A student investigated the effect of light intensity on the rate of the light-dependent stage of photosynthesis using a suspension of isolated chloroplasts and the redox indicator DCPIP (2,6-dichlorophenolindophenol). DCPIP is blue when oxidised and becomes colourless when reduced. The chloroplast suspension was mixed with DCPIP solution and exposed to white light at different intensities. The time taken for the DCPIP to become completely colourless was recorded. The temperature was kept constant at 20°C. The results are shown in the table.
| Light intensity (arbitrary units) | Time for complete decolourisation (s) |
|---|---|
| 10 | 120 |
| 20 | 60 |
| 40 | 30 |
| 80 | 20 |
| 160 | 18 |
(a) Predict the time for complete decolourisation at a light intensity of 200 units. Explain your prediction.
(b) Predict how the time for complete decolourisation would change if the temperature was raised from 20°C to 35°C while keeping the light intensity at 40 units. Explain your prediction.