Diffusion

Question 1

Define Diffusion

Answer 1

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

Question 2

What does diffusion continue until

Answer 2

Particles are evenly distributed throughout liquid/gas

Question 3

What is the concentration gradient in diffusion

Answer 3

the path from an area of higher concentration to an area of lower concentration

Question 4

What way do particles diffuse via the concentration gradient in diffusion

Answer 4

Down the concentration gradient

Question 5

Does diffusion require energy?

Answer 5

No, it is a passive process

Question 6

Can particles diffuse across cell membranes?

Answer 6

Yes, as long as they can move freely through the membrane

Question 7

What is it known as when molecules diffuse directly through a membrane

Answer 7

Simple diffusion

Question 8

Is rate of diffusion always the same

Answer 8

No

Question 9

What does rate of diffusion across membranes depend on

Answer 9

Concentration gradient, thickness of the exchange surface and surface area

Question 10

How does the concentration gradient effect the rate of diffusion across a membrane

Answer 10

The higher it is, 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 over time.

Question 11

How does the thickness of the exchange surface effect the rate of diffusion across a membrane

Answer 11

The thinner the exchange surface, the faster the rate of diffusion (shorter distance particles must travel).

Question 12

How does the surface area effect the rate of diffusion across a membrane

Answer 12

The larger the surface area (e.g. cell surface membrane) faster rate of diffusion.

Question 13

Why would larger molecules (e.g. amino acids, glucose) diffuse extremely slowly through the phospholipid bilayer

Answer 13

Because they are so big

Question 14

Why would charged particles (e.g. ions and polar molecules) diffuse extremely slowly through the phospholipid bilayer

Answer 14

Because they are water soluble, and the centre of the bilayer is hydrophobic.

Question 15

How do large or charged particles speed things up and diffuse through the bilayer

Answer 15

They diffuse through carrier proteins or channel proteins in the cell membrane - this is called facilitated diffusion

Question 16

What way does facilitated diffusion move particles across the concentration gradient

Answer 16

Down

Question 17

How do carrier proteins diffuse large molecules

Answer 17

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

Question 18

How do channel proteins diffuse charged particles

Answer 18

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

Question 19

What are the factors affecting the rate of facilitated diffusion

Answer 19

Concentration gradient, number of channel/carrier proteins

Question 20

How does concentration gradient effect the rate of facilitated diffusion

Answer 20

The higher the concentration gradient, the faster the rate of facilitated diffusion (up to a point). As equilibrium reached rate of facilitated diffusion will plateau.

Question 21

How does number of channel / carrier proteins effect the rate of facilitated diffusion

Answer 21

Once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient.

Question 22

How do you calculate the rate of diffusion

Answer 22

Draw a tangent on the graph, find change in y and change in x on tangent and do: change in y/change in x