JAMB Biology 2023 Objective Past Questions

All 40 questions from the Joint Admissions and Matriculation Board (JAMB) Biology 2023 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.

Biology 2023 Objective — Question 1

Taenia solium can be found in

• A. pigCorrect
• B. cow
• C. goat
• D. dog

Explanation

Taenia solium inhabits pigs, while Taenia saginata inhabits cows.

Biology 2023 Objective — Question 2

Proboscis is a structure that is mostly found in

• A. molluscs
• B. amphibians
• C. insectsCorrect
• D. reptiles

Explanation

The proboscis of insects is a long, tubular mouthpart used for feeding; it can be adapted for various feeding habits, such as sucking nectar, piercing, or sucking blood and lapping up fluids.

Biology 2023 Objective — Question 3

Which of the following is an adaptation for water conservation?

• A. prominent stomata in leaves
• B. spiny leavesCorrect
• C. spongy mesophyll
• D. broad leaves

Explanation

The larger the surface area of leaves, the higher the transpirational water loss; spiny (reduced) leaves minimize this loss to the barest minimum, while broad leaves would allow much greater water loss.

Biology 2023 Objective — Question 4

The digestive enzyme that is present in the saliva is

• A. renin
• B. ptyalinCorrect
• C. chymotrypsin
• D. pepsin

Explanation

Ptyalin is the digestive enzyme present in saliva; as food is chewed, ptyalin mixes with it and begins breaking down complex carbohydrates (e.g. starch) into simpler sugars such as maltose.

Biology 2023 Objective — Question 5

Plants that have special structures for trapping and digesting insects are

• A. saprophytic
• B. carnivorousCorrect
• C. parasitic
• D. symbiotic

Explanation

Carnivorous (insectivorous) plants have special structures for trapping and digesting insects, e.g. Venus flytrap, Pitcher plants, Sundews, Bladderworts and Butterworts.

Biology 2023 Objective — Question 6

Which of the following is a waste product of an insect?

• A. uric acidCorrect
• B. mucilage
• C. alkaloids
• D. sweat

Explanation

Insects primarily excrete nitrogenous waste as uric acid, formed from the breakdown of nitrogenous compounds - unlike mammals and birds, which mainly excrete urea; this is a water-conserving excretory adaptation.

Biology 2023 Objective — Question 7

The sensory cell that responds to dim light is called

• A. cone
• B. rodCorrect
• C. pupil
• D. iris

Explanation

Rod cells in the retina function in dim light and detect light intensity better than cone cells, though they do not permit detection of colours (which cone cells allow).

Biology 2023 Objective — Question 8

The opening of the guard cells of the epidermis in plants is by the process of

• A. diffusion
• B. osmosisCorrect
• C. active transportation
• D. transpiration

Explanation

Stomata (guard cells) open when the guard cells become turgid and close when they become flaccid; this turgidity change depends on the osmotic concentration/osmosis within the guard cells.

Biology 2023 Objective — Question 9

In humans, excretion of isotonic urine is associated with

• A. proximal convoluted tubuleCorrect
• B. distal convoluted tubule
• C. Bowman's capsule
• D. loop of Henle

Explanation

The concentration of urine in the nephron depends on the permeability of the tubules; in the proximal convoluted tubule, the urine remains isotonic.

Biology 2023 Objective — Question 10

The correct arrangement of food classes of the same quantity in the descending order of magnitude of energy values in animals is

• A. protein, fats and oils, water and carbohydrates
• B. carbohydrates, fats and oils, water and protein
• C. fats and oils, protein, carbohydrates and waterCorrect
• D. water, fats and oils, carbohydrates and protein

Explanation

Fats and oils contain a greater amount of energy than an equal quantity of carbohydrates, which contain more than protein; water has essentially no calorific/energy value: Fats and oils > Carbohydrates > Protein > Water.

Biology 2023 Objective — Question 11

Which of the following substances is not a complex carbohydrate?

• A. starch
• B. GlucoseCorrect
• C. cellulose
• D. glycogen

Explanation

Complex carbohydrates are long chains of sugar molecules (e.g. starch, cellulose, glycogen, chitin); glucose is a simple sugar (monosaccharide), not a complex carbohydrate.

Biology 2023 Objective — Question 12

The bacteria that convert soil nitrate into atmospheric nitrogen are called

• A. nitrifying bacteria
• B. denitrifying bacteriaCorrect
• C. putrefying bacteria
• D. saprophytic bacteria

Explanation

Denitrifying bacteria (e.g. Pseudomonas denitrificans) convert soil nitrate back into atmospheric nitrogen, completing the nitrogen cycle.

Biology 2023 Objective — Question 13

The main reason for immunizing children is to

• A. stimulate the production of blood
• B. stimulate the production of antibodiesCorrect
• C. increase the production of white blood cells
• D. destroy pathogens in their bodies

Explanation

Immunization protects individuals by stimulating the production of specific antibodies against particular pathogens, preparing the immune system to respond to future exposure.

