Exchange Across Cell Membranes

Question 1

Why are cell membranes described as having a fluid mosaic structure?

Answer 1

Fluid - phospholipids constantly moving

Mosaic - proteins scattered throughout bilayer

Question 2

What are glycoproteins?

Answer 2

Proteins with a carbohydrate (polysaccharide) attached

Question 3

What are glycolipids?

Answer 3

Lipids with a polysaccharide chain attached

Question 4

Why does the phospholipid bilayer not allow water soluble substances to pass through?

Answer 4

Head is hydrophilic - attracts water
Arrange themselves automatically into bilayer
Water can’t pass through hydrophobic tails

Question 5

What is the role of cholesterol in the membrane?

Answer 5

Provide stability

Question 6

How does cholesterol provide stability in the membrane?

Answer 6

Bind to hydrophobic tails of phospholipids
Packed closer together
Restricts movement - less fluid

Question 7

Why is cholesterol particularly important in animal cells?

Answer 7

They do not have a cell wall so helps maintain shape of cell

Question 8

What is diffusion

Answer 8

The random, net movement of particles from an area of higher concentration to an area of lower concentration

Question 9

Is diffusion active or passive?

Answer 9

Passive

Question 10

What is facilitated diffusion?

Answer 10

Diffusion using carrier proteins and protein channels

Question 11

Is facilitated diffusion active or passive?

Answer 11

Passive

Question 12

Describe the role of carrier proteins in facilitated diffusion

Answer 12

Attach to large molecule
Protein changes shape
Releases molecule on opposite side of membrane

Question 13

Describe the role of channel proteins in facilitated diffusion

Answer 13

Form pores in membrane
Charged/water soluble particles
Different proteins for different particles

Question 14

What three factors affect the rate of simple diffusion?

Answer 14

concentration gradient
Thickness of exchange surface
Surface area

Question 15

What two factors affect the rate of facilitated diffusion?

Answer 15

Concentration gradient

Number of channel/carrier proteins

Question 16

What is osmosis?

Answer 16

The diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential

Question 17

What is the water potential of pure water?

Answer 17

Zero

Question 18

What three factors affect the rate of osmosis?

Answer 18

Water potential gradient
Thickness of exchange surface
Surface area

Question 19

What are two methods of making up solutions of exact concentrations?

Answer 19

Scale factors

Serial dilutions

Question 20

What is active transport

Answer 20

The movement of particles across a membrane from an area of low concentration to an area of high concentration

Question 21

Active transport is active. What provides energy for this process?

Answer 21

ATP from respiration

Question 22

Active transport only uses one type of protein. What is this protein?

Answer 22

Carrier protein

Question 23

What are co transporters?

Answer 23

A type of carrier protein which binds two molecules at a time

Question 24

How do co transporters work?

Answer 24

The concentration gradient of one molecule is used to move the other molecule AGAINST their concentration gradient

Question 25

What three factors affect the rate of active transport?

Answer 25

The speed of carrier proteins
The number of carrier proteins
The rate of respiration

Question 26

Where does co transport take place with glucose?

Answer 26

Mammalian ileum

Question 27

How does glucose enter the blood stream from the small intestine?

Answer 27

Sodium ions transported into blood by Na/K pump - causes a conc gradient
Causes sodium to diffuse from the lumen into the epithelial cell via sodium-glucose co-transporter proteins
Co transporter carries glucose into cell with sodium
Glucose conc increases, diffuses out of cell via proteins