Biology 2025 Jamb Examination

Poliomyelitis, commonly known as polio, is a highly infectious disease caused by a virus (not bacteria). It primarily invades the nervous system and is capable of causing total paralysis in the limbs within a matter of hours, particularly affecting the legs. While it can affect people of any age, it mainly strikes children under five years of age. Fortunately, the disease is preventable through the administration of the polio vaccine (OPV or IPV).

In a typical Mendelian cross between a pure-breeding (homozygous) tall plant and a pure-breeding short plant, all the offspring in the first filial (F\(_1\)) generation will inherit one dominant allele for tallness and one recessive allele for shortness. This results in a heterozygous tall genotype. Phenotypically, because the tall allele is dominant over the short allele, 100% of the plants will appear tall.

The cortex is the region of the stem located between the epidermis and the vascular bundles. In herbaceous plants, the cortex is primarily composed of parenchyma cells, which function in food storage and photosynthesis, and collenchyma cells, which provide flexible mechanical support to the growing stem. Xylem is part of the vascular tissue, not the cortex, and sclerenchyma is more typically associated with older, woody structures or specific fibers.

Spermatophytes are seed-bearing plants. The angiosperms (flowering plants) are the most advanced and diverse group within this category. Unlike gymnosperms, which produce 'naked seeds' often in cones, angiosperms produce seeds enclosed within a fruit. They have dominated the Earth's flora for millions of years and encompass the vast majority of all known living plant species, ranging from grasses to massive hardwood trees.

Within the microscopic environment of a single animal cell, the cytoplasm serves as the primary medium for the transportation of materials. It is a jelly-like substance where nutrients, enzymes, and organelles move to different parts of the cell for metabolic processes. While blood is a major transport medium for a multi-cellular organism, cell sap is found in plant vacuoles, and latex is a milky fluid produced by certain plants.

In most generalized cell diagrams, the largest and most prominent organelle, often positioned centrally in animal cells, is the nucleus. It serves as the control center of the cell, housing the genetic material (DNA) and coordinating activities like growth, metabolism, and reproduction. If the label I points to this large spherical body, it is identifying the nucleus. This is distinct from the vacuole, which is usually larger and more central in plant cells, or the mitochondrion, which would be represented as a smaller, bean-shaped structure with internal folds.

An estuary is a coastal body of water where fresh water from rivers and streams meets and mixes with salt water from the ocean, creating a 'brackish' environment. A lagoon is a prime example of an estuarine habitat, as it is often partially enclosed by a barrier and receives both terrestrial runoff and oceanic inflow. Rivers are fresh water, oceans are purely salt water, and lakes are typically enclosed inland fresh water bodies (though some are salty, they lack the specific river-ocean mixing characteristic of estuaries).

Grasshoppers are herbivorous insects that consume tough plant materials like leaves and stems. To process this food, they possess 'mandibulate' mouthparts designed for biting and chewing. These include strong mandibles (jaws) that cut and grind the vegetation. This is in contrast to insects like mosquitoes (piercing and sucking), butterflies (siphoning/sucking), or houseflies (sponging).

Population growth is determined by the balance between 'plus' factors (natality and immigration) and 'minus' factors (mortality and emigration). Natality refers to the birth rate, which is a fundamental component used to calculate growth. However, in the context of environmental 'limiting factors' that restrain or affect the growth potential of a population, predators, food shortages, and diseases are external pressures. While the phrasing can be tricky, if the question asks for an external factor that limits growth, natality is the internal biological process of growth itself rather than an environmental constraint.

Ecological succession is the process by which the structure of a biological community evolves over time. It begins with pioneer species (the first to colonize bare area). Through various seral (intermediate) stages, the ecosystem eventually reaches a steady state where the species composition remains relatively stable and in equilibrium with the environment. This final stage is known as the climax community. For example, in a forest succession, the climax community might be a dense forest of mature hardwood trees.