Biology 2023 Jamb Examination

Sexual reproduction requires the fusion of male and female gametes, such as sperm and egg cells, from two parents. This process results in genetic recombination, producing offspring with genetic variation. Asexual reproduction, in contrast, involves a single parent producing genetically identical offspring without gametes. Options B, C, and D describe asexual reproduction, not sexual reproduction. Therefore, the correct description of sexual reproduction is that it involves gamete fusion from two parents, leading to genetic diversity.

Vegetative propagation is a type of asexual reproduction in plants where new plants grow from parts such as stems, roots, or leaves without the involvement of gametes or fertilization. Examples include runners in strawberries, tubers in potatoes, and bulbs in onions. Pollination and fertilization involve sexual reproduction, while seed dispersal is a process that spreads already formed seeds. Therefore, the correct method of asexual reproduction in plants is vegetative propagation.

The xylem is the vascular tissue responsible for transporting water and dissolved minerals from the roots to the stems and leaves. It functions through cohesion and adhesion forces, aided by transpiration pull. The phloem, in contrast, transports sugars and organic nutrients produced in leaves to other parts of the plant. Mesophyll is responsible for photosynthesis, and the epidermis provides protection. Hence, the tissue specialized for water and nutrient transport is the xylem.

Courtship behaviors are a set of rituals and displays, such as songs, dances, coloration, or pheromone release, that both males and females perform to attract potential mates and ensure reproductive success. These behaviors help in mate recognition, species identification, and selection of the fittest partner. They are not solely about dominance or aggression but rather about communication and attraction. Therefore, the best description is that courtship involves rituals performed by both sexes to attract a mate.

Physiological variation refers to differences in the functioning of body systems and processes, such as respiration rates, enzyme activity, blood pressure, or metabolic efficiency, among individuals of the same species. Morphological variation refers to physical differences, behavioral variation refers to habits and interactions, and genetic variation refers to DNA-level differences. Thus, physiological variation specifically involves the differences in biological functions and processes.

The primary excretory organs in animals include the kidneys, which filter blood to remove nitrogenous wastes; the lungs, which excrete carbon dioxide and water vapor; and the skin, which removes wastes through sweat. The stomach and intestines are part of the digestive system, the brain and nerves belong to the nervous system, and the heart, liver, and spleen are involved in circulation and metabolism, not excretion. Therefore, lungs, kidneys, and skin are the correct excretory organs.

Trophic levels refer to the hierarchical stages in a food chain that represent the flow of energy through an ecosystem. Producers (plants) occupy the first trophic level, primary consumers (herbivores) the second, secondary consumers (carnivores) the third, and so on. Each level depends on the one below for energy. This concept does not describe interactions, nutrient cycling, or biodiversity directly, but specifically energy flow. Hence, trophic levels are best defined as the levels of energy flow in an ecosystem.

Pollination is the process by which pollen grains are transferred from the anther (male reproductive part) to the stigma (female reproductive part) of a flower. This transfer may occur through wind, water, or pollinators like insects and birds. The process allows fertilization to take place once the pollen grain reaches the ovule. It is not the transfer from stigma to anther, nor is it the direct formation of seeds, which comes later after fertilization. Therefore, the most accurate definition is the transfer from anther to stigma.

A natural habitat refers to the natural environment where an organism lives, grows, and interacts with both living and non-living factors. It provides food, shelter, water, and space for the survival of species. While human-created reserves, laboratories, or protected areas can support organisms, they are artificial or managed environments. Therefore, the correct definition is an area where organisms naturally live and interact with their environment.

Viruses are unique entities that are not considered fully living because they lack cellular structures and metabolic processes. They cannot reproduce independently and require a host cell’s machinery to replicate. They consist of genetic material (DNA or RNA) enclosed in a protein coat. Since they are obligate intracellular parasites, the true statement is that viruses require a host cell to replicate.