5.3- Diffusion

Question 1

Explain diffusion.

Answer 1

The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.
- passive process which continues until there is a concentration equilibrium.
- particles move at high speeds and constantly collide which slows down the overall movement.
Diffusion rate slows down as diffusion distance increases (more collisions happen).

Question 2

What factors affect the rate of diffusion?

Answer 2

1. Temperature:
   - higher the temp, higher the rate of diffusion as particles have more kinetic energy (move faster).
2. Concentration difference:
   - greater the difference in conc, faster the rate of diffusion. Overall movement from hgh to low is larger.

Question 3

Explain diffusion across membranes.

Answer 3

Involves particles passing through the phospholipid bilayer.
-only happens if the membrane is permeable to the particles. Non-polar molecules diffuse freely.
-hydrophobic interior repels ions so they can’t pass through easily.
-polar molecules diffuse at very slow rates due to partial charges.
-small polar molecules diffuse more easily.
Therefore membranes = partially permeable.

Question 4

What factors affect the rate of diffusion across membranes?

Answer 4

1. Surface area:
   - larger the area of an exchange surface, higher the rate of diffusion.
2. Thickness of membrane:
   - the thinner the exchange surface, higher the rate of diffusion.

Question 5

Explain facilitated diffusion.

Answer 5

=Diffusion across a membrane through protein channels. (Down a concentration gradient)

• membranes with protein channels are selectively permeable. Most channels are specific to 1 ion/molecule.
• can involve carrier proteins which change shape when binding to a specific molecule.
• no external energy required.
• rate of diffusion affected by all other factors but also by the number of channel proteins present. (The more channel proteins, higher the rate of diffusion overall).