Exchange Across Cell Membranes - Diffusion

Question 1

What is diffusion?

Answer 1

Diffusion is the net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration

Question 2

Which way will molecules diffuse?

Answer 2

Molecules will diffuse both ways, but the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas

Question 3

What is a concentration gradient?

Answer 3

The concentration gradient is the path from an area of higher concentration to an area of lower concentration. Particles diffuse down a concentration gradient

Question 4

Does diffusion require energy?

Answer 4

Diffusion is a passive process - no energy is required for it to happen

Question 5

Can particles diffuse across the cell membrane?

Answer 5

Particles can diffuse across cell membranes, as long as they can move freely through the membrane i.e. they’re small enough or non-polar

Question 6

When molecules diffuse directly through a cell membrane it is also known as what?

Answer 6

Simple diffusion

Question 7

What is facilitated diffusion?

Answer 7

Facilitated diffusion is when large or charged particles diffuse through carrier proteins or channel proteins in the membrane

Question 8

Facilitated diffusion moves particles down a what?

Answer 8

A concentration gradient, from a higher to lower concentration

Question 9

What do carrier proteins do?

Answer 9

Carrier proteins move large molecules across membranes, down their concentration gradient

Question 10

How do carrier proteins work?

Answer 10

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

Question 11

What to channel proteins do?

Answer 11

Channel proteins form pores in the membrane for charged particles to diffuse through (down their concentration). Different channel proteins facilitate the diffusion of different charged particles

Question 12

Give three factors which the rate simple diffusion depends on

Answer 12

1. The concentration gradient
2. The thickness of the exchange surface
3. The surface area

Question 13

How does the concentration gradient affect the rate of simple diffusion?

Answer 13

The higher the concentration gradient, the faster the rate of diffusion. As diffusion takes place, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. This means diffusion slows down over time

Question 14

How does the thickness of the exchange surface affect the rate of simple diffusion?

Answer 14

The thinner the exchange surface, the faster the rate of diffusion

Question 15

How does the surface area affect the rate of simple diffusion?

Answer 15

The larger the surface area, the faster the rate of diffusion

Question 16

Give two factors which the rate of facilitated diffusion depends on

Answer 16

1. The concentration gradient

2. The number of channel or carrier proteins

Question 17

How does the concentration gradient affect the rate of facilitated diffusion?

Answer 17

The higher the concentration gradient, the faster the rate of diffusion. As diffusion takes place, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. This means diffusion slows down over time

Question 18

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

Answer 18

Once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient. So the greater the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion