1 Cells - simple & facilitated diffusion.

Question 1

What is simple diffusion?

Answer 1

The net movement of molecules or ions from an area of high concentration to an area of low concentration across a partially permeable membrane, this is a passive process.

Question 2

What factors affect simple diffusion?

Answer 2

• concentration gradient
• membrane thickness
• surface area
• temperature

Question 3

How does the concentration gradient affect the rate of simple diffusion?

Answer 3

• a greater gradient means a faster rate of diffusion
• a good blood/ air supply to cells maintain these concentration gradients
• transporting substances to and from the membrane ensures that the rate never reaches the equilibrium where it will slow.

Question 4

How does the membrane thickness affect the rate of simple diffusion?

Answer 4

• a thinner membrane means that the rate of diffusion will be faster
• as the distance that particles have to travel is reduced.

Question 5

How does surface area affect the rate of simple diffusion?

Answer 5

-a larger surface area increases the rate of diffusion
- as more particles can be exchanged in the same amount of time

Question 6

How does temperature affect the rate of simple diffusion?

Answer 6

• higher temperature means faster rate of simple diffusion
• as particles have more kinetic energy and move at a higher velocity across membranes, meaning that particles take less time to cross membranes

Question 7

Why does facilitated diffusion occur?

Answer 7

• large/ ionic moleucles cross the membrane too slowly
• use proteins to speed up the process

Question 8

Why do ionic molecules cross the membrane slowly?

Answer 8

• as ions can pass the phosphate group but struggle passing through the non-polar hydrophobic regoin of the bilayer

Question 9

What is facilitated diffusion?

Answer 9

Diffusion but with proteins facilitating the movement of large and polar molecules that have difficulty passing the phospholipid bilayer.

Question 10

What is the role of carrier proteins in facilitated diffusion?

Answer 10

• move large molecules across the membrane
• different proteins facilitate the diffusion of specific molecules
• large molecules attach to the specific shaped proteins for that particular substance
• proteins change shape
• protein releases the molecule on the other side

Question 11

What is the role of channel proteins in facilitated diffusion?

Answer 11

• move charged particles across the membrane, different proteins facilitate the diffusion of different particles
• the intrinsic proteins create a pore where charged particles move across the membrane.
• these channels do not change shape

Question 12

What factors affect facilitated diffusion?

Answer 12

• concentration gradient
• the number of channel and carrier proteins

Question 13

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

Answer 13

• increases the rate of facilitated diffusion until all proteins are in use for facilitated diffusion, the concentration doesn’t affect the rate of diffusion past this point as all proteins are constantly occupied

Question 14

How does the concentration gradient affect the rate of facilitated diffusion?

Answer 14

• a greater gradient means a faster rate of diffusion, particles move down the concentration gradient until equilibrium is reached.