4.3 - Osmosis

Question 1

Factors affecting the rate of osmosis (4 things)

Answer 1

1. temperature - water molecules have more KE at higher temperatures
2. Water potential gradient - steeper the gradient, faster the rate of osmosis
3. thickness of the membrane - water molecules travel shorter distances if thinner, diffuses faster
4. SA - larger means that more water molecules can cross the membrane at once

Question 2

Osmosis in animal cells (types of solutions)

Answer 2

1. hypotonic;
   * has a higher water potential than the cell
   * water molecules move into the cell
   * cell swells and bursts
2. Isotonic
   * same water potential as the cell
   * no net movement
3. Hypertonic
   * lower water potential compared to outside
   * water osmoses out
   * shrinks and plasmolyses

Question 3

What is osmosis? what does it diffuse across and until what

Answer 3

• the diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential
• water molecules diffuse directly through the cell membrane - large solute molecules cannot
• water molecules diffuse down a water potential gradient until the water potential is equal on both sides

Question 4

Pure water water potential

Answer 4

0 kPa, more solute means it becomes more negative

Question 5

High water potential vs low water potential

Answer 5

solution has a high water concentration so low solute vs low water concentration so more solute

Question 6

What is water potential?

Answer 6

pressure exerted by water molecules on the membrane surrounding a solution (kPa)

Question 7

What are solutions?

Answer 7

• mixtures made of a solute
• or dissolved in a solvent