4.3 - Osmosis

What is water potential? (Ψ) (1)

It is the pressure water molecules in a solution exert on a membrane or container.

What is a solution? (1)

A solute dissolved in solvent.

Why does pure water have a water potential of 0 kPa?

Because pure water has no solute molecule

Describe the relationship between the amount of solute and and water potential. (1)

As the amount of solute dissolved in the solvent increases, the water potential becomes more negative.

Define osmosis. (1)

It is the diffusion of water across a partially permeable membrane from an area of higher water potential to an area of lower water potential.

Osmosis occurs until a state is reached. Describe this state. (1)

Until equilibrium is reached and there is no net movement of water.

What are hypotonic solutions? (1)

Solutions which have a higher water potential than the cell placed into the solution

What happens when an animal cell enters a hypotonic solution? (2)

• Water enters the cell via osmosis from an area of higher water potential outside the cell to an area of low water potential in the cell.

• Causes animal cell to swell and burst.

What happens when a plant cell enters a hypotonic solution? (3)

• Water enters the cell via osmosis from an area of higher water potential outside the cell to an area of low water potential in the cell.

• Plant cell has cell wall, which prevents the cell from bursting.

• Causes cell to become turgid

What are isotonic solutions? (1)

Solutions which have the same water potential as the cell placed into the solution,

What happens when an animal or plant cell enters a isotonic solution? (2)

• No net movement of water

• Both cells maintain their size and shape

What are hypertonic solutions? (1)

Solutions where the water potential is lower than the cell placed into the solution.

What happens when an animal cell enters a hypertonic solution? (2)

• Water exits the cell from an area of higher water potential in the cell to an area of lower water potential outside the cell.

• Causing animal cell to shrink

What happens when an plant cell enters a hypertonic solution? (2)

• Water exits the cell from an area of higher water potential in the cell to an area of lower water potential outside the cell.

• Plant cell becomes plasmolysed

• Tissues become flaccid and plant wilts.

What does ‘plasmolysis’ refer to and when does it occur? (2)

• Occurs when cell membrane pulls away from cell wall

• Occurs when a plant cell is placed in a hypertonic solution.