AQA GCSE Biology
AQA GCSE Biology 4.7.4 Trophic Levels in an Ecosystem Exam Questions
Free AQA GCSE Biology exam questions for 4.7.4 Trophic Levels in an Ecosystem, with a mark scheme for every pack. Covers trophic levels, apex predators and decomposers, pyramids of biomass, and losses of biomass between trophic levels with efficiency calculations.
4.7.4 Trophic Levels in an Ecosystem exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Biology 4.7.4 Trophic Levels in an Ecosystem
Trophic levels is a Biology only section of AQA Ecology, examined on Paper 2. It describes the feeding levels within an ecosystem, how pyramids of biomass are constructed, and why only a small proportion of biomass passes from one level to the next. It links to photosynthesis in 4.4.1, respiration in 4.4.2 and food production in 4.7.5. Examiners frequently ask you to draw or interpret pyramids of biomass to scale, calculate the efficiency of biomass transfer, and explain the ways biomass is lost between trophic levels.
What you need to know
- Trophic levels Level 1 are producers (plants and algae) that make their own food by photosynthesis. Level 2 are primary consumers (herbivores). Level 3 are carnivores that eat herbivores. Level 4 are carnivores that eat other carnivores. Apex predators are carnivores with no predators.
- Decomposers Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism.
- Pyramids of biomass Pyramids of biomass represent the relative amount of biomass in each level of a food chain, drawn to scale with producers at the bottom. Biomass is the mass of living material.
- Transfer of biomass Producers transfer about 1% of the incident energy from light for photosynthesis. Only approximately 10% of the biomass from each trophic level is transferred to the level above it.
- Why biomass is lost Not all ingested material is absorbed; some is egested as faeces. Some absorbed material is lost as waste, such as carbon dioxide and water in respiration and water and urea in urine. Large amounts of glucose are used in respiration.
- Efficiency calculation Efficiency = (biomass transferred to the next level / biomass available at the previous level) x 100.
Common mistakes in 4.7.4 Trophic Levels in an Ecosystem
- Saying energy is 'used up' in respiration. Energy is transferred, much of it to the surroundings by heating.
- Drawing pyramids not to scale. Bar widths must be proportional to the biomass at each level.
- Saying biomass is lost as urea from plants. Urea is lost in urine by animals; describe the losses for the organism given.
- Inverting the efficiency equation. Divide the biomass at the higher level by the biomass at the lower level.
Try three 4.7.4 Trophic Levels in an Ecosystem exam-style questions
1. Grass has a biomass of 2000 kg and rabbits feeding on it have a biomass of 180 kg. Calculate the efficiency of biomass transfer. (2 marks)
Show the mark scheme answer
(180 / 2000) x 100; = 9%
2. Give three reasons why biomass is lost between trophic levels. (3 marks)
Show the mark scheme answer
Not all of an organism is eaten, such as bones or roots; not all ingested material is absorbed and is egested as faeces; some is lost as carbon dioxide and water in respiration; some is lost as urea in urine (any three)
3. Explain why food chains rarely have more than five trophic levels. (2 marks)
Show the mark scheme answer
Only about 10% of biomass is transferred to each level; so there is not enough biomass to support another level
4.7.4 Trophic Levels in an Ecosystem FAQs
What does AQA GCSE Biology 4.7.4 Trophic levels in an ecosystem cover?
It covers trophic levels, apex predators and decomposers, pyramids of biomass and the transfer and loss of biomass between levels.
Which paper is 4.7.4 examined on?
It is Biology only content in Ecology, assessed on Paper 2.
What equation do I need for trophic levels?
Efficiency of biomass transfer = biomass at the higher level divided by biomass at the lower level, multiplied by 100.
