TRANSPORT ACROSS CELL MEMBRANES Flashcards
What is osmosis?
Osmosis is the passage of water from an area with high water potential to an area with a lower water potential across a selectively permeable membrane down a water potential gradient.
What does selectively permeable mean?
Selectively permeable means that water molecules and a few other molecules can pass through it but not larger molecules.
What is water potential represented by and what is it measured in?
Psi (looks like a torch) and measure in pressure (KPa).
What is water potential?
A measure of tendancy of water molecules to diffuse to one place from another.
What water potential is pure water?
0
What are the rules of water potential?
- The addition of a solute lowers water potential, the more the solute is added, the less the water potential
- The water potential of a solution (water+solute) must be less than 0 (negative value)
- Water will move from by osmosis from a high concentrated area(less negative) to a lower concentrated area (more negative)
How do you find the water potential of cells or tissues?
Place them in a series of different water potentials
What is the correlation between value and water potential?
The more negative the value, the lower the water potential.
What happens if red blood cells are placed in pure water?
It will absorb water by osmosis because it has a lower water potential than water.
How are animal cells adapted to their function?
Cell surface membranes are very thin and so can break easily releasing it’s contents. To prevent this from happening, animal cells normally live in a liquid which has the same water potential as the cells so that it doesn’t burst.
What makes a plant cell turgid?
When too much water is added to a plant, the protoplast starts to swell and press on the cell wall and the cell is said to be turgid.
What is incipient plasmolysis?
This is where the cellulose no longer presses on the cell wall. Further loss of water causes the cell contents to shrink and the protoplast to move away from the cell wall.
What are solutions with the same water potential called?
Isotonic
What happens in isotonic cells?
They won’t loose or gain any water since there’s no net movement of molecules because there’s no difference in water potential between the cell and the surrounding solution
What is net movement?
The random motion of molecules or ions
