| Date | November 2015 | Marks available | 2 | Reference code | 15N.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 Haberlea rhodopensis plant is capable of tolerating extreme dryness. Chlorophyll levels and CO2 assimilation were evaluated during dehydration and rehydration using plants grown in shade and sunlight. Graph A shows the changes in chlorophyll content with increasing dehydration and during rehydration. Graph B shows the changes in CO2 assimilation with increasing dehydration and during rehydration.
State the level of chlorophyll at 50 % water content for plants growing in sunlight, giving the units.
Outline the effect of sunlight and shade on CO2 assimilation during dehydration.
Compare the effect of rehydration on chlorophyll levels in plants grown in shade and sunlight.
Using the data, deduce, with a reason, two stages of photosynthesis that may be limited during dehydration in a plant.
Markscheme
4.2 mg g–1 (units required)
Accept answers in the range of 4.1 mg g–1 to 4.3 mg g–1.
a. decreases with dehydration in both shade and sunlight;
b. greater decrease in sunlight than shade;
c. at 100/50 CO2 assimilation greater in sunlight than shade but at 25 shade greater than sunlight;
a. both increase (over the 25% water content);
b. (chlorophyll in) shade plants increase to almost the same/slightly less than original levels;
c. plants grown in sunlight have almost the same/slightly more than original levels;
d. the difference between plants grown in the shade and sunlight is less than at any time at dehydration;
a. decrease in chlorophyll causes lowered rate of light dependent reaction/less absorption of light energy;
b. decrease in CO2 assimilation causes lowered rate of light independent reaction/ less CO2 fixation/Calvin cycle;
c. both stages reduced due to wilting/less surface of leaf/closure of stomata;
Candidates must include a reason to receive the mark.
Examiners report
The candidates performed well in parts (a) (b) and (c) of the data question but found (d) difficult with many not giving a reason why dehydration affects photosynthesis.
The candidates performed well in parts (a) (b) and (c) of the data question but found (d) difficult with many not giving a reason why dehydration affects photosynthesis.
The candidates performed well in parts (a) (b) and (c) of the data question but found (d) difficult with many not giving a reason why dehydration affects photosynthesis.
The candidates performed well in parts (a) (b) and (c) of the data question but found (d) difficult with many not giving a reason why dehydration affects photosynthesis.
