4.3

Question 1

Define osmosis. (3)

Answer 1

(1) the movement of water…
(2) from an area of highER WP to an area of lowER WP…
(3) though a partially permeable membrane.

Question 2

What is water potential (WP)? (1)
What is its unit? (1)
What is the WP of pure water? (1)

Answer 2

(1) the pressure exerted by water molecules
(2) kPa
(3) zero

Question 3

What happens to the WP of a solution when more solute is added? (1)

Answer 3

(1) it decreases

Question 4

Should the value of the WP of a solution be negative or positive? (1)

Answer 4

(1) negative

Question 5

How does water move in terms of WP? Give an example. (2)

Answer 5

(1 + 2) from an area of highER WP (e.g. -20) to an area of lowER WP (e.g. -30)

Question 6

How do you find the WP of a cell / tissue? (2)

Answer 6

(1) place them in a series of solutions of different WP
(2) When there’s no net gain or loss of water from the cell, the WP inside = outside (isotonic)

Question 7

What is the explanation of osmosis? (3)

Answer 7

(1) solute & water molecules are in RANDOM MOTION due to their KE
(2) but the PP membrane only allows water to pass through..
(3) so the water molecules continue to diffuse through until dynamic equilibrium is established (no more movement)

Question 8

What happens when you put an animal cell in a solution of higher WP? (3)

Answer 8

(1) the cell will absorb water VIA OSMOSIS,
(2) as it has to move down the conc. gradient
(3) so it BURSTS

Question 9

What happens when you put a plant cell in a solution of higher WP? (4)

Answer 9

(1) the cell absorbs water VIA OSMOSIS,
(2) as it has to move down the conc. gradient
(3) so it becomes TURGID
(4) because the cell wall can withstand the pressure exerted

Question 10

What happens when you put an animal cell in a solution of lower WP? (3)

Answer 10

(1) water leaves the cell VIA OSMOSIS,
(2) as it has to move down the conc. gradient
(3) so the cell SHRINKS & SHRIVELS

Question 11

What happens when you put a plant cell in a solution of lower WP? (3)

Answer 11

(1) water leaves the cell VIA OSMOSIS,
(2) as it has to move down the conc. gradient
(3) so PLASMOLYSIS occurs,
(4) where the protoplast completely pulls away from the cell wall.

Question 12

What is the conc. of solute in hypotonic and hypertonic solutions? What does that indicate about the WP of each solution? (4)

Answer 12

Hypotonic = (1) LOW solute conc. = (2) HIGH WP
Hypertonic = (3) HIGH solute conc. = (4) LOW WP