NCERT Class 11-Biology: Chapter – 19 Excretory Products and Their Elimination Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 4:

How does tubular secretion help in maintaining ionic and acid-base balance in body fluids?


Tubular secretion is crucial as it helps in the maintenance of ionic balance in the body fluids.

Proximal Convoluted Tubule has simple cuboidal epithelium that increases the surface area for reabsorption. It also maintains the pH and ionic balance of the body fluids by selective secretion.

Distal Convoluted Tubule is where conditional reabsorption of sodium ions and water takes place. It is also responsible for selectively secreting hydrogen and potassium ion to maintain the ionic balance and .

Collecting Duct: From this long duct, large amounts of water could be reabsorbed to produce concentrated urine. It plays a role in the maintenance of pH and ionic balance of blood by the selective secretion of ions as well as maintain osmolality.

Collecting Duct

Question 5:

The glomerular filtrate in the loop of Henle gets concentrated in the descending and then gets diluted in the ascending limbs. Explain.


Reabsorption is minimum in its ascending limb which plays a significant role in the maintenance of high osmolality of medullary interstitial fluid.

The descending limb of loop of Henle is permeable to water but almost impermeable to electrolytes so water can flow out. This concentrates the filtrate as it moves down.

The ascending limb is impermeable to water but allows transport of electrolytes. Therefore, as the concentrated filtrate passes through the ascending limb, it gets diluted due to the passage of electrolytes to the medullary fluid.


Question 6:

Describe the structure of a human kidney with the help of a labelled diagram.

Human Kidney


Kidneys are reddish brown in colour, bean shaped, situated between the last thoracic and third lumbar vertebra level close to the dorsal inner wall of the abdominal cavity.

Towards the centre of the inner side of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter.

Inside the kidney, there are an outer cortex that extends in between the renal columns called Columns of Bernini and an inner medulla divided into medullary pyramids projecting into the calyx.

Each kidney has structures called nephrons which are the structural and functional units having two parts – the glomerulus and the renal tubule.

The renal tubule starts with a cup-like structure called Bowman՚s capsule, by the glomerulus is enclosed and together they are called the renal corpuscle.

The tubule continues to form proximal convoluted tubule (PCT) followed by a hairpin shaped Henle՚s loop having a descending and an ascending limb.

The ascending limb continues as another highly coiled tubular structure called distal convoluted tubule (DCT) . The DCTs open into a tube called collecting duct.