Success TutoringWorksheets

Relationships in Ecosystems: Competition, Predation and Symbiosis — Answers

Answer sheet with model answers and success criteria for the Year 7 ecosystems & food chains worksheet.

Download answers PDFPrint answersBack to worksheet
Success TutoringWorksheetsAnswer sheetYear 7 · Science · Ecosystems & Food Chains

Relationships in Ecosystems: Competition, Predation and Symbiosis — Answers

Part A: Living together

Read the passage, then circle the type of relationship.

Organisms in an ecosystem constantly interact. In predation, a predator hunts and eats its prey. In competition, organisms struggle for the same limited resources, such as food, water, light, space or partners to breed with.

Symbiosis is a close, long-term relationship between two different species. In mutualism both species benefit. In commensalism one benefits and the other is unaffected. In parasitism the parasite benefits and the host is harmed.

1.Bees collect nectar from flowers and carry pollen between them. Both benefit. This is …
  1. Amutualism
  2. Bcommensalism
  3. Cparasitism

Answer: mutualism

The bee gets food and the flower is pollinated, so both benefit: mutualism.

2.A tick feeds on the blood of a dog and can spread disease to it. This is …
  1. Amutualism
  2. Bcommensalism
  3. Cparasitism

Answer: parasitism

The tick benefits and the dog is harmed, so this is parasitism.

3.Barnacles attach to the skin of a whale and get carried to new feeding areas. The whale is not affected. This is …
  1. Amutualism
  2. Bcommensalism
  3. Cparasitism

Answer: commensalism

The barnacles benefit and the whale is neither helped nor harmed: commensalism.

4.A clownfish lives among the stinging tentacles of a sea anemone, which protect it; the clownfish cleans the anemone and drives away fish that eat it. This is …
  1. Amutualism
  2. Bcommensalism
  3. Cparasitism

Answer: mutualism

Both partners gain something, so it is mutualism.

5.Match each relationship to its effect on the two organisms.
  • mutualism
  • commensalism
  • parasitism
  • predation
  • one benefits, the other is unaffected
  • one benefits, the other is harmed
  • one organism hunts, kills and eats the other
  • both organisms benefit

Answer: mutualism → both organisms benefit; commensalism → one benefits, the other is unaffected; parasitism → one benefits, the other is harmed; predation → one organism hunts, kills and eats the other

Part B: Competition

6.Tall trees in a forest compete with smaller plants for light.

Answer: True

Tall trees shade the plants below, so plants compete for sunlight to make food.

7.Competition only happens between different species.

Answer: False

Members of the same species also compete, for example two male birds competing for the same territory.

8.When two species compete for the same food supply, the numbers of one or both species may be lower than if each lived there alone.

Answer: True

Sharing a limited resource means less is available to each, which can limit both populations.

9.An organism that lives on or in another organism and harms it is called a (answer space).

Answer: parasite

Part C: Predators and prey

Use the data to answer the questions.

Rabbit and fox populations in a valley (one survey each spring)

Survey 1: rabbits 200, foxes 10

Survey 2: rabbits 400, foxes 15

Survey 3: rabbits 600, foxes 30

Survey 4: rabbits 300, foxes 45

Survey 5: rabbits 150, foxes 25

Survey 6: rabbits 250, foxes 12

10.In which survey did the rabbit population peak, and in which survey did the fox population peak?

Answer: Rabbits peaked in survey 3 (600); foxes peaked in survey 4 (45).

11.By how much did the rabbit population change from survey 3 to survey 4?

Answer: It fell by 300 (from 600 to 300), so it halved.

  1. 600 − 300 = 300
12.Explain why the fox population rose between surveys 2 and 4.

Answer: There were more rabbits to eat, so more foxes survived and raised young.

13.Explain why the fox population fell between surveys 4 and 6.

Answer: The rabbit population had crashed, so there was less food for the foxes and fewer survived or reproduced.

14.Using the data, explain the predator–prey cycle. Then predict what would happen to the rabbit population, and to the grass the rabbits eat, if all the foxes were removed from the valley. Give reasons.

Model answer: When there is plenty of prey (rabbits), the predators (foxes) have lots of food, so their numbers rise, but a little later than the rabbits (rabbits peak in survey 3, foxes in survey 4). More foxes eat more rabbits, so the rabbit population falls. With fewer rabbits, foxes run short of food and their numbers fall too. With fewer foxes, rabbits survive and increase again (survey 6), and the cycle repeats. If all the foxes were removed, the rabbit population would grow quickly because nothing would be eating them. The rabbits would eat more and more grass, so the grass would decrease. Eventually the rabbits would run out of food and their population could crash from starvation, and other animals that depend on the grass could also be affected.

Success criteria:

  • Describes prey rising then predators rising after a delay
  • Explains the falls in each population
  • Uses data from the table
  • Predicts the rabbit increase and grass decrease with reasons
  • Mentions a later crash or wider effects
Free worksheets at worksheets.successtutoring.com · © Success Tutoring · Free for personal and classroom use

Marking tips

  • Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
  • For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
  • Celebrate what went well first, then pick one thing to work on next.

Great work. Here's what to try next: