2.5 Biological Membranes

Question 1

What are biological membranes made of?

Answer 1

A phospholipid bilayer

Question 2

What does a phospholipid bilayer contain?

Answer 2

• hydrophobic fatty acids facing inwards
• hydrophilic phosphate groups facing outwards
• cholesterol to regulate membrane permeability
• channel proteins for facilitated diffusion
• carrier proteins for facilitated diffusion and active transport
• glycolipids for cell signalling

Question 3

What is the function of channel proteins?

Answer 3

Allows polar compounds to avoid the non polar centre of the membrane. It is used for facilitated diffusion

Question 4

What is the function or carrier proteins?

Answer 4

To bind to large compounds and change shape so the compounds can be moved through the membrane. It is used for facilitated diffusion and active transport.

Question 5

Give 3 factors that affect membrane permeability.

Answer 5

• pH
• temperature
• solvent concentration

Question 6

How does the pH concentration affect membrane permeability?

Answer 6

A suboptimal pH can affect the channel and carrier proteins. Membranes are often surrounded by buffer solutions to control the pH.

Question 7

How does the temperature affect membrane permeability?

Answer 7

A higher temperature increases membrane fluidity which increases permeability.

Question 8

How does solvent concentration affect membrane permeability?

Answer 8

The more the bilayer is dissolved, the more permeable it is. Phospholipids can be dissolved by alcohols.

Question 9

What are the roles of biological membranes?

Answer 9

• to separate cell organelles from the external environment
• to release signal chemicals
• to regulate the transport of substances in and out of cells
• the site of some chemical reactions

Question 10

What is diffusion?

Answer 10

The net movement of particles from an area of high concentration to low.

Question 11

What is osmosis?

Answer 11

The diffusion of water across a partially permeable membrane from a dilute solution to a concentrated solution.

Question 12

Describe the isotonic point.

Answer 12

When both sides of the membrane have the same water potential, net water movement is 0.

Question 13

What is active transport?

Answer 13

Dissolved molecules moving from a less concentrated to more concentrated solution across the concentration gradient using carrier proteins. It requires energy.

Question 14

Other than permeability reasons, what factors affect the rate of diffusion?

Answer 14

• concentration gradient
• surface area of membrane
• thickness of membrane

Question 15

What is it called when animal cells lose water and shrink?

Answer 15

Crenation

Question 16

What is it called when animal cells gain water and burst?

Answer 16

Lysis

Question 17

What is it called when plant cells lose water and shrink?

Answer 17

Plasmolysis

Question 18

What is it called when plant cells gain water?

Answer 18

Turgid

Question 19

What processes/es use channel proteins?

Answer 19

Facilitated diffusion

Question 20

What processes/es use carrier proteins?

Answer 20

Facilitated diffusion and active transport.