| Date | November 2009 | Marks available | 1 | Reference code | 09N.3.SL.TZ0.7 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Compare | Question number | 7 | Adapted from | N/A |
Question
The graph below shows the results of an experiment to determine the effect of salt (NaCl) concentration on photosynthesis of the freshwater green alga Chlorella vulgaris. The experiment attempted to determine the effect of salt concentration on the light-dependent reactions overall and separately on photosystem I and photosystem II.
Describe the effect of salt concentration on the activity of the light-dependent reactions overall.
Compare the effect of increasing salt concentration on photosystem I with the effect on photosystem II.
When salt concentration is increased, some algal cells increase their rates of cyclic photophosphorylation. Deduce the reasons for this.
Using the graph, predict the effect of high salt concentration on the growth of Chlorella vulgaris. Give a reason for your answer.
Markscheme
overall photosynthesis rates go down with increasing salt concentration
decline in activity for photosystem II but not for photosystem I
cyclic photophosphorylation dependent on photosystem I;
photosystem I is not affected by increasing salt concentration;
reduced growth;
due to reduction in rates of photosynthesis/energy fixation;
Examiners report
Most candidates answered this question correctly.
Most candidates answered this question correctly.
Many of the candidates obtained one mark, although many did not seem to understand the functional difference between the two photosystems.
