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The diagram shows three duckweed plants in a beaker of distilled water - Edexcel - GCSE Biology - Question 6 - 2013 - Paper 1
Question 6
The diagram shows three duckweed plants in a beaker of distilled water. (a) (i) Explain how the water moves into these plants. (ii) Salt was added to the water in ... show full transcript
Worked Solution & Example Answer:The diagram shows three duckweed plants in a beaker of distilled water - Edexcel - GCSE Biology - Question 6 - 2013 - Paper 1
Step 1
Explain how the water moves into these plants.
Answer
Water moves into duckweed plants primarily through a process called osmosis.
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Osmosis: This is the movement of water molecules from an area of higher concentration (the distilled water outside the plant cells) to an area of lower concentration (the interior of the plant cells) through the semi-permeable cell membranes.
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Capillary Action: Water is also absorbed through the roots due to capillary action, where water rises in small tubes or spaces within the plant tissue.
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Transpiration: Additionally, as water evaporates from the leaves (transpiration), it creates a negative pressure that helps pull more water upward from the roots through the xylem tissue, facilitating further absorption.
Step 2
Explain how the salt solution would affect the movement of water into and out of the plant.
Answer
The addition of salt to the water creates a salt solution, which affects the movement of water into and out of the plant through the following processes:
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Osmotic Pressure: The concentration of salt in the water increases the osmotic pressure outside the plant cells. As a result, there may be a lower concentration of water outside the plant compared to the inside. This difference creates a hypertonic environment, leading to a decrease in water absorption.
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Water Movement: Instead of water moving into the plant, water may start to move out of the plant cells to balance the concentration gradient. This results in the plant experiencing water loss, which could lead to wilting if the salt concentration is significantly high.