Which of the following factors primarily affects the distribution of organisms in an ecosystem

Step 1: Analyze the question The question asks which factor primarily (mainly) affects where organisms are found in an ecosystem. All four options are real environmental (abiotic) factors, so we need to pick the one with the widest and strongest influence.

Step 2: Explain the concept Distribution is how organisms are spread across different areas. It is determined by whether an organism can survive, grow, and reproduce in a given place. Temperature is considered the most important factor because:

• It controls the rate of enzyme activity, and therefore metabolism, growth, and reproduction.
• It determines the major biomes. Tropical rainforests, savanna, desert, and tundra are largely separated by temperature (together with rainfall).
• Every organism has a tolerance range. Outside it, the organism cannot survive.
• It affects other factors too, such as evaporation, humidity, and water availability.

Step 3: Evaluate each option

• A. Wind speed: Important locally (it affects seed dispersal and water loss), but it is not the main driver of distribution.
• B. Soil pH: Affects which plants grow in a particular soil, but its effect is local and mainly limited to terrestrial habitats.
• C. Temperature: Affects all organisms in all habitats, on land and in water. It is the broadest and most primary factor.
• D. Day length: Mostly affects seasonal behaviour such as flowering and migration (photoperiodism), not the basic ability to survive in an area.

Step 4: Answer The correct option is C. Temperature.

Exam tip: When a question says "primarily" or "mainly" about distribution, think of the factor that affects every organism everywhere. That is usually temperature (or sometimes water or rainfall). Remember: Temperature sets the limits of life.