Biology 2023 Objective — Question 14

How do we justify the absence of digestive system in tapeworm?

• A. it does not feed
• B. it is too small in size
• C. its body absorbs its digested foodCorrect
• D. it has no enzymes

Explanation

Tapeworms do not possess a digestive system because their bodies absorb already-digested food directly from their host's intestine.

Biology 2023 Objective — Question 15

If a body has blood type O and his mother has blood type A, what is the likely genotype of his father?

• A. AB
• B. AOCorrect
• C. BB
• D. AA

Explanation

For a child to have blood type O, both parents must carry the recessive allele (genotype including O); given the mother is quoted as type A (which could be AA or AO), the father's genotype must be AO or BO (or O) to allow an O-type child - AO is the answer among the given options.

Biology 2023 Objective — Question 16

The organism above (an earthworm) is found in soils rich in

• A. mud
• B. sand
• C. clay
• D. humusCorrect

Explanation

Earthworms are found in soils rich in humus, since humus is organic matter that serves as their primary food source. (Note: the original scanned booklet did not include the source diagram; the image shown is a representative illustration.)

Biology 2023 Objective — Question 17

The branch of biology that deals with the principles of classification of organisms is known as

• A. population dynamics
• B. ecology
• C. taxonomyCorrect
• D. nomenclature

Explanation

Taxonomy is the science of classification, particularly the classification of organisms into a hierarchical system based on their similarities and evolutionary relationships.

Biology 2023 Objective — Question 18

The presence of a large number of ______ is an evidence that a cell utilizes a lot of energy

• A. Ribosomes
• B. vacuoles
• C. mitochondriaCorrect
• D. endoplasmic reticulum

Explanation

Mitochondria are the powerhouse of the cell; a cell that utilises a lot of energy will have an appreciable number of mitochondria.

Biology 2023 Objective — Question 19

Kreb's cycle occurs in the

• A. nucleus
• B. ribosomes
• C. cytoplasm
• D. mitochondriaCorrect

Explanation

The Krebs cycle (citric acid/tricarboxylic acid cycle) occurs in the mitochondria of eukaryotic cells, as a key component of cellular respiration.

Biology 2023 Objective — Question 20

A purple colour was obtained when sodium hydroxide solution and a drop of copper sulphate solution were added to a food substance. The food is likely to be a

• A. sugar
• B. proteinCorrect
• C. fat
• D. carbohydrate

Explanation

This describes the Biuret test for protein; a purple/violet colour with sodium hydroxide and copper sulphate solution indicates the presence of protein. (Note: the original scanned booklet did not include the source diagram; the image shown is a representative illustration.)

Biology 2023 Objective — Question 21

A sample of wet soil of a given weight was heated to constant weight. The loss in weight is due to loss of

• A. water
• B. humus
• C. water and humusCorrect
• D. inorganic matter

Explanation

When a wet soil sample is strongly heated to a constant weight, both the water and the humus (organic matter) in the soil are lost.

Biology 2023 Objective — Question 22

Adenine pairs with thymine because

• A. one is a purine with thymine because one is a purine base and the other, a pyrimidineCorrect
• B. they are both purines
• C. they are both pyrimidines
• D. the two occur in the same nucleic acid

Explanation

Two purines do not pair, nor do two pyrimidines; a purine pairs with the appropriate pyrimidine. Adenine (a purine) pairs with thymine (a pyrimidine); guanine pairs with cytosine. In RNA, thymine is replaced by uracil.

Biology 2023 Objective — Question 23

What is the role of the red head in male Agama lizard?

• A. To scare other males
• B. for camouflaging against predators
• C. to attract female lizards for mating purposesCorrect
• D. for respiration

Explanation

The red head in male Agama lizards serves to secure a mate by attracting female lizards.

Biology 2023 Objective — Question 24

An example of an endospermous seed is

• A. a bean seed
• B. cotton seed
• C. cashew nut
• D. maize grainCorrect

Explanation

Endospermous seeds have endosperm, a nutrient-rich tissue that surrounds and nourishes the developing embryo; examples include maize, rice, wheat, castor and coconut.

Biology 2023 Objective — Question 25

The movement response of cockroach away from a light source can be described as

• A. positive phototaxis
• B. positive phototropism
• C. negative phototropism
• D. negative phototaxisCorrect

Explanation

Since the cockroach's whole body moves away from the light source, this is a taxis (not tropism, which applies to plants), and movement away from a stimulus is negative - hence negative phototaxis.

Biology 2023 Objective — Question 26

If the cross of a red-flowered plant with a white-flowered plant produces a pink-flowered plant, it is an example of

• A. codominance
• B. convergent evolution
• C. incomplete dominanceCorrect
• D. linkage

Explanation

This illustrates incomplete dominance, where instead of one allele completely masking the other, the effects of both alleles are partially expressed, resulting in an intermediate (pink) phenotype different from both parents.

