Ecology and Ecosystems: Question 10

Worked solution

Step 1: Identify what the question is asking

The question asks for a reason that is not a cause of energy loss between two trophic levels already in the food chain, for example, between primary consumers and the secondary consumers that eat them. This means the correct answer describes something happening elsewhere, not at a transfer within the food chain.

Step 2: Check each genuine cause of transfer loss

• A: Not every organism at a trophic level is eaten by predators at the next level. Some die of other causes, or simply survive uneaten. This genuinely reduces the energy passed on, so A is a real reason for the loss.
• B: Energy used in respiration is eventually released as heat to the surroundings, rather than being stored as new tissue that a predator could eat. This is a real reason for the loss.
• C: Not all of the material an organism eats is digested and absorbed; the undigested portion is egested as faeces, taking its energy out of the food chain at that point. This is also a real reason for the loss.

Step 3: Examine option D separately

Option D describes producers converting only a small fraction of the Sun’s light energy into chemical energy during photosynthesis. This is a genuine source of energy loss, but it occurs at the very first step of energy flow, as light energy from the Sun enters the food chain through the producer. It is not a loss occurring between two trophic levels that are already part of the food chain (such as consumer to consumer), which is what the question specifically asks about.

Final answer

The statement that is not a reason for energy loss between two trophic levels within the food chain is that producers convert only a small fraction of sunlight into chemical energy, because this describes energy entering the food chain, not being transferred along it, option D.