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Osmosis

Osmosis is the net movement of water molecules down their water potential gradient across a partially permeable membrane

Exam

definition

What does it

mean?

A measure of the tendency of water molecules to move from one place to another What is water potential? Pure water has the highest possible water potential Ψ = 0 kPa This is the symbol for water potential These are the units

Put in order from highest to lowest

-16 -0. -37 - -0.170 -0.

Water potential explained simply

In which direction does osmosis occur? PURE WATER DILUTE SOLUTION CONCENTRATED SOLUTION

When solutes are added, water potential decreases, it gets more negative The more solutes, the lower the water potential

0 kPa -0. kPa A B -1. kPa -0. kPa A B -12. kPa -12. kPa A B

Which way will water

move?

-0. kPa -0. kPa A B

The effect of osmosis on cells

• (^) Cells contain a solution (water with dissolved solutes and organelles)
• (^) Cells are surrounded by a solution (tissue fluid with dissolved solutes)
• (^) The two solutions are separated by a partially permeable membrane – the plasma membrane
• (^) So water can move in and out of cells by osmosis depending on the water potential gradient

Tonicity

• (^) Tonicity describes the

concentrations of solutes in

solutions

It is used to compare solutions to

other solutions

A contains more solute than B

A has a higher concentration of solute

than B

A has a lower water potential than B