AQA Biology 4.7.4.1 · Triple only

Trophic levels

Number the positions in a food chain from the producer up, find the predator nobody eats, and see how decomposers feed without a mouth.

Triple Science · Higher tier

Start here

Grass, rabbit, fox.

Three organisms from one field.

If you had to guess, which comes first in the food chain: the grass or the fox?

Numbered levels

Count along the chain.

Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further trophic levels are numbered subsequently according to how far the organism is along the food chain. Each arrow points from the organism that is eaten to the organism that eats it: the direction in which energy and biomass are transferred.

Give each organism its level. Two of them are the same animal in two different chains.

Oak tree (makes its food by photosynthesis)

Which level?

Caterpillar (eats oak leaves)

Which level?

Blue tit (eats caterpillars)

Which level?

Sparrowhawk (eats blue tits)

Which level?

Fox eating rabbits (rabbits eat grass)

Which level?

The same fox eating blackberries

Which level?

Apex predators are carnivores with no predators. In the oak chain, which is the apex predator?

Pick one.

Decomposers

Feeding without a mouth.

Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism. Step through it.

A dead leaf lies on the soil. Bacteria and fungi (decomposers) live on it. Predict: where does digestion happen?

Only approximately 10% of the biomass from each trophic level is transferred to the level above it, which is why chains rarely pass level 4 or 5. The losses and the calculation are in Transfer of biomass.

Think again · always level 3?

“A fox is always at trophic level 3.”

Your call

Choose

A fox eats blackberries in autumn and rabbits in spring. What is its trophic level?

Sort

Which level?

Place each organism from the pond: algae, water fleas (eat algae), sticklebacks (eat water fleas), pike (eat sticklebacks), and the bacteria on the pond floor.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Describe: The differences between the trophic levels, and how decomposers feed.
Identify: The trophic level of an organism in a given chain.
Explain: Why the same animal can sit at different levels.

Key fact

Level 1 is the producer; each level after is numbered by how far along the chain the organism is. An apex predator is a carnivore with no predators. Decomposers secrete enzymes into the environment and small soluble food molecules diffuse into them.

Key note · AQA 4.7.4.1 (Biology only)

Trophic levels

Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further levels are numbered according to how far the organism is along the food chain.
Level 1 producers; level 2 primary consumers (herbivores); level 3 secondary consumers (carnivores eating herbivores); level 4 tertiary consumers (carnivores eating carnivores).
Apex predators are carnivores with no predators.
Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism.
Only about 10% of biomass passes to the next level, so chains are short (Transfer of biomass).

Photograph this card. Tomorrow, cover it and say each line first.

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Connects to

Ask MrBadmus

Numbering from the top down?

The chains are standard examples; no data are claimed.