WAEC Biology 2025 past questions and answers

Chemical digestion uses enzymes to break large, complex food molecules into small, simple ones that can be absorbed.

Protein digestion starts in the stomach, labelled I, where pepsin breaks proteins into peptones.

Fat digestion needs bile, made by the liver (III), and lipase, made by the pancreas (II). The gall bladder (IV) only stores bile and the stomach (I) makes no significant lipase.

Villi greatly increase the surface area of the small intestine for absorbing digested food; without them absorption of nutrients would suffer.

Tridax is a weed; it and the bean plant struggle for the same light, water and nutrients, which is competition.

Light, temperature and pressure (air pressure on land, water pressure in water) act in every habitat, but humidity, the amount of water vapour in air, applies only to terrestrial habitats.

The black-and-white disc lowered on a graduated rope or rod is a Secchi disc.

A Secchi disc is lowered into water to measure turbidity (how far light penetrates).

Fingerprint patterns and blood groups fall into distinct types with no in-between, so they are discontinuous. Height and weight vary continuously.

Alleles are alternative forms of a gene, and genes are located on chromosomes.

Aa x Aa gives AA, Aa, Aa and aa; only aa (one in four) is albino, so the probability is 1/4.

The double helix is unzipping and each strand is being built into a new double helix, so the DNA is copying itself (replication).

Adenine always pairs with thymine, so DNA has equal amounts of each: 32% thymine.

Lamarck taught that characters gained during life through use and disuse are passed on to offspring (inheritance of acquired characters).

A honeybee colony has a queen, workers (sterile females) and drones (males). Soldiers and kings are termite castes.

At carrying capacity births and deaths roughly balance, so the population goes up and down a little around that level.

Energy is lost as heat at every feeding level, so less energy reaches each higher level and the pyramid narrows upward.

A population is the number of individuals of one species in an area, such as Tilapia in a lake. The other options mix two species.

Population density = number ÷ area = 1,850 ÷ 100 m² = 18.50 per m².

Destroying their breeding places, ultraviolet light and disinfectants all kill or remove pathogens. A balanced diet keeps the body healthy but does not act on the pathogens themselves.

BCG (Bacille Calmette-Guérin) vaccine protects against tuberculosis.

Without tree cover, rain and wind wash and blow away the topsoil, so soil erosion is the main effect.

Forests, wildlife, minerals, soil and water are natural resources that can be conserved. Domestic waste is not a natural resource to be conserved; it is something to be disposed of or recycled.

Felling trees destroys the forest; the other activities protect or replace trees.

The cell flows around the bacterium and engulfs it as a solid particle: this is phagocytosis ('cell eating').

In humans, white blood cells (phagocytes) in the blood engulf bacteria, and blood is part of the circulatory system.

Respiration goes on in every living cell day and night and does not need light or chlorophyll; those are needed for photosynthesis.

As the filtrate flows along the tubule and collecting duct, much of its water is reabsorbed into the blood, so the urine left is more concentrated than blood.

Indole acetic acid (IAA) is the natural auxin; 2,4-D (dichlorophenoxyacetic acid) is a man-made one.

The sympathetic system prepares the body for action: it narrows arteries to the skin and gut and speeds the heart. The other effects are parasympathetic.

A long-sighted eye focuses near objects behind the retina; a converging (convex) lens brings the image forward onto the retina.

The eardrum passes its vibrations first to the malleus, then the incus and stapes; the oval window is the membrane between the middle and inner ear that receives them last.

A fibrous, air-filled covering (as in coconut) lets the fruit float and be carried by water.

Annuals complete their life cycle, from seed to fruit, in one year or season.

Man is Homo sapiens: the genus is Homo and the species is sapiens. Chordata is the phylum and Mammalia the class.

The nymph has long antennae, a flat oval body and cerci, like a small wingless cockroach.

A nymph grows by shedding its hard exoskeleton several times (moulting or ecdysis) before becoming an adult.

I is the tip (apex), II the central vein (midrib), III the flat blade (lamina), and IV the angle where the leaf joins the stem (axil).

The midrib (II) is the main vein, which carries the xylem and phloem through the leaf.

The vacuole stores cell sap and, by taking in water, keeps the cell turgid, which supports the plant.

The 6% solution is more concentrated than the cell, so the cell loses water and its cytoplasm shrinks away from the wall: it is plasmolysed.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, so each glucose needs 6 oxygen molecules; 3 × 6 = 18.

Sclerenchyma cells have thick lignified walls and give the plant mechanical strength and support.

(a) Excretion is the removal from the body of the waste products of metabolism (e.g. carbon (IV) oxide, urea, excess water and salts) which would be harmful if they built up.
(b)(i) Mammals, any two: carbon (IV) oxide; urea; water; mineral salts; bile pigments. (ii) Plants, any two: oxygen; carbon (IV) oxide; water vapour; tannins; resins; gums; latex; alkaloids.
(c) Paramecium - contractile vacuole / cell membrane - diffusion and osmoregulation (vacuole fills and bursts at the surface) - thin, semi-permeable membrane with large surface.
Planaria - flame cells - beating cilia drive waste into excretory canals and out through pores - many flame cells with cilia, joined to a network of tubules.
Leaf of plant - stomata (lenticels) - transpiration/diffusion of gases - many stomata, thin leaf with large surface and air spaces; guard cells control opening.
Earthworm - nephridia - waste filtered from body fluid through ciliated funnels (nephrostomes) and out through nephridiopores - ciliated funnel, long coiled tubule surrounded by capillaries.
(d) Any three: removes urea and other nitrogenous wastes; regulates water balance (osmoregulation); regulates salt balance and pH of blood; removes drugs/toxins; helps control blood pressure.

