JAMB Biology 1990

A: possess transmittable characters

Viruses contain genetic material whose characteristics can pass to new virus particles when they replicate inside suitable host cells. Heredity is a life-associated property, although viruses do not carry out independent cellular metabolism.

C: Contractile vacuole

Freshwater Amoeba and Paramecium possess contractile vacuoles that collect and expel excess water. This helps maintain water balance as water enters from their relatively dilute surroundings.

B: passing it through the mouth

Hydra has a gastrovascular cavity with a single opening. Food enters through this mouth, and undigested remains leave through the same opening because there is no separate anus.

D: Coelenterata

Hydra and several other cnidarians form buds that develop into new individuals. Coelenterata is the older grouping name used here for these familiar budding animals.

A: gametophyte

The gametophyte is the haploid generation that bears sex organs in bryophytes. These organs produce gametes; the dependent sporophyte instead produces spores following meiosis.

C: Lizard

Some lizards have numerous similarly shaped teeth, the homodont pattern. Humans and rats have differentiated tooth types, while a pigeon has a toothless beak rather than homodont dentition.

A: Toad

In typical toads, eggs are released into water and fertilised outside the female’s body as the male releases sperm. The other listed animals normally use internal fertilisation.

B: holding fast to the host

The suckers on a tapeworm’s scolex anchor it to the host’s intestinal wall. The worm absorbs nutrients through its body surface; the suckers are attachment structures rather than mouths for sucking blood.

D: excretory system

Earthworm nephridia collect fluid, reclaim useful substances and eliminate metabolic wastes. They form the excretory system rather than the reproductive, respiratory or circulatory system.

A: Yellow fever

Yellow fever is a viral infection transmitted by infected mosquitoes, not by houseflies. Houseflies can mechanically contaminate food or surfaces, a different transmission route from mosquito inoculation.

B: Sieve tube

Sieve-tube elements are living conducting cells with primary walls. At maturity they lose their nuclei and depend on companion cells. Collenchyma remains living but has unevenly thickened walls, while mature vessels and sclerenchyma are generally dead.

A: activation of the chlorophyll

Photosynthesis begins when pigments absorb light and their electrons become excited. This supplies energy for the light reactions; water splitting and the subsequent carbon-fixation reactions depend on this initial capture of light energy.

C: pancreas

The pancreas has both exocrine and endocrine functions. It releases digestive enzymes into the small intestine and hormones such as insulin and glucagon into the blood. These secretions use different routes.

A: increases the surface area for absorption

Villi are projections of the intestinal lining that provide a large surface for nutrients to enter the body. Blood capillaries and lacteals within them carry away absorbed materials, helping maintain uptake.

D: movement of mineral salts is hardly affected

Removing a ring of bark interrupts phloem transport of sugars. If the deeper xylem remains intact, its initial upward transport of water and dissolved mineral salts can continue, although later root starvation damages the plant.

C: potometer

A bubble potometer follows movement of an air bubble as a shoot takes up water. Under suitable conditions this uptake estimates water lost through transpiration, though some absorbed water is retained or used by the plant.

C: anthocyanins

Anthocyanins are pigments that can give flowers red, purple or blue colours. Their colour depends partly on chemical structure, acidity and interactions with other substances; they are useful pigments rather than simply excretory waste.

D: light

Etiolation occurs when seedlings develop with insufficient light. They typically become pale and elongated as normal light-dependent development is limited. Adequate light promotes greening and a more compact growth pattern.

C: tendons

Tendons connect skeletal muscles to bones and transmit the force of contraction. Ligaments chiefly connect bone to bone at joints, helping stabilise them rather than serving as the normal muscle attachment.

C: placenta

During human pregnancy, the placenta produces substantial progesterone and oestrogens that help sustain pregnancy. The umbilical cord provides the connection to fetal circulation, while the amnion and amniotic fluid protect the developing fetus.

A: parietal

The placentae arise from the inner wall of a single ovary cavity. This wall-based arrangement is parietal placentation. There is no central column or set of internal partitions meeting at a central axis.

B: parthenocarpic

Parthenocarpy is fruit development without fertilisation. Such fruits generally lack normally developed seeds. Simple, aggregate and compound instead describe how fruits arise from flowers or ovaries.

C: suckers

Elephant grass can be established from rooted basal shoots or clump divisions, often called slips or suckers. These retain living buds and roots that develop into new plants; stem cuttings are another propagation method.

A: semicircular canals

The semicircular canals detect rotational movements of the head and contribute to balance. Other vestibular structures detect tilt and linear acceleration. The incus and malleus transmit sound vibrations rather than detecting balance.

C: 8

Normal meiosis halves the chromosome number when producing gametes. A diploid cell with 2n = 16 therefore produces haploid gametes with n = 8 chromosomes, one chromosome from each homologous pair.

D: F1 all normal-winged; three quarters of F2 normal-winged

Let N represent the dominant normal-wing allele and n the short-wing allele. NN × nn gives only Nn offspring with normal wings. Crossing Nn × Nn gives NN, Nn, Nn and nn, so the expected normal-winged proportion is three quarters.

C: anaphase

The chromosomes are separated into two groups moving toward opposite poles. This is anaphase, when sister chromatids separate in mitosis. They are no longer lined up together at the equator and new nuclei have not yet formed.

D: there are no anti-A and anti-B antibodies in the serum

In the ABO system, group AB plasma lacks anti-A and anti-B antibodies. It therefore does not attack donor red cells solely because they carry A or B antigens. Other compatibility factors still need consideration in real transfusions.

B: water, temperature and soil

Abiotic factors are non-living physical and chemical parts of an environment. Water, temperature and soil all fit this category; organisms such as plants and reptiles are biotic components.

C: Mouse

The mouse receives food from maize and from animals in the stated web. Eating both plant and animal material makes it an omnivore. The grasshopper is a plant eater, while the mantis and hawk receive animal food.

D: increases during the dry season

During a dry season, reduced freshwater input and evaporation can concentrate the salts in brackish water. Rainfall generally dilutes salts, so the seasonal effect depends on the balance of water inputs and losses.

B: aestivation

Aestivation is a period of reduced activity and metabolism that helps some animals survive hot or dry conditions. It conserves resources while conditions are unsuitable; it is one adaptation rather than a name for every dry-environment trait.

C: denitrifying bacteria

Denitrifying microorganisms reduce oxidised nitrogen compounds such as nitrate, releasing gases that can include nitrogen gas. Nitrogen fixation moves atmospheric nitrogen into biologically usable compounds, the opposite overall direction.