The table below shows results from an investigation with pondweed collected from a freshwater island pond. A lamp was placed at different distances from the...
Question 1 Report
The table below shows results from an investigation with pondweed collected from a freshwater island pond. A lamp was placed at different distances from the pondweed for two minutes. The student counted bubbles of oxygen leaving the cut stem. The water temperature was kept close to 22 degrees C using a water bath. Fig. 1 shows the apparatus, including a ruler used to set the lamp distance. The student repeated each distance three times before calculating a mean.
| Distance of lamp from pondweed / cm | Mean number of oxygen bubbles in 2 minutes |
|---|---|
| 10 | 42 |
| 20 | 25 |
| 30 | 14 |
| 40 | 8 |
(a) Record the mean number of bubbles at 30 cm. [1]
(b) Describe the relationship between lamp distance and oxygen bubble production. [2]
(c) Explain why the water temperature was controlled. [1]
Answer Details
(a) 14 [1] (b) As distance increases, the number of bubbles decreases [1]; the decrease is not necessarily by an equal amount at each interval / highest rate is at 10 cm [1] (c) Temperature affects the rate of enzyme-controlled photosynthesis, so it must be kept constant for a fair test [1]
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