JAMB Biology 1992

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.

D: parthenocarpic

A parthenocarpic fruit develops without fertilisation. It normally lacks developed seeds. False, multiple and aggregate describe other aspects of fruit origin and do not specify fertilisation-independent development.

A: sensory neurons

Sensory neurons carry information from receptors toward the central nervous system. They report conditions at the body surface and within organs. Motor or efferent neurons carry commands outward, while relay neurons connect other neurons.

A: It persists until the environment or climate changes

In the classical succession model, a climax community is relatively stable while its environmental conditions remain similar. Disturbance or climatic change can alter it; stability does not mean every organism or population remains unchanged.

D: H

H is the top tier of the represented energy pyramid. Less energy is available at successive feeding levels because organisms use energy and release much of it as heat. The highest tier therefore represents the smallest energy supply.

B: Shark

In the represented chain, algae are producers, the tadpole is the primary consumer and tilapia the secondary consumer. The shark occupies the next feeding level, so it is the tertiary consumer in this model.

B: clay

Clay is the finest of the listed soil particle-size fractions. Silt particles are larger than clay, sand particles larger still, and gravel consists of much coarser fragments. Soil texture depends on the proportions of these sizes.

A: parasite products released when infected red blood cells rupture, triggering inflammation

When infected red blood cells rupture, parasite products enter the blood and stimulate inflammatory signals, including cytokines. These responses contribute to fever and chills in malaria. The symptomatic blood stage differs from the initial liver infection.

C: All their daughters will be carriers

For X-linked haemophilia, the father passes his affected X chromosome to every daughter and his Y chromosome to every son. A non-carrier mother supplies an unaffected X, so all daughters are heterozygous carriers and sons do not inherit the father’s affected X. Carrier daughters can still have bleeding symptoms.

C: 2RR, 2Rr

The RR parent contributes only R gametes, while the Rr parent contributes R or r. The expected offspring genotypes are RR and Rr in equal proportions. A four-cell Punnett square therefore gives two RR and two Rr entries.

B: uncontrolled out-crossing can introduce unwanted variability

Seeds formed after cross-pollination can inherit alleles from an uncontrolled pollen parent. Recombination and segregation can therefore produce offspring that differ from a desirable parent instead of faithfully cloning its traits.

C: DNA

DNA carries hereditary information in cells. Its nucleotide sequence encodes information that can be replicated and passed to daughter cells. RNA participates in gene expression, while proteins and carbohydrates have other major cellular roles.

A: fleshy tissues and reduced leaves

Fleshy tissues can store water, and reduced leaves can limit the surface available for water loss. Together these features help some plants persist in dry environments, although xerophytes use many different combinations of adaptations.

B: Darwin and Wallace

Charles Darwin and Alfred Russel Wallace independently developed explanations of evolution by natural selection. Their work linked differences in survival and reproduction to heritable variation within populations.

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

Sedimentary layers can preserve remains of organisms that lived when the deposits formed. Comparing fossils in successive layers reveals changes through time and helps reconstruct the history of life.