2.5 -Osmosis Flashcards
What is osmosis?
The passage of water molecules down their water potential gradient, across a partially permeable membrane.
What is water potential?
The measure of the tendency of water molecules to diffuse from 1 region to another (measured in kPa).
In a solution what is the solvent?
The liquid in which the solute molecules are dissolved .
What is the solvent in an aqueous solution?
Water
What can water molecules do?
They can pass directly through the phospholipid bilayer.
Water molecules have kinetic energy and move randomly but will spread out
What does the inside of the cell contain?
The inside of the cell and cytoplasm contains water and the external medium of the cells is also watery - as cells are surround by extracellular tissue fluid.
What is the definition of osmosis?
The net diffusion from a region where there are relatively more water molecules to an area where there are fewer water molecules across a partially permeable membrane.
What happens when solute molecules are added to water?
When solute molecules are added to water, the relative number of watermoelcules in the resulting solution is changed
What happens if the solute dissociates?
If the solute molecules dissociate into charge ions, such as sodium chloride dissociating into sodium and chloride ions, they exert more effect on the relative number of water molecules than do larger but non polar molecules such as glucose.
This is because, as sodium chloride molecules dissociate into sodium and chloride ions, the number of particles in the solution doubles
What happens with water potential in solution?
-When the solute molecules are added, they lower the water potential of the solution. The more solute molecules in the solution, the lower the water potential.
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WHat happens to the water potential in aqueous solution?
-If 2 aqueous solutions are separated by a partially permeable membrane, water molecules will move from the solution with the higher water potential to the solution with the lower water potential.
WHat happens to the water potential in if both sides are equal?
-If the water potential on both sides of the membrane becomes equal, there will be no net osmosis, although water molecules will continue to move randomly
What is water potential measured in?
Kilopascal (kPA)
Whats the value of pure water?
Pure water has the highest water potential available and has a value of 0(kPA).
What happens to the value of water potential when solutes are added?
As solute molecules are added, the water potential of the solution is lowered, so the value becomes negative.
-The more negative the value, the lower the water potential
WHat is the water potential inside the cell?
-The water potential inside cells is lower than that of pure water as there are solutes in the solution, in the cytoplasm and inside the large vacuole of plant cells.
What happens to the water potential when cells are placed into solution of high water potential?
-When cells are placed in a solution of higher water potential, water molecules move by osmosis, down the water potential gradient, across the plasma membrane and into the cell.
WHat happens to the inside of animal cells if there’s a lot of water?
-In animal cells, if a lot of water molecules enter, the cell will swell and burst as the plasma membrane breaks (this is cytolysis).
What happens in to water potential in plant cells high water potential?
In plant cells, the rigid and strong cellulose cell wall will prevent bursting. The cell will swell up to a certain size when its content push against the cell wall, which will resist any further swelling. Swollen cell known as turgid. Turgidity of plant cells helps support plants especially those that are not woody.
What happens when cells are in a solution of low water potential?
-When cells are placed in a solution of lower water potential, water leaves the cells by osmosis, across the partially permeable plasma membrane.
What happens when animal cells have low water potential?
-Animal cells shrivel and become crenated.
What happens when plant cells have low water potential?
-The cytoplasm of plant cells shrinks and the membrane pulls away from the cell wall. The cells become plasmolysed. Plant tissue with plasmolysed cells is describe as (flaccid).
What happens to cells that are plasmolysed?
Cells that are plasmolysed suffer a degree of dehydration and their metabolism cannot proceed, as enzymes catalysed reactions need to be in the solution
