Osmosis

Question 1

What is the definition of osmosis?

Answer 1

Diffusion of water, from an area of higher water potential to an area of lower water potential across a selectively permeable membrane

Question 2

Is osmosis a passive or active transport?

Answer 2

Passive transport

Question 3

What is water potential?

Answer 3

The tendency for water to leave a solution or cell by osmosis

Question 4

What is water potential measured in?

Answer 4

kPa

Question 5

The greater the number of free water molecules in a solution, the hight the what?

Answer 5

Water potential

Question 6

What has the greatest potential energy to move?

Answer 6

Pure water
Given the highest value of 0kPa

Question 7

What happens when you add a solute to water?

Answer 7

Number of free water molecules is decreased
Potential energy of the water decreases and therefore the water potential becomes more negative

Question 8

What is the definition of a hypotonic solution?

Answer 8

If the water potential of the external solution is less negative (higher) than the solution inside the cell, water flows into the cell

Question 9

What is the definition of a hypertonic solution?

Answer 9

If the water potential of the external solution is more negative (lower) than the solution inside the cell, water flows out of the cell

Question 10

What is the definition of an isotonic solution?

Answer 10

If the water potential of the external solution is the same as the solution inside the cell, so there is no net movement of water

Question 11

What is solute potential (Ψs)?

Answer 11

Due to the solutes in the vacuole & cytoplasm, it is the lowering of water potential due to the presence of solute molecules

Question 12

What is pressure potential (Ψp)?

Answer 12

The pressure exerted by the cell contents on the cell wall, a force which increases the tendency of water to move out

Question 13

Describe the process of water potential

Answer 13

Water enters a plant cell by osmosis, causing the vacuole and cytoplasm to swell - makes the cell turgid
Cell wall is inelastic and so outward pressure builds up as the cytoplasm pushes against the cell wall - pressure is the pressure potential

Question 14

How do you calculate water potential?

Answer 14

Ψ = Ψs + Ψp
Water potential of a cell = pressure potential + solute potential

Question 15

Why don’t plant cells burst?

Answer 15

Even though the cell cytoplasm and vacuole are full of water (turgid) the cell wall cannot stretch (inelastic), so this prevents the cell from overfilling with water and bursting

Question 16

How does a plant cell become plasmolysis?

Answer 16

If a plant cell is placed in a hypertonic solution = water moves out by osmosis
Vacuole shrinks and cytoplasm and cell membrane will withdraw from the cell wall

Question 17

What is incipient plasmolysis?

Answer 17

The point at which the cell membrane is just about to come away from cell wall (theoretical definition)
Is the point where 50% of the cells in a sample are plasmolysis (experimentally)

Question 18

Explain why animal cells burst in a hypotonic solution

Answer 18

Water moves into the cell by osmosis
From an area of higher water potential to an area of lower water potential
The cell cytoplasm swells & the cell bursts

Question 19

Explain why animal cells crenate in a hypertonic solution

Answer 19

Water leaves the cell by osmosis
From an area of higher water potential to an area of lower water potential
The cell cytoplasm shrinks and the cell crenate