All 40 questions from the Joint Admissions and Matriculation Board (JAMB) Biology 2021 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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1. The taxon containing the least similar set of organisms is the (a) species (b) genus (c) order (d) kingdom
The kingdom is the taxon in which all other taxa are embedded, i.e. it is the largest taxon and contains the most dissimilar set of organisms. Species is the smallest taxon and comprises the most closely related organisms.
2. Which of the following is true about sex-linked characters? (a) they are dominant and linked to X-chromosome (b) They are recessive and linked to X-chromosome (c) They are dominant and linked to Y-chromosome (d) they are recessive and linked to Y-chromosome
Sex-linked characters are recessive and are linked to the X-chromosome.
3. The smallest bone in the human body is the (a) stapes (b) femur (c) malleus (d) incus
The smallest bones in the human body are the ear ossicles - malleus (hammer), incus (anvil) and stapes (stirrup). Of these, the stapes is the smallest.
4. The instrument with which atmospheric pressure is measured is the (a) wind vane (b) hydrometer (c) barometer (d) hygrometer
The barometer measures atmospheric pressure. (Windvane measures wind direction, hydrometer measures relative density, and hygrometer measures relative humidity.)
5. Cutaneous respiration is peculiar (a) Pisces (b) amphibians (c) reptiles (d) Aves
Amphibians exhibit pulmonary, buccal and cutaneous (skin) respiration; cutaneous respiration is peculiar to them.
6. The content of which of the following acidic? (a) mouth (b) stomach (c) Duodenum (d) stomach & duodenum
Saliva in the mouth is alkaline, but this alkalinity is neutralised in the stomach by HCl, making the stomach's content acidic. The duodenum's content is alkaline due to bile.
7. Height, skin color, weight and colour of the eyes are examples of (a) morphological variation (b) physiological variation (c) discontinuous characters (d) sex-linked characters
Height, skin colour, weight and eye colour deal with physical appearance and therefore represent morphological (continuous) variation, since these features have many intermediates.
8. When an allele can express itself both in the homozygous pairing and the heterozygous pairing, it is said to be (a) recessive (b) dominant (c) an allelomorph (d) genetic
An allele that can express itself only in the homozygous pairing is recessive; one that expresses itself in both homozygous and heterozygous pairing is dominant.
9. Beriberi is a deficiency symptom of vitamin (a) A (b) K (c) B1 (d) C
Vitamin A deficiency causes night blindness, Vitamin K deficiency causes haemophilia-like bleeding, Vitamin B1 deficiency causes beriberi, and Vitamin C deficiency causes scurvy.
10. Which of the following animals has diastema? (a) fish (b) Human (c) Dog (d) rabbit
Diastema is a feature seen in the jaw of a herbivore — a gap between the incisors and premolars, caused by the absence of canines. The rabbit, being a herbivore, has a diastema.
11. The plant hormone that is responsible for ripening of fruits is (a) auxin (b) gibberellin (c) acetylene (d) ethylene
Ethylene (ethene) is the plant hormone responsible for the ripening of fruits. It should not be confused with acetylene (ethyne).
12. Which of the following blood types has no antibody? (a) O (b) A (c) AB (d) B
Blood type A has antigen A and antibody B; type B has antigen B and antibody A; type AB has antigens A & B but no antibody; type O has no antigen but has antibodies A & B. So AB has no antibody.
13. The bacteria that cannot convert atmospheric nitrogen to soil nitrate are called (a) denitrifying bacteria (b) nitrogen-fixing bacteria (c) putrefying bacteria (d) aerobic bacteria
Nitrogen-fixing bacteria are the ones that aid nitrogen fixation, i.e. convert atmospheric nitrogen to soil nitrate; other bacteria types cannot perform this conversion. These bacteria live mutualistically in the root nodules of leguminous plants.
14. In which of the following organisms is diffusion efficient as a means of gaseous exchange? (a) rat (b) lizard (c) earthworm (d) cockroach
Diffusion is an effective means of gaseous exchange in earthworms (through their moist skin) but not in organisms like the lizard and rat, which have too large a body mass for diffusion alone to suffice.
15. The cell organelle that is responsible for respiration is the (a) mitochondrion (b) ribosome (c) lysosome (d) endoplasmic reticulum
The mitochondrion is the organelle responsible for (cellular) respiration, which is why it is known as the powerhouse of the cell.
16. Taenia saginata is associated with (a) fish (b) pork (c) beef (d) dog
Taenia solium is associated with pork, while Taenia saginata is associated with beef.
17. The genetic make-up of an organism is known as its (a) phenotype (b) blood type (c) genotype (d) allelomorph
The genetic make-up of an organism is its genotype, while its physical appearance is its phenotype. The phenotype is determined by the genotype and the environment.
18. The seat of intelligence in the brain is the (a) Pons varolli (b) thalamus (c) cerebrum (d) cerebellum
The cerebrum is the seat of intelligence, consciousness, memory, alertness and judgement. The cerebellum, by contrast, is associated with the maintenance of balance.
19. The study of how and why population size changes over time is known as (a) population estimation (b) population cycle (c) population ecology (d) population dynamics
Population dynamics is the study of how and why population sizes change over time.
