Osmosis

Question 1

GCSE Definition

Answer 1

Osmosis is the diffusion of water molecules from a high water concentration to low water concentration across a partially-permeable membrane

Question 2

As-Level Definition

Answer 2

Osmosis is the movement of water from a less negative water potential to more negative water potential through a partially permeable membrane

Question 3

Dilute and Concentrated solutions

Answer 3

Dilute solution - High concentration of water molecules

Concentrated solution - Low concentration of water molecules

Water moves from Pure Water->Dilute Solution->Concentrated Solution

Question 4

Water Potential

Answer 4

Water potential is the pressure exerted by water molecules that are free to move in a system - it is measured in kPa (Kilopascals)

Question 5

Water Potential 2

Answer 5

A solution with a high water potential has a large number of water molecules that are free to move.

A solution’s water potential will fall as solutes (Sugar, salt, etc) are added because water molecules will cluster around the solute molecules making them less likely to move

Question 6

Solute Potential

Answer 6

A solute’s contribution to the water potential is called the solute potential.
As it always lowers the water potential, the solute potential will always be negative.
It becomes more negative as more solute is added to the system. The more solute added, the more negative a value for solute potential

Question 7

Pressure Potential

Answer 7

Pressure potential is the pressure exerted by the cell contents on the cell wall. It will be a positive value if the cell is turgid and so it always increases the water potential. Pressure potential is 0kPa in a plasmolysed cell. The cell is flaccid so doesn’t exert pressure