5.3 DIFFUSION

Question 1

What is diffusion?

Answer 1

The net movement of anything from a region of higher concentration to a region of lower concentration

Question 2

What is diffusion driven by?

Answer 2

a concentration gradient

Question 3

What is a concentration gradient?

Answer 3

A change in concentration over a distance

Question 4

What energy is required for diffusion and what is this process called?

Answer 4

Comes from internal kinetic energy of the particles - does NOT need external energy (ie.ATP)

It is a passive process

Question 5

What is Brownian Motion?

Answer 5

A single molecule moving around randomly when suspended in a liquid or a gas - relies on the kinetic energy of the molecule

Question 6

What happens when there are more molecules filling up a solution?

Answer 6

There is a statistical trend that the solute fills the container more and more uniformly

Question 7

What happens when there is a larger number of solute molecules in a solution?

Answer 7

All randomness is gone, the solute appears to move smoothly from high concentration areas to low concentration areas.

Question 8

What is the APPARENT force pushing molecules from high to low concentrations?

Answer 8

the Entropic force

Question 9

Why is the entropic force apparent?

Answer 9

there is no actual microscopic force moving molecules down a concentration gradient - there only appears to be one

Question 10

What are the key concepts of Fick’s Law?

Answer 10

Higher the temperature, higher the rate of diffusion
Higher the concentration difference, higher the rate of diffusion
Higher the surface area of the exchange surface, higher the rate of diffusion
Higher the membrane thickness, lower the rate of diffusion

Question 11

What is equilibrium?

Answer 11

Once a concentration gradient has been equalised, equilibrium has been reached.
Particles do not stop moving - moving equally in all directions.

Question 12

What is the difference between diffusion and bulk transport?

Answer 12

Diffusion is the moment of particles within other other particles down a concentration gradient,
Bulk Flow is the movement of a whole substance or all particles moving in one direction.

Question 13

Give an example of bulk flow:

Answer 13

air inside alveoli due to a pressure gradient - high pressure outside the lungs and low pressure in the alveoli when breathing in, this bulk flow stops when the pressure is equalised in the alveoli.

Question 14

Give an example of diffusion:

Answer 14

oxygen molecules in the air into blood due to a concentration gradient, the oxygen are the particles moving within all the other molecules in the air
e.g. nitrogen

Question 15

What are the two types of diffusion?

Answer 15

simple diffusion
facilitated diffusion

Question 16

What is simple diffusion?

Answer 16

-diffusion between phospholipids (across a membrane)

Question 17

What molecules are able to use simple diffusion across a membrane?

Answer 17

-small and non-polar molecules eg. oxygen/co2
-water (small/polar molecule) can diffuse but slower due to the partial charges (delta +/-) being repelled by the hydrophobic core of the membrane.

Question 18

What molecules find it difficult/can’t simple diffuse across a membrane?

Answer 18

-Large and Polar molecules eg. glucose
-Fully charged molecules or ions due to the charges being repelled by hydrophobic core

Question 19

What can affect what goes through a membrane through simple diffusion?

Answer 19

Bigger the non-polar molecule, lower the rate of diffusion

Question 20

What is facilitated diffusion?

Answer 20

Through a transmembrane protein
- channel/carrier

Question 21

What is a carrier protein?

Answer 21

has a pore that is never fully open across the membrane, it changes shape when a specific molecule/ion binds to the protein
-has a lower rate of diffusion due to the limited pores available
-energy for this shape change does NOT come from ATP

Question 22

What is a channel protein?

Answer 22

Has a permanently open pore/ pore that can open and close. this pore is specific to the molecule/ion
Has a high rate of diffusion but is saturable due to the limited pores available.

Question 23

What are the pores made out of in transmembrane proteins?

Answer 23

alpha helix, in a polypeptide chain - R groups control what can go through

Question 24

What is dialysis tubing?

Answer 24

artificial semi-permeable membrane tubing
- fine smooth membrane with holes in it (holes are large enough to fit water and other small molecules through but are too small to allow large molecules)