Transport across cell membranes

Question 1

name some features of cell surface membranes.

Answer 1

• partially permeable

- some substances can pass through and others cant

Question 2

why is the phospholipid bilayer referred to as the fluid mosaic model?

Answer 2

• fluid part is because the phospholipids are constantly moving.
• mosaic part is because proteins are scattered through the bilayer.

Question 3

what do the proteins allow?

Answer 3

large molecules and ions to pass through it

Question 4

what do receptor proteins do?

Answer 4

receptor proteins on the cell surface membrane detect chemicals released from other cells and they respond.

Question 5

anything that has a carbohydrate attached is known as a what?

Answer 5

glyco-

Question 6

what is the role of cholesterol?

Answer 6

membrane stability.

Question 7

what do glycoprotiens and glycolipids do?

Answer 7

cell signalling

cell recognition

Question 8

phospholipids have a what? what does lead to?

Answer 8

• hydrophillic head
• hydrophobic tail
• this leads to the membrane not allowing water soluble substances through

Question 9

how does cholesterol help with membrane stability?

Answer 9

• it binds to the hydrophobic tail so its less fluid and more rigid
• it helps maintain the shape of animal cells such as red blood cells
• has hydrophobic regions = barrier to polar substances

Question 10

what does a temp below 0 do to the membrane?

Answer 10

• the channel and carrier proteins denature
• this increases the membrane permeability
• ice crystals may form and pierce the membrane so its more permeable.

Question 11

what does a temp between 0-45 do?

Answer 11

• phospholipids can move and aren’t packed that tightly together.
• membrane is partially permeable
• as temp increases, phospholipids move more because they have more energy
• which increases the permeability of the membrane

Question 12

what does a temp above 45 do?

Answer 12

• the bilayer melts
• more permeable membrane
• water in the cells expand putting pressure on the membrane
• proteins denature which increases permeability.

Question 13

what is diffusion?

Answer 13

the net movement of particles from an area of high concentration to an area of low concentration. (passive)

Question 14

what are the 4 factors affecting diffusion?

Answer 14

1. surface area
2. gradient
3. thickness
4. temp

Question 15

why does facilitated diffusion occur ?

Answer 15

• large molecules (amino acids, glucose) diffuse too slowly because they’re extremely big.
• charged particles diffuse too slowly because they’re water soluble and the centre of the bilayer is hydrophobic.

Question 16

what do channel proteins do?

Answer 16

move charged molecules down conc gradient

Question 17

what do carrier proteins do?

Answer 17

move large molecules down the conc gradient

Question 18

factors affecting facilitated diffusion?

Answer 18

1. conc gradient

2. number of channel/carrier proteins.

Question 19

how do you calculate the rate of diffusion?

Answer 19

1. draw a tangent to the curve
2. gradient = (change in) y/x
3. units