(a) Describe the structure and function of the basic filtering unit of the kidney. (b) List two factors on which the reabsorption of water from urine depends.

(a) Structure and function of the basic filtering unit of the kidney:

The basic filtering unit of the kidney is called the nephron.

Structure of nephron:

1. Bowman’s capsule – A cup-shaped structure that surrounds a bunch of capillaries called the glomerulus.
2. Glomerulus – A network of capillaries where blood filtration starts.
3. Renal tubule – A long, coiled tube connected to Bowman’s capsule, responsible for reabsorption and secretion.
4. Collecting duct – Collects the final urine from multiple nephrons.

Function of nephron:

• Filtration: Blood enters the glomerulus under pressure, and waste products, water, glucose, salts, etc., are filtered into Bowman’s capsule.
• Reabsorption: Useful substances like glucose, water, and some salts are reabsorbed from the tubule into the blood.
• Secretion: Additional wastes are secreted into the tubule.
• Final urine (mostly urea, excess salts, and water) passes into the collecting duct.

(b) Two factors on which the reabsorption of water from urine depends:

1. Amount of excess water in the body – If the body is dehydrated, more water is reabsorbed.
2. Concentration of antidiuretic hormone (ADH) – ADH regulates water reabsorption by increasing permeability of the kidney tubules.