Sampling Ecosystems & Comparing Evidence — Practice · Grade 7 Science

Chapter: Ecological Evidence & Environmental Design

What this practice covers

By the end of Sampling Ecosystems & Comparing Evidence you should be able to:

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

Vocabulary used: sample, quadrat, transect, density, sampling bias.

Problem 1

Why specify whether sightings or individuals are counted?
Answer and explanation

Repeated sightings can involve one individual; the quantities answer different questions.

Problem 2

Can a mean remove biased site selection?
Answer and explanation

No. A biased set can still produce a precise-looking mean; location selection must be addressed.

Problem 3

Why can equal plot counts differ in density?
Answer and explanation

Plot areas can differ; count per area accounts for that boundary.

Problem 4

Does sample density establish the exact habitat total?
Answer and explanation

No. Extrapolation depends on sample representativeness, area definitions, and detection.

Problem 5

Illustrative four 1 m² plots contain 2, 4, 3, and 3 plants of one species. A habitat area is 20 m². Find sample density, calculate an extrapolated count, and state the assumptions that prevent calling it a complete census.
Answer and explanation

The sample density is 3 plants/m² and the extrapolated count is 60 plants. It is an estimate assuming the plots represent the 20 m² habitat and detection is adequate. Patchiness, omitted zones, or missed plants could change the result. The supplied data do not establish an exact total.

Total count: 12 across 4 m².

Density: 12/4=3 plants/m².

Estimated larger count: 3×20=60.

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 team uses four 1 m² plots in one habitat and four 2 m² plots in another. Can mean counts alone compare density?
Answer and explanation

No. Different plot areas require count-per-area calculations or an appropriately weighted comparison using comparable detection methods.

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 choice reduces the stated location-selection problem?
  1. Only sample favorite patches
  2. Use a predefined representative location plan
  3. Delete low counts
  4. Change plot size secretly
Answer and explanation

Use a predefined representative location plan

A planned sampling method helps address selection bias, though other limits remain.

Problem 8

A survey detects 18 plants across 6 m². Find density.
Answer and explanation

3 plants/m²

18/6=3 plants/m² under the stated detection method.

Browse all courses