Diffusion

Question 1

What is diffusion?

Answer 1

Movement of particles which have kinetic energy + movement is random.

Will continue until theres a concentration equilibrium between 2 areas. Particles still move but equal in both directions

Question 2

How does the rate of diffusion slow down?

Answer 2

When particles move, they constantly collide, slowing down rate of diffision.

Diffusion over small distances is faster
Diffusion over large distances is slower

Question 3

Why are cells permeable?

Answer 3

Movement of particles within cell relies on diffusion

Question 4

What is active movement of substances between cells?

Answer 4

No additional energy required. Uses energy from natural motion of particles. E.g. Diffusion

Question 5

What is passive movement of substances between cells?

Answer 5

Requires metabolic energy. E.g. Active transport against a conc gradient

Question 6

What are the factors affecting diffusion?

Answer 6

• Temp = Higher temp makes particles collide faster
• Conc difference = Higher conc means theres more particles to collide
• Surface area = Larger the SA to vol ratio, the faster the rate of diffusion

Question 7

Explain diffusion across a membrane:

Answer 7

• Involves passing particles through phospholipid bilayer.
• Can only happen if membrane is non polar = Non polar molecules can diffuse freely down a conc gradient
• Since any particle with a charge cant interact with hydrophobic membrane so cant easily pass through
• An exception is small polar molecules (e.g. water), that can diffuse at much slower rate. This makes membranes partially permeable

Question 8

What is rate of diffusion across a membrane affected by?

Answer 8

• Surface area = Larger surface area means higher rate of diffusion
• Thickness of membrane = Thinner exchange surface means higher rate of diffusion. Takes less time for particles to diffuse across

Question 9

What are the ways to calculate rates of diffusion?

Answer 9

1. Distance travelled / time (mm/s)
2. Volume filled / time (mm3/s)

Question 10

What is the rate of diffusion equation?

Answer 10

SA x conc difference / thickness of exchange surface means

Question 11

Why does temp affect the rate of diffusion?

Answer 11

Particles have more kinetic energy, making them move at higher speeds + colliding more

Question 12

Why does conc difference affect the rate of diffusion?

Answer 12

The greater the difference, faster the rate of diffusion

Since overall movement from higher conc to lower conc will be larger