JAMB Biology

B: suspends cytoplasmic organelles

Cytoplasmic organelles are suspended within the cytoplasm. The cell membrane forms the outer boundary, and cell division involves several coordinated cellular structures.

A: rise

Water moves from the distilled water into the sugar solution through the selectively permeable membrane. The added water pushes the solution higher in the narrow funnel stem.

D: Osmosis

The apparatus demonstrates osmosis: net water movement through a selectively permeable membrane toward the sugar solution. The membrane separates solutions with different water potentials.

C: haemolysis

Red blood cells take up water in a strongly hypotonic solution such as distilled water. If they rupture, the breakdown of the red cells is called haemolysis.

A: hydrotropism

Hydrotropism is directional plant growth in response to a water gradient. Roots can grow toward wetter conditions, helping the plant obtain water.

B: femur

The femur, or thigh bone, is the longest bone in the normal adult human skeleton. It extends between the hip and knee and supports substantial body weight.

D: Muscle

Bone and cartilage form supporting skeletal tissues in vertebrates, while chitin contributes to many arthropod exoskeletons. Muscle contracts to move supporting structures.

D: to allow adequate time for exchange of materials

Slow capillary flow gives more time for exchange of gases, nutrients and wastes across vessel walls. The large total cross-sectional area of capillary beds helps produce that low velocity.

A: Fishes, amphibians, birds, man

Fishes, amphibians, birds and humans are vertebrates that use kidneys for excretion and water–salt regulation. The other groups include organisms with different excretory structures.

A: possess valves at intervals throughout their length

Arteries carry blood away from the heart and have walls suited to pressure. They do not have repeated valves along their length like many limb veins.

B: The body temperature of the bird varied less than that of the lizard during changes in environmental temperature

The dashed bird line changes only slightly, whereas the lizard line changes substantially. The bird temperature is therefore less variable, but is not perfectly constant.

C: Poikilothermy

Poikilothermy describes variation in body temperature. The substantial change shown by the lizard is consistent with poikilothermy, rather than nearly constant body temperature.

C: to maintain the composition of body fluids

An appropriately formulated isotonic saline solution helps preserve extracellular osmotic conditions. Plain water introduced into the circulation can cause harmful osmotic shifts in blood cells.

A: cochlea

The cochlea contains the organ of Corti, whose sensory hair cells respond to mechanical vibrations. They convert movement into signals transmitted through auditory nerve fibres.

A: converging the Light rays before they enter the eye

A convex lens adds convergence to incoming light. In a long-sighted eye this helps bring the focus forward onto the retina rather than behind it.

B: Photosynthesis

Photosynthesis takes carbon dioxide from the surroundings and incorporates its carbon into organic compounds. Combustion and decomposition generally release carbon dioxide instead.

A: Water cycles

Precipitation returns atmospheric water to the surface, while transpiration releases water vapour from plants. Both are transfers within the water cycle.

C: intensity of light

Below the photic zone, insufficient light limits photosynthesis. Water may be abundant, but photosynthetic organisms still need enough usable light energy.

C: Quadrat

A quadrat defines a known sample area in which plants can be counted. Representative repeated samples can then estimate abundance across a habitat.

B: is light and easy to dig

Sandy soil is generally relatively loose and easy to work. Its large pores commonly promote drainage and aeration, though organic matter and compaction can modify its behaviour.

B: Sheep

A sheep feeding on plants is a primary consumer because it obtains energy directly from producers. Grass is a producer, while fungi commonly act as decomposers.

A: sunlight

In a grazing food chain beginning with a photosynthetic producer, sunlight supplies the initial energy. The producer converts some light energy into chemical energy passed along the chain.

D: is a secondary consumer

P is the producer and Q is the primary consumer. R feeds on Q, so R occupies the secondary-consumer level in this chain.

B: Scabies

Scabies is caused by infestation with the human itch mite. It is acquired through transmission of mites rather than inherited as a genetic condition.

B: nucleus

The nucleus contains most of the DNA in a typical eukaryotic cell, organised into chromosomes. Mitochondria and chloroplasts can also contain DNA.

A: daughter cells receive cytoplasm and organelles

Cytokinesis divides the cytoplasm between daughter cells, distributing cytoplasmic contents and organelles. Chromosome segregation occurs during nuclear division.

B: DNA analysis

DNA profiling compares genetic markers in biological samples. It can support identification when samples and statistical interpretation are reliable, but is one component of an investigation.

D: convergent evolution

The swimming surfaces of whale flippers and fish fins show functional similarity associated with life in water. Such independently evolved similarities are examples of convergence.

B: mosquitoes

Female mosquitoes have mouthparts adapted to pierce tissue and take a blood meal. The other listed insects have primarily biting and chewing mouthparts.

A: locust, camel, lizard and snakes

Camels and many desert reptiles are adapted to dry conditions, and locusts include arid-region forms. The other groups include organisms strongly dependent on moist or aquatic environments.

C: skull

Sutures are fibrous joints between many skull bones. They provide strong connections with little movement, unlike the freely movable joints of the limbs.

C: contractile vacuole

A contractile vacuole expels excess water entering a freshwater Paramecium. This helps maintain water balance in a cell whose surroundings are usually hypotonic.

B: initiating clotting

Platelets adhere at damaged blood vessels and help form a platelet plug. They also support clotting reactions that stabilise the plug with fibrin.

C: soften the leaf

Alcohol removes chlorophyll but leaves the leaf brittle. Rinsing the decolourised leaf in hot water softens it before iodine is added to test for starch.

D: commensalism

Commensalism describes a relationship in which one organism benefits while the other is not appreciably affected. A remora receiving transport under this assumption fits that definition.

C: low salinity

Freshwater habitats have low concentrations of dissolved salts compared with marine habitats. Their turbidity and current speed vary between rivers, ponds and lakes.

C: Vibrio cholerae

Cholera is caused by toxigenic strains of Vibrio cholerae. Infection can produce severe watery diarrhoea through the action of cholera toxin in the intestine.

D: reduction of carbon (IV) oxide

In the Calvin cycle, carbon derived from carbon dioxide is reduced using energy and reducing power supplied by the light reactions. The cycle does not require darkness.

D: cooling system

Older refrigeration and air-conditioning systems used CFC refrigerants. Leakage or improper handling could release them into the atmosphere, where they contribute to ozone depletion.

A: flowers lack nectar

Wind-pollinated flowers typically do not offer nectar to animal visitors. They commonly have exposed anthers, receptive stigmas and abundant lightweight pollen.

D: meiosis

In animals, meiosis in the germ line reduces chromosome number during gamete production. Fertilisation then joins haploid gametes and restores the diploid number.

D: 33.3

The remaining soil weighs 25 − 20 = 5 g. The mass lost is 7.5 − 5 = 2.5 g, so the estimated humus percentage is (2.5 ÷ 7.5) × 100 = 33.3%.

C: epidermis

The epidermis is the outer tissue of a young herbaceous root. Root hairs arise from epidermal cells and increase the surface available for absorption.

A: xylem and phloem

Xylem carries water and dissolved mineral nutrients, while phloem transports sugars and other organic solutes between sources and sinks. The order is xylem, then phloem.

D: sand

Sandy soil generally has less surface area and lower nutrient retention than comparable soils containing more clay and organic matter. Dissolved nutrients can be readily leached.

C: exchange surface

The long projections labelled III are gill filaments. Their thin, folded surfaces provide a large area where oxygen and carbon dioxide can diffuse between water and blood.

C: emigration

Overcrowding can increase competition for resources and encourage individuals to leave an area. Movement out of a population is called emigration.

C: axis and atlas

The atlas supports the skull and participates in nodding, while the atlas–axis joint permits rotation around the axis dens. Together these are the first two cervical vertebrae.

C: nucleus

Paternity comparisons commonly examine markers in nuclear DNA. An individual inherits nuclear genetic material from both biological parents, allowing marker comparisons.

D: raker

The short inward projections labelled II are gill rakers. They help prevent larger particles from entering or damaging the delicate respiratory filaments.

B: structural adaptation

The Venus flytrap has leaves modified into traps that can retain insects. The shape and specialised parts of those leaves are structural adaptations for obtaining nutrients.

B: weight, finger prints and body shape

Weight, fingerprint patterns and body shape describe bodily characteristics. Blood group concerns biochemical antigen differences, while tongue rolling concerns an ability.

C: Scaly skin

Keratinised scales protect lizard skin and help limit water loss. This covering supports life on land, unlike the generally more permeable skin of amphibians.

A: suitable mouthparts

Insect mouthparts are modified for tasks such as biting, sucking or piercing food. Their form is closely related to how an insect obtains its diet.

C: Nitrates formation

Nitrate formation belongs primarily to the nitrogen cycle. Photosynthesis, decomposition and organic carbon storage are directly involved in movement of carbon through ecosystems.

A: IV

A leaf is an organ containing several tissues that work together. Epidermal, vascular and photosynthetic tissues contribute different functions within that one structure.

D: adenosine triphosphate

Cellular respiration transfers some energy from fuels into ATP, adenosine triphosphate. Cells then couple ATP reactions to processes requiring energy.

D: green leaf

A green leaf is a major photosynthetic organ in a typical leafy plant. Its chloroplast-rich tissues capture light and produce organic compounds.

D: natural selection

Natural selection changes populations when heritable traits affect survival and reproduction. Individuals with advantageous variants can leave more descendants under the prevailing conditions.

C: tide

Tides are periodic changes in sea level driven chiefly by the gravitational effects of the Moon and Sun together with Earth’s rotation. Local coasts affect their pattern.

A: Nymphaea

Nymphaea, a water lily, photosynthesises and acts as a producer in aquatic habitats. Planarians and blackflies are consumers rather than photosynthetic plants.

D: III-I-IV-II

Cells form tissues, tissues form organs, and organs cooperate in organ systems. The sequence is therefore III, I, IV, II.

C: nitrogen fixing bacteria

Nitrogen-fixing bacteria convert atmospheric nitrogen into biologically usable nitrogen compounds. This introduces nitrogen into soil food webs rather than returning it to the atmosphere.

B: defence

Hedgehog spines deter predators, especially when the animal curls to expose its spiny covering. They are modified hairs serving a protective function.

A: Thermometer

A thermometer measures temperature using a property that changes predictably with thermal conditions. It is different from instruments for humidity, wind or liquid density.

C: kidney malfunction

Kidney dysfunction can impair salt and water regulation and contribute to swelling. Swelling has several possible causes, so this symptom alone is not a diagnosis.

B: Darwin

Darwin developed an account of descent with modification linking living forms through ancestry. Natural selection was a central proposed mechanism of evolutionary change.

C: ease digestion

Dietary fibre supports movement and bulk of intestinal contents in humans. Some fibre is fermented by gut microbes, but much resists digestion by human enzymes.

D: species

Species is the lowest taxonomic rank among the listed categories. Kingdom, phylum and class are broader groupings containing many species.

D: osmosis and diffusion

Osmosis moves water across selectively permeable membranes, while diffusion moves substances down concentration gradients. Both contribute to material movement in plants.

D: mitochondrion

Mitochondria are the sites of oxidative phosphorylation in typical eukaryotic cells. Glycolysis takes place in the cytosol, so cellular respiration is not exclusively mitochondrial.

B: Niger Delta

The Niger Delta includes coastal tidal wetlands supporting extensive mangroves. Mangroves tolerate saline, waterlogged conditions unlike the inland highlands and basins listed.

D: the surface area to volume ratio is large

Small cells have a relatively large surface area compared with their volume and short internal transport distances. These features make exchange by diffusion more effective.

B: Amphibians

Early land-going tetrapods were amphibian-like vertebrates descended from fishes. Modern amphibians retain features linking aquatic reproduction and terrestrial activity.

D: Temperature and rainfall

Temperature and precipitation strongly influence the broad distribution of terrestrial biomes. They affect water availability, growing seasons and the vegetation a region can support.

C: Xerophytes

Xerophytes are adapted to water-limited conditions. Hot, windy surroundings and porous dry soils can increase water stress, favouring traits that conserve or store water.

A: cholera

Cholera can cause profuse watery diarrhoea leading rapidly to dehydration and weakness. Other illnesses can also cause diarrhoea, so symptoms alone do not confirm the infection.

D: ability to roll the tongue

The ability to roll the tongue concerns how a person can move a body part. Fingerprints, body dimensions and outward appearance describe structural or morphological variation.

B: photolysis

The oxygen released during photosynthesis comes from water split in the light-dependent reactions. This photolysis supplies electrons and protons as well as oxygen.

