The interdependence of organisms

Define a food chain, identify the trophic levels (producer, consumers) within it, and explain how it shows the flow of energy in an ecosystem.
Define a food web and explain how it provides a more complex and realistic representation of feeding relationships compared to a simple food chain.
Predict the potential impact of changes in one population on other populations within a food web.

In any ecosystem – all the living things and their non-living environment in an area – organisms are connected because they rely on each other for food.
We can show these feeding relationships and how energy flows using food chains and food webs.

A food chain shows a simple, linear pathway of how energy is transferred when one organism eats another.
- It always starts with a producer. Producers are organisms, like plants or algae, that make their own food using energy from the sun through photosynthesis.
- The next link is a primary consumer. This is usually an herbivore (an animal that eats plants), which gets its energy by eating the producer.
- The primary consumer might then be eaten by a secondary consumer, which is often a carnivore (an animal that eats other animals) or an omnivore (an animal that eats both plants and animals).
- Sometimes, there's another level: a tertiary consumer, which eats the secondary consumer.
Example of a food chain: Grass (Producer) → Rabbit (Primary Consumer/Herbivore) → Fox (Secondary Consumer/Carnivore)

In reality, most animals eat more than one type of food, and are eaten by more than one type of predator.
An ecosystem has many interconnected food chains, forming a food web.
Food webs give a more realistic picture of the feeding relationships and energy flow.
Food webs clearly show how organisms in an ecosystem are interdependent (they rely on each other). For example:
- Foxes depend on rabbits and voles for food. If a disease reduces the rabbit population, foxes might eat more voles, or their own numbers might decrease due to less food overall.
- If the population of blue tits (which eat caterpillars) declines, the caterpillar population might increase, potentially leading to more damage to oak trees.
Changes in one population can have knock-on effects on many other populations in the food web, highlighting the delicate balance within an ecosystem.

Ecosystem: All the living organisms and the non-living parts of their environment in a specific area, and their interactions.
Food chain: A simple, linear diagram showing the pathway of energy transfer when one organism eats another.
Food web: A network of interconnected food chains in an ecosystem, showing multiple feeding relationships.
Energy flow: The movement of energy from one organism to another in a food chain or food web.
Producer: An organism (like a plant or algae) that makes its own food using energy from the sun.
Consumer: An organism that obtains energy by eating other organisms.
Primary consumer: A consumer that eats producers (usually a herbivore).
Secondary consumer: A consumer that eats primary consumers.
Interdependent: When organisms rely on each other for survival, often through feeding relationships.

Construct a food web for a specific local ecosystem (such as a garden, park, pond, or woodland patch) using identified organisms and showing the feeding relationships with arrows indicating the direction of energy flow.
Research the role of decomposers (like bacteria and fungi) in ecosystems, explaining how they break down dead organisms and waste and return essential nutrients that producers can then use.