Question

In a food chain, energy is transferred from one trophic level to another. What happens to the energy as it moves up the food chain?

• A. It increases
• B. It decreases
• C. It remains constant
• D. It fluctuates randomly

Hint:

• Energy flow in food chains is unidirectional and inefficient.
• Only about 10% of energy is typically transferred from one trophic level to the next (the "10% rule").
• The majority of energy (approx. 90\%) is lost as heat during respiration or is present in unconsumed/undigested parts.
• This leads to a progressive decrease in available energy at higher trophic levels.

Answer 1

The Correct Option is B

Energy transfer between trophic levels in a food chain is inherently inefficient. When organisms at one trophic level consume organisms from a lower trophic level, a significant portion of the energy is lost. This loss occurs primarily in two ways:

• Metabolic Heat Loss: Organisms use a large part of the consumed energy for their own metabolic processes, such as respiration, movement, and maintaining body temperature. This energy is ultimately dissipated as heat into the environment.
• Undigested Material: Not all parts of an organism are digestible or consumed, and this unutilized biomass still contains energy.

A general ecological rule, often called the "10% rule," states that only about 10% of the energy from one trophic level is transferred to and incorporated into the biomass of the next higher trophic level. The remaining 90% is lost or not utilized. As a result, the amount of available energy significantly decreases as it moves up the food chain from producers to primary consumers, then to secondary consumers, and so on. This energy decrease limits the number of trophic levels a food chain can support and the biomass at higher trophic levels. Option (a) is incorrect because energy does not increase. Option (c) is incorrect as energy is constantly being lost. Option (d) is incorrect; while there can be minor fluctuations, the overall trend is a consistent decrease. \[ \boxed{\text{It decreases}} \]