B: poor development of roots and xylem tissues

Many submerged aquatic plants have reduced roots and xylem because water is readily available and surrounding water supports their bodies. Hydrophyte anatomy varies with whether plants are submerged, floating or emergent.

C: Lamarck

Lamarck’s historical proposal included inheritance of changes acquired during an individual’s life. In that account, increased use of muscles could enlarge them and the enlargement was proposed to pass to descendants.

D: cytoplasm

Organisms historically grouped as Monera are prokaryotes, with chromosomes in a nucleoid region of the cytoplasm. They lack a membrane-bound nucleus and therefore do not contain nuclear nucleoplasm.

A: fats, proteins and carbohydrates

The pancreas releases enzymes that digest carbohydrates, proteins and fats in the small intestine. Vitamins and minerals generally do not need this kind of enzymatic breakdown.

B: virus

Bird flu is caused by avian influenza viruses. These infectious agents are viruses rather than bacteria, fungi or protozoa.

A: ecdysis

Ecdysis is shedding the old cuticle or exoskeleton. It allows an arthropod to expand before the new covering hardens.

A: lack of roughage

A diet low in fibre can contribute to constipation. Fibre helps stool retain bulk and water, although constipation has several possible causes.

A: adrenal gland

An adrenal gland lies near the upper end of each kidney in humans. The pancreas, thyroid and prostate are in different anatomical locations.

D: DNA analysis

DNA profiling compares variable DNA markers in biological samples. It can provide evidence about whose biological material is present, but does not by itself establish what happened or prove guilt.

B: African lungfish

African lungfish can aestivate when their aquatic habitat dries, reducing activity and surviving within a protective cocoon. They use air breathing during this dormant period.

B: osmosis

Osmotic movement of water changes guard-cell turgor and helps open or close a stoma. Ion transport and signalling regulate these water movements.

C: they undergo complete metamorphosis

Mosquitoes, houseflies and blackflies develop through egg, larva, pupa and adult stages. This sequence is complete metamorphosis.

C: vibrissae

Vibrissae are sensitive whiskers that detect nearby surfaces through touch. They help a rat assess spaces and obstacles in dark or confined surroundings.

C: tannin

Tannins bind proteins and are used in vegetable tanning to convert hides into leather. They are plant secondary compounds with biological functions, not merely useless waste.

C: chlorophyll and carotenoids

Chlorophylls and carotenoids absorb light in photosynthetic systems. Carotenoids can also protect against light-related damage, while chlorophyll participates centrally in light capture.

C: biosphere

The biosphere includes all ecosystems and regions supporting life on Earth. It is therefore broader than a single ecosystem or population.

A: astigmatism

Astigmatism can result from uneven curvature of the cornea or lens, causing light to focus differently in different directions. This can blur or distort vision.

B: mistletoe growing on an orange tree

Mistletoe obtains water and mineral resources from its living host and can reduce the host’s resources. This is parasitism, even though mistletoe can also photosynthesise.

B: drought

Drought can reduce water and food availability, increasing competition for the remaining resources. Its effect depends on the population and habitat.

D: mitochondrion

Mitochondria carry out the citric-acid cycle and oxidative phosphorylation in eukaryotic cells. Glycolysis occurs in the cytosol, so respiration is not confined entirely to mitochondria.

B: sexual reproduction in Rhizopus

Compatible Rhizopus hyphae form gametangia that fuse during sexual reproduction. The resulting thick-walled sexual structure can survive unfavourable conditions.

A: zygospore

The thick-walled product labelled I is conventionally called a zygospore in this school-level diagram. It develops after compatible fungal gametangia fuse.

B: cell

The cell is the smallest organisational level listed that can function as a basic unit of life. Tissues comprise cells, organs comprise tissues and organ systems contain cooperating organs.

A: II and III

Hooks and suckers on the scolex anchor the tapeworm to its host’s intestinal lining. Labels II and III indicate these attachment structures, rather than the developing segment below the neck.

B: IV

New proglottids form near the neck behind the scolex. The small segment labelled IV is therefore a young proglottid, while the other labels mark structures on the head region.

B: Spirogyra

Spirogyra forms filaments containing many cells joined end to end. The other listed organisms are ordinarily single-celled forms, despite differences in their organelles and nutrition.

C: gametophyte

Bryophyte antheridia and archegonia are borne by the haploid gametophyte. The diploid sporophyte produces spores and typically remains attached to the gametophyte.

C: efficient seed dispersal

Seeds protect an embryo and can aid dispersal and survival through unfavourable conditions. Efficient dispersal is one important contributor to the success of seed plants on land.

D: Bird

Many birds live, rest or nest in trees and are described as arboreal. The term describes a tree-associated way of life rather than the ability to fly alone.

D: a herbivore

The formula with no canines, additional upper incisors and numerous cheek teeth is characteristic of a rabbit, a herbivore. The cheek teeth process plant material.

D: phloem

Sieve-tube elements and companion cells are components of angiosperm phloem. They work together in moving sugars and other organic solutes between plant organs.

C: spiracle of insects

Stomata and insect spiracles are openings that regulate gas exchange with the environment. They belong to different organisms and structures but share that functional role.

B: cutaneous respiration

Cutaneous respiration is gas exchange across the skin. A moist surface allows respiratory gases to dissolve before diffusing across the thin exchange barrier.

D: transpiration

Transpiration is the loss of water vapour from a plant, especially through stomata. Evaporation and diffusion are physical processes involved in that overall biological loss.

A: rhizome

A rhizome is an underground stem that stores reserves and carries buds. It can survive an unfavourable season and produce new shoots when conditions improve.

B: nerves and hormones

Nervous signals and hormones coordinate mammalian activities. Nerves often act rapidly through specific pathways, while hormones circulate to cells carrying suitable receptors.

B: muscular activity

The cerebellum helps coordinate muscle movements, posture and balance. It compares information needed for smooth movement rather than acting as the sole source of motor commands.

D: Barometer

A barometer measures atmospheric pressure. The pressure reflects the force exerted by the overlying air, and changes can assist weather observation.

A: edaphic

Edaphic factors are soil-related influences, including texture, mineral content, moisture and acidity. They affect which organisms can live and grow in a habitat.

D: genotype

Genotype describes an organism’s genetic constitution. Phenotype is its observable expression, shaped by genotype and often influenced by environmental conditions.

A: Primary Consumers

Primary consumers eat producers directly, for example herbivores feeding on green plants. Secondary consumers feed on other consumers rather than directly occupying this first consumer level.

B: Population dynamics

Population dynamics concerns changes in population size through time and the processes producing those changes. Births, deaths, immigration and emigration contribute to the pattern.

D: Anabaena

Anabaena is a cyanobacterium, historically called a blue-green alga. Many forms fix atmospheric nitrogen, often using specialised cells called heterocysts.

A: Clayey soil

Clay-rich soils generally retain more total water than coarse sandy soils because of their fine particles and large surface area. Not all retained water is equally available to plant roots.

A: Virus

Poliomyelitis is caused by poliovirus. It is therefore a viral infection, not a fungal, protozoal or bacterial disease.

C: It can effectively be controlled by vaccination

Vaccination was central to the global eradication of smallpox, together with surveillance and containment. Smallpox is caused by variola virus rather than a bacterium.

A: Paramecium

Paramecium can undergo conjugation, exchanging nuclear genetic material between compatible cells. It also reproduces asexually by binary fission; conjugation itself does not immediately increase cell number.

B: Finger prints

Whorls, arches and loops describe arrangements of friction ridges in fingerprints. These patterns illustrate variation in a visible human physical characteristic.

B: easy movement

A streamlined body reduces resistance as a fish moves through water. Lower drag can make swimming more efficient, helping the fish perform many activities.

B: catabolism

Catabolism breaks larger molecules into smaller ones and often releases usable energy. Anabolism builds more complex molecules; metabolism includes both kinds of reaction.

D: mitochondria and chloroplast

Mitochondria support aerobic cellular respiration, while chloroplasts carry out photosynthesis. A photosynthetic plant cell can use both organelles because photosynthesis does not replace its need for respiration.

D: pig

Pigs are the usual intermediate hosts for Taenia solium, the pork tapeworm. Larval cysts can occur in pig tissues; adult worms live in the human intestine after infected pork is eaten.

C: clitellum

The thickened band labelled II is the clitellum. In a sexually mature earthworm it secretes material involved in cocoon formation; it is a body region rather than the separate cocoon itself.

B: humus

The illustrated earthworm feeds on and lives among decomposing organic material in soil. Humus-rich soil offers that organic material along with conditions that commonly support earthworm activity.

D: xerophytes

Xerophytes are plants adapted to dry environments. Their adaptations may include reduced leaves, water storage or physiological mechanisms that limit water loss; different species use different combinations.

C: spiny leaves

Reducing leaves to spines decreases the surface area available for water loss. Many desert plants combine this with other adaptations, such as water-storing tissues or specialised stomatal behaviour.

D: grasping prey

Long, sharp talons allow predatory birds to seize and hold prey. The hooked beak commonly performs much of the tearing, while the feet secure the captured animal.

B: translocation

Translocation is the transport of substances from one part of a plant to another, especially sugars through phloem. Water and mineral ions also move through the vascular system, chiefly in xylem.

D: ptyalin

Ptyalin is salivary alpha-amylase, which begins starch digestion in the mouth. Pepsin acts in the stomach, while salivary amylase targets carbohydrate rather than fats.

A: carnivorous

Carnivorous plants capture and digest small animals to supplement mineral nutrition, particularly in nutrient-poor habitats. They generally still photosynthesise rather than depending on prey for all organic food.

D: respiration

Cellular respiration transfers energy from organic fuels into ATP that cells can use. Plants respire as well as photosynthesise; the two processes perform different roles in energy conversion.

B: lack chlorophyll

Fungi lack chlorophyll and obtain organic carbon by absorbing materials from other organisms or their remains. Their heterotrophy is defined by this dependence on organic food, not by the shape of their bodies.

B: Plasmodium

Plasmodium species are parasitic protists with life cycles involving a vertebrate host and a mosquito. Several species cause human malaria, unlike the usual free-living examples in the other choices.

A: heart, arteries, capillaries and veins

The vertebrate circulation includes a heart and vessels organised as arteries, capillaries and veins. Arteries carry blood away from the heart, capillaries permit exchange and veins return blood.

D: Platelets

Platelets adhere at damaged vessels and aggregate to form an initial plug. They also support coagulation reactions, while soluble clotting factors in plasma contribute to fibrin formation.

C: plasma

Plasma is the fluid portion of blood and typically accounts for about55% of its volume. The remaining formed elements are mostly red blood cells, with much smaller contributions from white cells and platelets.

A: sweat glands

Sweat glands release water, salts and small quantities of nitrogenous substances onto the skin. Sweating is chiefly important for thermoregulation but also removes these substances from the body.

B: Uric acid

Many terrestrial insects excrete nitrogen chiefly as uric acid or urates. These poorly soluble products can be eliminated with relatively little water, which helps conserve water on land.

A: skeleton

The vertebrate endoskeleton supports the body and protects organs, such as the brain within the skull. Muscles act on the skeleton to produce movement, while ligaments connect bones at joints.

C: pollination

Pollination is the transfer of pollen from an anther to a stigma in flowering plants. Fertilisation occurs later, when gametes fuse following pollen germination and pollen-tube growth.

B: stamen

A stamen is the pollen-producing male reproductive structure of a flower, typically consisting of an anther and filament. A carpel contains the female reproductive structures.

C: pituitary

The pituitary lies beneath the hypothalamus and is connected to it by the infundibulum. Their close anatomical relationship supports coordination of several endocrine pathways.

C: rod

Rod photoreceptors respond effectively at low light levels and support dim-light vision. Cones provide colour and high-acuity vision under brighter conditions; lens and iris are not photoreceptor cells.

A: ovaries

In a typical nonpregnant reproductive-age female, the ovaries are the principal source of circulating oestrogens. Smaller amounts can arise in other tissues, so synthesis is not exclusive to the ovaries.

C: cataract

A cataract is clouding of the eye’s lens, which can scatter or block light and reduce clear vision. It is different from glaucoma, which involves damage to the optic nerve.

D: lithosphere

The lithosphere is Earth’s rigid outer rocky layer. The atmosphere is the gaseous envelope, the hydrosphere includes water and the biosphere encompasses living systems.

D: Syphilis

Treponema pallidum is the bacterium that causes syphilis. Gonorrhoea, leprosy and tuberculosis are caused by different bacterial species, despite also being infectious diseases.

D: AB

In the simplified ABO red-cell compatibility model, an AB recipient lacks anti-A and anti-B antibodies and can receive red cells of any ABO group. Actual transfusions still require other compatibility checks.

