The table below shows the number of daisy plants found by a student in five 0.25 m² quadrats placed at random positions in a school field. The student wants...
Question 1 Report
The table below shows the number of daisy plants found by a student in five 0.25 m² quadrats placed at random positions in a school field. The student wants an average value for the density of this species.
| quadrat number | number of daisy plants |
|---|---|
| 1 | 3 |
| 2 | 6 |
| 3 | 8 |
| 4 | 5 |
| 5 | 3 |
(a) Complete the calculation of the mean number of daisy plants per quadrat. [2]
(b) Describe how the student could use a tape measure and random numbers to place quadrats without choosing areas that look typical. [4]
(c) Explain why repeating the sampling with more quadrats would improve the estimate of the average number of plants. [2]
(d) State two reasons why counting individual grass plants in the same quadrats would be difficult. [2]
Answer Details
(a) Add the five counts:
\[3+6+8+5+3=25\]
\[\text{mean}=\frac{25}{5}=5\text{ plants per quadrat}\]
[2]
(b) Lay two tape measures at right angles to form axes across the field. Generate random pairs of distances, or coordinates. Measure each pair of distances along the tapes, place a quadrat at each selected position, and count the daisies. Random coordinates prevent the student choosing places that merely look typical. [4]
(c) More quadrats reduce the effect of unusual quadrats or anomalous results. The calculated mean is therefore more reliable and more representative of the field. [2]
(d) Individual grass plants can be difficult to count because they may be joined by runners, overlap, or have many shoots growing close together. Roots are also not visible. Any two are acceptable. [2]
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