2. Diffusion - facilitated

Question 1

Name some large molecules?

Answer 1

Amino acids.

Glucose.

Question 2

Why do large and charged molecules slowly diffuse through phospholipid bilayer?

Answer 2

As they are too big.

As charged molecules are water soluble and the centre of the bilayer is hydrophobic.

Question 3

What do large and charged particles do?

Answer 3

Diffuse through carrier or channel proteins in the cell membrane to speed things up - this is called facilitated diffusion.

Question 4

What type of process is facilitated diffusion?

Answer 4

Passive - doesn’t use energy.

Question 5

What is the function of carrier proteins?

Answer 5

Move large molecules across membrane down their concentration gradient.
Different carrier proteins facilitate the diffusion of different molecules.

Question 6

HOW do carrier proteins work?

Answer 6

1. Firstly, large molecule attaches to carrier protein in the membrane.
2. Then, protein changes shape.
3. This releases the molecule on the opposite of the membrane.

Question 7

What is the function of channel proteins?

Answer 7

They form pores in the membranes for charged particles to diffuse through and down their concentration gradient.
Different channel proteins facilitate the diffusion of different charged particles.

Question 8

Name the 2 factors which affect the rate of facilitated diffusion?

Answer 8

The concentration gradient.

Number of channel or carrier proteins.

Question 9

How does concentration gradient affect rate of diffusion?

Answer 9

Higher the concentration gradient , the faster the rate of diffusion. As equilibrium is reached, rate of diffusion levels off.

Question 10

How does the number of carrier and channel proteins affect rate of diffusion?

Answer 10

Once all proteins are in use, diffusion can’t happen any quicker, even if you increase concentration gradient.
Greater number of proteins - faster rate of diffusion.