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

Narrow tubing is used as it allows the air bubble to move more quickly and accurately indicate small changes in water uptake. The increased resistance in narrower tubes enhances resolution, making it easier to detect minor variations in the air bubble's position.

To calculate the rate of water uptake, we first find the distance moved by the air bubble (66 mm in 5 minutes). The rate can be calculated as follows:

$\text{Rate} = \frac{\text{Distance}}{\text{Time}} = \frac{66 \text{ mm}}{5 \text{ min}} = 13.2 \text{ mm/min}$

Next, we convert this to the volume by multiplying by the cross-sectional area:

$\text{Rate} = 0.8 \text{ mm}^2 \times 13.2 \text{ mm/min} = 10.56 \text{ mm}^3/min$

To plot the data, first plot each point corresponding to the time in minutes against the position of the air bubble in mm. Next, draw a line of best fit that represents the trend of the data and label it 'B'.

To represent the expected results for investigation C, draw a straight line on Figure 4 starting below the line for investigation A and showing a less steep gradient, indicating lower water uptake due to the drier conditions.

In the dark, the plant's stomata close to prevent water loss since no light is present for photosynthesis. As a result, there would be minimal transpiration, causing the air bubble not to move in the potometer due to reduced water uptake.