Interactions & Ecosystem Change — Practice · Grade 7 Science

Chapter: Ecological Evidence & Environmental Design

What this practice covers

By the end of Interactions & Ecosystem Change you should be able to:

8 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: competition, predation, mutualism, parasitism, disturbance.

Problem 1

Does sharing a habitat alone prove competition?
Answer and explanation

No. Resource overlap and limitation, or effects on performance, need evidence.

Problem 2

Why might a predator not fall immediately after one prey declines?
Answer and explanation

Alternative prey, movement, stored resources, and delayed responses can affect its population.

Problem 3

What observation could strengthen a predation explanation?
Answer and explanation

Relevant feeding evidence and repeated population records, considered with alternative resources and conditions, can strengthen it.

Problem 4

Does recovery require every count to return to its original value?
Answer and explanation

Not necessarily. Recovery depends on the defined function or condition; composition and counts can differ.

Problem 5

Illustrative records show plant cover falling from 80% to 50% while herbivore count rises from 10 to 20; drought also occurs. Describe the changes, explain two plausible contributions, and propose evidence that separates them.
Answer and explanation

Herbivory could reduce cover, while drought could also limit plant growth. The two recorded changes do not isolate either cause. Compare feeding observations, water conditions, and suitable reference plots across repeated intervals. Plant cover and counts are different measures, and the model should not claim a single cause from their association alone.

Cover falls 30 percentage points.

Herbivore count doubles.

Compare feeding effects with drought and a suitable matched observation.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A student labels every insect on a plant a parasite. Why is that premature?
Answer and explanation

Different insects can feed, pollinate, shelter, or interact in other ways. Identify effects and resource relationships before classifying the interaction.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which identifies competition most directly?
  1. Shared use of a limiting resource
  2. Any two different colors
  3. Every insect landing
  4. Any pair of graph axes
Answer and explanation

Shared use of a limiting resource

Competition concerns limiting-resource overlap and its effects.

Problem 8

Plant cover changes from 70% to 45%. Find the decrease in percentage points.
Answer and explanation

25 percentage points

70−45=25 percentage points, distinct from a percent decrease relative to 70.

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