Worked example
Three equal-area squares contain 4, 6 and 8 seedlings. What is the mean count per sampled square?
Answer & why
Answer: 6
(4 + 6 + 8) ÷ 3 = 6 seedlings per square.
Grade 7 · Science
Interpret a habitat sample
Use repeated samples and stated sampling limits to interpret habitat counts.
6 authored questions + worked example
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All questions
All 6 authored questions for this skill.
Question 1
Ten randomly placed equal-area squares are sampled instead of one conveniently chosen square. What is a reasonable improvement?
- Proof that every future year is identical.
- Less dependence on one convenient location.
- Elimination of all natural variation.
- A guarantee of the exact whole-park total.
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: Less dependence on one convenient location.
Broader selection reduces dependence on one chosen site without making an estimate exact.
Question 2
A sample covers 5 m² and contains 20 plants. What is the observed density in the sample?
- 4 plants per m²
- 25 plants per m²
- 100 plants per m²
- 0.25 plants per m²
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: 4 plants per m²
20 plants ÷ 5 m² = 4 plants per m².
Question 3
Counts in four equal squares are 1, 2, 12 and 13. Which statement respects the observed variation?
- The two highest counts must be mistakes.
- Every square has exactly 7 plants.
- Plant counts vary substantially between these squares.
- All unsampled squares are empty.
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: Plant counts vary substantially between these squares.
The counts range from 1 to 13; the data alone do not justify discarding them.
Question 4
Two teams compare counts, but one uses 1 m² squares and the other 4 m² squares. What should they calculate for an area-based comparison?
- The sum of their square sizes without counts.
- Only the longest team name.
- Counts per unit area.
- The count from whichever square looks greener.
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: Counts per unit area.
A common unit-area measure accounts for different sampled areas.
Question 5
Three equal-area squares contain 4, 6 and 8 seedlings. What is the mean count per sampled square?
- 18
- 9
- 6
- 3
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: 6
(4 + 6 + 8) ÷ 3 = 6 seedlings per square.
Question 6
A survey counts insects only beside a pond, then claims to represent an entire dry-and-wet park. What is its main sampling limitation?
- A pond cannot contain insects.
- The selected habitat may not represent the whole park.
- The park's name was not recorded.
- Counting always prevents evidence.
A hint
Keep sampled area, selection method and variation visible before generalizing to the whole habitat.
Answer & why
Answer: The selected habitat may not represent the whole park.
One habitat may have different conditions from the unsampled areas.