Topic 2 - B : Cell membranes

Question 1

What are cell membranes composed of

Answer 1

Protein
carbohydrate
lipid

Question 2

What are glycoproteins

Answer 2

proteins with carbohydrate attached

Question 3

What are glycolipids

Answer 3

lipid with carbohydrate attached

Question 4

How are phospholipids arranged in membrane

Answer 4

Head is hydrophilic
tail is hydrophobic
Bilayer : head faces out, tail faces in
as tails face in, the centre is hydrophobic, therefore the membrane doesn’t allow water-soluble substances through it
small non polar substances can diffuse through the membrane

Question 5

What is the function of cholesterol in membrane

Answer 5

type of lipid that’s present in all cell membranes, they go between phospholipids
bind to hydrophobic tails of phospholipids
this restricts movement of the phospholipids making the membrane less fluid and more rigid
Main function is to provide membrane with structure

Question 6

Define diffusion

Answer 6

net movement of particles from area of higher concentration to lower concentration.

Question 7

diffusion details

Answer 7

passive process
down concentration gradient

Question 8

Define facilitated diffusion

Answer 8

net movement of particles from an area of higher concentration to lower concentration using carrier or channel proteins

factors affecting it: concentration gradient
number of channel or carrier proteins

Question 9

Carrier proteins

Answer 9

move large molecules across membrane, down concentration gradient
large molecule attaches to carrier protein in membrane
protein changes shape
releases molecule on opposite side of membrane

Question 10

Channel proteins

Answer 10

diffuse charged particles

Question 11

Define osmosis

Answer 11

movement of water particles through a partially permeable membrane from area of higher concentration to lower concentration

Factors affecting it: water potential gradient
thickness of exchange surface
surface area

Question 12

define isotonic

Answer 12

two solutions have the same water potential

Question 13

define active transport

Answer 13

movement of molecules from lower to higher concentration using carrier and co transporter proteins

Question 14

difference between carrier proteins in active transport and facilitated diffusion

Answer 14

active transport moves solutes from low to high, whereas facilitated diffusion move from higher to lower
active transport requires energy and FD doesnt

Question 15

Describe co transporters

Answer 15

bind two molecules at a time. Concentration gradient of one of the molecules is used to move the other molecule against its conc gradient

Question 16

Describe co transport and the absorption of glucose

Answer 16

Sodium ions actively transported out of the epithelial cells in ileum by the sodium pump.
This creates conc. gradient.
Sodium ions diffuse from the lumen of ileum into epithelial cell.
This is done via sodium glucose co transporters
Glucose is carried into cell
Glucose then diffuses out of cell into blood down its conc. gradient through protein channel by FD