A: agglutination

Agglutination is the clumping of cells, such as red blood cells linked by antibodies reacting with their surface antigens. It differs from fusion, in which cell membranes merge.

D: aestivation

Aestivation is a period of reduced activity or dormancy that can help some animals survive hot or dry conditions. Reduced metabolism and activity can lower resource needs during unfavourable periods.

C: leaves to spines

In Opuntia, leaves are greatly reduced and spines help limit the surface associated with water loss. The flattened green stems perform much of the photosynthesis and may store water.

A: Hooked beak and sharp claws

A hooked beak can tear food, while sharp talons seize and hold prey. This combination is characteristic of many predatory birds and suits a diet of captured animals.

B: Species

Species is the lowest rank among class, family, genus and species. A genus contains related species; families contain genera, and classes are still broader groupings.

D: dicotyledons

Typical secondary growth in many dicots increases stem and root girth through lateral meristems. Vascular cambium adds secondary vascular tissues, and cork cambium contributes the outer protective covering.

A: radially symmetrical

Radial symmetry arranges body parts around a central axis so several planes through that axis divide the body into similar halves. Bilateral symmetry instead has one principal left-right plane.

B: whale

Whales are mammals and females produce milk in mammary glands to nourish their young. The other listed animals are fishes and do not possess mammary glands.

B: remain undetected

Countershading commonly makes an animal darker above and lighter below. This can reduce visual contrast or the appearance of shadow, helping the animal escape detection in its surroundings.

C: root

Young absorbing roots generally lack the thick waterproof cuticle found on aerial organs. This permits water and dissolved minerals to enter; older roots may develop other protective barriers.

A: urethra

The male urethra carries urine from the bladder and also carries semen during ejaculation. The ureters conduct urine from the kidneys to the bladder and do not carry semen.

A: Copper

Copper is an essential plant micronutrient needed in small quantities, including for enzyme activity. Potassium and phosphorus are macronutrients required in larger quantities.

B: Loranthus

Loranthus is a photosynthetic hemiparasite: it can make organic food while obtaining water and mineral resources from a host. Sundew captures insects but is not a parasitic plant on a host.

D: Cellulose

Cellulose is a polysaccharide made of many glucose units joined in long chains. Glucose is a monosaccharide, while sucrose and maltose each contain two sugar units and are disaccharides.

B: Bowman's capsule

Ultrafiltrate crosses the glomerular filtration barrier into the capsular space of Bowman’s capsule. This is the first stage of urine formation, before tubular reabsorption and secretion modify the filtrate.

C: Vascular cambium and cork cambium

Vascular cambium produces secondary xylem and phloem, while cork cambium contributes the protective periderm. Together these lateral meristems account for typical secondary growth of woody stems and roots.

C: bean

A bean pod is a legume that develops from a single carpel. It typically opens along two seams at maturity, whereas tomato, orange and okra ovaries contain multiple fused carpels.

B: heart beat

Autonomic nerves adjust heart rate and other involuntary functions. The heart has its own pacemaker activity, while autonomic input changes the rate and force of contraction to suit bodily needs.

D: montane forest

Tropical mountains have cooler conditions than nearby lowlands. Suitable montane environments can therefore support some plants of temperate origin, provided their other soil and moisture requirements are met.

B: evaporation and condensation of water in the environment

Evaporation transfers water into the atmosphere, and condensation forms droplets that can return as precipitation. Runoff, infiltration and biological processes also contribute to the full water cycle.

C: withstand wide fluctuations in salinity

Estuaries mix river water with seawater, so salinity can change with tides and freshwater flow. Resident organisms often tolerate a wider salinity range than species restricted to stable freshwater or marine conditions.

B: mangrove swamps

Mangrove habitats combine waterlogged, often oxygen-poor soils with saline conditions. Different mangrove species have adaptations such as aerial roots, supportive roots or mechanisms for managing salt.

C: lichen

Lichens can colonise exposed rock and contribute to weathering and accumulation of organic material. They are typical pioneer organisms in primary succession, helping make later colonisation possible.

D: remain steady

At carrying capacity in the simple logistic model, population size is approximately stable because net population growth is zero. Growth slows before the population reaches that level.

D: crop rotation and shifting cultivation

Crop rotation can replenish or conserve nutrients, and a sufficiently long fallow in shifting cultivation can allow soil fertility to recover. Their effectiveness depends on the crops, land pressure and fallow duration.

D: typhoid and cholera

Typhoid and cholera can both spread through water contaminated with human faeces. Their causative bacteria differ, but unsafe water is an important transmission route for both diseases.

C: a continuously varying character

The smooth distribution represents variation in height across a range of values. Height is a continuously varying character, unlike a trait that falls only into distinct, separate categories.

B: 50%

For XcY × XCXc, the equally likely children are XCXc, XcXc, XCY and XcY. Two of these four combinations express the recessive colour-vision trait, giving a probability of 50%.

A: adenine → thymine and guanine → cytosine

In ordinary double-stranded DNA, adenine pairs with thymine and guanine pairs with cytosine. These complementary pairs help preserve the sequence relationship between the two strands during replication.

A: crushing seeds

A short, stout beak can exert force to crack hard seeds. Nectar feeders instead tend to have more elongated feeding structures, while flesh-tearing birds commonly have hooked beaks.

B: raise their body temperature to become active

Agama lizards are ectotherms and can warm themselves by basking. Raising body temperature within a suitable range supports faster physiological activity and more effective movement.

B: ensure their perpetuation despite predatory pressure

Producing many winged reproductives increases the chance that some survive predators and establish colonies. Large numbers improve population persistence even though many individual termites fail to reproduce.

B: Lamarck’s theory

Lamarck’s historical account linked use and disuse of organs to changes that he proposed could be inherited. Modern evolutionary explanations distinguish acquired changes in an individual from inherited genetic variation.

A: comparative anatomy

Comparing the forms of finch beaks is a comparison of anatomy. Such structural differences can be related to feeding ecology and adaptation, although Darwin’s evolutionary theory drew on much broader evidence.

B: angiosperms and gymnosperms

Seed plants include gymnosperms, whose ovules are not enclosed in ovaries, and angiosperms, the flowering plants. Both groups reproduce using seeds, unlike ferns and bryophytes.

A: carbon (IV) oxide

Yeast fermentation releases carbon dioxide, which can pass through the delivery tube into limewater. Carbon dioxide reacts with limewater to form a calcium carbonate precipitate, making it appear milky.

C: fermentation

The sugar-and-yeast apparatus demonstrates fermentation. Yeast metabolises sugar and releases carbon dioxide; the connected limewater provides a means of detecting that gas.

D: Hypertonic solution

A hypertonic solution draws water out of a cell by osmosis and can cause the cell contents to shrink. A hypotonic solution instead favours water entry, while an isotonic solution causes no net osmotic change.

C: they are large and nucleated

Leucocytes are nucleated white blood cells involved in defence. They are generally larger than red blood cells, which are far more numerous in normal mammalian blood and lack nuclei when mature.

B: assimilation

Assimilation incorporates absorbed nutrients into the body’s own materials. Digestion breaks food down, while absorption transfers digested molecules across the intestinal lining before they can be used by cells.

B: irritability

Irritability is the capacity to detect and respond to stimuli. A response need not involve movement of the whole organism; growth, secretion or another physiological change can also be a response.

A: maize grain

A maize grain retains a substantial endosperm that stores nutrients for the developing seedling. In many other seeds, the cotyledons absorb most of that storage tissue before the seed matures.

B: II and III only

Dilute acid or the appropriate enzyme can hydrolyse sucrose into glucose and fructose. Water alone does not appreciably hydrolyse sucrose during the usual laboratory test period, so tubes II and III are positive.

C: sucrase

Sucrase hydrolyses sucrose into glucose and fructose. Maltase acts on maltose, whereas the protein-digesting enzymes in the other choices do not split the sucrose glycosidic bond.

A: trachea → bronchi → bronchioles → alveoli

Inhaled air passes down the trachea into bronchi, then progressively smaller bronchioles and finally the alveoli. The alveoli provide a large thin surface for exchange with pulmonary capillary blood.

B: negative phototaxism

Movement away from light is negative phototaxis. Taxis is directional movement of an organism relative to a stimulus; tropism usually describes a directional growth response, particularly in plants.

A: the movement of food and water

Xylem transports water and mineral ions, while phloem distributes sugars and other organic solutes. Together these vascular tissues connect sources, storage organs and growing parts of the plant.

B: Kidney

The kidneys filter blood and adjust tubular reabsorption and secretion. These processes regulate water, electrolytes and acid-base balance while allowing nitrogenous wastes such as urea to leave in urine.

D: mouth → gills → operculum

In a typical bony fish, water enters the mouth, passes over the gills and exits through the opercular openings. Oxygen diffuses from this water into blood across the thin gill surfaces.

D: fission

Paramecium commonly reproduces asexually by binary fission, dividing into two daughter cells. Fission also occurs in many other protists, although protist reproductive strategies are diverse.

C: an ecosystem

An ecosystem includes a community of organisms and the nonliving environment with which they interact. It therefore includes both biological relationships and physical conditions such as water and temperature.

B: female Anopheles mosquito

Female Anopheles mosquitoes transmit human malaria parasites when they take blood meals. Male mosquitoes do not take blood meals and are not the vectors in this transmission cycle.

C: Hygrometer

A hygrometer measures humidity, including relative humidity. Relative humidity compares the water vapour present with the amount needed for saturation at the same temperature.

A: liver of humans

Before infecting red blood cells, malaria sporozoites invade liver cells and develop there. This liver stage is termed exo-erythrocytic because it occurs outside erythrocytes.

B: aquatic and terrestrial

A broad habitat division separates water environments, aquatic habitats, from land environments, terrestrial habitats. Each category can be divided further into more specific environments.

B: drinking contaminated water

People can acquire Guinea worm infection by drinking water containing infected tiny crustaceans called copepods. Swallowing the intermediate host allows the parasite to enter the human body.

C: Food limitation, predation, disease and accumulation of metabolites

Food limitation, predation, disease and waste accumulation can become more important as population density rises. Their effects depend on biological interactions and the number of organisms sharing resources.

B: sex-linked

A gene on the X chromosome is X-linked, a type of sex linkage. Its allele can be dominant or recessive, so chromosomal location is a separate concept from dominance.

C: disease rate

Crowding can increase contact between individuals and facilitate the spread of infectious agents. The outcome depends on the pathogen and conditions, but increased disease transmission is a common density-dependent effect.

B: incomplete dominance

Incomplete dominance produces a heterozygous phenotype intermediate between the two homozygotes, such as pink flowers from red and white parental lines. Both alleles remain distinct rather than permanently blending.

A: cross-breeding

Cross-breeding combines individuals from genetically different lines or varieties within a species. It can combine useful traits, whereas inbreeding mates closely related individuals.

A: 3

The usual ABO inheritance model has three alleles in the population: IA, IB and i. Each person normally carries two of these, producing the familiar A, B, AB or O phenotypes.

A: convergent evolution

Bird and bat wings evolved independently as flight structures. Their underlying forelimbs are homologous through shared vertebrate ancestry, but the independent acquisition of wings for powered flight illustrates convergence.

C: the cell wall is made up of cellulose

A typical plant cell has a cell wall containing cellulose. In many mature cells, a large central vacuole occupies much of the volume and displaces the cytoplasm and nucleus toward the edge.

C: sporophyte

The familiar leafy fern is the diploid sporophyte, the larger and longer-lived generation. The gametophyte is usually a small prothallus, which bears the sexual reproductive organs.

B: monera

The historical group Monera consists of prokaryotic organisms, whose cells lack a membrane-bound nucleus. Modern classification separates these organisms into Bacteria and Archaea.

B: the xylem is more interiorly located than the phloem

In a typical dicot stem vascular bundle, xylem lies toward the centre and phloem toward the outside. Cambium is between them, and the bundles form a ring inside the outer tissues.

A: reducing sugar

A reducing sugar can reduce copper ions in warmed Benedict’s reagent, forming an orange to brick-red copper(I) oxide precipitate. The colour depends on the amount present and the test conditions.

D: left ventricle

The left ventricle ejects blood into the aorta, supplying the systemic circuit. The right ventricle supplies the pulmonary circuit, so the two sides of the heart serve different circulatory pathways.

B: systemic circulation

Systemic circulation supplies tissues through the aorta and its branches and returns blood to the right side of the heart. The pulmonary circuit carries blood between the heart and the lungs for gas exchange.

