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Mangrove trees grow near the sea - AQA - A-Level Biology - Question 6 - 2022 - Paper 1
Question 6
Mangrove trees grow near the sea. Sea water surrounds the lower parts of the trees at high tide. Scientists investigated the rate of transpiration in a mangrove tr... show full transcript
Worked Solution & Example Answer:Mangrove trees grow near the sea - AQA - A-Level Biology - Question 6 - 2022 - Paper 1
Step 1
Explain the rate of transpiration between 5 am and midday shown in Figure 9.
Answer
The rate of transpiration is linked to several factors that change throughout the morning until midday. Between 5 am and midday, there is an increase in sunlight, which leads to higher temperatures and increased kinetic energy in the air. This enhances the rate of evaporation from the leaf surfaces. Additionally, as the temperature rises, the air's capacity to hold moisture increases, resulting in lower humidity levels.
At around 11 am, the rate of transpiration peaks due to maximum temperature and light intensity, facilitating greater evaporation of water vapor from the stomata. Humidity may start to decrease around midday, while increased wind speeds can also contribute to higher transpiration rates.
Thus, from 5 am to midday, the rise in rates is primarily because of increased temperature and light, enhancing transpiration.
Step 2
Use Figure 9 to calculate the percentage increase in the rate of transpiration from 1 pm to 2 pm.
Answer
From Figure 9, at 1 pm, the rate of transpiration is approximately 0.25 cm/hr, and at 2 pm, it increases to about 0.6 cm/hr.
To calculate the percentage increase:
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Find the difference: 0.6 - 0.25 = 0.35 cm/hr
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Calculate the percentage increase:
ext{Percentage Increase} = rac{0.35}{0.25} imes 100 = 140 ext{%}
Therefore, the percentage increase in the rate of transpiration from 1 pm to 2 pm is 140%.
Step 3
Describe an experiment that you could do to investigate whether the mangrove root cells have a lower water potential than sea water.
Answer
To investigate whether mangrove root cells have a lower water potential than sea water, follow these steps:
- Preparation: Record the mass and length of the fresh mangrove root before starting the experiment.
- Soaking: Place the root in sea water for a specified period (e.g., 1 hour) to allow for water exchange to occur.
- Measurement: After soaking, remove the root, and measure its mass and length again to observe any changes. This will indicate the amount of water absorbed by the root.
- Microscopy: Prepare a microscope slide with slices of the mangrove root, and compare the cell structures under a microscope to look for any plasmolysis, which indicates osmosis occurring due to a lower water potential in the root cells compared to the surrounding sea water.
- Conclusion: If mass increases significantly or if plasmolysis is absent, it indicates that the root cells have a lower water potential than sea water, leading to water uptake through osmosis.