Which of the following factors exerts a major effect on the distribution of living organisms in the habitat?

Step 1: Analyze the question The question asks which factor has a major effect on where organisms live (their distribution) in a habitat. This is about ecological factors that limit or favor the presence of organisms.

Step 2: Explain the concept Distribution of organisms depends on abiotic (non-living) factors such as temperature, light, water, pH, salinity, and rainfall. Some factors act locally or on specific groups, while others influence nearly all organisms over wide areas.

Step 3: Evaluate each option

• A. Salt: Salinity affects organisms mainly in specific habitats such as estuaries, mangroves, and the sea. It is important locally, but not the broadest factor.
• B. pH: Soil or water pH influences certain plants and aquatic organisms, but its effect is usually limited to particular habitats.
• C. Light: Light is essential for photosynthesis and affects plant distribution. It is important, but it mostly affects where plants grow (for example, forest floor versus canopy) and is not the main control over large-scale distribution.
• D. Rainfall: Rainfall determines the availability of water, which every living organism needs. It shapes whole vegetation zones (rainforest, guinea savanna, Sahel/desert) in Nigeria and across the world. The type of plants present then determines which animals can live there. This makes rainfall the factor with the greatest overall effect on distribution.

Step 4: Answer Rainfall exerts the major effect on the distribution of living organisms. Light is a reasonable competing choice, but rainfall is the better answer because it controls the major vegetation belts and, through them, animal distribution too.

Exam tip: In Nigeria, think of the vegetation belts from south to north: rainforest → guinea savanna → sudan savanna → sahel. They change mainly because rainfall decreases northward. When a question asks about the "major" factor affecting distribution, think of rainfall or water availability.