JAMB Biology 2021 past questions

Checked by the Skolra question team · Last updated 23 October 2026

Ten questions from the 2021 JAMB Biology paper, with answers and explanations. We hold 39 questions from this paper, and the Skolra app has all of them.

JAMB Biology 2021 questions and answers

1. 1.

   Which of the following is NOT regarded as a pollutanton land or in the air?

   1. A
      Oxygen
      Correct
   2. B
      Sulphur(IV) oxide
   3. C
      Carbon(II) oxide
   4. D
      Smoke
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   Answer: A

   Oxygen is a natural component of clean air that living things depend on for respiration; it is not regarded as a pollutant on land or in the air.

2. 2.

   I. Rattusrattus. Il. Agama agama III. Bufo regularis IV. Tilapiazillii
   The order of evolutionary advancement of the above vertebrates is?

   1. A
      III, IV, I, II
   2. B
      IV, III, II, I
      Correct
   3. C
      I, II, III, IV
   4. D
      IV, II, III, I
   Show answerHide answer

   Answer: B

   Correct order: IV, III, II, I

   Evolutionary advancement among vertebrates follows the sequence: fish → amphibians → reptiles → mammals, reflecting the order in which these classes arose and became more structurally complex and better adapted to life away from water.

3. 3.

   The two key cations involved in the action potential of nervous transmissions are?

   1. A
      Potassium and Chloride ions
   2. B
      Sodium and Potassium ions
      Correct
   3. C
      Sodium and Calcium ions
   4. D
      Calcium and Potassium ions
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   Answer: B

   During an action potential, the nerve cell membrane changes its permeability to two main cations: sodium (Na⁺) and potassium (K⁺).

4. 4.

   I. Stomata --> Spirogyra

   II. Alveoli --> Earthworm

   III. Malpighian tubule -> Mammal

   IV. Contractile vacuole -> Protozoa

   Which of the above structures is correctly matched with the organisms in which it is found?

   1. A
      III only
   2. B
      II only
   3. C
      I only
   4. D
      IV only
      Correct
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   Answer: D

   Only the contractile vacuole and protozoa pairing is correct.

   The contractile vacuole is a well-known organelle of freshwater protozoa such as Amoeba and Paramecium. It collects excess water that enters the cell by osmosis and pumps it out, preventing the cell from bursting. This pairing is correctly matched, so IV only is the answer.

5. 5.

   In the mammalian respiratory system. exchange of gases occurs in the?

   1. A
      Trachea
   2. B
      Alveoli
      Correct
   3. C
      Bronchioles
   4. D
      Bronchi
   Show answerHide answer

   Answer: B

   Gas exchange in the mammalian respiratory system takes place in the alveoli, the tiny air sacs at the end of the bronchioles.

   Alveoli are adapted for efficient diffusion: their walls are one cell thick, they are moist, and they are surrounded by a dense network of blood capillaries, giving a very large surface area for oxygen to diffuse into the blood and carbon dioxide to diffuse out.

6. 6.

   People who suck petrol with their mouths run the risk of increasing in their blood the concentration of

   1. A
      Carbon (IV) oxide
   2. B
      Lead
      Correct
   3. C
      Carbon monoxide
   4. D
      Sulphur dioxide
   Show answerHide answer

   Answer: B

   Petrol (especially the leaded petrol widely used at the time this question was set) contains tetraethyl lead as an anti-knock additive. When people siphon or suck petrol with their mouths, they swallow and inhale droplets of the fuel, which allows lead compounds to be absorbed directly into the bloodstream through the mouth and lungs. This raises the concentration of lead in the blood, a condition known as lead poisoning, which damages the nervous system, kidneys and blood-forming tissues.

7. 7.

   If both parents are heterozygous for a trait. the probability that an offspring will be recessive for that trait is?

   1. A
      1/2
   2. B
      3/4
   3. C
      1/16
   4. D
      1/4
      Correct
   Show answerHide answer

   Answer: D

   When both parents are heterozygous (Aa) for a trait, crossing them (Aa x Aa) gives the classic Mendelian monohybrid ratio.

   A Punnett square gives four possible offspring combinations: AA, Aa, Aa, aa — that is 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.

   Only the aa combination shows the recessive trait, and it is 1 out of 4 possible offspring, so the probability is 1/4.

8. 8.

   Which of the following is TRUE of the process of conjugation in Paramecium?

   1. A
      It involves temporary fusion of two paramecia and exchange of micronuclear material between them
      Correct
   2. B
      It results in an immediate increase in the number of individuals
   3. C
      It involves fusion of the macronuclei of the two individuals
   4. D
      It occurs only under unfavourable conditions and results in cyst formation
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   Answer: A

   Conjugation in Paramecium is a form of sexual reproduction in which two individuals of compatible mating types come together and temporarily join (fuse) at their oral surfaces, forming a cytoplasmic bridge.

9. 9.

   Aged erythrocytes are destroyed in the?

   1. A
      Kidney
   2. B
      Spleen
      Correct
   3. C
      Pancreas
   4. D
      Lungs
   Show answerHide answer

   Answer: B

   Aged (worn-out) erythrocytes are destroyed in the spleen (often called the "graveyard of red blood cells"), along with some breakdown occurring in the liver. The spleen filters blood and its macrophages engulf and break down old, fragile red blood cells, recycling their components such as iron and breaking down haemoglobin into bilirubin.

10. 10.

    When the original king and queen of termites die, they are replaced by

    1. A
       Supplementary (secondary) reproductives developed from nymphs
       Correct
    2. B
       Winged alates that fly back into the same nest
    3. C
       Worker termites chosen at random to mate
    4. D
       Soldiers that develop functional reproductive organs
    Show answerHide answer

    Answer: A

    Termite colonies have distinct castes: workers and soldiers are sterile and cannot reproduce, so they can never replace the king and queen.

    When the original king and queen die, the colony raises supplementary (secondary) reproductives, which develop from nymphs that keep their reproductive potential. These nymphs mature functional gonads and take over egg-laying and fertilization, keeping the colony alive.

The questions come from past JAMB, WAEC and NECO papers. We use software to help write the answer options and explanations, and every answer is checked twice before it goes on the site. How we check

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Practise all 39 questions we hold from the 2021 paper, on a timed CBT screen

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