Q1. Define Glomerular Filtration Rate (GFR)
Answer: Glomerular Filtration Rate (GFR) is the amount of filtrate formed by the kidneys per minute. In a healthy person, the GFR is about 125 mL per minute, which equals around 180 litres of filtrate formed per day.

Q2. Explain the autoregulatory mechanism of GFR.
Answer: The kidneys have an inbuilt autoregulatory system to maintain a constant Glomerular Filtration Rate (GFR). This control is mainly performed by the Juxta Glomerular Apparatus (JGA). The JGA is a sensitive region formed where the distal convoluted tubule (DCT) touches the afferent arteriole. When GFR falls, the JG cells release renin, which increases blood pressure and restores the normal GFR.

Q3. 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 helps in water reabsorption and prevents diuresis)
(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule. → True (All plasma constituents except proteins pass into Bowman’s capsule)
(d) Henle’s loop plays an important role in concentrating the urine. → True
(e) Glucose is actively reabsorbed in the proximal convoluted tubule. → True

Q4. 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. The filtrate in the descending and ascending limbs of Henle’s loop flows in opposite directions, creating a counter current. This arrangement maintains a concentration gradient in the medulla, increasing from 300 mOsmol L⁻¹ in the cortex to about 1200 mOsmol L⁻¹ in the inner medulla. Sodium chloride and urea mainly cause this gradient, which helps in reabsorbing water from the collecting ducts, thereby producing concentrated urine.

Q5. Describe the role of liver, lungs and skin in excretion.
Answer: Apart from the kidneys, the liver, lungs, and skin also help in excretion. The lungs remove large amounts of carbon dioxide (about 200 mL per minute) and water vapour. The liver secretes bile containing bilirubin, biliverdin, cholesterol, and drugs, which are excreted with digestive wastes. Sweat glands in the skin remove water, salts, urea, and lactic acid, while sebaceous glands excrete sterols, hydrocarbons, and waxes through sebum.

Q6. Explain micturition.
Answer: Micturition is the process of releasing urine from the urinary bladder. Urine formed in the nephrons passes to the urinary bladder where it is stored. When the bladder stretches, it activates stretch receptors that send signals to the central nervous system (CNS). The CNS then triggers the contraction of bladder muscles and relaxation of the urethral sphincter, leading to the release of urine. This reflex action is known as the micturition reflex.

Q7. Match the items of column I with those of column II:
(a) Ammonotelism → Bony fish
(b) Bowman’s capsule → Renal tubule
(c) Micturition → Urinary bladder
(d) Uricotelism → Birds
(e) ADH → Water reabsorption

Q8. What is meant by the term osmoregulation?
Answer: Osmoregulation is the process by which the body maintains the proper balance of water and ions. It ensures that the osmotic pressure and fluid levels within body cells and tissues remain constant despite changes in the external environment.

Q9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic. Why?
Answer: Terrestrial animals are ureotelic or uricotelic to conserve water. Ammonia, being highly toxic, needs a large amount of water for excretion, so it is suitable for aquatic animals. Urea and uric acid are less toxic and can be excreted with minimal water loss. Uric acid, being the least toxic, is excreted as a semi-solid paste in birds and reptiles, helping them save water.

Q10. What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Answer: The Juxta Glomerular Apparatus (JGA) helps regulate kidney function by maintaining the Glomerular Filtration Rate (GFR). When blood pressure or GFR falls, the JG cells release renin. Renin activates the renin-angiotensin mechanism, which increases blood pressure and restores GFR to normal levels.

Q11. 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 Henle’s loop → Vasa recta

Q12. Fill in the gaps:(a) Ascending limb of Henle’s loop is _______ to water whereas the descending
limb is _______ to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone
_______.
(c) Dialysis fluid contain all the constituents as in plasma except _______.
(d) A healthy adult human excretes (on an average) _______ gm of urea/day.
Answer:
(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 the ADH hormone.
(c) Dialysis fluid contains all the constituents of plasma except nitrogenous wastes.
(d) A healthy adult human excretes on an average 25–30 gm of urea per day.