A food chain shows the feeding relationship between organisms.
If we look at the food chain below, locust eats maize, lizard eats locust, and snake eats lizard.
The arrow in a food chain always points from the food to the feeder.
Each stage in a food chain is called the trophic level.
- Producers
- Producers are always at the bottom of the food chain.
- They are usually plants or algae, which can provide food by photosynthesis.
- Primary consumer
- Primary consumers eat plants (producers), so they are usually herbivores
- Secondary consumer
- Secondary consumers are carnivores that eat primary consumers
- Tertiary consumer
- Carnivores that eat secondary consumers
- Predators that are at the top of the food chain and have no predators are called apex predators
- Decomposer
- Bacteria and fungi that feed on dead organisms or feces
A food web is a collection of food chains in an ecosystem that shows how different organisms depend on each other.
👇 An example of a food web 👇
Some questions that may be asked on IGCSE Biology exam are:
1. Identify all the producers in the food web.
- Producers are organisms at the bottom of the food chain.
- Producers: carrots, grasses, grains
2. Give the trophic level of owls in this food web.
- There are three food chains involving owls.
- grasses → grasshoppers → owls
- grains → grasshoppers → owls
- grains → mice → owls
- In all three food chains, owls are secondary consumers.
3. Name an organism that occurs at two different trophic levels in this food web.
- Foxes can be either a secondary consumer or tertiary consumer.
- Birds can be either a primary consumer or a secondary consumer.
4. Give the food chain from this web that contains four different organisms including grasses.
grasses → grasshoppers → birds → foxes
Energy Transfer Along the Food Chain
In a food chain, only around 10% of energy is transferred from one trophic level to the next trophic level. Energy is lost along the food chain because:
- Energy is used for life processes, such as movement.
- A lot of energy is used for respiration.
- Not all biomass can be eaten by consumers. For example, bones, teeth and claws cannot be eaten.
- Not everything that is eaten by consumers can be digested, and biomass may be lost as feces.
- Some waste is excreted as urine.