1. TROPHIC LEVELS, FOOD CHAINS AND FOOD WEBS
UNIT 5
Ecosystems
TROPHIC LEVELS, FOOD CHAINS AND FOOD WEBS
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2. UNIT 5
Producers
Producers are autotrophic organisms that create organic matter from inorganic matter: hence the name “producers.”
Tulips
Ash tree
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3. UNIT 5
Primary consumers
Primary consumers are animals that feed on autotrophic organisms like algae and plants. Herbivores are primary consumers.
Rabbit
Horse
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4. UNIT 5
Secondary consumers
Secondary consumers feed on primary consumers. Carnivores are secondary consumers.
Penguins
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5. UNIT 5
Tertiary consumers
Tertiary consumers feed on secondary consumers. Birds of prey and wolves are examples of tertiary consumers.
Wolves
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6. Other types of consumers
UNIT 5
Other types of consumers
Omnivores are consumers with a varied diet: they can be both herbivores and carnivores. Examples are human beings, bears and ants. They can be classified in different trophic levels in a single ecosystem.
Bear
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7. Other types of consumers
UNIT 5
Other types of consumers
Detritivores are consumers that feed on decomposing organic matter or excrement. Examples are earthworms, woodlice and some beetles.
Woodlouse
Earthworm
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8. Decomposers
They are heterotrophic organisms which feed on the remains of the other trophic levels.
They transform organic matter in inorganic matter.
They are bacteria and fungi.

9. UNIT 5
Let’s make a food chain
To make a food chain, we draw the organisms that form part of an ecosystem.
Then we use arrows to represent the feeding relationship between them. The tip of the arrow points to the organism that eats, and the end of the arrow indicates the organism that is eaten.
Great tit
Strawberry tree
Common kestrel
Grasshopper
is eaten by
is eaten by
is eaten by
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10. UNIT 5
Let’s make a food web
Food webs are made in the same way as food chains, but they show multiple feeding relationships within an ecosystem. In other words, they represent how different food chains are interconnected.
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