A: alcohol

During alcoholic fermentation, yeast produces ethanol and carbon dioxide from the products of glycolysis. Regeneration of NAD+ permits glycolysis to continue when oxygen is unavailable.

A: diaphragm

The diaphragm is a sheet of skeletal muscle separating the thoracic and abdominal cavities. Its contraction increases thoracic volume and contributes to inhalation.

B: sebaceous glands

Sebaceous glands release sebum, an oily secretion that lubricates skin and hair. Sweat glands principally produce a watery secretion and are not the main source of this oil.

A: cortex

Renal corpuscles, including Bowman’s capsules and their glomeruli, lie in the kidney cortex. The medulla contains renal pyramids, while the pelvis collects urine toward the ureter.

C: epididymis

Sperm mature and are stored in the epididymis after leaving the testis. During ejaculation they travel into the vas deferens and onward through the reproductive tract.

A: stomach

The stomach normally has a strongly acidic lumen because gastric glands secrete hydrochloric acid. Acid helps activate pepsin and supports protein digestion before intestinal neutralisation.

D: IV

Contractile vacuoles occur in many freshwater protozoans and remove excess water. Spirogyra has no stomata, earthworms do not have alveoli, and mammals do not use Malpighian tubules.

A: placenta

Maternal and fetal blood are normally separated by placental tissues while gases, nutrients and wastes pass across the exchange barrier. The placenta is an exchange organ, not a completely impermeable wall.

C: erythrocytes

Erythrocytes contain haemoglobin, which binds and transports most blood oxygen. White blood cells primarily support defence, while platelets are chiefly involved in blood clotting.

C: dogfish

Dogfish are sharks that live in marine environments. The other listed organisms are principally land animals or freshwater fishes, so dogfish is the marine choice.

A: pubic symphysis

The left and right hip bones meet anteriorly at the pubic symphysis, a joint containing fibrocartilage. Each hip bone also joins the sacrum posteriorly.

B: desert

A hot desert commonly has low rainfall and sparse vegetation. Dry air and limited cloud cover can allow strong daytime heating and rapid cooling at night, producing a wide daily temperature range.

C: a biotic factor

A biotic factor arises from living organisms, such as predation, competition or mutualism. It can affect another organism’s survival, reproduction or access to resources.

A: population density

Population density is the number of individuals per unit area or volume. Population size is the total count, while distribution describes how individuals are arranged in space.

A: Aedes mosquito

Aedes mosquitoes can transmit yellow fever virus. In the urban transmission cycle, Aedes aegypti is an important vector; the other listed insects do not identify that usual urban vector.

A: female Anopheles mosquitoes

Female Anopheles mosquitoes transmit Plasmodium falciparum during blood feeding. Parasites develop through mosquito and human stages, with sporozoites entering the person in an infective bite.

A: III

Curve III extends from 2 m to 4 m on the horizontal axis. Thus the trees represented by that distribution fall within the stated height interval; the other curves extend outside it.

C: behavioural patterns

Thyroid hormones influence metabolic activity, and adrenaline contributes to rapid responses to stress. Changes in these physiological states can influence behaviour, unlike inherited blood-group identity.

D: 2n → n

Meiosis reduces the chromosome-set number from diploid, 2n, to haploid, n. DNA replicates before the first division, but replication does not itself double the number of chromosome sets.

C: 1⁄4

For Aa × Aa, each parent produces A and a gametes equally. The four equally likely combinations are AA, Aa, aA and aa, giving a recessive aa phenotype in one quarter of offspring.

D: at conception

In the usual mammalian XX/XY system, fertilisation establishes the zygote’s sex-chromosome combination. Subsequent development determines the gonads and other sex characteristics through additional genetic and hormonal processes.

C: absence of wings, possession of strong mandibles and a large head

A typical mandibulate soldier termite is wingless and has an enlarged head with strong jaws used in colony defence. Winged reproductives serve a different role, particularly during dispersal.

D: convergent evolution

Whales and fishes independently evolved body features suited to swimming. Their similarly functioning external swimming structures illustrate convergence, although deeper vertebrate ancestry links parts of their skeletal history.

C: increase in solute concentration in the guard cells

An increase in guard-cell solute concentration lowers water potential. Water enters by osmosis, turgor rises and the guard cells bow apart, opening the pore.

A: contains selectively permeable cell membranes

Living yam tissue contains selectively permeable cell membranes. These permit osmotic water movement while restricting solute movement, which is the property used in this demonstration.

C: dicot stem and monocot roots

A typical dicot stem has vascular bundles around a central pith, and a typical monocot root also has a broad central pith. Monocot stems generally have scattered bundles without the same distinct pith region.

D: prolactin

Prolactin stimulates milk synthesis in mammary glands. Milk supply also depends on effective milk removal and other factors, so low production alone does not diagnose a hormone deficiency.

C: lipases

Lipases hydrolyse fats into smaller products, including fatty acids and monoglycerides during digestion. They are a specific type of hydrolase, the broader class of enzymes that break bonds using water.

D: Na⁺ and K⁺

In a typical neurone action potential, sodium entry depolarises the membrane and potassium exit helps repolarise it. The relevant cations are Na+ and K+.

A: anther

II points to the pollen-bearing tip of a slender stalk: the anther. The filament supports the anther, while the style and stigma belong to the central female structure.

C: II to III

Pollination transfers pollen from an anther to a stigma. In this figure, II indicates an anther and III the stigma, so the transfer is from II to III.

D: a net 2 ATP molecules and alcohol

Alcoholic fermentation in yeast allows glycolysis to continue without oxygen. Glycolysis provides a net two ATP per glucose; fermentation produces ethanol and carbon dioxide while regenerating NAD+.

B: budding

Hydra and yeast can both reproduce by budding. A new outgrowth develops on the parent and can eventually separate, producing a new individual without fusion of gametes.

B: more rapid elongation of the hypocotyl than the epicotyl

During epigeal emergence, elongation of the hypocotyl raises the cotyledons above the soil. In hypogeal emergence, the cotyledons remain below ground while growth above them becomes prominent.

D: provides an aqueous medium for metabolic reactions

Water provides an aqueous medium in which many metabolic reactants dissolve and interact. It also participates in reactions and helps regulate temperature; it is not the cell’s main energy source.

A: capillaries

Pulmonary capillaries form a fine network around alveoli. Their thin walls and close contact with the alveolar surface allow oxygen and carbon dioxide to diffuse between air and blood.

C: the same egg and sperm

Identical, or monozygotic, twins develop when a single fertilised egg gives rise to two embryos. They therefore originate from the same egg and sperm, although later mutations can create small genetic differences.

A: DNA analysis

DNA analysis compares inherited genetic markers and can assess whether a proposed parent is genetically compatible with a child. Ordinary fingerprints, tongue rolling and blood groups provide far less discriminatory information.

B: pink

With incomplete dominance, crossing true-breeding red and white four-o’clock plants produces pink heterozygous offspring. The intermediate phenotype does not mean the inherited alleles blend permanently.

B: cells

Rods are specialised photoreceptor cells in the retina. They are particularly sensitive in dim light and are individual cells within retinal tissue, not whole organs or organ systems.

C: wriggler

A mosquito larva is commonly called a wriggler because of its movement in water. The pupal stage is often called a tumbler, and the adult is the flying stage.

D: cell walls that are rigid and contain chitin

Fungal hyphae usually have rigid cell walls containing chitin. Some hyphae are divided by septa, while others are coenocytic and contain many nuclei without complete cross walls.

C: chisel-like front teeth

Rodents gnaw with their chisel-shaped incisors at the front of the mouth. These teeth grow continuously and are maintained by wear; the cheek teeth mainly grind food.

A: palaeontology

Palaeontology studies fossils, providing direct evidence of extinct organisms. Comparing fossil features with living organisms helps reconstruct evolutionary relationships and changes through time.

D: storing water in large parenchyma cells

Some plants store water in enlarged parenchyma cells, allowing them to endure dry periods. This is one drought-survival strategy, alongside other features that reduce water loss.

D: clayey

Wet clay-rich soil tends to be sticky and plastic because of its fine particles and water retention. These properties can make cultivation difficult; working it when too wet can also damage soil structure.

C: keratinous scales

The keratinised outer covering of reptiles forms a barrier that helps reduce water loss. This supports life on land, although reptiles still lose water and need suitable sources or conservation strategies.

B: raising the mortality rate

Severe food shortage can raise mortality, directly removing individuals and reducing population size. A lower reproductive rate reduces additions, whereas immigration adds individuals.

A: mutualism

In termites that harbour these protozoans, the microorganisms help break down cellulose and obtain food and a protected habitat in the gut. Both partners benefit, making the association mutualistic.

C: pileus

The pileus is the expanded cap of a typical mushroom. The stipe supports it, while the mycelium is the network of fungal hyphae and a basidium is a microscopic spore-producing cell.

A: evaporation and osmosis

Water can evaporate from a frog’s moist skin exposed to air. Water can enter the submerged skin by osmosis when the surrounding water has a higher water potential than the body fluids.

D: kingdom

A kingdom is the broadest taxonomic rank listed and contains organisms from many lower groups. Members of a species are generally much more similar than members of the same kingdom.

A: ribosome

Prokaryotic cells contain ribosomes that synthesise proteins. They lack a membrane-bound nucleus and the mitochondria and chloroplasts characteristic of eukaryotic cells.

B: embryo disc

In a fertilised bird egg, early embryonic cells form a disc on the yolk surface. The yolk supplies nutrients, while the chalazae support the yolk and albumen surrounds it.

A: transpiration occurs through the leaves

The leafy shoot produces water vapour that condenses on the jar. Comparison with the leafless shoot supports water loss through leaves, while the oil limits evaporation directly from the beaker.

C: Evaporation

The oil layer covers the free water surface in each beaker, reducing direct evaporation. This helps distinguish water released by the shoot from water evaporating from the container.

C: xylem

Water absorbed by a plant moves upward mainly through xylem. A suitable dissolved dye can follow that water stream and stain the conducting xylem tissues.

B: compatible Rhizobium bacteria

Compatible Rhizobium bacteria can form nitrogen-fixing nodules on legume roots. They convert atmospheric nitrogen into compounds that can support the plant’s nitrogen nutrition.

B: IV

The ratios correspond to 0.5, about 0.33, 0.25 and 0.20 units of surface area per unit volume. IV has the least exchange surface relative to its volume and therefore the greatest transport challenge on this criterion.

C: the part played by the pleural cavity and diaphragm in respiration

Pulling the sheet down increases the enclosed volume and lowers pressure, so air enters and expands the sacs. The model illustrates the mechanical role of diaphragm movement and a sealed chest space in ventilation.

A: diaphragm

The movable rubber sheet represents the diaphragm. Pulling it downward increases the space inside the jar, modelling how diaphragm contraction increases thoracic volume during inhalation.

C: Ethylene

Ethylene promotes ripening in many climacteric fruits. It can trigger changes in texture, colour and aroma, although ripening control differs among fruit types.

D: liver

The liver converts nitrogenous products of amino-acid breakdown into urea. Urea then circulates to the kidneys for excretion; the bladder mainly stores urine.

D: urethra

The male urethra provides a route for urine and also for semen at different times. The ureters carry urine to the bladder, while the vas deferens transports sperm toward the ejaculatory pathway.

A: stem cuttings

Sugarcane is commonly propagated using pieces of stem containing viable buds. The buds produce shoots and roots, preserving the selected variety through vegetative propagation.

A: nastic movement

Nastic movement responds to a stimulus without its direction being determined by the direction from which the stimulus comes. This differs from directional growth responses such as phototropism and gravitropism.

A: peripheral and central nervous systems

Neurones occur in both the central and peripheral nervous systems. The illustrated cell has a body, branched processes and a long insulated process, features not restricted to only one of those divisions.

C: node of Ranvier

I marks a gap between successive insulating segments along the long process. Such gaps are nodes of Ranvier, where the membrane can regenerate an action potential during saltatory conduction.

A: meiosis

Homologous chromosomes separate during the first meiotic division. Sister chromatids separate later in meiosis II; in ordinary mitosis it is sister chromatids rather than homologous pairs that separate.

D: maize grain

A maize grain is a caryopsis, a dry one-seeded fruit with the fruit wall fused to the seed coat. This close fusion is characteristic of cereal grains.

A: roots of higher plants

Mycorrhizae are associations between fungi and plant roots. The fungus can improve uptake of water and minerals, while receiving carbon compounds from the plant.

B: Sahel savanna → Sudan savanna → Guinea savanna → tropical rain forest → estuarine

Across the broad north-to-south climatic gradient, Nigerian vegetation passes from drier savanna zones toward wetter forest and coastal environments. Sahel, Sudan and Guinea savannas precede tropical rain forest and estuarine areas in that order.

