Trophic levels represent the position of an organism in a food chain, indicating its role in the flow of energy through an ecosystem. Energy is transferred between trophic levels, but much is lost at each stage.

Key Points

1. Trophic Levels Defined:

• Producers (Level 1): Autotrophic organisms, such as plants and algae, that produce their own food through photosynthesis.
• Primary Consumers (Level 2): Herbivores that feed on producers.
• Secondary Consumers (Level 3): Carnivores or omnivores that feed on primary consumers.
• Tertiary Consumers (Level 4): Predators that feed on secondary consumers.
• Decomposers: Not a distinct trophic level but recycle nutrients by breaking down dead organic matter.

2. Energy Transfer:

• Only around 10% of energy is transferred to the next trophic level. The rest is lost through:
• Respiration (heat loss).
• Excretion and egestion (faeces and urine).
• Uneaten parts of organisms (e.g., bones, fur).

3. Energy Pyramid:

• Energy decreases as it moves up trophic levels.
• This limits the number of trophic levels in a food chain, as there is insufficient energy to support higher levels.

4. Food Webs:

• Interconnected food chains showing multiple feeding relationships in an ecosystem.
• More complex food webs lead to greater stability, as the loss of one species has less impact.

Exam Tip

Be able to draw and interpret food chains, food webs, and energy pyramids. Understand how energy losses affect trophic levels and the maximum length of food chains. Use terms like efficiency of energy transfer in your explanations.