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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 t... 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 the duckweed plants primarily through a process known as osmosis. Osmosis is the movement of water molecules from an area of higher water concentration (in this case, the distilled water) to an area of lower water concentration (inside the plant cells) across a semi-permeable membrane.
In addition to osmosis, water can also enter the plants through capillary action, which allows water to move through small tubes in the plant. Once inside, the water travels through the xylem, which transports it to various parts of the plant, including the leaves and stems. The process of transpiration—where water evaporates from the leaves—creates a negative pressure that helps draw more water up from the roots, ensuring a continuous flow of water into the plant.
Step 2
Explain how the salt solution would affect the movement of water into and out of the plant.
Answer
When salt is added to the distilled water, it creates a salt solution which has a higher osmotic concentration than the inside of the duckweed plants. Due to osmosis, water will move from an area of lower solute concentration (inside the plant) to an area of higher solute concentration (the salt solution). This leads to a net movement of water out of the plant, which can result in the wilting or dehydration of the duckweed.
Additionally, if the salt concentration is too high, it can lead to plasmolysis, where the plant cells lose water and shrink away from their cell walls. This can severely impact the plant's health and its ability to undergo photosynthesis.