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A student used a potometer to measure the movement of water through the shoot of a plant - AQA - A-Level Biology - Question 6 - 2017 - Paper 3

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A student used a potometer to measure the movement of water through the shoot of a plant. The potometer is shown in Figure 5. As water is lost from the shoot, it is ... show full transcript

Worked Solution & Example Answer:A student used a potometer to measure the movement of water through the shoot of a plant - AQA - A-Level Biology - Question 6 - 2017 - Paper 3

Step 1

Calculate the rate of water uptake by the shoot in this experiment.

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Answer

To determine the rate of water uptake, we first calculate the cross-sectional area of the capillary tube using the formula: A = rac{ heta^2}{4} imes ext{π} where ( \theta ) is the diameter.

  1. Calculate the area:

    • Diameter = 1.0 mm.
    • Radius = 0.5 mm.
    • Area = (0.5)24×extπ=0.19635 extmm2\frac{(0.5)^2}{4} \times ext{π} = 0.19635 \, ext{mm}^2 (approximately).

  2. Convert the movement of air bubble into an hour:

    • Air bubble movement = 7.5 mm in 15 minutes.
    • In 60 minutes, the movement = 7.515×60=30 mm.\frac{7.5}{15} \times 60 = 30 \, mm.

  3. Calculate water uptake rate:

    • Rate = 30 extmm0.19635 extmm2≈152.27 mm2 extperhour.\frac{30 \, ext{mm}}{0.19635 \, ext{mm}^2} \approx 152.27 \text{ mm}^2 \, ext{per hour}.

Step 2

Outline a method she could have used to find this rate.

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Answer

  1. Measure leaf area: Draw round each leaf on graph paper and count the number of squares covered.

  2. Account for both sides: For each leaf, record the area for both sides by measuring the surface area.

  3. Calculate water loss rate: Divide the total rate of water loss (measured via the potometer) by the total surface area of the leaves to find the rate of water loss per mm².

Step 3

Suggest one reason why.

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Answer

One reason is that the potometer measures only the water uptake through the shoot, whereas the whole plant also has roots which take in water directly from the soil, affecting the overall rate of water movement.

Step 4

Suggest two reasons why water molecules and carbon dioxide molecules can both pass through PIP1.

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Answer

  1. Both water and carbon dioxide are small enough to pass through the pore of the aquaporin.
  2. Both molecules are polar, allowing favorable interactions with the aquaporin, which facilitates their transport.

Step 5

Using this information, what can you conclude about the effect of the foreign DNA in the transgenic poplar trees?

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Answer

The foreign DNA likely inhibits the production of PIP1, reducing its overall levels in the transgenic poplar trees, which could impact their ability to transport water efficiently.

Step 6

Suggest why.

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Answer

The transgenic poplars still produced some PIP1 because not all gene expression is entirely silenced; there may still be residual activity or compensatory mechanisms in the plant.

Step 7

Evaluate the importance of PIP1 in the movement of carbon dioxide and water through leaves of poplar trees.

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Answer

PIP1 is crucial for the efficient movement of water due to its role in facilitating membrane permeability. The data may show higher rates of water movement in wild type compared to transgenic, indicating that PIP1 enhances this transport. For carbon dioxide movement, the reduced levels in transgenic poplars could restrict gas exchange and limit photosynthesis efficiency, thereby demonstrating PIP1’s role in both water and carbon dioxide transport.

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