GCSE Biology, Unit 7, Lesson 5 of 8

Trophic levels, pyramids and efficiency

GCSE Biology, Ecology, 20 minutes

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Trophic levels, drawing pyramids of biomass to scale, why biomass is lost at each step, and calculating the efficiency of transfer (Biology only).

What you will learn

  • Number the trophic levels in a chain
  • Draw a pyramid of biomass to scale
  • Calculate the efficiency of biomass transfer between levels
  • Explain where the lost biomass goes

Trophic levels and pyramids

Each step of a food chain is a trophic level.

Level 1 is the producers, level 2 the primary consumers (herbivores), level 3 secondary consumers, level 4 tertiary consumers. Apex predators are at the top. Decomposers break down dead material from every level.

A pyramid of biomass has one bar per level, its width in proportion to the dry biomass. Dry biomass is measured by drying samples in an oven and weighing them again and again until the mass stops changing, so that all the water has gone; the mean per m² × the area gives the total. Only about 1% of the light reaching producers is used in photosynthesis, and each level has less biomass than the one below.

  1. Producers 1500 g/m² drawn 15 cm wide: 1 g/m² = 0.01 cm
  2. Herbivores 240 g/m²: 240 × 0.01 = 2.4 cm
  3. Carnivores 30 g/m²: 0.3 cm

The rest of this lesson and its 11 practice questions are locked.

In this lesson

  1. Trophic levels and pyramids
  2. Efficiency of transfer
  3. Try it: Your first efficiency

11 practice questions, marked as you go; about 20 minutes in all.

Key terms

Trophic level, Pyramid of biomass, Dry biomass, Respiration

In this unit: Ecology

Communities and adaptations, sampling with quadrats, transects and capture-recapture, food chains and the carbon, water and nitrogen cycles, decay, parasitism and mutualism, eutrophication, biodiversity and human impact, biomass transfer and food security.

All of Ecology

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