Chapter 16: Excretory Products and their Elimination Short Questions | biology Class 11 CBSE

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Chapter 16: Excretory Products and their Elimination Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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What is ammonotelism? Name two animals that exhibit it.

Ammonotelism is the process of excreting nitrogenous waste primarily in the form of ammonia.
Many bony fishes and aquatic amphibians are ammonotelic animals.
Ammonia is excreted by diffusion across body surfaces or through gill surfaces as ammonium ions, with no significant role of kidneys.

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Question 2

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Why is urea considered more suitable than ammonia as an excretory product for terrestrial animals?

Ammonia is highly toxic and requires a large amount of water for its elimination, making it unsuitable for water-scarce terrestrial habitats.
Urea is far less toxic than ammonia and requires significantly less water for excretion.
Terrestrial adaptation therefore drove the evolution of ureotelism, allowing better conservation of water while still removing nitrogenous wastes efficiently.

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Question 3

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State the location and dimensions of human kidneys.

Human kidneys are situated between the levels of the last thoracic and third lumbar vertebra, close to the dorsal inner wall of the abdominal cavity.
Each kidney measures 10-12 cm in length, 5-7 cm in width, and 2-3 cm in thickness.
The average weight of each kidney is 120-170 g.

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Question 4

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What is the hilum of the kidney? What structures pass through it?

The hilum is a notch present towards the centre of the inner concave surface of the kidney.
The ureter, blood vessels (renal artery and renal vein), and nerves enter or exit the kidney through the hilum.
Inner to the hilum is a broad funnel-shaped space called the renal pelvis with projections called calyces.

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Question 5

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Distinguish between cortical and juxtamedullary nephrons.

Cortical nephrons have a short loop of Henle that extends only very little into the medulla and the vasa recta is absent or highly reduced.
Juxtamedullary nephrons have a very long loop of Henle that runs deep into the medulla.
Juxtamedullary nephrons are critical for concentrating urine due to their long loop contributing to the medullary osmotic gradient.

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Question 6

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What is the malpighian body? Name its components.

The malpighian body, also called the renal corpuscle, is the filtration unit at the beginning of each nephron.
It consists of the glomerulus, which is a tuft of capillaries, enclosed within the Bowman's capsule.
Together, these two structures initiate the process of ultrafiltration during urine formation.

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Question 7

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Define GFR and state its normal value in a healthy adult.

Glomerular Filtration Rate (GFR) is the amount of filtrate formed by the kidneys per minute.
In a healthy individual, GFR is approximately 125 ml per minute, which amounts to about 180 litres per day.
GFR is regulated by the juxtaglomerular apparatus (JGA) to maintain stable kidney function.

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Question 8

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Why is glomerular filtration referred to as ultrafiltration?

Glomerular filtration is called ultrafiltration because blood is filtered so finely that almost all constituents of plasma, except proteins, pass into the Bowman's capsule.
The filtration occurs through three layers: the endothelium of glomerular blood vessels, the basement membrane, and the podocytes of Bowman's capsule with their filtration slits.
The selective exclusion of large molecules like plasma proteins while allowing small solutes to pass makes it a process of ultra-fine filtration.

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Question 9

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What is the role of the JGA in regulating GFR?

The JGA is a special sensitive region formed by cellular modifications in the DCT and the afferent arteriole at their contact point.
A fall in GFR activates JG cells to release renin, which stimulates increased glomerular blood flow and thereby restores GFR to normal.
This autoregulatory mechanism ensures that the kidneys maintain a stable filtration rate despite fluctuations in blood pressure.

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Question 10

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State any two functions of the Proximal Convoluted Tubule (PCT).

PCT reabsorbs nearly all essential nutrients and 70-80% of electrolytes and water from the glomerular filtrate.
PCT helps maintain pH and ionic balance of body fluids by selectively secreting H+ ions and ammonia into the filtrate.
It also reabsorbs HCO3- from the filtrate, contributing to the buffering capacity of the blood.

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Question 11

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How does the descending limb of Henle's loop differ from the ascending limb in terms of permeability?

The descending limb is permeable to water but almost impermeable to electrolytes, causing the filtrate to become concentrated as it moves down.
The ascending limb is impermeable to water but allows active or passive transport of electrolytes, causing the filtrate to become diluted as it moves upward.
This differential permeability is essential for the counter current mechanism and the formation of the medullary osmotic gradient.

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Question 12

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What is the role of the collecting duct in urine formation?

The collecting duct extends from the cortex to the inner medulla and reabsorbs large amounts of water to produce concentrated urine.
It allows small amounts of urea to pass into the medullary interstitium, contributing to the osmotic gradient necessary for water reabsorption.
The collecting duct also maintains pH and ionic balance by selective secretion of H+ and K+ ions.

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Question 13

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What is ADH? How does it regulate kidney function?

ADH (Antidiuretic Hormone), also called vasopressin, is a hormone released by the neurohypophysis in response to signals from the hypothalamus when body fluid volume falls.
ADH facilitates water reabsorption from the latter parts of the renal tubule, thereby reducing urine output and preventing diuresis.
ADH also constricts blood vessels, raising blood pressure and increasing glomerular blood flow and GFR.

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Chapter 16: Excretory Products and their Elimination | Short Questions

What is ammonotelism? Name two animals that exhibit it.

Why is urea considered more suitable than ammonia as an excretory product for terrestrial animals?

State the location and dimensions of human kidneys.

What is the hilum of the kidney? What structures pass through it?

Distinguish between cortical and juxtamedullary nephrons.

What is the malpighian body? Name its components.

Define GFR and state its normal value in a healthy adult.

Why is glomerular filtration referred to as ultrafiltration?

What is the role of the JGA in regulating GFR?

State any two functions of the Proximal Convoluted Tubule (PCT).

How does the descending limb of Henle's loop differ from the ascending limb in terms of permeability?

What is the role of the collecting duct in urine formation?

What is ADH? How does it regulate kidney function?

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