Biology 2025 Jamb Examination

Lichen is a classic example of mutualism, a type of symbiotic relationship where both organisms benefit. The fungus provides a physical structure, protection from the environment, and absorbs water and minerals for the pair. In return, the alga (or cyanobacteria) performs photosynthesis to produce organic food (carbohydrates) which it shares with the fungus. Neither can easily survive alone in the harsh environments where lichens typically grow.

Pepsin is a protease enzyme produced in the stomach that breaks down proteins into smaller peptides. It is specifically adapted to work in a highly acidic medium, with an optimal pH of approximately 1.5 to 2.5. This acidity is provided by the hydrochloric acid (HCl) secreted by the gastric glands in the stomach lining. In an alkaline or neutral environment, such as the small intestine, pepsin becomes inactive.

An epidemic disease is one that spreads rapidly and affects a large number of people in a community or region within a short period. Cholera is a major epidemic disease in Nigeria, often occurring in outbreaks linked to contaminated water and poor sanitation. While malaria and schistosomiasis are 'endemic' (constantly present in the population), and polio is a targeted disease for eradication, cholera's tendency for sudden, massive outbreaks defines it as an epidemic threat.

Camels have large, flat, spreading feet with two toes joined by a web of skin. This enlarged foot surface acts like a snowshoe, distributing the camel's heavy weight over a wider area. By increasing the surface area, the pressure exerted on the sand is reduced (Pressure = Force/Area), preventing the camel from sinking into the soft desert dunes while walking.

Amphibians like the Toad utilize buccal respiration (also called buccal pumping). In this process, the animal moves the floor of its mouth (buccal cavity) up and down to draw air in through the nostrils and push it into the lungs. This is one of the three ways toads breathe, alongside cutaneous (skin) and pulmonary (lung) respiration. Fish use gills, birds use lungs with air sacs, and grasshoppers use a tracheal system.

In an ecosystem, factors are divided into abiotic (non-living) and biotic (living). Since pests (like insects or rodents) and diseases (caused by bacteria, fungi, or viruses) are living organisms or are caused by them, they are classified as biotic factors. These factors directly influence the survival and population dynamics of other organisms through interactions like parasitism and competition.

Sickle cell anaemia is a genetic disorder where the haemoglobin molecule is abnormal, causing red blood cells to take on a rigid, sickle (crescent) shape. These distorted cells can get stuck in small blood vessels, hindering the free flow of blood and causing pain and organ damage. Haemophilia is a bleeding disorder, while albinism and colour blindness affect pigmentation and vision, respectively.

In a standard Mendelian monohybrid cross (e.g., Tt x Tt), the second filial (F\(_2\)) generation typically results in three different genotypes. The genotypic ratio is 1 : 2 : 1, representing 1 homozygous dominant (TT), 2 heterozygous (Tt), and 1 homozygous recessive (tt). Note that the phenotypic ratio would be 3:1 (Tall:Short), but the question specifically asks for the genotypic ratio.

In an open circulatory system, which is common in arthropods like insects and most molluscs, the blood (haemolymph) is not entirely contained within vessels. Instead, it is pumped into a large body cavity called the haemocoel, where it directly bathes the internal organs. Veins, arteries, and arterioles are characteristic of a closed circulatory system, where blood remains confined within vessels.

A long beak with saw-like edges (serrations) is an adaptation found in certain fish-eating birds, such as the merganser (often associated with the 'duck' family in general biology classifications) or specific species of kingfishers. These serrations help the bird maintain a firm grip on slippery prey like fish. While ducks have filter-feeding lamellae and woodpeckers have chisel-like beaks, the saw-like edge is a specific predatory adaptation for gripping.