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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 tre... 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 from 5 am to midday shows a consistent increase. This can be attributed to several factors. Firstly, the temperature tends to rise during this period, which increases the kinetic energy of water molecules, leading to more evaporation from the leaves. Additionally, the sun rises, resulting in increased light intensity that enhances photosynthetic activity, which in turn opens the stomata. As stomata are open, water vapor is lost, increasing the transpiration rate. At midday, when temperatures are at their peak, the transpiration rate reaches its highest point, possibly influenced by high temperatures, sunlight, and lower humidity.
Step 2
Use Figure 9 to calculate the percentage increase in the rate of transpiration from 1 pm to 2 pm.
Answer
To calculate the percentage increase in the rate of transpiration from 1 pm to 2 pm, first note the values at these times from Figure 9. If the rate is 0.65 cm/hr at 1 pm and 0.75 cm/hr at 2 pm, the calculation is:
Percentage Increase = rac{(0.75 - 0.65)}{0.65} imes 100
This results in approximately 15.38%. Therefore, the percentage increase in the rate of transpiration is approximately 15.4%.
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 if mangrove root cells have a lower water potential than sea water, the following experiment can be conducted:
- Prepare Samples: Cut equal lengths of fresh mangrove root and immerse them in sea water for a specified duration (e.g., 2 hours).
- Measure Initial Mass: Record the initial mass of the mangrove root pieces before immersion in sea water.
- Remove and Dry: Gently remove the roots, blot them to dry, and quickly weigh them again.
- Analyse Changes: Calculate the mass difference to determine if there has been weight gain. If the roots have gained mass, this indicates water absorption, suggesting that they have a lower water potential compared to the sea water. This indicates osmosis has occurred, confirming that the cells absorb water from the seawater into the roots.