2-B: Cell Membranes

Question 1

Describe the fluid mosaic model of membranes:

Answer 1

• Fluid: phospholipid bilayer in which individual phospholipids can move, membranes have a flexible shape
• Mosaic: extrinsic and intrinsic proteins are embedded

Question 2

Explain the role of cholesterol in membranes (3)

Answer 2

• reduces fluidity making it more stable
• connects phospholipids
• steroid molecule in some plasma cells

Question 3

Explain the role of glycolipids in membranes:

Answer 3

Cell signalling and recognition

Question 4

Explain the function of extrinsic proteins in cell membranes:

Answer 4

• binding site
• antigens (glycoproteins)
• bind cells together
• involved in cell signalling

Question 5

Explain the function of intrinsic proteins in cell membranes:

Answer 5

• electron carriers (respiration/photosynthesis)
• channel proteins (facilitated diffusion)
• carrier proteins (facilitated diffusion/active transport)

Question 6

What is the function of membranes within cells?

Answer 6

• internal transport system
• selectively permeable (regulates)
• reaction surface
• isolate organelles from cytoplasm for specific metabolic reactions

Question 7

What is the function of membranes?

Answer 7

• selectively permeable (regulates)
• cell signalling/recognition
• isolates cell from environment

Question 8

Name and explain 3 factors that impact membranes permeability:

Answer 8

• temp: denatures proteins/phospholipids have too much kinetic energy, move apart
• PH: changes mermbrane proteins tertiary structure
• Solvent use: may dissolve membrane

Question 9

Describe the fluid mosaic model of cell membranes

Answer 9

• fluid: phospholipid bilayer in which individual phospholipids can move
• mosaic: extrinsic and intrinsic proteins are embedded

Question 10

Explain the role of cholesterol in cell membranes (2)

Answer 10

• steroid molecule in some membranes
• connects phospholipids/ reduces fluidity making it more stable

Question 11

Explain the role of glycolipids in cell membranes (2)

Answer 11

• Cell signalling
• cell recognition

Question 12

Explain the function of extrinsic proteins (4):

Answer 12

• binding site/ receptors
• antigens (glycoproteins)
• bind cells together
• individual cell signalling

Question 13

Explain the function of intrinsic proteins (4):

Answer 13

• electron carriers (respiration/photosynthesis
• channel proteins (facilitated diffusion)
• carrier proteins (facilitated diffusion/active transport)

Question 14

Explain the function of membranes within cells:

Answer 14

• internal transport system
• selectively permeable, regulate
• reaction surface
• isolate organelles for specific metabolic reactions

Question 15

Explain the function of the cell surface membrane:

Answer 15

• selectively permeable, regulate
• cell signalling/recognition
• isolate cytoplasm from extracellular environment

Question 16

Name and explain 3 factors that affect membrane permeability:

Answer 16

• temp: denatures membrane proteins, phospholipids increase kinetic energy
• PH: changes proteins tertiary structure
• solvent: may dissolve membrane

Question 17

Define osmosis:

Answer 17

The net movement of water from an area of high to low concentration through a partially permeable membrane untill dynamic equilibrium is established

Question 18

How does osmosis affect plant and animal cells?

Answer 18

In
- plant: turgid (protoplast swells)
- animal: lysis
Out
- plant: flaccid (protoplast shrinks)
- animal: crenation

Question 19

Define simple diffusion

Answer 19

Passive process (no ATP). Net movement of small, non-polar (lipid-soluble) substances directly through the bilayer down the concentration gradient

Question 20

Define facilitated diffusion

Answer 20

Passive process (no ATP). Specific carrier or channel proteins with complementary binding sites transport large/polar molecules down conc gradient

Question 21

Explain how channel proteins work

Answer 21

Hydrophilic channels bind to specific ions, one side closes and the other opens, ion goes through

Question 22

Explain how carrier proteins work

Answer 22

• binds to completely molecule
• conformation change releases molecule on other side
• active transport (ATP) or facilitated diffusion (passive)

Question 23

Name 5 factors that affect the rate of diffusion:

Answer 23

• temp
• diffusion distance
• SA
• molecule size
• steepness of conc gradient

Question 24

How are cells adapted to maximise their rate of transport across membranes?

Answer 24

• folded membrane increases SA
• many carrier/channel proteins with

Question 25

What does the facilitated diffusion graph look like and why?

Answer 25

- as conc increase rate increases - levels off when Cartier/channel become saturated

Question 26

Describe active transport through cell membranes

Answer 26

- ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape - specific carrier protein (only) transports molecule against conc gradient

Question 27

What is a co transporter?

Answer 27

A specific kind of carrier protein that moves of substances against their conc gradient by coupling it with the movement of another substance down its conc gradient

Question 28

Describe the co transport of sodium and glucose

Answer 28

- Na moves down its conc gradient while bonded to glucose, which moves against its conc gradient by

Question 29

Explain the sodium potassium pump

Answer 29

- Na ions exit epithelial cells via active transport into the blood by the sodium-potassium pump - creates conc gradient, Na enters cell from ileum side via Na-glucose co-transporter. - glucose conc increases and diffuses out of cell into blood

Question 30

Factors affecting active transport

Answer 30

- speed of individual carrier proteins - no. Carrier proteins - rate of respiration and the availability of ATP

Question 31

Factors affecting rate of facilitated diffusion

Answer 31

- conc gradient - no. Channel/carrier proteins with complementary

Question 32

How is the movement of substances affected by the structure of the cell membrane (8):

Answer 32

- phospholipid bilayer allows diffusion of non- polar substances - prevents diffusion of polar substances - carrier proteins allow active transport - channel/carrier allow facilitated diffusion - shape/charge of channel determines which substance moves - number of carriers/ channel determines how much movement - SA determines how much diffusion - cholesterol affects permeability

Question 33

Explain how pigment is gets released from cells

Answer 33

- increase temp/Ph/ add lipid solvent - damage to cell surface membrane - proteins denature - increases fluidity and permeability