Trophic levels
A simple food chainA sequence (usually shown as a diagram) of feeding relationships between organisms, showing which organisms eat what and the movement of energy through trophic levels. in a fresh water pond is:
algae 鈫 mosquito larvae 鈫 dragon fly larvae 鈫 perch
All other food chains in an ecosystemThe living organisms in a particular area, together with the non-living components of the environment. can be added together to make a food web. These stages in a food chain or web are called trophic levelThe position of an organism in a food chain, food web or pyramid.. The arrows show the transfer of biomass from one trophic level to another.
At the bottom of all food chains is a producerPlants that begin food chains by making energy from carbon dioxide and water.. This is almost always a plant or alga which can photosynthesisA chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. to convert carbon dioxide and water into glucose. This provides all the biomass for the food chain. Algae are the producers in the food chain above.
The second trophic level in all food chains is an herbivore or omnivoreAn animal that eats both plants and meat. called a primary consumerThe name given to an organism that eats a producer. A herbivore.. Mosquito larvae are the primary consumers in the above food chain. The third stage is a carnivore or omnivore which eats the primary consumer. This is called the secondary consumerAn organism that obtains its energy by eating the primary consumer. and is dragonfly larvae in the above food chain. There may be additional carnivorous consumers here which would be called tertiary and quaternary. The final level is perch, also a carnivore and is often called the top or apex predator when it is the last organism in the food chain. Organisms at the tops of food chains have no predators.
decomposerAn organism which eats dead organisms, fallen leaves, animal droppings, etc, and breaks them down into simpler materials. are bacteria and fungi which break down dead plant and animal matter. They secrete enzymeA protein which catalyses or speeds up a chemical reaction. on the surface of the dead organisms to break them down and then absorb the digested, smaller food molecules.
Common words used with food chains and their meaning
| Word | Meaning |
| Producers | Green plants - they make biomass from glucose via photosynthesis. |
| Primary consumers | Usually eat plant material - they are herbivores. For example rabbits, caterpillars, cows and sheep. |
| Secondary consumers | Usually eat animal material - they are carnivores. For example cats, dogs and lions. |
| Predators | Kill for food. They are either secondary or tertiary consumers. |
| Prey | The animals that predators feed on. |
| Scavengers | Feed on dead animals. For example, crows, vultures and hyenas are scavengers. |
| Decomposers | Feed on dead and decaying organisms, and on the undigested parts of plant and animal matter in faeces. |
| Word | Producers |
|---|---|
| Meaning | Green plants - they make biomass from glucose via photosynthesis. |
| Word | Primary consumers |
|---|---|
| Meaning | Usually eat plant material - they are herbivores. For example rabbits, caterpillars, cows and sheep. |
| Word | Secondary consumers |
|---|---|
| Meaning | Usually eat animal material - they are carnivores. For example cats, dogs and lions. |
| Word | Predators |
|---|---|
| Meaning | Kill for food. They are either secondary or tertiary consumers. |
| Word | Prey |
|---|---|
| Meaning | The animals that predators feed on. |
| Word | Scavengers |
|---|---|
| Meaning | Feed on dead animals. For example, crows, vultures and hyenas are scavengers. |
| Word | Decomposers |
|---|---|
| Meaning | Feed on dead and decaying organisms, and on the undigested parts of plant and animal matter in faeces. |
More guides on this topic
- What happens during photosynthesis? - OCR 21st Century
- How do producers get the substances they need? - OCR 21st Century
- How do producers transport substances they need? - OCR 21st Century
- How are levels maintained within an ecosystem? - OCR 21st Century
- How are populations affected by conditions in an ecosystem?
- Sample exam questions - living together - OCR 21st Century