasa recta. Similarly, urea enters the thin segment of the ascending limb and is transported back to the interstitium by the collecting tubule. This mechanism helps in the easy passage of water from the collecting tubule, concentrating the urine.
5. Describe the role of liver, lungs and skin in excretion. Answer:
6. Explain micturition. Answer: Micturition is the process of release of urine from the urinary bladder. It is initiated by a voluntary signal from the CNS triggered by the stretching of the bladder wall. Stretch receptors send signals to the CNS, which then initiates the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter, causing the release of urine. This neural mechanism is called the micturition reflex.
7. Match the items of column I with those of column II:
8. What is meant by the term osmoregulation? Answer: Osmoregulation is the process of maintaining the constant osmotic pressure of the body's fluids by controlling the concentration of water and salts.
9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why? Answer: Ammonia is highly toxic and requires a large amount of water for its elimination. Terrestrial animals, to conserve water, convert ammonia into lesser toxic nitrogenous wastes like urea (ureotelic) or uric acid (uricotelic), which can be removed with much less water.
10. What is the significance of juxta glomerular apparatus (JGA) in kidney function? Answer: JGA plays a complex regulatory role in monitoring GFR. A fall in glomerular blood pressure or GFR activates JG cells to release renin, which triggers the Renin-Angiotensin mechanism to increase blood pressure and GFR back to normal.
11. Name the following: (a) A chordate animal having flame cells as excretory structures: Amphioxus (b) Cortical portions projecting between the medullary pyramids in the human kidney: Columns of Bertini (c) A loop of capillary running parallel to the Henle’s loop: Vasa recta
12. Fill in the gaps: (a) 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 ADH. (c) Dialysis fluid contain all the constituents as in plasma except nitrogenous wastes. (d) A healthy adult human excretes (on an average) 25-30 gm of urea/day.
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