Distance of lamp from pondweed / cm Number of oxygen bubbles in 4 minutes Rate of bubble production / bubbles per minute 10 48 12 20 32 8 30 20 5 40 12 The ...
Question 1 Report
| Distance of lamp from pondweed / cm | Number of oxygen bubbles in 4 minutes | Rate of bubble production / bubbles per minute |
|---|---|---|
| 10 | 48 | 12 |
| 20 | 32 | 8 |
| 30 | 20 | 5 |
| 40 | 12 |
The table below shows results from an investigation using pondweed. A lamp was placed at different distances from the pondweed in a tube of water containing sodium hydrogencarbonate solution. The solution provided carbon dioxide. Scientists counted oxygen bubbles released in four minutes. A diagram of the apparatus is shown in Fig. 1. The same piece of pondweed was used for every distance.
| Distance of lamp from pondweed / cm | Number of oxygen bubbles in 4 minutes | Rate of bubble production / bubbles per minute |
|---|---|---|
| 10 | 48 | 12 |
| 20 | 32 | 8 |
| 30 | 20 | 5 |
| 40 | 12 |
(a) Complete the missing value in Table 1. [1]
(b) Describe the effect of increasing distance from the lamp on the rate of photosynthesis. [2]
(c) Use the results to explain why light was a limiting factor in this investigation. [2]
Answer Details
(a)
\[\frac{12\text{ bubbles}}{4\text{ min}}=3\text{ bubbles min}^{-1}\]
The missing rate is 3 bubbles per minute. [1]
(b) The rate of photosynthesis decreases as distance from the lamp increases. For example, it falls from 12 bubbles per minute at 10 cm to 3 bubbles per minute at 40 cm. Oxygen-bubble production is used as an indication of photosynthesis because oxygen is a product of photosynthesis. [2]
(c) Moving the lamp further away reduces light intensity. Less light energy is absorbed for photosynthesis, so the rate of oxygen-bubble production falls. Therefore light was a limiting factor under these conditions. [2]
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