JAMB Biology 1990 Past Questions & Explanations

Brackish environments have a mixture of saltwater and freshwater. During the dry season, there is reduced rainfall and increased evaporation, which concentrates the salt content in the water body, thus increasing salinity. Option A is incorrect because rain dilutes salinity. Option B is vague and doesn't represent peak salinity. Option C is incorrect because micro-organism abundance does not directly decrease salinity.

Aestivation is the physiological adaptation where animals enter a dormant state during extended dry periods to conserve water and energy. Hibernation (A) occurs in winter, not specifically for dry conditions. Rejuvenation (C) is renewal, not an adaptation. Xeromorphism (D) refers to morphological (structural) adaptations in plants to dry conditions, not physiological adaptations in animals.

Malaria is spread by mosquitoes, river blindness (onchocerciasis) is spread by blackflies, and cholera can be associated with water-borne transmission but has insect vector involvement. Option A includes taenia (tapeworm, food-borne) and gonorrhoea (sexually transmitted). Option B lists diseases spread by droplet/contact, not insect vectors. Option C includes tuberculosis which is airborne. Option D best represents insect-vector diseases.

Pollution is the introduction of harmful substances or noise into the environment. Loud disco sound is noise pollution that negatively impacts the environment and organisms. Option A (bird droppings) is a natural occurrence. Option C (cigarettes) is a product, not pollution itself. Option D (refuse in an incinerator) is being properly disposed of through controlled burning, not constituting pollution.

Flocculation improves acidic soil by promoting soil aggregation and reducing acidity through the action of calcium and magnesium ions that neutralize hydrogen ions. Sedimentation (A) is particle settling, not soil improvement. Leaching (B) removes minerals, worsening acidic soil. Watering (D) alone does not improve soil acidity; it may temporarily dilute but doesn't address the root cause.

Denitrifying bacteria convert nitrates back to nitrogen gas ($N_2$), releasing free nitrogen into the atmosphere. Nitrogen-fixing bacteria (A) convert atmospheric nitrogen to usable forms. Nitrifying bacteria (B) convert ammonia to nitrites and nitrates. Saprophytic bacteria (D) decompose organic matter but do not specifically release free nitrogen.

The gametophyte is the haploid generation that produces gametes through sexual organs (gametangia). Sex organs are characteristic of gametophytes in plants with alternation of generations. The rhizoid (B) is a root-like structure for attachment and absorption, not for reproduction. The protonema (C) is the filamentous structure in moss development. The sporophyte (D) produces spores, not sex organs.

Viruses possess transmittable characters (genetic material that can be passed on), which is a key characteristic of living organisms. This demonstrates inheritance and variation. Option B is incorrect because many viruses do not move independently. Option C is problematic because viral response to stimulation is indirect and debated. Option D is incorrect because viruses do not ingest food; they lack metabolism and require host cells.

Both Amoeba and Paramecium possess contractile vacuoles, which are organelles that regulate water balance by collecting and expelling excess water from the cell. This is essential for osmoregulation in freshwater protozoans. Option A (oral groove) is specific to Paramecium. Option B (trichocyst) is specific to Paramecium for defense. Option D (cilia) are characteristic of Paramecium but Amoeba uses pseudopodia for movement.

Hydra has a single opening called the hypostome (mouth), which serves both as an entrance for food and an exit for undigested waste. Undigested food particles are egested through the same mouth opening. Option A is incorrect because Hydra lacks an anus. Option C is incorrect because contractile vacuoles are cellular organelles, not involved in organism-level waste removal. Option D is incorrect because Hydra does not have specialized surface pores for egestion.

Coelenterata (now called Cnidaria), which includes organisms like Hydra and sea anemones, reproduce asexually by budding. A small outgrowth develops on the parent organism and eventually detaches as a new individual. Arthropoda (A) includes insects, crustaceans, and arachnids that reproduce sexually. Annelida (B) are segmented worms that reproduce sexually. Mollusca (C) includes snails, clams, and octopuses that primarily reproduce sexually.

Algae, bryophytes (mosses and liverworts), and pteridophytes (ferns) all require moisture/water for sexual reproduction because their sperm are flagellated and must swim through water to reach the egg. Option A is incorrect because not all are seaweeds (algae can be freshwater, bryophytes and pteridophytes are terrestrial). Option B is incorrect because pteridophytes have vascular tissue (xylem and phloem). Option D is incorrect because many forms are visible to the naked eye.

Fern spores are dispersed primarily by wind. Spores are tiny, light, and produced in large numbers in sporangia (spore cases) on the underside of fronds. When mature, sporangia release spores that are carried by air currents. Option B (water) is not a primary mechanism for fern spore dispersal. Option C (insects) is not a major vector for spore dispersal. Option D (explosive mechanism) occurs in some plants but not typically in ferns.

Homodont dentition means all teeth are of the same type and shape. Lizards have homodont dentition—all their teeth are similar conical teeth used for gripping prey. Rats have heterodont dentition with incisors, canines, and molars of different shapes. Man also has heterodont dentition with incisors, canines, premolars, and molars. Pigeons have no teeth at all; they use a gizzard for grinding food.

External fertilization occurs when gametes (sperm and egg) are released into the environment and fertilization happens outside the female's body. Toads are amphibians that lay eggs in water where external fertilization occurs. Lizards, birds, and cockroaches are all terrestrial or internal fertilizers—they have internal fertilization where sperm meets egg inside the female's reproductive tract.

The scolex is the head region of a tapeworm. The suckers (and sometimes hooks) on the scolex are attachment structures used to grip and hold fast to the intestinal wall of the host. This prevents the parasite from being washed away by intestinal contents. Tapeworms absorb nutrients across their body surface, not through sucking blood. The reproductive organs are located in the proglottids (body segments), not the scolex. Tapeworms do not use suckers for locomotion.

Light bones (hollow or pneumatic bones) are a crucial adaptation for flight in birds. They reduce body weight while maintaining structural strength, allowing birds to achieve the low body mass needed for sustained flight. Scaly legs and two walking legs are not flight adaptations—they are shared with reptiles and other animals. A pointed beak is useful for feeding but is not specifically an adaptation for flight itself; many non-flying animals also have pointed beaks.

Nephridia are the excretory organs of earthworms and other invertebrates. They function to filter metabolic wastes (particularly nitrogenous wastes like ammonia and urea) from the coelom and blood, then expel these wastes through nephridiopores. While nephridia may be located near reproductive organs, they are not part of the reproductive system. They have no role in respiration or circulation.

Houseflies are mechanical vectors for many bacterial and viral diseases including dysentery (caused by bacteria), typhoid fever (caused by Salmonella bacteria), and poliomyelitis (caused by poliovirus). They transmit these pathogens on their bodies and through their faeces. Yellow fever, however, is an arboviral disease spread primarily by mosquitoes (particularly Aedes aegypti), not houseflies. Houseflies play a negligible role in yellow fever transmission.