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  • Created on: 07-10-20 20:00

Osmosis defenition

Osmosis is the diffusion of water through a selectively permeable membrane from a dilute solution to a concentrated solution,i.e., from where water levels are high to where water levels are low

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osmosis in plant cells

A plant cell when placed in water or dilute solutions

When a plant cell is placed in water, then water moves into the plant cell by osmosis as there is a more dilute solution outside the cell.

the cytoplasm and vacuole swell and increase in size, pushing the cell contents and membrane against the cell wall making it turgid. This turgor pressure gives the cell support. The cell wall counteracts the outward force of the cell contents so the cell does not burst. The cell wall limits the entry of water into the cell.


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osmosis in plant cells

A plant cell placed in a concentrated solution

-When a plant cell is placed in a concentrated solution, then water moves out of the plant cell by osmosis as there is a more concentrated solution outside the cell.

-As the water moves out, the vacuole and cytoplasm shrink and the membrane pulls away from the cell. This is called plasmolysis and the cell is described as plasmolysed. This kills the cell as the membrane is damaged.

-The gaps are filled with the external solution. Since the cell wall is fully permeable to the external solution it moves through the wall and occupies the space


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Transport of Water in plants

Water moves into the roots of the plants from the soil by osmosis. The roots have a larger surface area to achieve this. The water moves across the root from cell to cell by osmosis and enters the xylem tubes which also transports minerals.

Xylem can be found through the plant and they form continuous tubes to transport water upwards to all parts of the plant.

The upward movement of water is called the transpiration stream.


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Transport of Water in plants

Loss of Water from the Leaves

Plants lose water by evaporation, mostly from their leaves. This process is known as transpiration, which takes place through tiny openings called stomata on the underside of each leaf.

the spongy mesophyll cells inside the leaves are covered with a thin layer of water which evaporates into the air spaces and then diffuses out of the leaf through the stomata. This is replaced by water from the xylem vessels in the leaf.

Transpiration is the evaporation of water from the mesophyll cells by diffusion through the air spaces and stomata.

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