2B Cell Membranes

Question 1

What does partially permeable mean?

Answer 1

The membrane allows some substance through

Question 2

How do different substances cross the membrane?

Answer 2

Diffusion, osmosis, active transport and facilitated diffusion

Question 3

Describe the structure of the membrane.

Answer 3

Bi-layer of phospholipids
Embedded integral proteins 
Channel proteins 
Carbohydrates 
Cholesterol 
Peripheral proteins

Question 4

What is the structure of the membrane known as and why!

Answer 4

Fluid mosaic model as it is made up of different sized molecules and fluid as bi later constantly moving

Question 5

What is a glycolipid?

Answer 5

Chain of carbohydrates attached to lipid
A recognition cell and gives membrane stability
Variation of glycolipid on red blood cells which determine blood type

Question 6

What does a glycoprotein do?

Answer 6

Cell recognition

Protects membrane

Question 7

Wear is a channel protein?

Answer 7

Is a hydrophilic pore that allows molecules to pass through the membrane

Question 8

What does a channel protein do?

Answer 8

It allows lager substances to pass through the membrane by binding to them and changing shape of molecule so can get thorough eg glucose

Question 9

What do cell surface membranes do?

Answer 9

Surround cells protect from environment by controlling substances in and out as partially permeable

Question 10

What does cholesterol do in the membrane?

Answer 10

Keeps rigidity of bi layer

Binds to hydrophobic tails making it less fluid

Question 11

Describe the layout of phospholipid in the bi later.

Answer 11

They arranged in bi layer as hydrophobic tails repeal the water so the hydrophilic heads form a barrier around them.
Centre of the bi layer is hydrophobic so no water soluble things can get through including ions and polar molecules.
Small non polar molecules can fit through eg CO 2

Question 12

Factors affecting membranes

Answer 12

Temperature and pH of solution

Question 13

How does temperature affect membranes?

Answer 13

If temp below 0 enzymes not have enough energy to move around so the channel proteins and carrier proteins denatures so increase permeability .

Question 14

What do ice crystals do to membrane layer?

Answer 14

Ice crystals pierce membrane making holes and therefore increasing the permeability

Question 15

As the temperature increases, what happens to the memebrane?

Answer 15

As the temp increases the more kinetic energy the phospholipids have to move around more and collide more frequently and vigorously with substances therefore increasing the permeability.

Question 16

What dies a too high temperature do?

Answer 16

Too much energy, the atoms in the proteins collide to frequently and vigorously and break the weak hydrogen bonds changing the tertiary structure, and denature. Permeability is increased

Question 17

How does ethanol effect membranes?

Answer 17

Ethanol dissolves the phospholipids making holes in the bi layer increasing the permeability

Question 18

What is diffusion?

Answer 18

The net movement of particle from an area of high concentration to low concentration.
It’s a passive process as it doesn’t need any energy

Question 19

What 3 factors effect the rate of diffusion?

Answer 19

Concentration gradient
Thickness of exchange surface
Surface area

Question 20

Explain how the three factors effect the rate if diffusion?

Answer 20

Concentration gradient- the higher the difference in concentration the faster the rate of diff. Until reach equilibrium then rate slow down as no concentration gradient.
Thickness of exchange surface- thinner surface shorter diffusion pathway so faster.
Surface area- larger SA faster more surface for particles to diffuse.