Habitats, Resources & Population Change — Practice · Grade 7 Science

Chapter: Ecosystems, Matter & Energy

What this practice covers

By the end of Habitats, Resources & Population Change you should be able to:

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

Vocabulary used: population, community, biotic factor, abiotic factor, carrying capacity.

Problem 1

Why should a count include area and effort?
Answer and explanation

Without them, equal or different counts might reflect different survey scope rather than biological change.

Problem 2

Does an increased count prove more births?
Answer and explanation

No. Immigration or detection differences can also increase the recorded number.

Problem 3

Why can carrying capacity change?
Answer and explanation

Resources, habitat, and environmental conditions change, altering what the modeled setting can support.

Problem 4

Why might a lower observed count not mean the same number died?
Answer and explanation

Movement or lower detectability can affect counts; births and deaths are not the only pathways.

Problem 5

Illustrative interval: population begins at 50; births add 12; immigration adds 5; deaths remove 8; emigration removes 4. No other pathways are stipulated. Calculate ending count and explain why a before-after count alone cannot identify all pathways.
Answer and explanation

The modeled population ends at 55, a net increase of five. The same net change could result from other combinations of births, deaths, and movement. Before-after counts alone do not identify the mechanism; pathway observations, boundaries, and detection methods are needed. This model does not establish a permanent habitat capacity.

Gains: 12+5=17.

Losses: 8+4=12.

End: 50+17−12=55.

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 field count rises after a survey team doubles its observation time. Can the increase be assigned directly to population growth?
Answer and explanation

No. More effort can detect more individuals. Use comparable survey effort and methods before interpreting the difference as true growth.

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 is an abiotic factor?
  1. Temperature
  2. A predator
  3. A decomposer
  4. A competing plant
Answer and explanation

Temperature

Temperature is a physical condition, while the others involve organisms.

Problem 8

A population of 40 gains 10 and loses 7 under a complete model. Find ending count.
Answer and explanation

43 individuals

40+10−7=43.

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