4.3- OSMOSIS

Question 1

What molecules does osmosis only involve?

Answer 1

water molecules only

Question 2

What is the definition of osmosis?

Answer 2

passage of water from region where it has higher water potential to region where it has lower water potential through selectively permeable membrane

Question 3

Examples of selectively permeable membranes?

Answer 3

cell-surface membranes and other plasms membranes i.e. those around organelles

Question 4

How are plasma membranes and cell-surface membranes selectively permeable?

Answer 4

permeable to water molecules and a few other small molecules, but not to larger molecules

Question 5

What is a solute?

Answer 5

any substance that’s dissolved in a solvent i.e. water

Question 6

What does a solute and solvent form?

Answer 6

solution

Question 7

What Greek symbol is water potential represented by?

Answer 7

psi (Ψ)

Question 8

What unit is water potential measured in?

Answer 8

unit of pressure, usually kiloPascals (kPa)

Question 9

What is water potential?

Answer 9

pressure created by water molecules

Question 10

What is standard conditions of temperature and pressure?

Answer 10

25°C and 100kPa

Question 11

Under standard conditions of temperature and pressure, pure water is said to have what water potential?

Answer 11

zero

Question 12

What will happen to the water potential when a solute is added to pure water?

Answer 12

lower its water potential

Question 13

What must the water potential of a solution always be less than?

Answer 13

less than zero, negative value

Question 14

What will happen to water potential when more solute is added?

Answer 14

water potential becomes lower (more negative)

Question 15

When water molecules move by osmosis from which region of water potential do they go to?

Answer 15

region of higher (less negative) water potential to one of lower (more negative) water potential

Question 16

What is one way of finding the water potential of cells or tissues?

Answer 16

place them in a series of solutions of different water potentials
where there’s no net gain/loss of water from cell or tissues, water potential inside cells/tissues must be same as that of external solution

Question 17

What do animal cells i.e. red blood cells contain a variety of?

Answer 17

solutes dissolved in their watery cytoplasm

Question 18

What would happen if a red blood cell is placed in pure water?

Answer 18

it will absorb water by osmosis as it has a lower water potential

Question 19

How thin are cell surface membrane?

Answer 19

very thin (7nm)

Question 20

Although the cell surface membrane is flexible, what can it not do?

Answer 20

cannot stretch to any great extent

Question 21

As the cell-surface membrane cannot stretch what will happen?

Answer 21

it will break, bursting the cell and releasing its contents

Question 22

What is it called when red blood cells burst?

Answer 22

haemolysis

Question 23

To prevent the animal cells from bursting where do they normally live?

Answer 23

in a liquid which has the same water potential as the cells

Question 24

What does red blood cells have the same water potential as?

Answer 24

blood plasma

Question 25

What happens if red blood cells were placed in a solution with a water potential lower than its own?

Answer 25

water leaved by osmosis and cell shrinks and becomes shrivelled