A student investigates the rate of photosynthesis in the aquatic plant Elodea canadensis by measuring the volume of oxygen produced per minute. The plant is placed in a beaker of water containing different concentrations of sodium hydrogencarbonate (which provides carbon dioxide). The beaker is placed at different distances from a lamp to vary light intensity, and the water temperature is controlled using a water bath. The results are shown in the table.
| Condition | Light intensity (arbitrary units) | CO₂ concentration (mg dm⁻³) | Temperature (°C) | Oxygen production (cm³ min⁻¹) |
|---|---|---|---|---|
| 1 | 200 | 20 | 15 | 1.2 |
| 2 | 200 | 20 | 25 | 2.5 |
| 3 | 200 | 20 | 35 | 3.8 |
| 4 | 200 | 20 | 45 | 3.8 |
| 5 | 200 | 40 | 25 | 4.0 |
| 6 | 400 | 20 | 25 | 3.0 |
| 7 | 400 | 40 | 25 | 5.0 |
(a) Predict which factor is limiting the rate of photosynthesis in Condition 2. Explain your answer.
(b) Predict which factor is limiting the rate of photosynthesis in Condition 5. Explain your answer.
(c) Predict which factor(s) are limiting the rate of photosynthesis in Condition 6. Explain your answer.
(d) Predict which factor is likely to become limiting if the temperature in Condition 7 is increased to 50 °C. Explain why.