The major problem experience by organisms living in small water bodies is

Analyze the question

The question asks about the main problem faced by organisms living in small water bodies such as ponds, puddles, and small streams. Think about what makes a small water body different from a large one such as a lake, river, or sea.

Concept

Small water bodies have these features:

• They hold only a small volume of water.
• They have a small surface area, so there is little exchange of gases with the air.
• They are shallow, so they heat up and lose water quickly.
• They often depend on seasonal rainfall.

Compare this with a large water body, which holds a large volume of water, is permanent, and has waves, currents, and plenty of dissolved oxygen.

Evaluating the options

• A. Drying up: Small ponds and pools, especially in Nigeria's dry season (harmattan and hot months), can evaporate completely. Organisms are then left without a habitat. This is the problem unique to small water bodies.
• B. Oxygen deficiency: This can happen in stagnant ponds, but it is not the major problem. It also occurs in large water bodies, for example at depth or when there is pollution. It is a possible distractor.
• C. Scarcity of food: Small ponds often have plenty of algae and detritus, so this is not the main problem.
• D. Wave action: This is a problem for large water bodies like seas and big lakes, not small ones.

Answer

The defining threat to organisms in small water bodies is that the water can dry up, especially in the dry season. This leads to the death of the organisms or forces them to migrate or go dormant. Examples are lungfish aestivating in mud and some insects having resistant eggs or larval stages.

Exam tip

When a question says "small water body," think "small volume, so it dries up." When it says "large water body," think "waves, currents, and depth."