4.1 Cell-surface Membrane Structure

Question 1

How is the cell membrane partially permeable?

Answer 1

• membranes control which substances enter and leave
• let some molecules through but not others

Question 2

What are the 3 ways substances can move across a cell-surface membrane?

Answer 2

• diffusion
• osmosis
• active transport

Question 3

Why is the structure of a cell membrane ‘fluid mosaic’?

Answer 3

• bilayer made of constantly moving phospholipids =
  fluid
• different components in a membrane = mosaic

Question 4

What are the 4 types of molecules in a cell-surface membrane?

Answer 4

1. phospholipids
2. cholesterol
3. proteins
4. carbohydrates (attached to proteins or lipids)

Question 5

What is the role of channel and carrier proteins in the bilayer

Answer 5

• allow large molecules and ions to pass through the membrane

Question 6

What is the role of receptor proteins in the membrane?

Answer 6

• allows the cell to detect chemicals released from other cells
• the chemicals signal to the cell to respond in some way

Question 7

What are glycoproteins?

Answer 7

• proteins with a polysaccharide chain

Question 8

What are glycolipids?

Answer 8

• lipids with a polysaccharide chain

Question 9

Describe the role of phospholipids in the membrane

Answer 9

• automatically arrange themselves in the bilayer with hydrophilic heads facing out to the water on either side of membrane
• centre of bilayer is hydrophobic so membrane doesn’t allow water-soluble substances (ions) to enter

Question 10

Describe the role of cholesterol in the membrane

Answer 10

• type of lipid that is present in all cell membranes except bacteria
• bind to the hydrophobic tails of phospholipids making membrane less rigid and more fluid
• helps maintain the shape of cells especially those that aren’t supported by other cells

Question 11

How does temperature below 0° affect membrane permeability?

Answer 11

• phospholipids don’t have much energy so they can’t move
• channel and carrier proteins deform and increase permeability
• ice crystal may form and burst membranes

Question 12

How does temperature between 0° and 45° affect membrane permeability?

Answer 12

• phospholipids can move around and aren’t packed as tightly together = partially permeable membrane
• increase temp = increase energy of molecules = increase permeability

Question 13

How does temperature above 45° affect membrane permeability?

Answer 13

• phospholipid bilayer starts to melt and membrane becomes more permeable
• water inside the cell expands = increase pressure
• channel and carrier proteins deform so they can’t control what enters the permeability of the membrane