Light intensity (units) Rate at 0.04% CO2 Rate at 0.10% CO2 2 10 10 4 18 20 6 22 32 8 22 42 A researcher measured the rate of photosynthesis of a tomato pla...
Question 1 Report
| Light intensity (units) | Rate at 0.04% CO2 | Rate at 0.10% CO2 |
|---|---|---|
| 2 | 10 | 10 |
| 4 | 18 | 20 |
| 6 | 22 | 32 |
| 8 | 22 | 42 |
A researcher measured the rate of photosynthesis of a tomato plant at two different carbon dioxide concentrations while steadily increasing the light intensity. Table 3.1 shows the rate of photosynthesis, in arbitrary units, recorded at each condition. All the other conditions, including the temperature, were kept constant throughout the investigation.
| Light intensity (units) | Rate at 0.04% CO2 | Rate at 0.10% CO2 |
|---|---|---|
| 2 | 10 | 10 |
| 4 | 18 | 20 |
| 6 | 22 | 32 |
| 8 | 22 | 42 |
(a) State the rate of photosynthesis at a light intensity of 4 units and 0.04% carbon dioxide. [1]
(b) Describe what happens to the rate at 0.04% carbon dioxide as light intensity increases from 6 to 8 units. [1]
(c) Explain what is limiting the rate of photosynthesis at 0.04% carbon dioxide above 6 units of light. [2]
(d) Explain why the rate is higher at 0.10% carbon dioxide than at 0.04% carbon dioxide when the light is bright. [3]
(e) Define the term limiting factor. [2]
(f) Suggest one other factor, not shown in the table, that could limit the rate of photosynthesis. [1]
(g) Explain how a greenhouse grower could use this information to increase the yield of a tomato crop. [4]
Answer Details
This question tests reading photosynthesis data and the idea of limiting factors: the rate is set by whichever required factor is in shortest supply. The graph below plots both carbon dioxide conditions from the table.
(a) At 4 units of light and 0.04% carbon dioxide the rate is 18 units, read directly from the table [1].
(b) At 0.04% carbon dioxide, as light increases from 6 to 8 units the rate stays the same / levels off at 22 units [1].
(c) Because the rate has plateaued, extra light makes no difference, so light is no longer the limiting factor [1]; instead the carbon dioxide concentration is now limiting the rate [1] (there is not enough \(CO_2\) to use the extra light).
(d) In bright light the rate is higher at 0.10% because more carbon dioxide is available [1]; carbon dioxide is a raw material for photosynthesis [1]; so when light is not limiting, the extra \(CO_2\) allows a faster rate (42 units versus 22) [1].
(e) A limiting factor is a factor that, when in short supply [1], limits or holds back the rate of a process such as photosynthesis [1].
(f) One other factor not shown: temperature (accept concentration of chlorophyll / water availability) [1].
(g) A greenhouse grower could raise yield by controlling every factor so none is limiting: increase the carbon dioxide concentration [1]; provide bright or artificial lighting [1]; keep the temperature warm at an optimum [1]; so that photosynthesis and growth are faster, giving a greater crop yield [1].
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