Biology 2006 Jamb Examination

B. Fish

Fishes possess the most primitive vertebrate heart structure, consisting of only two chambers: one atrium and one ventricle. This simple structure supports their single circulatory system. In contrast, amphibians have a three-chambered heart, reptiles have a partially divided three-chambered heart, and mammals have a fully four-chambered heart suitable for a double circulatory system.

B. Radial symmetry

Coelenterates such as Hydra and jellyfish exhibit radial symmetry, meaning their body parts are arranged around a central axis. This is considered primitive because more advanced animals evolved bilateral symmetry, which allows directional movement and specialization of body parts.

A. Viviparous mode of reproduction

Mammals are evolutionarily advanced because most exhibit viviparity, giving birth to live young and providing parental care through placental development and milk production. Other vertebrates may lay eggs or show less developed reproductive strategies, highlighting viviparity as a key evolutionary trait.

D. Rhizopus

Rhizopus, a fungus, carries out extracellular digestion by secreting enzymes outside its body to break down complex organic matter before absorption. Protozoans like Amoeba and Paramecium digest food intracellularly inside vacuoles, so they do not perform extracellular digestion.

A. Salmonella

Typhoid fever is caused by Salmonella typhi, a pathogenic bacterium transmitted through contaminated food or water. It primarily affects the intestines and bloodstream, leading to prolonged fever, abdominal pain, and weakness.

A. Perennating organs

Grasses possess underground perennating organs, such as rhizomes and corms, that store nutrients. When fires destroy above-ground parts, these organs allow rapid regrowth. This adaptation ensures their survival in fire-prone savanna ecosystems.

C. A stable composition of plant and animal species

A climax community represents the final, stable stage of ecological succession. At this stage, species composition becomes relatively constant over time. The balance between species interactions and environmental conditions maintains stability, unlike earlier successional stages which are dynamic.

B. Clayey

Clayey soils hold nutrients tightly because of their fine particle size and poor aeration. Although they are rich in minerals, these nutrients are not easily available to plant roots. In contrast, loamy soils provide a balanced, fertile environment where nutrients are readily accessible.

B. Exponential growth

Exponential growth occurs when resources are abundant, and reproduction is unchecked, causing population size to double at regular intervals. This produces a J-shaped growth curve, unlike sigmoid growth, which levels off due to limiting factors like food and space.

D. They are raised in different environment

Identical twins have the same genotype, but environmental factors such as nutrition, health, and exercise can influence phenotype. Hassan’s greater height and weight compared to Hussain result from environmental differences, demonstrating the effect of nurture over genetics in this context.