Each row of the table needs a structure, a mechanism and an adaptation.

(a) Any two: photosynthesis uses light energy, chemosynthesis uses energy from chemical reactions (oxidation of substances); photosynthesis needs chlorophyll, chemosynthesis does not; photosynthesis is carried out by green plants and algae, chemosynthesis by some bacteria (e.g. Nitrosomonas, iron and sulphur bacteria); photosynthesis releases oxygen, chemosynthesis usually does not.
(b)(i) Saprophytes are organisms that feed on dead and decaying organic matter.
(ii) Any two: Mucor; Rhizopus; mushroom; yeast; bacteria of decay.
(iii) They release digestive enzymes onto the dead matter (extracellular digestion), and the soluble products are absorbed through their hyphae or cell surface.
(iv) Any three: decompose dead bodies and recycle nutrients; yeast is used in baking and brewing; some are eaten (mushrooms); some give antibiotics; they spoil food, timber and leather.
(c) Any three: have special structures (pitchers, sticky hairs, hinged leaves) to trap insects; secrete enzymes to digest the prey; absorb nitrogen compounds from the prey; are green and photosynthesise; usually grow in soils poor in nitrogen.
(d)(i) Butterfly - sucking (fluid feeder, nectar through the proboscis). (ii) Mosquito larva - filter feeding. (iii) Mucor - saprophytic. (iv) Housefly - sponging/sucking of liquid food.

Keep the differences in (a) as matching pairs.

(a) Green plants take in carbon (IV) oxide and give out oxygen in photosynthesis; plants, animals and decomposers take in oxygen and give out carbon (IV) oxide in respiration (and burning adds CO₂). The two processes balance each other, keeping the amounts in the air fairly constant.
(b) Any five: light; temperature; rainfall/water; soil type and nutrients; pH; humidity; wind; topography; competition; animals (grazers, pollinators).
(c)(i) Overcrowding is when there are more organisms in an area than its resources can support.
(ii) Any five: competition for food, water, light and space; spread of diseases; shortage of food; build-up of wastes/pollution; stunted growth; increased death rate; emigration; lower reproduction; aggression.
(d)(i) Density-dependent factors have a greater effect as the population becomes denser; density-independent factors affect the population the same way whatever its density.
(ii) Any two: food supply; competition; disease; predation; accumulation of wastes; space.
(iii) Density-dependent factors increase deaths or lower births when the population is large and ease off when it is small, so the population is held around a balance (carrying capacity). Density-independent factors such as floods, drought, fire or sudden temperature change can kill many organisms at any density and upset the balance; the population later recovers.

In (d)(i) the difference is whether the effect depends on population size.

(a)(i) Heredity (both parents carry the recessive allele for shortness) and environmental factors such as poor nutrition or disease.
(ii) Both parents must be heterozygous: Tt x Tt. Gametes T, t and T, t. Offspring: TT, Tt, Tt, tt (3 tall : 1 short).
(iii) tt.
(b)(i) Genotype is the genetic make-up of an organism (the alleles it carries for a trait).
(ii) Any two: crossing over and independent assortment in meiosis; random fertilisation; mutation; environment (food, climate).
(c)(i) An allele is one of two or more alternative forms of a gene at the same position on a pair of chromosomes.
(ii) Genotype is the genetic make-up; phenotype is the observable characteristics. Genotype cannot be seen; phenotype can be seen or measured. Genotype is inherited; phenotype results from genotype acting with the environment.

Show parents, gametes and offspring in the genetic diagram.

(a) Any five: increased water loss and wilting/dehydration; denaturing of enzymes and death; faster metabolism and respiration; animals seek shade or burrow (behavioural changes); aestivation; reduced dissolved oxygen in water; heat stress/sunburn; affects germination and flowering.
(b) Any five: kills plants, animals and soil organisms; destroys habitats; removes vegetation cover, leading to erosion; destroys humus and soil structure; releases carbon (IV) oxide and smoke (air pollution, global warming); loss of nutrients by volatilisation; encourages fire-resistant grasses (succession changes).
(c) Any four: monitors and reports disease outbreaks worldwide; issues guidelines and alerts to countries; supports vaccine development and vaccination campaigns; supplies drugs, equipment and experts; trains health workers; coordinates research and public health education.
(d)(i) Tilapia is dark on its back and pale on its belly. Seen from above it blends with the dark water/bottom, and seen from below it blends with the bright surface, so predators find it hard to see.
(ii) Seasonal migration is the regular movement of birds from one region to another at certain seasons (e.g. to escape cold or dry seasons and find food or breeding places), and their return later, e.g. swallows, cattle egrets.
(e)(i) Bacteria; viruses; fungi; protozoa; algae (accept rickettsia).
(ii) Any two of: bacteria, viruses, fungi, protozoa.
(f)(i) Any two: A; B; AB.
(ii) Any two: agglutination (clumping) of the donor red cells; blocked blood vessels; haemolysis of red cells; fever, shock, kidney failure or death.

Group O has anti-A and anti-B antibodies in its plasma, so it can receive only group O blood.