AQA GCSE Biology Foundation (8461), Foundation tier · Ecology › Trophic levels in an ecosystem
Practise Trophic levels. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Trophic levels number the feeding positions in a food chain, from producers at level 1 up to apex predators. You also need to describe how decomposers feed. This subtopic is in GCSE Biology only, not Combined Science.
Key facts
Level 1: producers (plants and algae)
Level 2: primary consumers (herbivores)
Level 3: secondary consumers (carnivores that eat herbivores)
Level 4: tertiary consumers (carnivores that eat other carnivores)
Apex predator = a carnivore with no predators
Decomposers secrete enzymes; small soluble food molecules diffuse into them
Notes
Numbering trophic levels
diagram
Each feeding position in a food chain is given a number. Plants and algae are level 1, and the number rises by one for each step further along the chain.
Level 1: producers, i.e. plants and algae, which make their own food.
Level 2: primary consumers, the herbivores that eat plants or algae.
Level 3: secondary consumers, the carnivores that eat herbivores.
Level 4: tertiary consumers, carnivores that eat other carnivores.
Longer chains continue the numbering (level 5 and so on).
Apex predators are carnivores with no predators.
Trophic levels are numbered up the food chain from the producer.
Trophic levels in food webs
In a food web, an animal can feed at more than one trophic level.
Example: a mouse that eats seeds is at level 2, but when it eats beetles that feed on leaves it is at level 3.
Decomposers
diagram
Decomposers (bacteria and fungi) break down dead plant and animal matter.
They secrete enzymes into the environment, onto the dead material. The enzymes digest large molecules into small soluble food molecules.
The small soluble food molecules then diffuse into the microorganism.
Decomposers digest their food outside their cells, then absorb the products.
Decomposers feed on dead material and waste from every trophic level.
How to answer each type of question
Identify trophic levels in a food chain
1 mark eachGrade 3
Start at the producer: level 1.
Add 1 for each arrow you follow.
Give the matching name if asked: producer, primary, secondary or tertiary consumer.
Example. Here is a food chain from the Southern Ocean: phytoplankton → krill → penguin → leopard seal → killer whale (a) What trophic level is the penguin? (b) Which organism is the apex predator? Give a reason. (3 marks)
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(a) Level 3 (1) (b) Killer whale (1); it is a carnivore with no predators (1)
Describe the differences between trophic levels
2 to 3 marksGrade 5
Say how each gets its food: producers make it by photosynthesis; consumers eat other organisms.
Say what each consumer eats: herbivores eat plants or algae; carnivores eat animals.
Use the level numbers.
Example. Describe the differences between organisms at trophic level 1 and trophic level 3. (3 marks)
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Level 1 organisms are producers that make their own food by photosynthesis (1). Level 3 organisms are carnivores / secondary consumers (1) that eat herbivores, which are at level 2 (1).
Don’t lose marks
Starting the count at the first consumer. The producer is level 1.
Saying decomposers 'eat' dead matter or digest it inside their bodies. They secrete enzymes outside and absorb the products by diffusion.
Saying an apex predator is 'the biggest animal'. It is a carnivore with no predators.
Calling a secondary consumer a herbivore.
More tips
Memory tricks
Trophic level = number of arrows from the producer + 1.
Decomposers: Secrete, Digest, Diffuse.
Apex means top: nothing eats an apex predator.
Exam technique
Give the level number and the name if you are unsure which one is wanted.
In decomposer questions, use the key words secrete, enzymes, soluble and diffuse.
In food webs, check every arrow into an animal before deciding its level.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Number the trophic levels in a food chainLevel 1 is the producer, level 2 the primary consumer, and so on along the chain.
Grade 4
Describe producers, herbivores and carnivoresProducers make their own food, herbivores eat plants or algae, and carnivores eat other animals.
Grade 5
Define an apex predatorA carnivore with no predators.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Organisms in an ecosystem can be placed into trophic levels. What name is given to the organisms at trophic level 2?
Primary consumers (herbivores)
Herring gulls have no predators on this shore. What name is given to a carnivore with no predators?
Apex predator
In the Arctic Ocean:
phytoplankton are single-celled algae
zooplankton are small animals that eat phytoplankton