20. Which of the following sits comfortably at the borderline between living and non-living things? (a) virus (b) bacteria (c) protozoan (d) alga
The virus sits at the borderline between living and non-living things — it behaves as a living thing inside a host cell but assumes a crystalline, non-living form outside a living system.
21. The pigment utilized by the chameleon for changing colour is (a) pneumatophore (b) carotene (c) melanin (d) chromatophore
The chromatophore is the pigment cell utilised by the chameleon for changing colour. (A pneumatophore is a breathing root used by mangrove plants for gaseous exchange, not a pigment.)
22. Which of the following serves as a passage for both urine and semen is the (a) urinary bladder (b) urethra (c) ureter (d) seminal vesicle
The urethra plays a urinogenital role — it serves as a passage for both urine and semen (in males).
23. Which of the following is not a process in urine formation? (a) detoxification (b) ultrafiltration (c) hormonal secretion (d) selective re-absorption
Ultrafiltration and selective re-absorption are processes involved in urine formation. Detoxification (the breaking down of harmful substances) occurs in the liver, not as part of urine formation.
24. The water cycle is maintained mainly by (a) evaporation (b) condensation (c) evaporation and condensation (d) transpiration and respiration
Evaporation removes water from the earth's surface into the atmosphere, while condensation returns it as precipitation — together these mainly maintain the water cycle.
25. Which of the following involves only one living organism? (a) predation (b) commensalism (c) saprophytism (d) mutualism
Predation, commensalism and mutualism each involve two living organisms, while saprophytism involves only one living organism (a living organism feeding on dead/decaying matter).
26. The competition between paramecium Aurelia and paramecium caudatum is (a) interspecific (b) intraspecific (c) intergeneric (d) intrageneric
Since P. aurelia and P. caudatum are two different species within the same genus, the competition between them is interspecific.
27. The theory of use and disuse was propounded by (a) Jean Lamark (b) Gregor Mendel (c) Charles Darwin
Jean Baptiste Lamarck propounded the theory of use and disuse, while Charles Darwin propounded the theory of natural selection. (Note: only three options were legible in the source scan; a fourth option may be missing.)
28. The number of chromosomes in the check [cheek] cell and the sperm cell of a human are respectively (a) 50 & 25 (b) 46 & 23 (c) 23 & 46 (d) 92 & 46
A somatic cell (such as the cheek cell) has 46 chromosomes, while a sex cell (such as the sperm cell) has 23 chromosomes — a somatic cell has twice the number of chromosomes of a sex cell.
29. The bright coloured eye spots on the hind wings of a moth are an example of (a) mimicry (b) cryptic colouration (c) disruptive colouration (d) warning colouration
The bright coloured eye spots on a moth's hind wings serve as warning colouration, intended to scare off potential predators.
30. Given that both parents are heterozygous for a particular trait the probability that an offspring will be recessive for that trait is (a) 1/2 (b) 3/4 (c) 1/4 (d) 1
Crossing two heterozygotes (Tt x Tt) gives offspring in the ratio 1 TT : 2 Tt : 1 tt, so the probability of a recessive (tt) offspring is 1/4.
31. Which of the following is not part of the axial skeleton? (a) Ulna (b) skull (c) sternum (d) rib
The axial skeleton comprises the skull, vertebral column, sternum and ribs. The ulna is a bone of the forearm and is part of the appendicular skeleton.
32. The feature that makes locomotion in water easy for fish is the (a) lateral line (b) streamlined body (c) slimy body (d) scaly body
Locomotion in water is made easy for fish by its streamlined body. (The lateral line, by contrast, is used to detect vibrations in water.)
33. [See diagram] The fingerprint shown above is (a) loop (b) whorl (c) arch (d) compound
The diagram shows an arch fingerprint. Arch fingerprints have ridges that form a hill-like pattern.
34. The diagram shows what type of variation? (a) morphological (b) physiological (c) both (d) neither
Fingerprints show morphological variation (variation in physical form/structure).
35. The structure is effective for (a) resolving paternity dispute (b) detection (c) ancestral tracing (d) B and C
Since no two people share exactly the same fingerprint, fingerprints are effective for detection (crime detection/identification).
36. The only blood vessel that begins and end in capillaries is (a) aorta (b) hepatic artery (c) hepatic portal vein (d) renal vein
The hepatic portal vein is the only blood vessel that begins and ends in capillaries. It transports blood containing digested food substances from the gut to the liver.
37. Which of the following is not a digestive enzyme? (a) erepsin (b) lipase (c) trypsin (d) bile
Bile is not a digestive enzyme; it is a substance that emulsifies fats (breaks fat into smaller droplets), aiding digestion but not itself acting as an enzyme.
38. The vertebrate group that shows the most parental care to their offspring is (a) amphibian (b) mammalia (c) aves (d) reptilia
Mammals show the most parental care to their offspring, followed by birds (aves).
39. The hardest material in the human body is (a) enamel (b) pulp cavity (c) bone (d) dentine
Enamel is the hardest material in the human body. It forms the outermost part of the teeth.
40. Which of the following bears naked seeds? (a) mango (b) moss (c) cycad (d) fern
Cycad is a conifer, and conifers bear naked seeds. Mango is a flowering plant (seeds are not naked), while fern and moss are seedless.
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