AQA · GCSE · Biology · Higher

Tadpole survival percentage calculation

Q03.4 3 marks

Table 1

Sample number	0 weeks	1 week	2 weeks	3 weeks	5 weeks	8 weeks
1	11	17	8	9	5	0
2	15	11	12	7	0	5
3	23	16	14	10	7	3
4	11	14	16	X	4	4
Totals	60	58	50	32	16	12

Figure 4 represents the Table 1 total numbers of tadpoles against time. Its x-axis is time in weeks and its y-axis is total number of tadpoles; a curved line of best fit follows the Table 1 totals.

After 0 weeks, no more tadpoles hatched in the pond. Calculate the percentage of the tadpoles that would still be found in the pond at 4 weeks compared with 0 weeks. Use information from Figure 4.

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Marking points

1 Uses valid 0-week and 4-week readings from the plotted line (or the official no-line fallback values).
2 Divides the 4-week value by the 0-week value and multiplies by 100.
3 Gives a percentage consistent with the values used, such as 36.7% for 22 and 60.

Full-mark answer

A typical line of best fit gives about 60 tadpoles at 0 weeks and 22 at 4 weeks. Percentage remaining = (22 ÷ 60) × 100 = 36.7% (about 37%). A correct calculation from the learner's own valid graph readings is also accepted; the official no-line fallback using 24 and 60 gives 40%.

Why this answer loses marks

Find the decrease and divide it by the later reading.

The question asks for the percentage remaining, so use the target-time amount over the starting amount.

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