2024 - JAMB Biology Past Questions and Answers - page 3

Xerophytes are plants adapted to survive in environments with little water. Arid lands, characterized by very little rainfall, contain the greatest concentration of xerophytes.

Continuous variation refers to traits that show a range of values with no distinct categories. Examples include height, weight, and skin color. Since there are no significant gaps between the extreme individuals, this describes continuous variation.

The ground layer of a tropical rainforest is the lowest layer, receiving the least sunlight. Plants here are typically small and shade-tolerant.

• Liverworts: Small, non-vascular plants that thrive in moist, shaded environments.
• Obeche, Mahogany, Oil palm: Trees found in the upper layers of the rainforest, not the ground layer.

The cells responsible for transmitting messages to the effectors are motor neurons.

• Motor neurons: Carry signals from the central nervous system (brain and spinal cord) to effectors (muscles or glands), causing responses.
• Sensory neurons: Carry signals from sensory receptors to the central nervous system.
• Hair cells: Sensory receptors in the inner ear for hearing and balance.
• Relay neurons (interneurons): Connect sensory neurons to motor neurons within the central nervous system.

Selective reabsorption primarily occurs in the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule. The loop of Henle mainly reabsorbs water and ions like sodium and chloride.

• Glomerulus: Filtration occurs here.
• Bowman's capsule: Receives filtrate from the glomerulus.
• Henle's loop: Key site for water and ion reabsorption.
• Urethra: Tube that carries urine out of the body.

The central nervous system (CNS) is the control center of the body, consisting of the brain and spinal cord. It processes information and coordinates responses.

The respiratory organ in mammals is the lungs, responsible for gas exchange (oxygen in, carbon dioxide out). The other options are not respiratory organs:

• Skin: Protection and excretion.
• Mouth: Digestive system.
• Heart: Circulatory system, pumps blood.

The carbon cycle involves the movement of carbon through the atmosphere, oceans, land, and organisms. Combustion releases carbon from organic matter into the atmosphere as carbon dioxide.

• Evaporation: Part of the water cycle.
• Nitrification: Part of the nitrogen cycle.
• Combustion: Part of the carbon cycle.
• Transpiration: Part of the water cycle.

Counter-shading is a camouflage strategy where an animal is dark on top and light on the bottom, helping it blend in with the environment.

• Grasshopper: Camouflage with green color, not counter-shading.
• Toad: Uses camouflage, not counter-shading.
• Fish: Often displays counter-shading; dark back blends with depths, light belly with surface.
• Chameleon: Changes color to blend, but not counter-shading.

The cochlea is the part of the inner ear responsible for hearing. It contains hair cells that convert sound vibrations into electrical signals sent to the brain. Other options are involved in balance and equilibrium.