Cell membrane and transport

Question 1

Why is the cell membrane described as a fluid mosaic model

Answer 1

Phospholipids and proteins are fluid as they can move about the membrane
Phospholipids move side to side
The pattern produced by the scattered proteins molecules when viewed from above looks like a mosaic

Question 2

Phospholipids

Answer 2

Hydrophobic tails
Hydrophilic heads
Tails come together so stay away from water and in doing so produce a bilayer
Tails act as barriers to most water soluble substances

Question 3

Cholesterol

Answer 3

Small molecule with hydrophobic tails and hydrophilic heads do they fit between the phospholipid molecules with their heads at the membrane surface
At low temperatures cholesterol increases the fluidity of the membrane as it prevents close packing of the phospholipids
Helps stabilise the membrane at higher temperatures when it could become too fluid
Helps mechanical stability of membrane as without it membranes can break and so cells can burst open

Question 4

Glycolipids

Answer 4

Lipids with short carbohydrate chains attached to them
The carb chains project into the watery fluid surrounding the cell where they form H-bonds with the water molecules to help stabilise the membrane structure

Question 5

Glycoproteins

Answer 5

Proteins with short carbohydrate chains attached to them
The carb chains project into the watery fluid surrounding the cell where they form H-bonds with the water molecules to help stabilise the membrane structure
Act as receptors

Question 6

Proteins

Answer 6

Membrane proteins form specific channels or carriers for substances into and out of the cell

Question 7

Channel proteins

Answer 7

Water filled pores that allow charged substances (usually ions) to diffuse through the membrane
Gated

Question 8

Carrier proteins

Answer 8

Used to provide a passageway for polar molecules or ions through the membrane
Flip between two shapes, big find site alternately open to one side of the membrane then the other
Molecules will move down a concentration gradient from high to low when diffusing across the membrane

Question 9

Carbohydrate chains of glycoproteins and glycolipids

Answer 9

Help them to act as receptor molecules at the cell surface and bind with particular substances
Some glycoproteins and glycolipids act as antigens allowing cell-cell recognition

Question 10

Cell signalling

Answer 10

Involves the ways in which cells respond to various signals, coordinating the activities of the cells
Some cell signalling molecules are hydrophobic and diffuse across the cell surface membrane to bind to receptors in the cytoplasm or nucleus
More commonly, the signalling molecule is water soluble and attach to a cell surface receptor

Question 11

SA:V ratio decreases as the size of any 3D object

Answer 11

Increases

Question 12

Water potential of pure water

Answer 12

0

Question 13

Water potential value of solutions

Answer 13

Negative