Diffusion

Question 1

What does passive transport mean?

Answer 1

• Energy comes from the natural motion of particles, rather than an external source such as ATP.
• No energy used.

Question 2

What is diffusion?

Answer 2

• Net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distrusted.

Question 3

What is the concentration gradient?

Answer 3

The path from an area of higher concentration to an area of lower concentration.

Question 4

How do particles diffuse?

Answer 4

Down concentration gradients

Question 5

What type of transport is diffusion?

Answer 5

Passive

Question 6

What energy does diffusion rely on?

Answer 6

• Inbuilt motion ( kinetic energy ) of diffusing molexcules.

Question 7

What are the two types of protein involved in diffusion?

Answer 7

• Protein channels

* Carrier Proteins

Question 8

What is simple diffusion?

Answer 8

When molecules diffuse directly through a cell membrane.

Question 9

Why is oxygen and carbon dioxide able to easily diffuse through cell membranes?

Answer 9

• They are small, they are able to pass through spaces between phospholipids.
• They are non polar, allowing them to be soluble in lipids, so they can dissolve in the hydrophobic layer.

Question 10

Why are charged particles and ions not able to diffuse easily?

Answer 10

Water soluble, and the centre of the bi-layer is hydrophobic, meaning that they cannot pass through.

Question 11

How do protein channels work?

Answer 11

• They form water filled hydropillic channels across the membrane.
• They allow specific water soluble ions to pass through
• The ions then bind with the protein, resulting in it changing shape in a way that closes it to one side of the membrane, and opens it on the other.

Question 12

How are protein channels selective?

Answer 12

• Each channel opens in the presence of a specific ion, if the ion is not present, the channel remains closed.
• This allows control over entry and exit of ions

Question 13

How do carrier proteins work?

Answer 13

• A large molecule attaches to a carrier protein in the membrane.
• Protein will then change shape.
• This will release it the molecule on the opposite side of the membrane.

Question 14

Where are carrier proteins present?

Answer 14

They span the cell plasma membrane.

Question 15

What do carrier proteins transport?

Answer 15

Large molecules

Question 16

What do protein channels transport?

Answer 16

Ions

Question 17

What factors affect simple diffusion?

Answer 17

• Concentration Gradient
• Thickness of exchange surface
• Surface area

Question 18

How does concentration gradient affect simple diffusion?

Answer 18

• Higher concentration gradient is, the faster the rate of diffusion.
• As diffusion takes place, the difference in concentration between two sides of the membrane decreases until it reaches an equilibrium ( concentrations on both sides are equal )
• This also means diffusion slows down over time

Question 19

Why does diffusion slow down over time?

Answer 19

• Higher concentration gradient is, the faster the rate of diffusion.
• As diffusion takes place, the difference in concentration between two sides of the membrane decreases until it reaches an equilibrium ( concentrations on both sides are equal )
• This also means diffusion slows down over time

Question 20

How does thickness of exchange surface affect rate of diffusion?

Answer 20

The thinner the exchange surface, the shorter the distance the particles will have to travel, and therefore the faster the rate of diffusion.

Question 21

How does surface area affect rate of diffusion?

Answer 21

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

Question 22

What factors affect rate of facilitated diffusion?

Answer 22

• Concentration Gradient

* Number of channel or carrier proteins.

Question 23

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

Answer 23

Once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, the greater the number of channel or carrier proteins in the cell membrane, the faster