The diagram shows a student using a lamp and a ruler to investigate light intensity and bubbles from Cabomba. A beaker of water contains sodium hydrogencarb...
Question 1 Report
The diagram shows a student using a lamp and a ruler to investigate light intensity and bubbles from Cabomba. A beaker of water contains sodium hydrogencarbonate. Table 1 shows the bubble count in 1 minute.
| lamp distance / cm | bubbles per minute |
|---|---|
| 10 | 42 |
| 20 | 19 |
| 40 | 6 |
(a) Use Table 1 to state the bubble count at 20 cm. [1]
(b) Describe the trend as lamp distance increases. [1]
(c) Suggest why sodium hydrogencarbonate was added. [1]
(d) Suggest one reason why counting bubbles is less accurate than measuring gas volume. [1]
Fig. 1 shows a student testing oxygen released by pondweed in a water bath. The capillary tube collects gas for 10 minutes.
Table 1 shows the gas volume at two temperatures.
| temperature / degrees C | oxygen volume / cm3 |
|---|---|
| 20 | 4.0 |
| 30 | 7.5 |
(a) Name the process in the pondweed that produces the oxygen. [1]
(b) Use Table 1 to state the temperature giving the greater volume of oxygen. [1]
(c) Suggest why the student kept the lamp at the same distance for both tests. [1]
Answer Details
Cabomba and light intensity
- (a) At 20 cm, the bubble count was 19 bubbles per minute. [1]
- (b) As lamp distance increases, the bubble count decreases. The lamp provides less light at greater distances, reducing photosynthesis rate. [1]
- (c) Sodium hydrogencarbonate provides carbon dioxide for photosynthesis. [1]
- (d) Bubble counting is less accurate because bubbles differ in size. Bubbles may also join together or be missed. [1]
Pondweed and temperature
- (a) Oxygen is produced by photosynthesis. [1]
- (b) 30 degrees C gave the greater oxygen volume. [1]
- (c) Keeping the lamp at the same distance keeps light intensity constant, making the test fair. [1]
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