2.1.6 - Diffusion & Facilitated Diffusion

Question 1

Define Diffusion?

Answer 1

Passive net movement of small, non-polar, lipid soluble molecules, from an area of high to low concentration.

Question 2

Where Can Diffusion Occur?

Answer 2

Across a cell membrane.

Question 3

In Diffusion Where Do The Molecules Or Ions Move Down?

Answer 3

A concentration gradient.

Question 4

What Is A Concentration Gradient?
(2 Points)

Answer 4

~ The difference between the concentration of a substance in one location compared to another.

~ The bigger the difference, the steeper the concentration gradient and the faster the rate of diffusion.

Question 5

What Type of Process Is Diffusion & What Does This Mean?
(2 Points)

Answer 5

~ Passive process / passive transport.

~ Does not require energy in order to occur.

Question 6

When Will Diffusion Continue Up Until?

Answer 6

The concentration of a substance on each side of a membrane has become equal, known as equilibrium.

Question 7

What Is Simple Diffusion?
(4 Points)

Answer 7

When molecules are able to diffuse directly between the phospholipids of a membrane.

~ Molecules that can move by simple diffusion tend to be small and non-polar.

~ Small -> Fit between phospholipids.

~ Non-Polar -> Able to interact with the non-polar tails of the phospholipids.

Question 8

What Does Non-Polar Mean?

Answer 8

The electrons are shared equally, the molecule is not charged.

Question 9

What Does The Rate Of Diffusion Depend On?
(4 Points)

Answer 9

~ Steepness of the concentration gradient.

~ Temperature.

~ Surface area.

~ Properties of molecules or ions.

~ Diffusion distance.

Question 10

How Does Steepness Of The Concentration Gradient Affect The Rate Of Diffusion?

Answer 10

A greater difference in concentration gradient means a greater difference in the number of molecules passing in the two directions, faster rate of diffusion.

Question 11

How Does Temperature Affect The Rate Of Diffusion?
(2 Points)

Answer 11

~ Molecules and ions have more kinetic energy at higher temperatures.

~ Move faster, resulting in a higher rate of diffusion.

Question 12

How Does Surface Area Affect The Rate Of Diffusion?
(3 Points)

Answer 12

~ Greater the SA, the greater number of molecules or ions that can cross it therefore a faster diffusion occurs.

~ The SA of a cell membrane can be increased b folding.

~ As a cell increases in size, the SA:V decreases, slowing the rate at which substances can diffuse as the distance becomes too great.

Question 13

How Does Properties Of Molecules Or Ions Affect The Rate Of Diffusion?
(3 Points)

Answer 13

~ Large molecules diffuse more slowly as they require more energy to move.

~ Uncharged and non-polar molecules diffuse directly across the phospholipid bilayer.

~ Non-polar molecules diffuse more quickly than polar ones as they are soluble in the non-polar phospholipid bilayer.

Question 14

What Is Facilitated Diffusion?

Answer 14

Requires a protein channel in the cell membrane to transport polar, charged and water-soluble molecules across the membrane.

Question 15

What Does Polar Mean?

Answer 15

Contains a region of positive and negative charge.

Question 16

What Are The 2 Types Of Transport Proteins That Enable Facilitated Diffusion?

Answer 16

~ Channel proteins.

~ Carrier proteins.

Question 17

What Are Channel Proteins?
(4 Points)

Answer 17

~ Are pores that extend through the membrane from one side to the other.

~ Have a fixed shape.

~ Allow charged substances to diffuse through the membrane.

~ Are gated to allow control of the exchange of ions.

Question 18

What Are Carrier Proteins?
(2 Points)

Answer 18

~ Changes shape, causing the binding site to open on one side of the membrane first and vice versa.

~ Net movement of molecules or ions into or out of a cell will occur down a concentration gradient.