JAMB Biology 1995

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.