Cell Surface Membrane

Question 1

What is cell membrane made of ?

Answer 1

• phospholipids bilayer
• protein
• cholesterol
  -glycolipids
• glycoproteins

Question 2

Fluid Mosaic model

Answer 2

• fluid gives membrane a flexible structure that can constantly change shape = bec. Individual phospholipids can move
• mosaic = bec. Proteins embedded in phospholipids vary in shape and size

Question 3

Phospholipids bilayer

Answer 3

• hydrophilic heads point outside of the cell membrane = attracts water
• hydrophobic tail of fatty acids point inwards = repels water

Question 4

Functions of phospholipids bilayer

Answer 4

• allow lipid soluble in/ out of cell membrane
• prevent water soluble in/out cell membrane
• make membrane flexible and self sealing

Question 5

Extrinsic proteins

Answer 5

-embedded in phospholipids bilayer
- in surface of bilayer

Question 6

Functions of extrinsic proteins

Answer 6

• give mechanical strength to membrane
• join with to form glycoproteins/ lipids as cell receptors e.g.hormones

Question 7

Intrinsic proteins

Answer 7

• involved in transport of molecules across membranes
• span across one side of bilayer to other

Question 8

Functions of channel proteins

Answer 8

• form tubes that fill with water = enable water soluble ions to diffuse

Question 9

Functions of carrier proteins

Answer 9

• bind with large molecules e.g. glucose + amino acids and change shape to transport to other side of membrane

Question 10

Cholesterol

Answer 10

• occur in phospholipids bilayer
• very hydrophobic = prevent water loss and dissolved ions from the cell
  Limit movement of fatty acids tails = prevent membrane goes to rigid

Question 11

Functions of cholesterol

Answer 11

• reduce lateral movement of other molecules
• maintain fluidity at high temperature
• strengthen bilayer by interaction with other hydrophobic tails

Question 12

Functions of glycolipids

Answer 12

• act as cell receptors
• help maintain stability of membrane
• help cells to attach to one another to form tissues
• allow cell recognition of one another

Question 13

Functions of glycoproteins

Answer 13

• act as cell receptors
• help cells to attach one another to form tissues
• allow cell recognition

Question 14

What type of molecules cannot pass through partial permeable membrane ?

Answer 14

• too large e.g. glucose
• not soluble in lipids = can’t pass through bilayer
• same charge as protein channels will repel
• electrically charged (polar)= cannot pass through hydrophobic tails (non polar)

Question 15

E.g. what are 2 advantages of giving results as a ratio (2)

Answer 15

• easier to draw comparison
• discs may had different starting masses

Question 16

E.g. explain how taking editorial readings can improve reliability of results ? (2)

Answer 16

• so anomalies can be identified
• a mean value can be calculated

Question 17

Factors affecting membrane’s permeability (4)

Answer 17

• high temperature
• extreme PH
• proportions of saturated and unsaturated fatty acids
• use of ethanol or detergent as solutions = dissolve phospholipid

Question 18

How does temperature and PH affect permeability ?

Answer 18

High temp= phospholipid gain more KE = move more = membrane structure more fluid = more gaps to let pigments diffuse out, also denatures transport proteins = substances easily diffuse out
Extreme PH = denatures proteins = diffusion of substances quicker out

Question 19

How does saturated or unsaturated FA affect membrane permeability ?

Answer 19

• more unsaturated C=C = the phospholipid tails have kinks = causes more gaps in between each PL molecule= pigments can diffuse out easily, increase fluidity of membrane
• C—C bond saturated = tails lined more straight = no gaps to allow pigments diffuse out

Question 20

The movement of substances across cell membranes is affected by membrane structure. Describe how (5)

Answer 20

1) phospholipid allows diffusion of lipid soluble substances
2) carrier proteins allow active transport
3) channel and carrier proteins allow f.d
4) number of channels and carrier proteins determines how much movement
5) cholesterol affects permeability and rigidity, allow exocytosis

Question 21

Explain how the movement of Na+ out of the cell allows absorption of glucose into the cell lining of ileum (2)

Answer 21

1) maintains a concentration grad by decreasing conc of sodium in the cell
2) Na+ movinf in the cell bringing glucose with it by f.d

Question 22

Explain function of ATP hydrolase in transportation of substances across membrane (2)

Answer 22

1) release energy by hydrolysing ATP to ADP and Pi
2) allow ions to move against conc grad by active transport

Question 23

How increase temperature of water caused the release of red pigment (2)

Answer 23

Damage to membrane
Proteins denature, causing increase fluidity of phospholipid bilayer as can move arond more