Excretion – Modes of Excretion: NEET MCQs with Answers

15 free questions on Excretion – Modes of Excretion for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Modes of Excretion: Ammonotelism, ureotelism, uricotelism

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Question 1

Previous-year question
Adaptation to life on land required the production of: [NEET 2022 (Overseas)]
  1. Lesser toxic nitrogenous wastes like urea and uric acid
  2. Lesser toxic nitrogenous wastes like ammonia and urea
  3. Highly toxic nitrogenous wastes like ammonia and urea
  4. Highly toxic nitrogenous wastes like urea and uric acid
Show answer
Answer: (A) Lesser toxic nitrogenous wastes like urea and uric acid
Explanation: NCERT states that terrestrial adaptation necessitated the production of lesser toxic nitrogenous wastes like urea and uric acid for conservation of water. Ammonia is the most toxic waste and needs large amounts of water for its elimination, so it suits aquatic animals.

Question 2

Previous-year question
Nitrogenous waste products are eliminated mainly as [AIPMT 1991]
  1. urea in tadpole and ammonia in adult frog
  2. ammonia in tadpole and urea in adult frog
  3. urea in both tadpole and adult frog
  4. urea in tadpole and uric acid in adult frog
Show answer
Answer: (B) ammonia in tadpole and urea in adult frog
Explanation: Ammonia is highly soluble in water but very toxic, so a large amount of water is required for its excretion. The tadpole is aquatic and lives in plenty of water, and therefore eliminates ammonia; the adult frog, being amphibious, switches to excreting urea.

Question 3

Previous-year question
Uric acid is the nitrogenous waste in [AIPMT 1994]
  1. mammals and molluscs
  2. birds and lizards
  3. frog and cartilaginous fishes
  4. insects and bony fishes
Show answer
Answer: (B) birds and lizards
Explanation: Uric acid is the least soluble nitrogenous waste and only about 10 mL of water is required to expel 1 g of it. It is also the least toxic, so it can be retained in the body for longer periods — a great advantage to animals with limited access to water, such as birds and lizards.

Question 4

Previous-year question
The kidney of an adult frog is [AIPMT 1997]
  1. pronephros
  2. mesonephros
  3. metanephros
  4. opisthonephros
Show answer
Answer: (B) mesonephros
Explanation: The mesonephric kidney consists of a large number of tubules which develop internal glomeruli enclosed in capsules forming Malpighian bodies. In amphibians such as the frog it is functional both in the embryo and in the adult.

Question 5

Previous-year question
In ureotelic animals, urea is formed by the [AIPMT 1997]
  1. ornithine cycle
  2. Cori cycle
  3. Krebs' cycle
  4. EMP pathway
Show answer
Answer: (A) ornithine cycle
Explanation: Urea is the main nitrogenous excretory product of ureotelic animals. It is produced by liver cells from deaminated excess amino acids via the urea cycle, also called the ornithine cycle or Krebs–Henseleit cycle.

Question 6

Previous-year question
Aquatic reptiles are [AIPMT 1999]
  1. ammonotelic
  2. ureotelic
  3. ureotelic in water
  4. ureotelic over land
Show answer
Answer: (C) ureotelic in water
Explanation: Aquatic reptiles such as turtles and crocodiles excrete mainly urea while living in water, i.e. they are ureotelic in water; terrestrial reptiles are uricotelic.

Question 7

Previous-year question
In living beings, ammonia is converted into urea through the [AIPMT 2000]
  1. ornithine cycle
  2. citrulline cycle
  3. fumarine cycle
  4. arginine cycle
Show answer
Answer: (A) ornithine cycle
Explanation: Ornithine combines with one molecule of NH₃ and CO₂ to produce citrulline; citrulline combines with another molecule of NH₃ to form arginine; and arginine is then broken down into urea and ornithine, which repeats the cycle. This is called the ornithine cycle, urea cycle or Krebs–Henseleit cycle.
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Question 8

Previous-year question
Uricotelism is found in [AIPMT 2004]
  1. mammals and birds
  2. fishes and freshwater protozoans
  3. birds, reptiles and insects
  4. frogs and toads
Show answer
Answer: (C) birds, reptiles and insects
Explanation: Animals which excrete mainly uric acid are called uricotelic and the phenomenon is called uricotelism. Uric acid is excreted by terrestrial reptiles (lizards, snakes, etc.), birds and insects, all of which need to conserve water in their bodies.