D: coal

Coal forms from ancient organic material altered by burial, heat and pressure over geological time. It is therefore a fossil fuel, unlike freshly cut firewood.

D: sexual

Sexual reproduction combines genetic material from parents and involves meiotic processes that reshuffle alleles. This creates new combinations among offspring, although mutations can also generate variation in asexual lineages.

C: AGT

DNA base pairing matches thymine with adenine and cytosine with guanine. Written opposite 5′-TCA-3′, the complementary strand is 3′-AGT-5′.

D: reduce water loss

Sunken stomata and folded leaves can shelter moist air near exchange surfaces. This reduces exposure to moving dry air and can lower transpiration and water loss.

A: physical defence

Spines can make an animal difficult to grasp or swallow, and shells form a protective barrier. Both provide physical defence against injury or predation.

A: aestivation

Aestivation is a dormant state associated with hot or dry conditions. It reduces activity and metabolic demand when heat or water shortage makes normal activity difficult.

C: a single cell

Amoeba is a unicellular organism, while an unfertilised chicken ovum is a single reproductive cell. The ovum is not the whole shelled egg with its surrounding membranes and albumen.

A: Chlamydomonas and Euglena

Chlamydomonas and Euglena can swim using flagella. Amoeba moves by pseudopodia, and Paramecium uses many cilia rather than the flagellar swimming pattern of the first pair.

C: cell wall and chloroplast

Photosynthetic plant cells can have a cellulose wall and chloroplasts, whereas animal cells lack both. Cell membranes, cytoplasm, chromatin and nucleoli are shared eukaryotic features.

C: opposable

Opposable digits can close against other digits, improving the grip on branches. This is useful for climbing and holding supports during movement through trees.

D: seed dispersal

Seed dispersal carries offspring away from the parent and from one another. This can reduce local competition for light, water, nutrients and space.

A: 1.2 per m²

The sampled area is 20 × 2 = 40 m². Dividing the total count, 48 plants, by 40 m² gives an estimated density of 1.2 plants per square metre.

C: submerged water plants

Submerged plants receive mechanical support from the surrounding water and can absorb water across much of their surface. Their supporting and conducting xylem is often reduced compared with terrestrial plants.

A: a tropical rain forest

Tropical rain forests generally support high species richness because of their complex structure and diverse ecological opportunities. Comparable representative sampling commonly finds more species there than in the other listed regional habitats.

B: the most successful organisms are those best adapted to their environment

Natural selection favours inherited variants that improve reproductive success in the current environment. Individuals carrying favourable variants tend to leave more descendants, changing their frequency over generations.

B: fish catchers

Long legs and necks allow a wading bird to reach into water, and a long pointed bill can seize aquatic prey. These features are consistent with a fish-catching bird such as a heron.

D: Rhizopus, housefly and Hydra

Rhizopus releases digestive enzymes outside its cells. A housefly digests food externally or in its gut, and Hydra begins digestion in its gastrovascular cavity. All therefore have extracellular digestion.

B: discoid and enucleated

Typical mature mammalian red blood cells are disc-shaped and lack a nucleus. Losing the nucleus helps provide space for haemoglobin, although shape varies in some mammalian groups.

B: vertebrata

Vertebrates characteristically have an internal skeleton of cartilage or bone. This endoskeleton supports the body and provides attachment points for muscles.

B: heterotrophic

Capturing and digesting insects supplies nutrients from other organisms, a heterotrophic supplement to the pitcher plant’s photosynthesis. The plant can still obtain much of its carbon by photosynthesis.

D: The leaves outside the flask serve as control

The outside leaves provide a comparison with leaves exposed to ordinary air. Caustic soda removes carbon dioxide inside the flask, so the enclosed leaf has a different carbon dioxide supply.

D: carbon (IV) oxide is necessary for photosynthesis

Caustic soda absorbs carbon dioxide, changing the supply available to the enclosed leaf. The setup is intended to test the need for CO2 in photosynthesis; meaningful starch comparisons also require appropriate prior preparation and matched conditions.

C: lungs and heart

The heart and lungs occupy the thoracic cavity, anterior to the main abdominal organs in a typical quadruped. The kidneys and ovaries lie farther back in the abdominal region.

C: parasitic

A tapeworm obtains nutrients from a living host and can harm it. This is parasitism. Its body surface absorbs nutrients already digested in the host’s intestine.

B: pancreas

The head of the pancreas lies within the curve of the duodenum. Pancreatic secretions reach the small intestine through ducts and assist digestion.

D: Caryopsis

A caryopsis is a dry, one-seeded fruit in which the fruit wall is closely fused with the seed coat. Cereal grains such as maize are examples.

C: release of energy for body use

Cellular respiration transfers energy from food molecules into forms cells can use, especially ATP. Breathing and gas exchange supply or remove gases but are different processes.

B: have red–green colour-vision deficiency

In the stated X-linked recessive model, the boy has only the Xⁿ allele at this locus because the Y chromosome lacks a corresponding dominant allele. The colour-vision deficiency is therefore expressed.

D: ½

With independent births and a probability of one half for a girl in this model, the previous four outcomes do not change the fifth. The probability remains 1/2.

A: ¼

For Aa × Aa, the equally likely allele combinations are AA, Aa, aA and aa. With complete dominance, only aa expresses the recessive phenotype, giving a probability of 1/4.

D: symbiosis

Rhizobium bacteria in legume root nodules obtain carbon compounds and a suitable habitat from the plant. In return, nitrogen fixation supplies nitrogen compounds useful to the plant. This is a mutualistic symbiosis.

B: in water and on moist land

Amphibians are commonly associated with aquatic habitats and moist land. Their skin and, in many species, reproduction depend on moisture, making dry terrestrial conditions less suitable for typical amphibian activity.

A: mammals

Live birth is characteristic of most mammals, including marsupials and placental mammals. Egg-laying monotremes are exceptions. Some reptiles and amphibians also bear live young, so the feature is not exclusive to mammals.

C: antenna

An insect antenna bears sensory receptors that can detect chemicals, touch and movement or vibration. The paired antennae are jointed appendages on the head.

B: crustacea

Water fleas, woodlice and barnacles are crustaceans despite their very different appearances and habitats. Woodlice are terrestrial members of the group, while barnacles are highly modified attached forms.

A: heterotrophic

Amoeba and Hydra obtain organic food from other organisms. This makes their feeding heterotrophic, rather than producing organic food from inorganic carbon by photosynthesis.

B: Volvox

Volvox normally forms a coordinated spherical group of many cells. The other listed organisms are commonly represented by single free-living cells, making Volvox the exception.

B: male organs and rhizoid

II points to the small male reproductive structures near the lower region of the fern prothallus. III points to the slender rhizoids. The female organs are nearer the notch.

C: cerebrum

The cerebrum contains networks central to learning and memory, including cortical and associated structures. Different kinds of memory involve several interconnected regions rather than one isolated point.

B: liver

The liver converts nitrogen from amino-acid breakdown into urea through the urea cycle. The kidneys then remove much of that urea from the blood in urine.

D: III

III identifies a twisted cord alongside the yolk. These cords, the chalazae, help keep the yolk positioned within the surrounding egg white.

A: calcium hydroxide

Carbon dioxide reacts with calcium hydroxide solution, or limewater, to form a cloudy calcium carbonate precipitate. This visible change can identify the carbon dioxide released during aerobic respiration.

C: glucose and fructose

Sucrose contains glucose and fructose joined by a glycosidic bond. Invertase catalyses hydrolysis of that bond, releasing one glucose molecule and one fructose molecule.

C: alcohol

During alcoholic fermentation, yeast converts sugars into ethanol and carbon dioxide while regenerating NAD+ so glycolysis can continue. Ethanol is the alcohol referred to in the options.

D: erythrocytes

Erythrocytes contain haemoglobin, which transports most blood oxygen and part of the carbon dioxide. They also help convert carbon dioxide into bicarbonate, much of which is carried in plasma.

A: vascular bundles

Leaf veins contain vascular bundles with xylem and phloem. These tissues carry water, minerals and organic solutes and also contribute support to the leaf.

B: Starch

Iodine forms a blue-black complex with starch, particularly the helical amylose component. The other listed sugars do not give this characteristic starch-test colour.

D: cervical vertebra

The paired small openings in the transverse processes identify a cervical vertebra. These transverse foramina distinguish it from the ordinary thoracic and lumbar patterns.

C: V

V points to a transverse foramen. In cervical vertebrae, these openings provide passage for blood vessels; the much larger central vertebral foramen carries the spinal cord.

C: 46%

The total count is 15 + 5 + 7 + 23 = 50 plants. Imperata accounts for 23 of them, so its percentage of the total is 23 ÷ 50 × 100 = 46%.

A: arboreal

A plant growing on a tree as an epiphyte occupies an arboreal habitat. The tree provides support; an epiphyte does not necessarily draw its food from the host.

C: producers

Producers introduce energy into a grazing food chain by fixing it into organic matter. Only a fraction passes to each higher trophic level, so the energy available is greatest at the producer level.

A: relative humidity

A hygrometer measures humidity. Relative humidity expresses the water-vapour condition as a percentage relative to saturation at the same temperature.

B: at corresponding loci on a homologous chromosome pair

Alternative alleles of the same gene occupy corresponding loci on a homologous chromosome pair. In a heterozygote, one copy may be dominant and the other recessive.

A: father’s sex cell

In the usual XX–XY inheritance pattern, the egg contributes an X chromosome. The fertilising sperm contributes either X or Y, producing an XX or XY chromosome complement respectively.

C: Group AB is the universal recipient

In the ABO model for red cells, group AB lacks anti-A and anti-B antibodies and can receive cells from any ABO group. Rh type, other antibodies and compatibility testing also matter in real transfusions.

D: organic evolution

Darwin explained organic evolution through natural selection acting on inherited variation. Alfred Russel Wallace independently developed natural selection, so this historical contribution was not Darwin’s alone.

C: mate with the queen

The male honey bee, or drone, has a reproductive role: mating with a queen. Workers perform most hive maintenance, ventilation and brood care.

D: adaptation

An adaptation is a feature or inherited characteristic that improves an organism’s fit to its environment. Such traits can increase survival or reproductive success under particular conditions.

A: silk thread

II points to the thin supporting strand that runs from the plant stem across the pupa. This is the silk girdle. The attachment at the lower tip is separate from that supporting strand.

C: One seed leaf, petals in threes or groups of threes and parallel venation of leaves

Typical monocots have one cotyledon, parallel leaf veins and floral parts arranged in threes or multiples of three. These characteristics are useful together when comparing monocots with typical eudicots.

B: pectoral and pelvic

The paired pectoral and pelvic fins help a fish manoeuvre and maintain its orientation. They can affect steering, balance and pitching, while the caudal fin is particularly important in propulsion.

D: Cnidaria (coelenterates)

Cnidarians have a digestive cavity but no true coelom lined by mesoderm. A digestive cavity is not a coelom. Molluscs and arthropods have a reduced coelom, while reptiles have a well-developed body cavity.

A: head region

Growth hormone is secreted by the anterior pituitary, located at the base of the brain in the head. It influences growth and metabolism, often through effects mediated by other tissues.

C: appendicular skeleton

The scapula belongs to the pectoral girdle and the ischium to the pelvic girdle. Both girdles are components of the appendicular skeleton, which includes the limbs and their attachments.

D: concave

A concave lens diverges incoming light. This reduces the excessive convergence associated with myopia, helping distant objects focus on the retina rather than in front of it.

B: cochlea and semi-circular canals

The cochlea and semicircular canals are both in the inner ear. The cochlea is involved in hearing, while the semicircular canals contribute to sensing head rotation and maintaining balance.

C: anabolism must exceed that of catabolism

Anabolism builds complex substances, whereas catabolism breaks them down. Net accumulation of body material requires synthesis to exceed breakdown over the growth period.

A: protein

A violet Biuret reaction indicates peptide bonds, which occur in proteins. Copper ions in alkaline solution form a coloured complex with those bonds.

B: butter

Butter is predominantly fat, which releases more energy per gram on oxidation than carbohydrate or protein. For equal masses of ordinary forms of these foods, butter therefore usually supplies the most energy.

D: left ventricle

The left ventricle pumps blood through the systemic circulation and must generate higher pressure than the right ventricle. Its muscular wall is consequently the thickest heart chamber wall.

C: lacks the blood protein fibrinogen

Serum is the liquid remaining after blood has clotted. Fibrinogen is converted into fibrin during clot formation, so serum lacks the fibrinogen present in plasma.

