2.5- osmosis

what is osmosis?

the diffusion of water, the net movement of water molecules from a region of high water potential to a region of low water potential, down a water potential gradient

define solute

a substance that can dissolve

define solvent

the liquid a solute dissolves in

define solution

the combination of a solute and a solvent

define water potential

a measure of the tendancy of water molecules to diffuse from one region to another 

fill the gaps:

if two aqueous solutions are separated by a partially permeable membrane, water will move from the ——— water potential to the ——— water potential.

highest, lowest

what happens if the water potential on both sides of the membrane is equal?

there will be no net osmosis, although water molecules will continue to move randomly

give the units fro measuring water potential

kPa ( kilopascals)

describe the highest water potential

0 kPa, pure water, no solutes dissolved

describe low water potential

-10 kPa, dilute solution, small amount of dissolved solutes

describe very low water potential 

-500 kPa, concentrated solution, large amount of dissolved solutes

which way will the water move?

a               b

-250kPa   -275kPa

the net movement will be from b to a, because b is hypertonic to a 

what happens to plant cells in a high water potential/ pure water?

water moves in by osmosis down a water potential gradient and the membrane pushes against the cell wall and it becomes turgid

what happens to animal cells in a high water potential/ pure water?

water moves in by osmosis down a water potential gradient and the cell bursts open/ is cytolysed

what happens to plant cells in a low water potential?

water moves out by osmosis and the membrane pulls away from the cell wall/ is plasmolysed

what happens to animal cells in a low water potential?

water moves out by osmosis and the cell shrinks/ its crenated

what is a hypotonic solution?

when the extracellular fluid has a higher water potential than the cells cytoplasm

what is an isotonic solution?

a solution that maintains balance of the water potential on both sides of the cell

what is a hypertonic solution?

a higher concentration of dissolved solutes so a lower water potential outside the cell so the water is taken out of the cell via osmosis