TOPIC 2B - CELL MEMBRANES

Question 1

Describe the fluid mosaic structure of cell membranes.

Answer 1

(see page 36 in the revision guide)

Question 2

What is the role of phospholipids in the cell membrane?

Answer 2

Phospholipids form a barrier to dissolved substances.
The centre of the bilayer is hydrophobic so the membrane doesn’t allow water-soluble substances into the cell. This acts as a barrier against dissolved substances.

Question 3

What is the role of cholesterol in the cell membrane?

Answer 3

Cholesterol gives the membrane stability.
They bind to the hydrophobic tails of the phospholipids causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid.

Question 4

How do you investigate cell membrane permeability in the lab?

Answer 4

(see page 37 in the revision guide)

Question 5

How do you investigate the effect of temperature on cell membrane permeability in the lab?

Answer 5

(see page 37 in the revision guide)

Question 6

What is diffusion?

Answer 6

Diffusion is the net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration.
(see page 39 in the revision guide for more information)

Question 7

What is facilitated diffusion?

Answer 7

Facilitated proteins uses carrier proteins and channel proteins.
(see page 38 in the revision guide for more information)

Question 8

What are carrier proteins?

Answer 8

Carrier proteins move large molecules across membranes, down their concentration gradient.
(see page 38 in the revision guide for a diagram)

Question 9

What are channel proteins?

Answer 9

Channel proteins form pores in the membrane for charged particles to diffuse through, down their concentration gradient.
(see page 38 in the revision guide for a diagram)

Question 10

What 3 factors affect the rate of simple diffusion across a membrane?

Answer 10

(see page 39 in the revision guide)

Question 11

What 2 factors affect the rate of facilitated diffusion across a membrane?

Answer 11

(see page 39 in the revision guide)

Question 12

What is osmosis?

Answer 12

Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential.
(see page 40 in the revision guide for more information)

Question 13

What 3 factors affect the rate of osmosis?

Answer 13

(see page 40 in the revision guide)

Question 14

How do you investigate water potential using serial dilution in a lab?

Answer 14

(see page 40 in the revision guide)

Question 15

What is active transport?

Answer 15

Active transport uses energy to move molecules and ions across membranes, against a concentration gradient.

Question 16

What 3 factors affect the rate of active transport?

Answer 16

(see page 42 in the revision guide)

Question 17

How is glucose absorbed in the mammalian ileum (the final part of the small intestine)? Draw a diagram.

Answer 17

By co-transport.

see page 43 in the revision guide