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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
Question 6
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.
Answer
To calculate the rate of water uptake, we first need to find the cross-sectional area of the capillary tube using the formula for the area of a circle:
A = rac{ ext{π}d^2}{4}
Where:
- is the diameter of the capillary tube (1.0 mm).
Substituting in the value:
A = rac{3.14(1.0)^2}{4} = 0.785 \text{ mm}^2
Next, calculate the volume of water taken up in 15 minutes:
- The bubble moved 7.5 mm in 15 minutes, so the volume of water taken up is:
To find the rate per hour:
- There are 4 fifteen-minute intervals in an hour, so the volume taken up in an hour is:
Now converting to mm² per hour using the area:
Step 2
Outline a method she could have used to find this rate.
Answer
-
Measure Leaf Area: Draw around each leaf on graph paper or using transparent graph squares to estimate the surface area.
-
Calculate Total Leaf Area: Record the dimensions for each leaf and calculate the area of each. Include both sides of each leaf if possible.
-
Calculate Water Loss: Use the potometer to measure the rate of water loss from the shoot over a defined time period.
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Compute Rate of Water Loss per Area: Divide the total water loss by the total leaf surface area measured in step 2 to find the water loss rate in mm² per hour.
Step 3
Step 4
Suggest two reasons why water molecules and carbon dioxide molecules can both pass through PIP1.
Answer
-
Size and Polarity: Both molecules are small and can fit through the pore of the aquaporin, making them compatible with the channel's structure.
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Similar Transport Mechanism: The aquaporin allows for facilitated diffusion, wherein water and carbon dioxide can both traverse the membrane efficiently, given their differences in polarity and size.
Step 5
Using this information, what can you conclude about the effect of the foreign DNA in the transgenic poplar trees?
Answer
The foreign DNA likely reduces the expression of the PIP1 gene, resulting in lower levels of PIP1 proteins in the leaves. This suggests that foreign RNA interferes with normal gene expression necessary for the production of PIP1.
Step 6
Step 7
Using only Figure 7, evaluate the importance of PIP1 in the movement of carbon dioxide and water through leaves of poplar trees.
Answer
The data from Figure 7 shows that transgenic poplars have a significantly lower rate of water movement compared to wild type. This suggests that PIP1 plays a crucial role in facilitating water movement. Likewise, the carbon dioxide movement is also reduced in transgenic poplars, indicating that PIP1 is important for gas exchange as well. Therefore, PIP1 is critical for maintaining efficient transport of water and carbon dioxide in poplar tree leaves.