Biology 2023 Objective — Question 27

What is the number of alleles controlling blood groups in humans?

• A. 2
• B. 3Correct
• C. 4
• D. 5

Explanation

Blood groups in humans are controlled by three alleles: A, B and O; these determine the presence or absence of specific antigens on red blood cells, giving rise to four blood types: A, B, AB and O.

Biology 2023 Objective — Question 28

In terms of the number of individuals, which of the following taxa is the most inclusive?

• A. specie
• B. order
• C. classCorrect
• D. family

Explanation

In descending order of inclusivity, taxa are arranged: Kingdom > Phylum/Division > Class > Order > Family > Genus > Species; among the options given, Class is the most inclusive and Species the least inclusive.

Biology 2023 Objective — Question 29

In the alimentary system of a bird, the function of teeth is carried out by the

• A. tongue
• B. gizzardCorrect
• C. beak
• D. crop

Explanation

Birds don't have teeth; they use their gizzard to mechanically grind their ingested food substances.

Biology 2023 Objective — Question 30

Exhaled air differs from inhaled air in that it is

• A. usually has more water vapourCorrect
• B. is usually lower in temperature
• C. has less amount of carbon dioxide
• D. often has more oxygen

Explanation

Exhaled air usually has more water vapour and is usually higher (not lower) in temperature than inhaled air; it also has greater CO2 and less oxygen than inhaled air.

Biology 2023 Objective — Question 31

The ability of a chameleon to change its colour is an adaptive feature for

• A. attack
• B. defenceCorrect
• C. display
• D. attraction

Explanation

Chameleons lack traits such as sharp teeth or claws, venom and speed, so they rely on being able to blend into their surroundings to evade predators - a defensive mechanism.

Biology 2023 Objective — Question 32

Primary growth in plants is brought about by the activity of the

• A. epidermis
• B. endodermis
• C. mesophyll
• D. meristemCorrect

Explanation

Primary growth in plants is controlled by root meristems and shoot apical meristems; lateral meristems control secondary growth.

Biology 2023 Objective — Question 33

Which of the following processes is not an example of a reflex action?

• A. sneezing
• B. beating of the heart
• C. blinking of the eye
• D. readingCorrect

Explanation

Reading is a voluntary action, not an involuntary reflex action like sneezing, heartbeat or blinking.

Biology 2023 Objective — Question 34

The following are examples of discontinuous variation except

• A. sex type
• B. skin colourCorrect
• C. fingerprint
• D. ability to taste PTC

Explanation

Skin colour is a continuous variation, while sex type, fingerprint pattern, and the ability to taste phenylthiocarbamide (PTC) are discontinuous variations.

Biology 2023 Objective — Question 35

Which of the following is an anabolic process?

• A. excretion
• B. photosynthesisCorrect
• C. respiration
• D. photolysis

Explanation

Anabolic processes build complex molecules from simpler ones, e.g. photosynthesis and protein synthesis; catabolic processes (like respiration) break complex molecules down into simpler ones.

Biology 2023 Objective — Question 36

Amoeba engulfs food particles by means of its

• A. pseudopodiaCorrect
• B. food vacuoles
• C. contractile vacuole
• D. cytoplasmic membrane

Explanation

Amoeba engulfs food particles using pseudopodia via phagocytosis, forming a temporary food vacuole that later fuses with lysosomes to digest the food.

Biology 2023 Objective — Question 37

The type of association in which one organism benefits and the other neither benefits nor suffers any harm is called

• A. mutualism
• B. parasitism
• C. saprophytism
• D. commensalismCorrect

Explanation

In commensalism, one organism benefits while the other neither benefits nor is harmed; in mutualism both benefit, and in parasitism one benefits at the other's expense.

Biology 2023 Objective — Question 38

Intercoastal muscles are found in the ______ region

• A. limb
• B. abdominal
• C. head
• D. chestCorrect

Explanation

Intercostal muscles are located between the ribs in the chest region of the human body, essential for breathing (expanding and contracting the ribcage).

Biology 2023 Objective — Question 39

Meiosis involves the following except

• A. exchange of genes
• B. production of four daughter cells
• C. production of cells with haploid number of chromosomes
• D. production of cells with diploid number of chromosomesCorrect

Explanation

Meiosis produces four haploid daughter cells (with half the chromosome number of the parent cell), not diploid cells.

Biology 2023 Objective — Question 40

The network of blood capillaries in the kidney capsule is referred to as

• A. capsule
• B. glomerulusCorrect
• C. pelvis
• D. pyramid

Explanation

The glomerulus is a network of tiny blood capillaries within the Bowman's capsule of the nephron, playing a crucial role in the first step of urine formation (glomerular filtration).