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For gases to enter a leaf, the stomata must be open - OCR Gateway - GCSE Biology - Question 22 - 2022 - Paper 1
Question 22
For gases to enter a leaf, the stomata must be open. The diagram shows a stoma and two guard cells. When the stomata are open, the guard cells are described as bein... show full transcript
Worked Solution & Example Answer:For gases to enter a leaf, the stomata must be open - OCR Gateway - GCSE Biology - Question 22 - 2022 - Paper 1
Step 1
Explain how the guard cells help control the size of the stoma.
Answer
Guard cells regulate the size of the stoma primarily through their turgidity, which is influenced by the movement of ions, particularly potassium ions. When guard cells take in ions, water follows by osmosis, causing the cells to swell and become turgid. This turgidity opens the stoma, allowing gas exchange to occur. Conversely, when ions are released from the guard cells, water exits, leading to a loss of turgidity and closure of the stoma, thus controlling the gas exchange process.
Step 2
Calculate the actual size of the stoma. Give your answer in micrometres.
Answer
To calculate the actual size of the stoma, we utilize the formula:
Actual Size = Image Size / Magnification
Given that the width of the stoma is 5 mm and the magnification is less than 400, we take the magnification as 400 for our calculation.
Convert the width of the stoma to micrometres:
5 mm = 5000 micrometres.
Now, using the formula:
Actual Size = 5000 micrometres / 400 = 12.5 micrometres.
Thus, the actual size of the stoma is approximately 12.5 micrometres.