Question 20N.3.SL.TZ0.3c
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.3.SL.TZ0.3c |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | 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.]
Suggest how a plastic bag placed around the plant pot prevents carbon dioxide from reaching the plant’s leaves.
[1]
a. to prevent CO2 from (organisms in) the soil affecting the experiment;
b. the plastic bag is impermeable to gases;
The plastic bag caused considerable confusion with many candidates stating that it was to prevent carbon dioxide reaching the roots and being taken up the stem to the leaves for photosynthesis.
