Plasma Membranes

Question 1

Function of membranes at the surface of cells

Answer 1

Barrier between cell and environment
Control what enters and leaves - partially permeable.
Cell communication

Question 2

Function of membranes and within cells

Answer 2

Separate components - divide cell into different compartments.
Form vesicles to transport substances.
Control what enters and leaves.
Site of chemical reactions

Question 3

Fluid mosaic structure

Answer 3

Phospholipids form a bilayer which is fluid.
Contains cholesterol and protein molecules which are scattered through the membrane.
Some proteins have carbohydrate attached - glycoprotein.
Some have lipids attacked - glycolipid.

Question 4

Phospholipids

Answer 4

Hydrophilic head which attracts water
Hydrophobic tail which repels water.
Heads face out towards the water and tails face in.
The centre is hydrophobic so water soluble substances cannot move through it - acts as a barrier

Question 5

Cholesterol

Answer 5

Type of lipid
Fits between phospholipids which bind to tails of phospholipids making them pack more tightly and closer together. This makes the membrane less fluid and more rigid.

Question 6

Proteins

Answer 6

Channels in the membrane which allow small or charged particles through.
Carrier proteins transport molecules and ions across the membrane by active transport and facilitated diffusion

Also act as receptors for cell signalling

Question 7

Glycolipids and glycoproteins

Answer 7

Stabilise membrane by forming hydrogen bonds with surrounding water molecules.
Site of which drugs, hormones and antibodies bind.
Act as receptors for cell signalling.
Antigens - involved in the immune response.

Question 8

Cell signalling

Answer 8

How cells communicate with each other.
One cell releases a messenger molecule which travels to another cell, it is detected by the cell because it binds to a receptor on its membrane.