| Date | May 2017 | Marks available | 2 | Reference code | 17M.3.SL.TZ1.2 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Compare and contrast | Question number | 2 | Adapted from | N/A |
Question
Students exposed the water plant Cabomba caroliniana to different light intensities. The bubbles of oxygen gas released by the plant were counted each minute.
Compare and contrast the experimental results for the effect of light intensity on the rate of photosynthesis of a green plant with the expected trend line.
C. caroliniana can grow well in water at 27°C. This experiment was carried out at 25°C.
Describe the effect of carrying out the same experiment at 15°C.
This experiment measured the quantity of oxygen gas released by the water plant. State one other way of measuring the rate of photosynthesis.
Markscheme
Compare:
a. both the theoretical data and the experimental data show an increase in photosynthetic rate/oxygen production with increased light intensity
OR
the rate of photosynthesis in the experimental data starts to level off at high light intensity as expected in theoretical data
Contrast:
b. the experimental data do not reach a plateau whereas theoretical data do
OR
data show photosynthesis is occurring at zero lux/light intensity whereas theoretical data would not
Accept answers using an annotated graph.
Accept answers as annotations of the graph or a new graph drawn:
«the rate of photosynthesis» would be slower/fewer bubbles
OR
rise to lower level/would plateau at a lower level/would be half the height
a. measure the absorption/decrease of CO2
b. measure the increase in biomass
c. measure rise in pH
