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Photosynthesis at very high temperature
A student investigated the relationship between temperature and the rate of photosynthesis. The student measured the volume of gas produced by an aquatic plant in 1 hour and collected the gas in a measuring cylinder. Table 2 shows the results.
| Temperature in °C | Volume of gas produced in 1 hour in cm³ |
|---|---|
| 10 | 1 |
| 15 | 2 |
| 20 | 4 |
| 25 | 8 |
| 30 | 16 |
| 35 | 16 |
| 40 | 2 |
| 45 | 0 |
Explain why no gas was produced by the plant at 45 °C.
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Marking points
- 1 States that the relevant enzymes are denatured/destroyed at 45 °C.
- 2 Explains that the active site changes shape.
- 3 Explains that the substrate can no longer fit/bind to the active site.
Full-mark answer
At 45 °C the enzymes involved in photosynthesis are denatured. Their active sites change shape, so the substrates no longer fit and the reactions producing oxygen stop.
Why this answer loses marks
The enzymes are killed by the high temperature.
Enzymes are denatured rather than killed; describe the active-site shape change or loss of substrate fit.