Movement of substances into / out of cells

Question 1

Describe the process of diffusion

Answer 1

• net movement of particles from an area of higher concentration to lower concentration
• passive - requires no energy
• liquids and gases
• the bigger the difference in concentration, the faster the diffusion rate

Question 2

What is the definition of osmosis?

Answer 2

• net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
• happens in water
• water can go through partially permeable membrane, bigger molecules (eg sucrose) cannot

Question 3

Explain what active transport is

Answer 3

• works against concentration gradient
• movement of particles from an area of lower concentration to higher concentration using energy released from respiration
• requires energy from respiration

Question 4

Name the four factors which affect the movement of substances

Answer 4

1. surface area to volume ratio
rate of movement is higher in cells with a larger SA to volume ratio
2. distance
short distance is faster
3. temperature
warmer = more energy = faster
4. concentration gradient
faster when theres a big difference in concentration between the inside + outside of the cell

Question 5

What is the practical to investigate osmosis in living systems?

Answer 5

potato cylinders
1. cut potato into cylinders
2. beakers with different sugar solutions - 1 pure water, 1 concentrated sugar solution, others in between
3. measure lengths of potato cylinders
4. put a few in each beaker + leave for half an hour
5. take out and measure lengths again
if they’re bigger, they have drawn in water by osmosis
if they’re smaller, water has been drawn out by osmosis

Question 6

What is the practical to investigate osmosis in non-living systems?

Answer 6

visking tubing
1. put sugar solution in visking tubing
2. put into beaker of pure water
3. measure where the sugar solution goes up to on the glass tube
4. leave for few hours
5. measure where the sugar solution goes up to on the glass tube
6. water will osmose through visking tubing, forcing solution up the glass tube