Osmosis. Flashcards
Movement into and out of cells.
What type of molecules do the cell membrane partially permeable membrane allow through?
The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules).
Define osmosis.
Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane, down the water potential gradient.
What happens if you place a plant cell into a solution that has a higher water potential than the water potential of the cell e.g. distilled water?
When the cell is more concentrated than the surrounding cells, water molecules diffuse into the cell via osmosis, making it turgid.
What happens if you place a plant cell into a solution that has a lower water potential than the water potential of the cell e.g. strong sugar solution?
When it is less concentrated than the surrounding cells, water molecules will leave the cell, making it flaccid leading to plasmolysis (the cell membrane peels away from the cell wall).
What happens if you put a cell into a solution that has the same water potential as the water potential of the cell?
There is no net movement of water in or out of the cell.
What causes a plant to wilt?
If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts.
What prevents the plant cells from taking in too much water and bursting?
Plant cells that are turgid are full of water and contain a high turgor pressure. The pressure created by the cell wall stops too much water from entering and prevents the cell from bursting.
How are plant cells supported by the pressure of water?
When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall.
Why is it important for plant cells to be firm?
This is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant.
Define turgid.
Cells are described as turgid when they are swollen due to high water content.
Define turgor pressure.
The pressure on the cell wall from the cell membrane pushing upon it. This is a result of the cell becoming turgid as water moves into the cell via osmosis.
Define flaccid.
Occurs when water moves out of the cell via osmosis. The cell shrinks but the cell membrane does not peel away from the cell wall.
Define plasmolysis.
The process by which the cytoplasm pulls away from the cell wall as a result of water loss from the cell.
What happens when an animal cell is placed into a solution that has a higher water potential than the water potential of the cell?
There is a net movement of water into the cell which causes the animal cell to burst.
What happens if you place an animal cell into a solution that has a lower water potential than the water potential of the cell?
There is a net movement of water out of the cell which causes the animal cell to shrink (crenate).
