5.5. OSMOSIS

Question 1

What is water potential represented by?

Answer 1

psi/ Ψ

Question 2

How is a solution formed?

Answer 2

When a solute (i.e. salts) is dissolved in a solvent (water)

Question 3

What is osmosis measured in?

Answer 3

Water potential (NOT concentration)

Question 4

What is the definition of water potential?

Answer 4

pressure exerted by water molecules as they hit a container/ membrane

Question 5

What are the units of water potential?

Answer 5

kPa/ kiloPascal/ 1000Nm-2

Question 6

What do water potential do?

Answer 6

quantifies the tendency of water to move from one area to another due to osmosis and hydrostatic pressure effects

Question 7

What does it mean by hydrostatic pressure effects?

Answer 7

movement of water into the cells causes the cell volume to increase - increase in hydrostatic pressure in the cell

Question 8

What is osmosis?

Answer 8

where water molecues move down a water potential gradient - from high to low - through PARTIALLY permeable membrane

Question 9

What is osmosis a type of and how does it differ from regular __ ?

Answer 9

• diffusion
• only applies to water molecules

Question 10

What water potential does pure water have?

Answer 10

At 25*C, and atmospheric pressure of 100kPa, it has a water potential of 0kPa

Question 11

What is the highest water potential possible?

Answer 11

0kPa, when lower, it goes into the negative numbers

Question 12

Why is osmosis diffusion?

Answer 12

because it is the solvent molecules (water) moving within the solute molecules/ions.

Question 13

When is osmosis complete?

Answer 13

When it reaches equilibrium

This can be shown when one side of the partially permeable membrane has a solution higher than the other side

Question 14

In animal and plant cells, what are the three stages of osmosis?

Answer 14

-hypERtonic
-isotonic
-hypOtonic
-very hypOtonic (only in animals)

Question 15

What does hypertonic mean in animal cells i.e. red blood cells?

Answer 15

-the solution outside the cell has a lower Ψ than inside, so water leaves the cell
-causes the cells to shrivel up
-cells become CRENALATED

Question 16

What does isotonic mean in animal cells i.e. red blood cells?

Answer 16

-the solution outside the cells has equal Ψ as inside the cell
-water is moving in equilibrium
-cell is happy

Question 17

What does hypotonic mean in animal cells i.e. red blood cells?

Answer 17

-the solution outside the cell has a higher Ψ than inside the cell so water moves to inside the cell
-cells swell

Question 18

What does red blood cells being very hypotonic mean?

Answer 18

-the cell bursts
-causing cytolysis

Question 19

What does hypertonic mean in relation to plant cells?

Answer 19

-cell wall stays the same shape but membrane shrinks inwards
-becomes plasmolysed
-higher Ψ inside the cell than outside so water leaves the cell

Question 20

What does isotonic mean in relation to plant cells?

Answer 20

-Ψ inside the cell and outside the cell is the same
-water moves in equilibrium
-cell becomes flaccid

Question 21

What does hypotonic mean in relation to plant cells?

Answer 21

-Ψ outside the cell is higher than inside so water enters the cell
-develops turgor pressure
-then becomes turgid
-cell cannot burst due to the strong cellulose cell walls