Cell membranes

Question 1

What does it mean that cell membranes are partially permeable?

Answer 1

They let some substances cross via diffusion, osmosis or active transport.

Question 2

Describe the fluid mosaic structure

Answer 2

Phospholipid molecules form a bilayer
Cholesterol molecules
Channel proteins scattered (allow large molecules and ions to pass)
Receptor proteins (detect chemicals from other cells)
Polysaccharide chain (glycoproteins, glycolipids)

Question 3

Name the role of phospholipids in the cell membrane

Answer 3

Hydrophobic head and hydrophilic tail
Heads face out
Doesn’t allow water-soluble molecules through and act as a barrier

Question 4

Name the role of cholesterol in the cell membrane

Answer 4

It's a type of lipid, not found in bacterial membranes
Fit between phospholipids 
Bind to tails 
Pack more closely together 
Less fluid and more rigid

Question 5

Permeability at temperatures below 0 degrees

Answer 5

Phospholipids have little energy, packed close and rigid. Channel/carrier proteins deform making it more permeable. Ice crystals may pierce.

Question 6

Permeability at temperatures 0-45 degrees

Answer 6

Phospholipids can move and are less packed. Membrane is partially permeable. As temp increases so does permeability due to more energy in phospholipids.

Question 7

Permeability at temperatures above 45 degrees

Answer 7

Phospholipid bilayer begins to melt and becomes more permeable. Water expands and puts pressure on membrane and channel/carrier proteins deform.

Question 8

What is Fick’s law?

Answer 8

rate of diffusion = (surface area X concentration)/ diffusion pathway

Question 9

Talk about facilitated diffusion

Answer 9

Use of carrier proteins and channel proteins

They passively move molecules which are too big or ionic

Question 10

How do carrier proteins work?

Answer 10

Large molecules attaches to the carrier protein
Causes the protein to change shape
Releasing a molecule on the other size

Question 11

How do channel proteins occur?

Answer 11

Form pores in the membrane

Allowing a pathway for charged particles to pass

Question 12

What factors does simple diffusion depend on?

Answer 12

The concentration gradient
Thickness of the exchange surface
The surface area

Question 13

What factors does facilitated diffusion depend on?

Answer 13

The concentration gradient

The amount of channel/ carrier proteins available

Question 14

What does the rate of osmosis depend on?

Answer 14

The water potential gradient
The thickness of exchange surface
The surface area of exchange surface

Question 15

Describe how carrier proteins are involved in active transport

Answer 15

A molecule attaches to the carrier protein
The protein changes shape moving the molecule
The molecule is released using energy from ATP
Unlike other types of diffusion this can happen against a concentration gradient

Question 16

Describe how co transporters are involved in active transport

Answer 16

The protein binds to two molecules at the same time
The concentration gradient of one of the molecules allows the other molecule to move against its gradient
The protein changes shape and moves both molecules to pass the membrane

Question 17

Describe how glucose can be absorbed using co transport

Answer 17

Sodium ions are actively transported into the blood (sodium-potassium pump)
Causes sodium ions to diffuse into the epithelial cells down the concentration gradient, via co transporter proteins
The co transporter protein also carries glucose into the cell so glucose concentration increases inside the cell
Finally glucose diffuses out the cell down its concentration gradient through a protein channel (facilitated diffusion)