A student used a potometer to investigate the rate of water uptake in a plant shoot - AQA - GCSE Biology Combined Science - Question 3 - 2019 - Paper 1
Question 3
A student used a potometer to investigate the rate of water uptake in a plant shoot.
Figure 3 shows a potometer.
As the shoot takes in water the air bubble moves.
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Worked Solution & Example Answer:A student used a potometer to investigate the rate of water uptake in a plant shoot - AQA - GCSE Biology Combined Science - Question 3 - 2019 - Paper 1
Step 1
Suggest how the student moved the air bubble back to 0 mm for the start of investigation B.
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Answer
The student likely opened and closed the tap gently to allow water to enter the reservoir and move the air bubble back to the starting position of 0 mm.
Step 2
Explain why narrow tubing was used.
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Answer
Narrow tubing allows the air bubble to move more quickly and makes it easier to see small changes in the volume of water taken up by the plant shoot. This improves the resolution of the measurements, allowing for more accurate data collection.
Step 3
Calculate the rate of water uptake for investigation A in mm/min.
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Answer
The position of the air bubble at 5 minutes is 66 mm. Therefore, the rate of water uptake is calculated as:
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Answer
The data points from Table 4 should be plotted on Figure 4 at the respective time intervals. A line of best fit should be drawn through the points, and it should be labeled as line B.
Step 5
Draw a line on Figure 4 to show the results you would expect for investigation C.
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Answer
A straight line starting at (0, 0) but with a steeper gradient than Investigation A should be drawn on Figure 4, labeled as line C, representing higher water uptake under dry air at 25 °C conditions.
Step 6
Explain why the air bubble would not move if the investigations were done in the dark.
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Answer
In the absence of light, the plant would undergo minimal to no photosynthesis. As a result, the stomata would close to prevent water loss, and therefore, there would be little to no transpiration. This would lead to a reduced rate of water uptake, causing the air bubble to remain stationary.
