Producers and consumers
Big idea: All life in ecosystems depends on how energy enters the system and moves between organisms.
Energy does not appear randomly in ecosystems. It must first be captured and stored before it can be used by living organisms.
Producers are the starting point of almost all ecosystems.
- Most producers are green plants and algae
- They use photosynthesis
- They store energy as biomass
All other organisms depend on producers, either directly or indirectly.
Consumers cannot make their own food, so they must eat plants or other animals to survive.
- Herbivores eat producers (plants)
- Carnivores eat other animals
- Omnivores eat both plants and animals
Without producers, no consumers could survive — producers are the energy foundation of ecosystems.
Food chains and trophic levels
Energy moves through ecosystems in feeding relationships that can be shown using a food chain.
Each step in a food chain represents a different trophic level.
- Trophic level 1 → producers
- Trophic level 2 → primary consumers (herbivores)
- Trophic level 3 → secondary consumers
- Higher levels → tertiary consumers
Energy always flows in one direction: from producers to consumers.
IB exam tip: arrows in food chains show the direction of energy flow, not who eats whom.