Question 9

Previous-year question
In the ornithine cycle, which one pair of the following wastes is removed from the blood? [AIPMT 2006, 2005]
  1. CO₂ and urea
  2. CO₂ and ammonia
  3. Ammonia and urea
  4. Urea and sodium salts
Show answer
Answer: (B) CO₂ and ammonia
Explanation: CO₂ and ammonia are the pair of wastes removed from the blood in the ornithine cycle. Urea is formed in this cycle from two molecules of ammonia and one molecule of CO₂ — it is a product, not a substrate.

Question 10

Previous-year question
Uric acid is the chief nitrogenous component of the excretory products of [AIPMT 2009]
  1. man
  2. earthworm
  3. cockroach
  4. frog
Show answer
Answer: (C) cockroach
Explanation: The cockroach excretes uric acid as its chief nitrogenous excretory product. Man excretes urea; the earthworm excretes about 40% urea, 20% ammonia and 40% amino acids; and the frog excretes urea as its chief nitrogenous product.

Question 11

Previous-year question
The uricotelic mode of passing out nitrogenous wastes is found in [AIPMT 2011]
  1. birds and annelids
  2. amphibians and reptiles
  3. insects and amphibians
  4. reptiles and birds
Show answer
Answer: (D) reptiles and birds
Explanation: Reptiles, birds, land snails and insects excrete nitrogenous waste as uric acid in the form of a pellet or paste with a minimum loss of water, and are therefore called uricotelic animals. Mnemonic — BIRD: B-Birds, I-Insects, R-Reptiles, D-Desert animals.

Question 12

Previous-year question
Select the option which shows the correct matching of an animal with its excretory organ and excretory product. [NEET 2013]
  1. Labeo (Rohu) — Nephridial tubes — Ammonia
  2. Salamander — Kidneys — Urea
  3. Peacock — Kidneys — Urea
  4. Housefly — Renal tubules — Uric acid
Show answer
Answer: (B) Salamander — Kidneys — Urea
Explanation: The salamander is an amphibian; it excretes urea through its kidneys, so this pair is correct. In Labeo the excretory organ is the mesonephric kidney and excretion is ammonotelic. The peacock has metanephric kidneys with uric acid as the excretory matter. In the housefly, excretion occurs through Malpighian tubules and the waste is chiefly uric acid.

Question 13

Previous-year question
Match the items in Column I with those in Column II. Column I — 1. Podocytes; 2. Protonephridia; 3. Nephridia; 4. Renal calculi Column II — i. Crystallised oxalates; ii. Annelids; iii. Amphioxus; iv. Filtration slits [NEET (Odisha) 2019]
  1. 1-iii, 2-iv, 3-ii, 4-i
  2. 1-iii, 2-ii, 3-iv, 4-i
  3. 1-iv, 2-iii, 3-ii, 4-i
  4. 1-iv, 2-ii, 3-iii, 4-i
Show answer
Answer: (C) 1-iv, 2-iii, 3-ii, 4-i
Explanation: Podocytes are the cells of Bowman's capsule that create filtration slits through which blood is filtered (1-iv). Protonephridia, found in Amphioxus among others, help in osmoregulation (2-iii). Nephridia are the excretory and osmoregulatory organs of annelids (3-ii). Renal calculi are kidney stones consisting mainly of crystallised oxalates (4-i).

Question 14

Previous-year question
Nitrogenous waste is excreted in the form of a pellet or paste by [NEET 2022]
  1. Salamandra
  2. Hippocampus
  3. Pavo
  4. Ornithorhynchus
Show answer
Answer: (C) Pavo
Explanation: Pavo (the peacock) belongs to class Aves and therefore excretes its nitrogenous waste as uric acid in the form of a pellet or paste, with minimum loss of water. Hippocampus excretes ammonia, while Ornithorhynchus and Salamandra excrete urea.

Question 15

Previous-year question
A terrestrial animal must be able to [2004]
  1. actively pump salts out through the skin
  2. excrete large amounts of water in urine
  3. excrete large amounts of salts in urine
  4. conserve water
Show answer
Answer: (D) conserve water
Explanation: Life on land involves continuous loss of water by evaporation and in the urine, with no external supply to draw on freely. Terrestrial animals therefore possess a range of water-conserving devices — an impermeable body covering, a concentrating kidney, and the excretion of urea or uric acid in place of ammonia.

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