CAIE A Level Biology 9700 · Photosynthesis
A student placed a pondweed in a beaker of water and measured the number of oxygen bubbles produced per minute at different distances from a lamp. The results are shown in the table.
| Distance from lamp / cm | Bubbles per minute |
|---|---|
| 10 | 60 |
| 20 | 40 |
| 30 | 25 |
| 40 | 15 |
| 50 | 10 |
| 60 | 8 |
| 70 | 8 |
| 80 | 8 |
Describe the shape of the graph of bubbles per minute against distance from lamp, and explain why the rate of photosynthesis becomes constant at distances greater than 60 cm.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.