2.5 biological membranes

Question 1

What is the role of a membrane?

Answer 1

• site of biochemical reactions
• allows cell to change shape
• allows cell signaling
• allows movement in and out of cells
• compartmentalization

Question 2

What is the fluid mosaic model?

Answer 2

Phospholipid free to move and proteins embedded in bilayer with varying size and shape

Question 3

What is the role of phospholipids?

Answer 3

• have hydrophillic head on outside
• have hydrophobic tail on inside
• center is hydrophobic so does not allow water soluable substances through (acts as barrier)

Question 4

What is the role of cholesterol?

Answer 4

• maintains flexibility/stability
• binds to phospholipid tail
• prevents phospholipids from packaging together too closely

Question 5

What is the role of glycolipids?

Answer 5

• antigens
• carbohydrate chain attached to lipid

Question 6

What is the role of glycoproteins?

Answer 6

• receptor for chemical signals
• branching carbohydrate chain attached (recognition site for chemicals)

Question 7

What is an intrinsic protein?

Answer 7

Embedded in cell surface membrane

e.g. channel protein/carrier protein

Question 8

What is an extrinsic protein?

Answer 8

• on one side of bilayer
• hydrophobic R-groups on surface interact with phospholipid head

Question 9

What is the role of channel proteins?

Answer 9

form pores in membrane for charged particles to diffuse through

Question 10

What is the role of carrier proteins?

Answer 10

more large molecules in/out of cell
large molecule attaches to carrier protein which then changes shape and releases molecule on other side

Question 11

What are the roles of membrane-bound receptor sites?

Answer 11

• responsible for chemical signals
• cell communication/signalling
• hormones or drugs may bind to membrane-bound receptors

Question 12

Effect of temperature on membrane?

Answer 12

• can no longer control movement through membrane
• proteins denature
• membrane loses structure
• phospholipids gain kinetic energy so move more

Question 13

Effect of solvents on membrane?

Answer 13

• increases permability
• lipids dissolve in solvent
• membrane becomes more fluid and permeable
• membrane loses structure

Question 14

Practical investigation into factors affecting membrane structure and permeability.

Question 15

What is a passive method or transport?

Answer 15

• small non-polar molecules
• net movement of particles from high to low concentration

thicker membrane = faster rate
larger surface area = faster rate
steeper concentration gradient = faster rate
increased temperature = faster rate

Question 16

What is an active method of transport?

Answer 16

• uses ATP
• movement from area of low conc. to high conc.
• process involves carrier proteins

Question 17

What is facilitated diffusion?

Answer 17

• uses carrier proteins and channel proteins
• is a passive process so does not use energy

Question 18

What is active transport?

Answer 18

• active transport uses energy to move molecules and ions across plasma membrane against a conc gradient

Question 19

What is endocytosis?

Answer 19

some molecules are too large to be taken into cell by carrier proteins
instead…
the cell surrounds substance with membrane that then pinches it off to form vesicle inside cell containing substance
e.g. white bloodcells to destroy foreign substances

process uses atp

Question 20

What is exocytosis?

Question 21

What factors affect rate of diffusion?

Question 22

Factors affecting rate of diffusion in a practical setting?

Question 23

What is osmosis?

Question 24

Practical investigation into osmosis?

Question 25

What is water potential?

Question 26

What is a hypotonic solution?

Question 27

What is a hypertonic solution?

Question 28

Diffusion in plant cell?

Question 29

Diffusion in animal cell?

Question 30

What is bulk transport?