Question 20N.3.SL.TZ0.a
| Date | November 2020 | Marks available | [Maximum mark: 2] | Reference code | 20N.3.SL.TZ0.a |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Describe | Question number | a | Adapted from | N/A |
To investigate whether carbon dioxide is required for photosynthesis, a plant was irrigated using water from which carbon dioxide had been removed and was then placed in the apparatus shown in the diagram. The apparatus was left in darkness for 24 hours to destarch the leaves. Then, after several hours in light, a leaf was removed from the plant and found to contain no starch when tested. A control was performed using a second plant. A leaf from this plant tested positive for starch.
[Source: © International Baccalaureate Organization 2020.]
Describe the control for this experiment.
[2]
a. same apparatus with carbon dioxide present;
b. (control has) no sodium hydroxide/alkali;
c. control irrigated with untreated water/water with CO2;
“Same apparatus” alone does not get the mark.
Many candidates had difficulty describing the control for this experiment. The question states that the experiment was to investigate whether carbon dioxide is required for photosynthesis therefore it seems straightforward that the plant would be in similar conditions with and without carbon dioxide. Some candidates assumed that the control plant would have similar conditions and no light.