A: mesocarp

II points into the thick fibrous middle layer of the fruit wall. This is the mesocarp. The epicarp is the outer layer and the endocarp is the inner layer surrounding the seed.

B: water

The fruit has a thick fibrous husk and an enclosed inner body, characteristic of a coconut. This construction enables floating and transport by water, a natural dispersal mechanism for coconut fruits.

D: r<p+q

The initial soil volume includes air-filled pore spaces. When water enters those spaces and air escapes, the final mixture occupies less than the sum of the separately measured water and soil volumes.

A: an increase in species diversity

As succession proceeds, new species can establish and additional habitats and interactions develop. This often increases species diversity compared with an early pioneer stage, although the pattern is not universal.

B: I and III

High births and immigration add individuals, while low mortality and emigration minimise losses. Combining I and III therefore most consistently favours rapid population increase.

A: IV

Region IV has the highest element concentrations and declining growth. This is the excess range, where an otherwise essential nutrient can inhibit growth through toxicity.

B: III

The maximum-growth plateau is region III. Within that range, the essential element is sufficient for growth without the high-concentration inhibition seen farther to the right.

C: Buttress roots

Buttress roots spread outward from the base of some tall tropical forest trees. They enlarge the supporting base and help stabilise the tree, especially where much of the root system is shallow.

A: temperature, light, rain and humidity

Temperature and water availability strongly influence broad vegetation patterns. Light and humidity also affect plant growth and water balance, so the first set includes major climatic controls.

D: chlorofluorocarbons

Chlorofluorocarbons can reach the stratosphere, where ultraviolet light releases chlorine that catalyses ozone destruction. This reduces the protective stratospheric ozone layer.

B: invertebrates rather than birds

Invertebrate lineages existed long before birds evolved. Older fossil-bearing deposits can therefore preserve invertebrates from periods before birds appeared, although preservation varies among environments.

A: dominant

Dominant breeding males of Agama agama typically display conspicuous head and body colours. Colour can also vary with physiological and environmental conditions, so it is a social signal rather than an exact measure of age or size.

D: dracunculiasis and haemophilia

Dracunculiasis can be acquired by drinking water containing infected copepods. Haemophilia A and B are usually inherited in an X-linked pattern, which differs from sexual transmission of an infection.

B: Hugo de Vries

Hugo de Vries developed the historical mutation theory, presenting it in Die Mutationstheorie. He emphasised sudden heritable changes as a source of new forms, distinct from Darwin’s emphasis on natural selection.

B: muscles of pig

In the usual life cycle of Taenia solium, pigs act as intermediate hosts and cysticerci develop in their tissues, especially muscle. The adult tapeworm, by contrast, lives in the human intestine.

A: birds and reptiles

Birds and reptiles both include animals with scales, shelled eggs and a bony skull. Bird scales can be seen on the legs and feet. These features are not the same as saying every species in each group lays eggs.

C: Arachnida

Arachnids lack antennae. Their anterior appendages include chelicerae and pedipalps rather than the antennae found in insects, centipedes, millipedes and crustaceans.

B: liver

The liver is an organ composed of several tissue types working together. A guard cell is a single cell, blood is connective tissue and a xylem bundle is part of a conducting tissue system.

A: bilateral symmetry

Bilateral symmetry means that one longitudinal plane divides the body into matching left and right halves. A section is a cut through a body, whereas symmetry describes how its parts are arranged.

D: Spirogyra

Spirogyra has a filament of relatively similar photosynthetic cells. Ordinary vegetative cells can grow and participate in reproduction, including conjugation, rather than being separated into the organs of a fern or moss.

C: lenticels

Lenticels are regions in the bark through which gases can pass between internal tissues and the surrounding air. They provide exchange routes through the otherwise relatively impermeable outer tissues of a woody stem.

C: sieve tubes

Sieve tubes are the main conducting pathways in angiosperm phloem for sugars and other organic solutes. Companion cells support their activity but are not the longitudinal sieve-tube conduits.

C: hepatic portal vein

During absorption of glucose from digested yam, blood from the small intestine enters the hepatic portal vein before reaching the liver. This route carries the newly absorbed glucose and can have a higher glucose concentration than the other listed vessels.

C: the stimulation of marrow to produce more erythrocytes

At high altitude, reduced oxygen partial pressure can stimulate erythropoietin signalling and increase red blood cell production in the bone marrow. More erythrocytes increase the blood’s oxygen-carrying capacity during acclimatization.

B: red palm oil and carrots

Red palm oil and carrots supply substantial provitamin A carotenoids, which the body can convert to vitamin A. Ordinary unfortified groundnut oil and rice are much poorer sources; oranges are less concentrated sources than red palm oil.

A: cohesion of water molecules to one another by hydrogen bonds

Hydrogen bonds between water molecules produce cohesion. This helps maintain a continuous column of water in xylem as transpiration creates tension. Attraction to the vessel walls is adhesion, a different interaction.

B: subclavian vein

Lymph returns to the venous circulation near the junctions of the subclavian and internal jugular veins. The main lymphatic ducts discharge there, returning fluid collected from the tissues to the bloodstream.

D: upper part of the oviduct

Human fertilization usually occurs in the ampulla, the widened part of the uterine tube toward the ovary. The early embryo then travels toward the uterus, where implantation normally occurs later.

A: feed on the nectar

Many insects visit flowers to obtain food such as nectar. Pollen can be transferred during feeding, but pollination is a consequence of the visit rather than the insect’s food-seeking purpose.

A: carried above the ground by the elongating hypocotyls

In epigeal germination, elongation of the hypocotyl lifts the cotyledons above the soil. The hypocotyl is the embryonic axis below the cotyledons; the epicotyl lies above them.

C: binary fission

Most bacteria reproduce by binary fission: DNA is copied and one cell divides into two daughter cells. Repeated divisions can rapidly increase a population when conditions support growth.

D: dissolved chemicals → sensory cells → olfactory nerve → brain

Odorant molecules dissolve in nasal mucus and interact with receptors on olfactory sensory cells. Signals then travel through their nerve fibres to brain pathways where the smell is processed.

B: hinge joint

The elbow joint between the upper limb bone and the adjacent forearm bone allows mainly bending and straightening. This is a hinge arrangement, unlike the broad rotation of a ball-and-socket joint.

D: IV

IV points to the radius, one of the two forearm bones. II marks the other forearm bone near its upper projection, III the upper limb bone and I the broad shoulder blade.

D: malaria, bilharziasis and onchocerciasis

Water projects can change mosquito, snail and blackfly habitats. Under suitable local conditions, these changes can increase malaria, schistosomiasis and onchocerciasis risks; the effect is not inevitable at every dam.

B: commensalism

Commensalism describes an interaction in which one participant benefits while the other has no significant effect under the conditions considered. It is represented by the signs + and 0.

C: 2,3 and 7

Primary consumers obtain food directly from the producer. The arrows from plant 1 lead to moth 2, grasshopper 3 and herbivorous bug 7, so those three occupy primary-consumer positions.

D: 5 → 4 → 3 → 1

In the usual upright biomass pattern for a terrestrial food chain, biomass tends to be greater toward the producer level. The feeding chain plant 1 → grasshopper 3 → praying mantis 4 → lizard 5 is therefore read in reverse for increasing biomass.

B: 3

The first cross bb × BB produces Bb offspring. Crossing two of those offspring gives BB, Bb, bB and bb. Bb and bB are the same genotype, so there are three distinct genotypes: BB, Bb and bb.

B: invertebrates as opposed to vertebrates

Invertebrate animal lineages appear in the fossil record before vertebrates. Very old fossil-bearing deposits are therefore more likely to preserve invertebrates than vertebrates, although the actual fossils depend on the environment and preservation.

D: counter shading of coat colour

Countershading affects how an animal is seen by others. It does not directly provide grip or mechanical balance for climbing, unlike limbs, claws and, in many tree-living species, a balancing tail.

D: new species originate through the inheritance of acquired traits

Lamarck proposed that characteristics acquired during an organism’s lifetime could be inherited. This historical idea differs from natural selection acting on inherited variation across generations.

D: warn its chicks and other chickens of impending danger

A hen’s alarm call can alert chicks and other chickens to a nearby predator. The response helps others take cover or remain vigilant and differs from a territorial advertisement.

A: contains the genetic material

The nucleus contains genetic information used to direct protein production and many cellular activities. Its regulatory role comes from that information and its expression, rather than simply its position or enclosing membrane.

D: mantle

The mantle secretes the shell material of a snail, including its calcium-containing mineral layers and organic components. The shell protects the soft body while remaining associated with the mantle tissue.

D: dorso-ventrally flattened body

A cockroach’s flattened body allows it to fit into narrow spaces with little vertical clearance. This helps it hide and move through cracks and crevices that a deeper-bodied animal could not enter.

B: worker

Termite workers are generally pale and soft-bodied compared with the more strongly pigmented reproductive adults and the hardened heads of soldiers. They perform much of the colony’s feeding, care and construction work.

C: rakers

Gill rakers are projections along the gill arches that help retain food particles and protect the delicate gill surfaces. They differ from the filaments and lamellae, which provide large surfaces for gas exchange.

D: Cambium

Cambium is a meristematic tissue whose cells divide to produce new tissues. Vascular cambium can form additional xylem and phloem, contributing to increasing stem thickness.

C: chlorophyll-containing parts

Photosynthetic carbohydrate production requires photosynthetic tissues containing chlorophyll and the associated machinery. Such tissues may occur in leaves and green stems, so it is not restricted to one organ or to flowering plants.

B: a large surface-area-to-volume ratio

A small unicellular organism has much surface area relative to its volume and short internal diffusion distances. These features help substances cross its surface and reach the cell interior without a large transport system.

D: one ventricle and two auricles

The adult frog heart has two atria, also called auricles, and one ventricle. The atria receive blood from different circuits, while the single ventricle pumps blood into the outflow pathways.

B: inferior

The flower parts arise above the swollen ovary in this section. This arrangement places the ovary below their attachment level, so the ovary is described as inferior.

A: I

The corolla is the collective term for the petals. I points to a broad petal in the flower section; the smaller outer lobe and narrow reproductive structures are not the corolla.

D: dry weight

Dry mass estimates the amount of material remaining after water is removed. It therefore avoids temporary changes in water content that can alter fresh size, volume or mass without an equivalent increase in biomass.

B: chorion

The chorion is the outermost extraembryonic membrane in the mammalian conceptus. The amnion encloses the embryo and amniotic fluid, while the yolk sac and allantois have other developmental roles.

C: ganglia

Ganglia are clusters of neurone cell bodies in the peripheral nervous system. Each cell body contains a nucleus. Nerve roots are bundles of processes, while synapses are communication junctions.

A: low soil oxygen

Low oxygen favours denitrification by organisms that use nitrate in anaerobic respiration. This can convert nitrogen compounds into gaseous forms that leave the soil, especially in waterlogged conditions.

C: cycling of nutrients

Soil microorganisms break down organic material and transform nutrient compounds. Their activities help recycle elements into forms that other organisms, including plants, can use.

D: antibodies bind to their corresponding antigens on red blood cells

Agglutination can occur when antibodies bind to their corresponding antigens on red blood cells and link cells together. Compatibility matters because an antibody reacts with its specific target rather than with any different antigen.

C: variation

The chicks have different body masses despite sharing several stated conditions. Differences among individuals of the same species are variation. A single set of masses does not establish their growth rates or the genetic cause of the differences.

A: totality of the expressed traits

Phenotype includes expressed characteristics, such as visible appearance, physiology and biochemical traits. It reflects the interaction of genetic information with environmental influences and is broader than external appearance alone.

C: blood-feeding female mosquitoes, tsetse flies and aphids

Blood-feeding female mosquitoes, tsetse flies and aphids use piercing and sucking mouthparts to obtain liquid food. The other groups include insects with chewing, sponging or siphoning mouthparts.

D: reducing transpiration

Reducing leaves to small scales limits exposed leaf area and can reduce water loss. Green branchlets continue photosynthesis, allowing the plant to obtain carbon while retaining the reduced-leaf form.

B: chromosomes

Mutations change genetic material. Among the listed choices, chromosomes contain that material and can undergo sequence or structural changes. A phenotype may change as a consequence, rather than being the molecular target.

A: Meristem

Meristematic tissue consists of relatively undifferentiated cells that divide to produce new plant tissues. Its cells remain capable of active growth, unlike the more specialised tissues listed.

C: are metamerically segmented

Annelids have repeated body segments, a condition called metameric segmentation. Nematodes are unsegmented roundworms, although they share other general features such as bilateral symmetry and three germ layers.

