Diffusion

Question 1

Define diffusion

Answer 1

the net movement of particles down a concentration gradient from an area of higher concentration to an area of lower concentration until equilibrium is reached.

Question 2

What is facilitated diffusion?

Answer 2

Large, polar molecules and charged ions can only enter the cell with the aid of proteins.

Question 3

What is simple diffusion?

Answer 3

Lipid soluble molecules and very small molecules such as oxygen and carbon dioxide can diffuse directly through the lipid bilayer.

Question 4

How do carrier proteins work?

Answer 4

• have a specific shape that match the shape of the molecule to be transported
• the molecule or ion binds to this site snd the protein changes shape.
• this moves the substance across the membrane

Question 5

How do channel proteins work?

Answer 5

• have water filled pores that span the membrane.
• each has a specific shape through which a particular molecule or ion can pass.

(some are gated and can be open or closed)

Question 6

When does the rate of uptake increase in simple diffusion?

Answer 6

• When the concentration of the substance outside of the cell increases because there is a bigger concentration gradient.
• When the temperature increases because the molecules/ions have more kinetic energy therefore move faster.

Question 7

When does the rate of uptake change in facilitated diffusion?

Answer 7

• levels off at high concentrations because the carrier/channel proteins are becoming saturates with molecules/ions
• at high temperatures, the rate of uptake may change because the carrier/channel proteins have denatured.

Question 8

Why is diffusion called ‘passive transport’?

Answer 8

• doesn’t require ATP

- moves down a concentration gradient.