osmosis & water potential

Question 1

define osmosis

Answer 1

osmosis is the diffusion of water molecules across a semi permeable membrane from an area of higher water potential to an area of lower water potential

Question 2

define water potential

Answer 2

the potential (likelihood) of water molecules to diffuse into or out of a solution

Question 3

what sort of molecule is water? what does this mean?

Answer 3

polar, so many substances will dissolve in it so its a solvent

Question 4

what is the name for the thing that dissolves in water?

Answer 4

solute

Question 5

how does water dissolve solutes?

Answer 5

the water molecules cluster around the solute molecules. This means there’s less free molecules to diffuse, therefore lowering the concentration of the water

Question 6

why can water molecules diffuse easily?

Answer 6

they’re small

Question 7

what is the water potential of pure water?

Answer 7

0

Question 8

what happens to the water potential when you add a solute?

Answer 8

lowers the water potential (always negative)

Question 9

if the water potential is more negative, what does this mean?

Answer 9

a stronger concentration of solutes

Question 10

explain what it means when a cell is in an isotonic solution

Answer 10

there’s no net movement of water molecules as there’s no difference in water potential. There’s an equal solute concentration compared to another area. If 2 solutes have the same water potential, they’re isotonic

Question 11

explain what it means when a cell is in a hypertonic solution

Answer 11

there’s a high solute concentration compared to another area. Water moves out of the cell. Low water potential

Question 12

explain what it means when a cell is in a hypotonic solution

Answer 12

there’s a low solute concentration compared to another area. Water moves into the cell. High water potential

Question 13

what factors affect the rate of osmosis?

Answer 13

1. the water potential gradient- the higher the gradient, the faster the rate. As osmosis is taking place, the difference in water potential on each side decreases to the rate levels off
2. the thickness of exchange rate surface- the thinner the exchange surface, the faster the rate
3. the surface area of the exchange surface- the larger the SA the faster the rate

Question 14

what is water potential measured in?

Answer 14

kiloPascals (kPa), the highest is 0kPa

Question 15

why is water loss in animal cells more severe in animal cells compared to plant cells?

Answer 15

they don’t have a cell wall

Question 16

what happens when an animal cell is placed in a solution with a lower water potential? what environment is this?

Answer 16

1. water leaves cell through membrane by osmosis
2. the volume of the cell decreases
3. the cell shrinks/shrivels up
   HYPERTONIC

Question 17

what happens when an animal cell is placed in a solution with a higher water potential? what environment is this?

Answer 17

1. water enters the cell through membrane by osmosis
2. the volume will increase
3. there’s no cell wall to withstand the increased pressure
4. cell membrane eventually stretched too far and cell bursts
   HYPOTONIC

Question 18

what happens when a plant cell is placed in a solution with a higher water potential?

Answer 18

1. water enters the cell by osmosis
2. as water enters the vacuole, the volume increases
3. the protoplast expands and pushes against the cell wall and pressure increases
4. the inelastic cell wall prevents the cell from bursting and limits the amount of water moving in

Question 19

what word is used to describe a fully inflated plant cell? why is this positive?

Answer 19

turgid, its provided with strength and support and can stand upright to catch light from the sun

Question 20

what happens when a plant cell is placed in a solution with a lower water potential?

Answer 20

1. water leave the plant
2. as water leaves the vacuole, the volume of the plant decreases
3. the protoplast shrinks and no longer exerts pressure and pulls away from cell wall. This is known as plasmolysis, the cell has been plasmolysed

Question 21

what is the protoplast?

Answer 21

living part of cell inside cell wall