Excretory Products and Their Elimination — Class 11 MCQs with Answers

Excretory Products and Their Elimination — important questions & MCQs with answers (Class 11 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Functional unit of kidney:

   ANephronBNeuronCAlveolusDHepatocyte
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   Answer: Nephron

   Explanation: The nephron filters, reabsorbs and secretes to form urine — the name sounds like neuron but that's the nerve cell's unit, and alveolus belongs to the lung.

2. Q2 of 6Easy

   Animals that excrete mainly ammonia are termed:

   AUreotelicBAmmonotelicCUricotelicDAminotelic
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   Answer: Ammonotelic

   Explanation: Ammonotelic animals excrete nitrogen mainly as ammonia, the most toxic form but cheapest to make. It needs plenty of water to dilute, so it suits aquatic animals like bony fishes.

3. Q3 of 6Medium

   ADH (vasopressin) acts on:

   ALiverBHeartCLungsDCollecting duct
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   Answer: Collecting duct

   Explanation: ADH acts on the collecting duct, inserting aquaporin channels so water is reabsorbed and urine concentrates. It doesn't touch the liver, heart or lungs directly.

4. Q4 of 6Medium

   Glomerular filtration occurs in:

   ABowman's capsuleBLoop of HenleCCollecting ductDBladder
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   Answer: Bowman's capsule

   Explanation: Glomerular filtration happens in Bowman's capsule, where blood pressure forces plasma past the glomerulus wall. The loop of Henle and collecting duct concentrate urine afterward, they don't filter it.

5. Q5 of 6Hard

   Excretion as uric acid involves:

   ALess ATP and more waterBMore ATP expenditure but less water lossCNo ATP and most water lossDOnly passive process
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   Answer: More ATP expenditure but less water loss

   Explanation: Making uric acid costs more ATP than urea or ammonia synthesis, but its near-insolubility means excretion loses far less water — an energy-for-water trade-off.

6. Q6 of 6Hard

   Renin is released by kidney to regulate:

   ABlood pressureBBody temperatureCVisionDBone density
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   Answer: Blood pressure

   Explanation: Renin, released by juxtaglomerular cells when blood pressure or GFR falls, triggers the RAAS to raise blood pressure — not temperature, vision or bone density.

Excretory Products and Their Elimination notes: key concepts (Class 11 Biology)

Nitrogenous wastes must be voided without losing too much water. This chapter compares ammonotelism, ureotelism and uricotelism, dissects the nephron, and follows urine formation through filtration, reabsorption and secretion, the counter-current multiplier that concentrates urine, hormonal control, and dialysis.

Modes of excretion

Animals are ammonotelic (ammonia, aquatic), ureotelic (urea, mammals) or uricotelic (uric acid, birds and reptiles) by water availability and toxicity.

Human excretory system

Two kidneys, two ureters, a urinary bladder and the urethra; each kidney has an outer cortex, an inner medulla with pyramids, and a pelvis.

Nephron

The nephron is the functional unit: a glomerulus in Bowman's capsule (Malpighian body), proximal tubule, loop of Henle, distal tubule and collecting duct.

Cortical vs juxtamedullary

Cortical nephrons have short loops barely entering the medulla; juxtamedullary nephrons have long loops with vasa recta, key to concentrating urine.

Glomerular filtration

Blood is filtered under high pressure in the glomerulus; the ultrafiltrate is plasma minus proteins, and glomerular filtration rate is about 125 mL/min.

Tubular reabsorption

Nearly 99% of filtrate is reclaimed — glucose, amino acids and Na⁺ actively, water passively — mostly in the proximal convoluted tubule.

Tubular secretion

Tubule cells actively secrete H⁺, K⁺ and ammonia into the filtrate, maintaining the ionic and acid–base balance of body fluids.

Counter-current mechanism

The loop of Henle and vasa recta act as counter-current systems that build a medullary osmotic gradient, letting the collecting duct concentrate urine.

Role of loop segments

The descending limb is permeable to water, the ascending limb pumps out NaCl but blocks water — this separation drives the multiplier effect.

Micturition

A filled bladder triggers stretch receptors; the CNS then relaxes the sphincter and contracts the bladder wall to release urine in the micturition reflex.

ADH regulation

ADH from the posterior pituitary makes the distal tubule and collecting duct reabsorb more water, concentrating urine when the body is dehydrated.

Renin–angiotensin system

Low blood pressure makes the JGA release renin, activating angiotensin II, which constricts vessels and triggers aldosterone to reabsorb Na⁺ and water.

Atrial natriuretic factor

ANF, released when the atria stretch under high blood volume, dilates vessels and increases Na⁺ excretion, acting to counter the renin system.

Dialysis and disorders

Uraemia (urea build-up) from kidney failure is treated by haemodialysis using an artificial membrane; kidney stones and glomerulonephritis are other disorders.