1.1. A group of students wanted to investigate how the rate of photosynthesis is affected by temperature.

They grew some tomato plants in a greenhouse on school grounds then cut disks from the leaves of the plants in their experiments.

To show the rate of photosynthesis, the students measured the rate of carbon dioxide uptake by the leaf disks.

In the dark, the leaf disks did not take up any carbon dioxide, but did produce it.

Explain this observation.

1.2. In their investigation, the scientists measure the rate of carbon dioxide taken in by the leaf discs in the light.

The scientists then measured the rate of carbon dioxide produced by the leaf discs when they were placed in the dark.

The graph in Figure 1 shows the effect of temperature on:

• Carbon dioxide uptake in the light

• Carbon dioxide uptake in the light added to carbon dioxide production in the dark

Figure 1

Use the information in Figure 1 to describe the effect of temperature on carbon dioxide uptake in the light.

1.3. Explain the effect of temperature on carbon dioxide uptake in the light when the temperature is increased from 20 °C to 35 °C and then from 45 °C to 50 °C.

1.4. Higher Tier Only

The students want to maximise the rate of growth of their tomatoes.

Suggest the best temperature that they should heat their greenhouse to, and give a reason for your suggestion.