GCSE Science Exam Questions by Topic

A student investigates the effect of light intensity on the rate of photosynthesis by counting bubbles of oxygen released by pondweed. At a lamp distance of 20 cm the student counts 36, 40 and 38 bubbles in two minutes, and one run of 62 bubbles. Calculate the mean rate in bubbles per minute, and state how the anomaly should be treated.

1. Identify the anomaly: 62 is far outside the cluster of 36, 40 and 38, so it is anomalous and should be excluded from the mean, with that exclusion stated in the answer.
2. Add the remaining results: 36 + 40 + 38 = 114 bubbles.
3. Divide by the number of results: 114 / 3 = 38 bubbles in two minutes.
4. Convert to a rate per minute: 38 / 2 = 19 bubbles per minute.
5. State the treatment of the anomaly: it is excluded from the mean but not deleted from the results table, and the likely cause (for example a bubble released from a previous run, or the lamp being moved) is given.
6. Final answer: mean rate = 19 bubbles per minute, with the 62-bubble result identified as an anomaly and excluded.