D: Strobili and inflorescence

Strobili group reproductive structures on an axis, while an inflorescence groups flowers. Both organise reproductive units together, even though their component structures and the plants that bear them differ.

D: is diploid and independent of the gametophyte

The mature fern sporophyte is diploid and can live independently. It produces haploid spores by meiosis. The young sporophyte initially develops on the gametophyte before becoming an independent fern.

C: houseflies, beetles and butterflies

Houseflies, beetles and butterflies pass through egg, larva, pupa and adult stages. The distinct pupal stage is a feature of complete metamorphosis, unlike the nymphal development of cockroaches and grasshoppers.

C: uric acid

Birds eliminate much of their nitrogenous waste as uric acid and urates. These can be excreted with relatively little water, helping conserve water compared with eliminating large amounts of dissolved ammonia.

B: cardiac sphincter

The cardiac, or lower oesophageal, sphincter is at the junction where the gullet enters the stomach. The pyloric sphincter is at the other end, where stomach contents pass toward the duodenum.

D: guttation

Guttation is the release of liquid water from leaf edges or tips, usually through hydathodes. It can occur when root pressure is relatively high and transpiration is low, as in humid conditions.

B: calcium

Calcium ions are required at several stages of the blood-clotting cascade. They help the clotting reactions proceed toward fibrin formation, alongside clotting proteins and platelet-related processes.

C: a smaller amount of usable energy and alcohol

Alcoholic fermentation in yeast yields ethanol and much less usable energy per glucose than aerobic respiration. Only the small ATP yield of glycolysis is obtained, while fermentation regenerates NAD+ for glycolysis to continue.

C: formation of urea

Deamination removes nitrogen-containing amino groups from amino acids. In mammals, the resulting nitrogen can be incorporated into urea for excretion, preventing toxic ammonia from accumulating.

A: pelvic girdle, forelimbs and hindlimbs

The appendicular skeleton includes the limb girdles and the limbs they support. Together, the pectoral girdle, pelvic girdle, forelimbs and hindlimbs form this division of the skeleton.

B: phloem

Companion cells are associated with sieve-tube elements in angiosperm phloem. They provide metabolic support and participate in loading and unloading substances transported through the phloem.

B: adventitious bud

The small new plants arise from buds along the leaf margin. These are adventitious buds because they occur outside the usual shoot-tip and axillary positions, allowing vegetative propagation from the leaf.

D: drupe

Coconut and oil-palm fruits are drupes. Each has a fruit wall differentiated into layers, including a hard inner layer around the seed; coconut also has a conspicuously fibrous outer portion.

C: auxin

Auxin produced near the shoot tip contributes to apical dominance, helping suppress the growth of lateral buds. Removing the tip changes hormonal interactions and can allow side shoots to grow.

D: accommodation

Accommodation is adjustment of the eye’s optical power to focus objects at different distances. Changes in lens curvature help bring light from nearby or distant objects into focus on the retina.

C: anemometer

An anemometer measures wind speed. A wind vane indicates wind direction instead. The other instruments listed measure properties of liquids or underwater visibility rather than wind movement.

B: Rat

The rat receives food from rice and from weevils in the represented web. Eating both plant and animal material makes it an omnivore. The other listed consumers have only plant or only animal food links here.

D: interspecific competition

Competition for a limited shared food supply between different species is interspecific competition. Toads and lizards are different groups, so the interaction is not competition within one species.

C: more rainfall and taller grasses

The Southern Guinea Savanna generally has a wetter climate and taller grass vegetation than the Northern Guinea Savanna. The regional pattern reflects the south-to-north gradient toward drier conditions.

D: sedimentation

Sedimentation separates suspended soil particles by differences in settling behaviour. Under controlled conditions, measurements at suitable times help estimate sand, silt and clay fractions and therefore soil texture.

D: provision of potable drinking water

Access to safe drinking water prevents people from swallowing infected copepods, a major route of Guinea worm transmission. Education and surveillance also help, but protected water supply directly addresses this exposure.

A: mitosis

In a typical unicellular eukaryote reproducing by binary fission, mitosis separates duplicated nuclear chromosomes before the cell divides. This usually preserves the chromosome complement in the daughter cells.

B: introduced quantitative and qualitative elements into his work

Mendel carefully distinguished contrasting traits and counted their occurrence in offspring. Combining controlled crosses with numerical results allowed him to recognise regular inheritance ratios.

B: ¼

Each HbA/HbS parent can contribute HbA or HbS. The four equally likely combinations are HbA/HbA, HbA/HbS, HbS/HbA and HbS/HbS. Only one has no HbS allele, giving a probability of one quarter for each pregnancy.

B: workers, soldiers and reproductives

The main termite caste categories are workers, soldiers and reproductives. The reproductive category includes the king and queen, so it covers roles omitted when only one royal sex is listed.

A: the deposits have remains of organisms characteristic of when they were formed

Fossils in sedimentary deposits can record organisms that lived during the period when those deposits formed. Comparing fossil assemblages through successive layers provides evidence of biological change over time.

B: Mitochondria and chloroplasts

Chloroplasts carry out photosynthesis, while mitochondria support aerobic cellular respiration. A photosynthetic plant cell can contain both and use each organelle for its distinct energy-conversion pathway.

C: produce spores that are dispersed

Fungi and many algae, mosses and ferns form spores that can disperse and develop into new individuals. They do not all contain chlorophyll, and their life cycles do not all use the same reproductive mechanisms.

A: Lymphatic filariasis

Lymphatic filariasis is caused by parasitic worms transmitted by mosquitoes. The mosquito carries infective larvae between people. The other listed diseases use different transmission routes or vectors.

D: Cockroach

Cockroaches enclose their eggs in a protective capsule called an ootheca. Its firm case helps protect the developing embryos and is characteristic of their reproductive biology.

D: Frog

A frog has moist, permeable skin through which oxygen and carbon dioxide can diffuse. This cutaneous respiration supplements lung breathing and is an important part of amphibian gas exchange.

B: feathers which cover the body

Feathers trap air near the body and reduce heat loss, providing insulation. Birds also produce metabolic heat and regulate circulation and behaviour, so feathers support temperature control rather than generating heat themselves.

C: cambium

The vascular cambium produces secondary xylem inward and secondary phloem outward, increasing stem thickness. Cork cambium also contributes to secondary growth by producing protective outer tissues.

A: washed sand

Washed sand provides a comparatively nutrient-poor support medium. Adding defined nutrient solutions with and without nitrogen then helps isolate nitrogen availability while other conditions are kept similar.

B: Vitamin K

Vitamin K is needed for normal production of several functional blood-clotting proteins. It supports the clotting system through a specific protein-modification process, rather than serving as the clot itself.

A: pyruvic acid

Glycolysis splits a six-carbon glucose molecule into two three-carbon pyruvate molecules. It also yields a small net amount of ATP and reduced NAD. Pyruvate then enters other pathways according to cellular conditions.

D: intercellular spaces

Intercellular spaces allow gases to diffuse through plant tissues. Stomata and lenticels provide openings to the outside, while the connected internal air spaces distribute gases among cells.

C: nephridium

Earthworms possess nephridia that help remove metabolic wastes and regulate water and solutes. These excretory organs collect fluid, modify it and discharge waste from the body.

A: contracts and the triceps muscle relaxes

During a simple elbow-flexion movement, the biceps contracts as a flexor while the triceps, its antagonist, relaxes. Their opposing actions allow controlled bending and straightening of the arm.

A: non-illuminated side of the shoot

In a young shoot exposed to light from one side, auxin becomes more concentrated on the shaded side. Greater elongation there bends the shoot toward the light, producing positive phototropism.

B: marginal

In marginal placentation, ovules are attached along the joined margin of a single carpel. The section shows this side attachment rather than a central axis with radiating partitions or a free central column.

C: testa and pericarp are fused

A caryopsis is a dry, one-seeded fruit in which the seed coat is closely fused with the fruit wall. Cereal grains are examples. This fusion distinguishes it from fruits whose seed coat and pericarp remain separate.

C: fertilization

In the usual human XX/XY model, the egg and sperm chromosome complements combine at fertilisation. An X-bearing egg joins an X- or Y-bearing sperm, establishing the zygote chromosome complement at that stage.

C: cerebellum

The cerebellum helps coordinate movement, balance and timing, all of which are important for walking smoothly. Walking also involves the cerebral cortex, brainstem, spinal circuits and sensory feedback.

B: thyroid gland

Thyroid hormones influence basal metabolic rate and are important for growth and development. Their effects occur across many tissues, whereas the other glands listed have different principal functions.

D: motor neurone

The cell has a long extension ending on muscle fibres, showing a pathway that carries commands to an effector. A motor neurone transmits signals toward muscles, unlike incoming sensory or afferent pathways.

B: cell body

X points to the region surrounding the nucleus from which the branches and long extension arise. This is the cell body, or soma, which contains organelles supporting the neurone’s activities.

B: secchi disc

A Secchi disc estimates water transparency by recording the depth at which the disc disappears from view. It provides an indicator of underwater visibility, rather than a direct measurement of all light at every depth.

D: secondary consumer gets only a small portion of the energy captured by the primary producer

Only part of the energy at one feeding level becomes available to the next. Organisms use energy in metabolism and release heat, and not all biomass is consumed or assimilated, so less reaches secondary consumers.

C: shade-loving species

Many terrestrial ferns in a tropical rainforest grow in the shaded understory. Their habitat differs from canopy epiphytes and the tall trees that form the upper canopy or emergent layer.

C: primary succession

Primary succession begins on a surface without an established soil community, such as newly exposed bare rock. Pioneer organisms contribute to changes that can eventually allow other species to establish.

B: Targeted application of approved molluscicides by trained programme staff

Freshwater snails are intermediate hosts of schistosome parasites. Professionally managed snail-control programmes can use approved molluscicides to reduce transmission, alongside sanitation, safe water and other public-health measures.

A: Tuberculosis, gonorrhoea and syphilis

Tuberculosis, gonorrhoea and syphilis are caused by bacteria. AIDS results from infection with HIV, and poliomyelitis is caused by poliovirus, so sets containing either of those are not entirely bacterial.

B: genetic and environmental factors

Human height reflects inherited variation as well as environmental influences such as nutrition and illness during growth. The measured height is a phenotype resulting from those interacting influences.

D: nucleotides

DNA is a polymer of nucleotides. Each nucleotide contains a sugar, a phosphate group and a nitrogenous base; the nucleotides join to form the strands of the DNA molecule.

C: 2N

A diploid cell contains two sets of chromosomes, conventionally written 2N or 2n. N denotes one set. The actual number differs among species, so a fixed count such as 23 is not a universal somatic-cell number.

B: tonoplast

The tonoplast is the membrane enclosing a plant cell vacuole. It helps control exchanges between the vacuole and cytoplasm, supporting storage, ion balance and the development of turgor pressure.

D: gizzard

The earthworm gizzard has muscular walls that grind swallowed material, often using ingested grit. The resulting material passes into the intestine, where digestion and absorption continue.

C: contractile vacuole

The contractile vacuole collects and expels excess water from a freshwater amoeba. Water enters by osmosis, and periodic expulsion helps prevent excessive swelling while maintaining internal water balance.

A: biting and chewing

A cockroach has mandibulate mouthparts suited to biting and chewing solid food. This differs from the piercing and sucking apparatus of a mosquito or the specialised sucking mouthparts of some other insects.

A: I

The small outward projections at I are root hairs. They increase the surface area in contact with soil, helping the root absorb water and dissolved mineral ions efficiently. The broad inner tissue has a different role.

B: II

II points to the broad cortex region of the root. Its parenchyma cells can store starch. The outer surface is specialised for uptake, while the central tissues principally support transport.

D: dog

The formula gives three incisors, one canine and four premolars on each side of both jaws, with two upper and three lower molars. This is the typical adult dog formula and totals 42 teeth.

A: nitrites

Nitrosomonas oxidises ammonia or ammonium to nitrite in the first stage of nitrification. Other nitrifying organisms can then oxidise nitrite to nitrate, which plants can use as a nitrogen source.

D: acid

Ptyalin is salivary amylase, which works well near neutral pH. Increasing acidity sufficiently lowers its activity because the altered chemical environment disrupts conditions needed for effective starch breakdown.

A: food storage

Phloem parenchyma consists of living cells that can store organic substances such as starch. Long-distance sugar transport mainly occurs through sieve elements, while water transport is chiefly associated with xylem.

D: haemolysis

Haemolysis is rupture of a red blood cell with release of its contents. Distilled water can cause this by entering the cell osmotically, but osmosis names the water movement rather than the final rupture.

