2.1.5 Biological Membranes – Osmosis Flashcards
(15 cards)
What does osmosis mean?
The movement of water molecules from a higher water potential to a lower water potential across a partially permeable membrane.
What does the term ‘water potential is’ mean?
The measure of the tendency of water molecules to move from one region to another.
Pure water has the _______ possible water potential.
Highest
If solutes are added to water, what happens to the water potential?
It will become lower.
What unit is water potential measured in?
Kilopascals (kPa).
What is the symbol for water potential?
Ψ (the Greek letter psi)
What is the water potential of pure water?
0kPa
What happens to the water potential value as more solute molecules are added to the solution?
The value becomes more negative.
What happens to plant cells if they are placed in a solution with a higher water potential than the cell?
The cell wall will prevent bursting and the cell will swell to a point where it pushes against the wall to resist further swelling- the swollen cell is turgid.
What happens to animal cells if they are placed in a solution with a higher water potential than the cell?
The animal cell with burst or lyse. This can also be called cytolysis or for red blood cells haemolysis.
What happens to animals cells when they are placed in solution of lower water potential than the cell?
Water will leave the cell by osmosis and the animal cell shrivels up and is described as crenated.
What happens to a plant cell when placed in a solution of lower water potential than its contents?
Water moves out of the cell by osmosis, causing the cytoplasm to shrink and the plasma membrane to pull away from the cell wall. The cell is plasmolysed. Plant tissue with plasmolysed cells is described as flaccid.
When a plant cell is plasmolysed and the cell surface membrane is pulled away from the cell wall, what is in the gap between the cell surface membrane and the cell wall?
The solution that is surrounding the cell.
What does the term isotonic mean?
It means that the two solutions, on both sides of the membrane have the same water potential.
