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Excretory Products

Biology · Class 11NCERT pp. 205–2142 sets × 25 questions

Key facts and formulas for Excretory Products, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.

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Key facts for this chapter

IdeaRule or fact
Nitrogenous wastesAmmonia (most toxic, most water), urea (moderate), uric acid (least toxic, pellet or paste, least water)
Ammonotelic, ureotelic, uricotelicAquatic animals: ammonia. Mammals: urea from the liver. Reptiles, birds, insects: uric acid
Excretory organsProtonephridia: flatworms. Nephridia: annelids. Malpighian tubules: insects. Antennal glands: crustaceans
NephronsAbout 85 per cent cortical (short loop); about 15 per cent juxta medullary (long loop, vasa recta)
FiltrationThree layers: endothelium, basement membrane, podocytes. NFP = glomerular P − (capsular P + osmotic P)
GFRAbout 125 mL per minute, about 180 L per day. GFR = U × V / P with inulin
Tubule functionsPCT: 70 to 80 per cent reabsorption. Descending limb: water out. Ascending limb: minimal reabsorption. DCT: conditional Na+ and water, secretes H+, K+, NH3
Concentrating urineLoop of Henle is the multiplier, vasa recta the exchanger. Gradient 300 to 1200 mOsm per litre, four-fold
Hormonal controlADH (neurohypophysis) opens aquaporins. Renin (JG cells) → angiotensin II → aldosterone (adrenal cortex). ANF (atria) opposes
DisordersUremia: urea in blood. Calculi: stones. Glomerulonephritis: inflamed glomeruli. Glycosuria: glucose in urine. Gout: uric acid crystals

Three sample questions

Q1. Consider these statements about nitrogenous wastes.
I. Ammonia is the most toxic and needs plenty of water for removal.
II. Uric acid is the least toxic and is removed with the least water.
III. Urea is released as a pellet or paste.
Which are correct?
  1. II and III only
  2. I and II only
  3. I and III only
  4. I, II and III
Hint and solution

Hint: Pellet or paste means almost no water is used. Which waste is the driest one?

  1. Toxicity: NH3 > urea > uric acid — Ammonia is the most toxic, urea is moderate and uric acid is the least toxic.
  2. Statement I: true; statement II: true — Ammonia needs a lot of water for removal, while uric acid needs the least water. So I and II are correct.
  3. Pellet or paste = uric acid — Uric acid is almost insoluble and leaves as a pellet or paste. Urea leaves dissolved in urine, so III is false.
  4. Correct set: I and II only — Only statements I and II are correct, so the answer is I and II only. Option B.
Answer: B. Pellet or paste is the form of uric acid, not urea.
Q2. Match the animal group with its main nitrogenous waste.
Column I: a. Aquatic amphibians; b. Mammals; c. Reptiles; d. Marine fishes
Column II: (i) Ammonia; (ii) Urea; (iii) Uric acid
  1. a-(i), b-(ii), c-(ii), d-(i)
  2. a-(ii), b-(ii), c-(iii), d-(i)
  3. a-(i), b-(iii), c-(ii), d-(ii)
  4. a-(i), b-(ii), c-(iii), d-(ii)
Hint and solution

Hint: Reptiles save water, so they make the driest waste. Mammals make the waste in the liver that is also found in sharks.

  1. Aquatic amphibians: ammonotelic (i) — Animals with plenty of water remove ammonia. So a matches (i).
  2. Mammals: ureotelic (ii) — Mammals convert ammonia to urea in the liver. So b matches (ii).
  3. Reptiles: uricotelic (iii) — Reptiles save water and excrete uric acid. So c matches (iii).
  4. Marine fishes (d) with urea (ii) — Here d is taken as urea, as in the key. Combined: a-(i), b-(ii), c-(iii), d-(ii). Option D.
Answer: D. Aquatic amphibians are ammonotelic; mammals and marine fishes ureotelic; reptiles uricotelic.
Q3. Which animal and excretory organ pair is NOT correct?
  1. Cockroach: antennal glands
  2. Planaria: protonephridia
  3. Earthworm: nephridia
  4. Most insects: Malpighian tubules
Hint and solution

Hint: Antennal glands are named after antennae, which crustaceans such as prawns possess in a special way. Insects use tubules.

  1. Match organ to group — Protonephridia: flatworms. Nephridia: annelids. Malpighian tubules: insects. Antennal glands: crustaceans.
  2. Check each option — Planaria with protonephridia, earthworm with nephridia and insects with Malpighian tubules are all correct pairs.
  3. Cockroach is an insect — The cockroach has Malpighian tubules, not antennal glands.
  4. Wrong pair: cockroach - antennal glands — So the incorrect pair is cockroach with antennal glands. Option A.
Answer: A. Antennal (green) glands belong to crustaceans like prawns; the cockroach has Malpighian tubules.

How to use this chapter

Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.

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