A: Carbon dioxide

Carbon dioxide produced during respiration can diffuse out of plant tissues through stomata and lenticels. These openings exchange gases; non-volatile compounds such as tannins and alkaloids do not leave through them as respiratory gases.

C: before fertilization

In the usual animal sexual life cycle, meiosis produces haploid gametes before fertilisation. Fertilisation then combines two gametes and restores the diploid chromosome number in the zygote.

C: thalamus

The thalamus, also called the floral receptacle, is the enlarged end of the flower stalk on which floral organs are borne. The calyx consists of sepals, while the hypothalamus is a part of the vertebrate brain.

B: in front of the retina

In myopia, parallel rays from a distant object are brought to a focus in front of the retina when the eye is uncorrected. The light is therefore out of focus when it reaches the retinal surface.

C: The dog’s body temperature is approximately independent of the external temperature

Over the range represented, the dog maintains an approximately constant body temperature while the lizard temperature rises with the surroundings. This illustrates different patterns of temperature regulation within the plotted conditions.

D: medulla oblongata

The medulla oblongata contains centres involved in regulating breathing and cardiovascular activity. These support vital involuntary functions, working with other brain regions and sensory feedback.

B: a community

A community consists of populations of different species living in the same area. Mango, speargrass, goats and sheep represent different living species, whereas an ecosystem also includes their physical surroundings.

B: Mushrooms, Rhizopus and bacteria

Many fungi, including mushrooms and Rhizopus, and many bacteria release enzymes onto dead organic material and absorb the breakdown products. This external digestion makes them major decomposers in ecosystems.

C: 1 → 4 → 5 → 3 → 2

The represented chain starts with grasses, followed by grasshoppers that eat them, lizards that eat grasshoppers, snakes that eat lizards and hawks that eat snakes. Food-to-consumer arrows preserve this feeding order.

D: climax community

In the classical model of succession, a climax community is a relatively stable community reached after successive changes in species composition. Continued stability depends on environmental conditions and disturbance.

A: reduced biochemical activities

Water stress can reduce photosynthesis and other biochemical activities, slowing plant growth. Stomatal closure limits water loss but can also reduce carbon dioxide entry, while dehydration affects cellular processes.

A: diversity

Diversity describes the variety among living organisms, including differences in structures, functions and inherited characteristics. Shared features also help organise organisms into related groups.

C: Both parents have brown eyes

In the stated single-gene model, a BB child must receive B from each parent, while a bb child must receive b from each. Both parents must therefore be Bb and show the dominant brown-eye phenotype in this model.

C: haemophilia

Haemophilia is an inherited bleeding disorder caused by deficiency of particular clotting factors. Common forms are X-linked and can cause prolonged bleeding, though the severity varies among affected people.

A: mangrove swamp

Breathing roots, or pneumatophores, project above waterlogged soil and allow gas exchange with the air. They help certain mangroves obtain oxygen when the surrounding mud has little available oxygen.

B: the underlying pentadactyl limb pattern, modified in different groups

The shared underlying limb pattern in these vertebrates is evidence of common ancestry. The structures have been modified for swimming, grasping, flying or running, but comparable bones remain recognisable.

C: Chromosomes

Genes are units of hereditary information carried in DNA organised into chromosomes. Ribosomes translate genetic messages, while the Golgi apparatus and endoplasmic reticulum handle production or processing of cellular materials.

B: conifers

Conifers are gymnosperms and produce seeds not enclosed within an ovary-derived fruit. Grasses, legumes and palms are flowering plants, whose seeds develop within fruits. Naked does not mean lacking a seed coat.

D: Presence of a vascular system

Pteridophytes possess vascular tissues for water and food transport, while bryophytes lack a true xylem-and-phloem system. Both groups lack flowers and have alternating generations, and their motile sperm need water for fertilisation.

C: Chloroplasts

In a typical green fern life cycle, both the leafy sporophyte and the small gametophyte photosynthesise and contain chloroplasts. The gametophyte has rhizoids, while the sporophyte has true roots and leaves.

B: Euglena

A typical photosynthetic Euglena is a single cell with chloroplasts and a flagellum. It can carry out photosynthesis, movement and the other life processes within that cell. Spirogyra forms filaments rather than this flagellated unicellular body.

C: Rattus

Rattus is the rat genus, and rats store carbohydrate as glycogen, particularly in liver and muscle. The listed green algae and mango plant instead use starch as their principal storage polysaccharide.

B: Arthropoda

Arthropoda includes insects, arachnids, crustaceans and other joint-legged animals. It contains more described animal species than any other phylum, largely because of the enormous diversity of insects.

D: it pollinates flowers of crops and other plants

Butterflies can transfer pollen between flowers as they visit them. This supports fertilisation and seed or fruit production in plants they pollinate, giving them an important ecological and agricultural role.

B: phloem

Phloem transports organic products of photosynthesis, especially sugars, from source regions to sinks where they are used or stored. Xylem chiefly carries water and mineral nutrients from roots.

D: fatty acids and glycerol

Complete hydrolysis of a triglyceride releases its glycerol backbone and three fatty acids. During intestinal digestion, partial products such as monoglycerides also occur before absorption and further processing.

A: excretory materials from tissues

Blood carries metabolic waste products away from tissues toward organs that remove them. It also supplies oxygen and nutrients, but the directions given for those substances in the other alternatives are incorrect.

D: to remove excess water

A contractile vacuole collects excess water and expels it from the cell. This is especially important for freshwater protists, which continually gain water by osmosis because their surroundings are more dilute.

D: geotropism

Geotropism, also called gravitropism, is directional growth in response to gravity. Roots usually grow toward gravity, while shoots grow away from it. Light, water and touch are different directional stimuli.

C: Atlas → axis → remaining cervical → thoracic → lumbar → sacral

The atlas and axis are the first two cervical vertebrae. Moving toward the tail, they are followed by the remaining cervical vertebrae, then the thoracic, lumbar and sacral regions.

C: courtship

The conspicuous feathers and displays of a peacock act as courtship signals. Such traits can influence mate choice and are examples of sexual selection, rather than simply features for human appreciation.

A: attract pollination agents

Petals often provide colour, scent or visual patterns that attract animal pollinators. Some also provide a landing surface. Sepals usually protect the developing flower while it is still enclosed in the bud.

A: sympathetic and parasympathetic systems

The sympathetic and parasympathetic divisions are the two principal divisions traditionally described in the autonomic nervous system. They regulate involuntary functions such as heart activity and digestion.

B: the hypocotyl grows faster than the epicotyl

In epigeal germination, elongation of the hypocotyl lifts the cotyledons above the soil. In hypogeal germination the cotyledons remain below ground while the epicotyl extends upward.

B: constrict to reduce the amount of blood flowing to the skin

When the body is cold, constriction of small blood vessels supplying the skin reduces skin blood flow. Less warm blood reaches the surface, helping reduce heat loss to the surroundings.

C: Eardrum → ossicles → oval window

Sound causes the eardrum to vibrate. These vibrations pass through the middle-ear ossicles to the oval window, where they generate pressure waves in the fluid of the inner ear.

A: The level of blood sugar would increase

The pancreas supplies insulin, which helps regulate blood glucose by promoting its uptake and storage. Removing the pancreas without replacement insulin removes this control and can cause blood glucose to rise.

B: Tertiary consumers

A persistent pollutant that biomagnifies can become more concentrated at successive feeding levels. Tertiary consumers feed above primary and secondary consumers, so they may have the greatest concentration among these levels.

A: Microscope

A microscope magnifies small structures rather than directly measuring an abiotic habitat condition. A thermometer measures temperature, a hygrometer humidity and a wind vane wind direction.

C: halophytes

Halophytes are plants adapted to saline conditions, including salt marshes. Their adaptations can include excluding salt, secreting it or storing it in tissues while maintaining water uptake.

B: crop rotation and cover crops

Rotating crops and using cover crops can maintain soil structure, protect the surface and return organic material. Including suitable legumes may also add biologically fixed nitrogen to the cropping system.

C: combining with haemoglobin

Carbon monoxide binds to haemoglobin, forming carboxyhaemoglobin. This reduces effective oxygen transport and delivery to tissues. The resulting oxygen deprivation is a major mechanism of carbon monoxide toxicity.

B: Tongue rolling

When tongue rolling is recorded simply as can roll or cannot roll, the observations fall into separate categories. Height and body weight vary across a range, and skin pigmentation is also a quantitative trait.

B: 1 homozygous smooth : 2 heterozygous smooth : 1 wrinkled

The four cells contain SS, Ss, sS and ss. Ss and sS are the same heterozygous genotype, giving one homozygous smooth, two heterozygous smooth and one homozygous wrinkled entry.

A: poikilothermic

Poikilothermic describes an animal whose body temperature varies substantially. This differs from homeothermy, in which body temperature is relatively stable. Heat source and temperature variability are related but distinct classifications.

D: mitochondrion

Mitochondria carry out major stages of aerobic cellular respiration and produce much of a cell’s ATP. Glycolysis occurs in the cytosol, so mitochondria are not the site of every reaction involved in respiration.

D: Prothallus → spermatozoid + egg cell → leafy plant → sporangium → spore

The prothallus is the fern gametophyte and produces sperm and eggs. Fertilisation gives a zygote that develops into the leafy sporophyte, whose sporangia produce spores. Each spore can grow into another prothallus.

B: is diploblastic, tapeworm is triploblastic

Hydra develops from two principal embryonic germ layers and is described as diploblastic. A tapeworm, a flatworm, has three germ layers including mesoderm and is triploblastic. This is a structural developmental difference.

A: oesophagus

Structure X is the channel through which food is carried inward after entering the oral region. Its transport role resembles the human oesophagus, which passes swallowed material toward the stomach rather than carrying air.

C: macronucleus

Y points to the large macronucleus of Paramecium. It supports the organism’s everyday cellular activities. The small micronucleus is distinct, while food and contractile vacuoles perform digestive and water-balance functions.

B: Termite

Termites develop through immature stages that resemble the adult body plan without a pupal stage. Mosquitoes, houseflies and moths pass through larva and pupa stages, which is complete metamorphosis.

B: has a reduced stem and thick fleshy leaves

An onion bulb consists of a short reduced stem surrounded by thick fleshy leaf bases that store food. These storage leaves distinguish a bulb from a solid swollen stem such as a corm.

D: guard cells

Guard cells change shape as their turgor changes, opening or closing the stomatal pore. This regulates gas exchange and loss of water vapour from the leaf; the pore itself is the passage rather than the controlling cell pair.

D: lack chlorophyll

Fungi do not possess chlorophyll for photosynthesis and obtain organic nutrients from other sources. Having no leaves or roots is not enough to establish heterotrophy, since some photosynthetic organisms also lack those organs.

D: protein

In the Biuret test, copper ions in alkaline solution form a violet complex with peptide bonds. A purple result therefore indicates protein or sufficiently long peptides, unlike the tests used for sugars, starch or fats.

C: hepatic portal vein

The hepatic portal vein carries blood from much of the digestive tract to the liver. This allows absorbed nutrients and other substances to be processed before the blood enters the wider systemic circulation.

C: ethanol

During alcoholic fermentation in yeast, pyruvate is decarboxylated to acetaldehyde, releasing carbon dioxide. Acetaldehyde is then reduced to ethanol, regenerating NAD+ so glycolysis can continue.

B: Malpighian tubule

Malpighian tubules remove nitrogenous wastes and other solutes from insect body fluid and deliver them to the gut. Subsequent water recovery helps conserve water, especially in terrestrial insects.

C: atlas

The atlas is the first cervical vertebra and supports the skull through its articulation with the occipital condyles. The axis below it provides a pivot that helps the head turn.

D: Amylase, lipase and trypsinogen

The pancreas secretes amylase for starch digestion, lipase for fat digestion and trypsinogen, the inactive precursor of trypsin. Trypsinogen is activated after reaching the small intestine.

B: formation of an embryo and the endosperm

In angiosperm double fertilisation, one sperm fuses with the egg to form the zygote, while another fuses with the central cell to initiate endosperm. These lead to the embryo and its associated nutritive tissue.

A: supply nutrients to the embryo

In egg-laying mammals, yolk provides stored nutrients for the developing embryo. It is a food reserve rather than an air supply, a shock-absorbing fluid or the main route for removing wastes.

D: elongation of the epicotyl

In hypogeal germination, the cotyledons remain below the soil. Growth of the epicotyl carries the young shoot upward. In epigeal germination, elongation of the hypocotyl instead raises the cotyledons.