Osmosis Flashcards
Define osmosis.
Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane.
Describe cell membranes - how do they allow diffusion of water?
They are partially permeable, meaning they are selective to what enters/leaves the cell.
What is water potential?
The tendency of water molecules to move.
What does ‘higher water potential’ mean?
A solution where the water concentration is very high - the solution is dilute.
What is a ‘more lower’ water potential?
A solution where the water concentration is low and solute concentration is high
State the water potential of pure water in kPa.
0kPa
What does hypotonic mean?
Water potential outside the cell is higher (less negative) than inside the cell
What does isotonic mean?
The water potential on either side of a membrane is equal, so there is no net movement of water.
What does hypertonic mean?
Where water potential outside of the cell is more negative than the inside of the cell.
Describe what happens to plant cells when they are hypertonic.
What happens to the cytoplasm and vacuole?
The water potential outside the cell is more negative than inside of the cell, so water is drawn out of the cell.
This pulls the cell cytoplasm away from the cell wall and the vacuole shrinks, so the cell plasmolyses.
What happens to plant cells when they are hypotonic?
Water potential outside the cell is less negative while the inside of the cell is more negative.
This causes water to be drawn into the cell, so the cell swells, the cytoplasm pushes against the cell wall and the vacuole increases in size. The cell is said to be turgid.
What happens to plant cells when they are isotonic?
There is no net movement of water in/out of the cell.
What happens to animal cells when they isotonic?
There is no net movement of water so they remain the same.
What happens to animal cells when they were hypotonic?
Water potential outside of the cell is lower than the water potential inside the cell. This draws water out of the cytoplasm so the cell shrinks.
What happens when animal cells are hypotonic?
Water is drawn into the cell so it swells. The cell eventually bursts.
