This how it works covers How It Works: Energy Flow Through Trophic Levels within Ecosystems Communities for GCSE Biology. Topic 1: Ecosystems Communities It is section 7 of 15 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
How It Works: Energy Flow Through Trophic Levels
Every ecosystem is powered by energy from the Sun. Producers (plants and algae) capture solar energy through photosynthesis and convert it into organic molecules — glucose, proteins, and fats. When a herbivore eats a plant, some of that stored energy passes to the herbivore. When a carnivore eats the herbivore, another transfer occurs. Each step in this sequence is called a trophic level.
The critical point is that only approximately 10% of the energy at one trophic level is transferred to the next. The remaining 90% is lost — mainly as heat released during cellular respiration (organisms use energy to move, grow, and maintain body temperature), but also in undigested material that passes out as faeces. This means food chains rarely extend beyond four or five trophic levels: by the fifth level, so little energy remains that it cannot sustain a viable population.
This energy loss also explains why there are always far more producers than primary consumers, and far more primary consumers than secondary consumers — a pattern we see in pyramids of biomass. Interdependence arises because every organism relies on the trophic level below it for energy. Remove any single species and the effects cascade upwards and downwards through the food web, potentially causing population crashes or explosions throughout the ecosystem.
Practice questions for Ecosystems Communities
What is a community in ecology?
Explain what is meant by interdependence in an ecosystem.