Plant cells and water

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  • Created by: racheon
  • Created on: 20-03-14 18:56
Define water potential.
The total potential energy of the water molecules in a system. It's a measure of how likely it is that water will be lost from the system by diffusion down it's water potential gradient.
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What is water potential a measure of?
The tendency of water molecules to diffuse from one place to another.
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Where does water always move from and to?
It always moves from a region of high water potential to a lower water potential.
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What is the water potential of pure water?
0.
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What do plant cells' cytoplasm contain?
Salts and sugars
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What do the salts and sugars in plant cells do in terms of water potential and why?
They will reduce the water potential because there are fewer 'free' water molecules available that there are in pure water.
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What is the water potential in plant cells' cytoplasm?
Always negative.
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If you place a plant cell in pure water what will happen?
It will take up water molecules by osmosis because the water potential in the cell is lower than in pure water, but the cell won't continue to absorb water until it bursts because the cell has a strong cellulose wall.
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What happens when a plant cell becomes full with water?
It becomes turgid.
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What happens to the water inside a turgid plant cell?
It starts to exert pressure on the wall, called the pressure potential.
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What happens as the pressure potential builds up?
It reduces the influx of water.
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What happens if a plant cell is placed in a solution with low water potential?
It loses water by osmosis because the water potential of the cell is higher than the solution's, so water diffuses down its potential gradient out the cell, causing it to lose its turgidity.
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What happens if water loss continues to a plant cell that has been placed in a solution with low water potential?
The cytoplasm and vacuole shrink until the cytoplasm no longer pushes against the cell wall, which is incipient plasmolysis.
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What happens if water continues to leave a plant cell after incipient plasmolysis?
The plasma membrane will lose contact with the cell wall which is plasmolysis.
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In terms of water molecules what happens when plant cells are touching?
Water molecules can pass from one cell to another.
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Where will water molecules move to and from in cells touching each other?
They will move from the cell with the higher water potential to the cell with the lower water potential.
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What do cellulose cell walls have between the cellulose molecules?
Water filled spaces.
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What happens in the apoplast pathway?
Water moves through spaces between cellulose molecules in the cell wall and in between cells.
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Where doesn't water pass through in the apoplast pathway, and therefore what can the water carry?
It doesn't pass through any plasma membranes, meaning that dissolved minerals and salts can be carried with it.
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What happens in the symplast pathway?
Water enters the cell cytoplasm through the plasma membrane. It can pass through the plasmodesmata from one cell to the next.
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What are plasmodesmata?
Gaps in the cell wall that contain a thin strand of cytoplasm, therefore the cytoplasm of adjacent cells is linked.
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What is the vacuolar pathway similar to, and why is it different to it?
It's similar to the symplast pathway, but it's different because the water isn't confined to the cytoplasm of the cells, it's able to enter and pass through the vacuoles as well.
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What should you always refer to water potential as?
More or less negative.
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What is a high water potential the same as?
A less negative water potential.
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Card 2

Front

What is water potential a measure of?

Back

The tendency of water molecules to diffuse from one place to another.

Card 3

Front

Where does water always move from and to?

Back

Preview of the front of card 3

Card 4

Front

What is the water potential of pure water?

Back

Preview of the front of card 4

Card 5

Front

What do plant cells' cytoplasm contain?

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