7.16 Trophic levels and pyramids of biomass
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What is an apex predator?
Mark scheme
a carnivore with no predators / at the top of the food chain
Model answer
A carnivore with no predators of its own.
In the food chain grass → grasshopper → frog → snake, which trophic level is the frog?
Mark scheme
level 3 / secondary consumer
Model answer
Trophic level 3 (secondary consumer).
Explain why a pyramid of biomass is almost always pyramid shaped.
Mark scheme
- biomass is lost at each trophic level (1)
- so each level has less biomass than the one below (1)
Model answer
Biomass is lost between each trophic level, so there is less biomass at each level than at the level below.
Describe how decomposers feed.
Mark scheme
- secrete enzymes onto dead material (1)
- small soluble molecules diffuse / are absorbed into the microorganism (1)
Model answer
Decomposers secrete enzymes onto dead material, and the small soluble molecules produced diffuse into their cells.
In a field, the biomass of producers was 500 kg, primary consumers 50 kg and secondary consumers 5 kg.
Describe how you would draw a pyramid of biomass for these data.
Mark scheme
- choose a suitable scale, e.g. 1 cm = 50 kg (1)
- bars drawn to scale with producers at the bottom (1)
- bars centred and labelled (1)
Model answer
Choose a scale, such as 1 cm = 50 kg, so the producer bar is 10 cm wide, the primary consumer bar 1 cm and the secondary consumer bar 0.1 cm. Draw the producers at the bottom, centre the other bars above and label each.
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