Biological Membranes

Question 1

What is the function of a cell surface (plasma membrane)?

Answer 1

They control substances leaving and entering the cell

Question 2

What is meant by partially permeable?

Answer 2

They only allow some molecules through, non polar and small

Question 3

What is contained in the fluid mosaic model?

Answer 3

Phospholipid bilayer
Glycoproteins
Glycolipids
Cholesterol
Carrier protein
Channel protein

Question 4

What is a phospholipid bilayer and what is its basic function?

Answer 4

They form a barrier with hydrophobic tails and hydrophilic heads.
The heads face outwards and tails face inwards.
The centre of the bilayer is hydrophilic and outside is hydrophobic

Question 5

What is cholesterol and what is its basic function?

Answer 5

It is a type of lipid

It fits between the phospholipids and gives the membrane stability.

Question 6

What are the functions of glycoproteins and glycolipids?

Answer 6

They act as receptors for message molecules in cell signalling
They are also antigens

Question 7

What factors affect membranes permeability?

Answer 7

Solvents and Temperature

Question 8

How does increased temperature increase a membrane’s permeability?

Answer 8

It causes the bilayer to move more meaning they phospholipids are less tightly bound together resulting in them becoming more permeable. At a high temperature they begin to break down and proteins denature.

Question 9

How do solvents effects membranes permeability?

Answer 9

They dissolve the lipids

Question 10

What is cell signalling?

Answer 10

Communication between cells using messenger molecules

Question 11

What are membrane receptors?

Answer 11

Proteins within cells act as receptors. Receptor proteins have specific shapes so only messenger molecules with complementary shapes can bind to them

Question 12

What is diffusion?

Answer 12

Diffusion is a passive process. It is the net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient.

Question 13

What factors affect diffusion?

Answer 13

Concentration gradient
Thickness of the exchange surface
Surface area
temperature

Question 14

What is osmosis?

Answer 14

Osmosis is a passive process. It is the net moment of water molecules from a region of high water potential to a region of low water potential down a concentration gradient.

Question 15

What is an isotonic solution?

Answer 15

When two solutions have the same water potential

Question 16

What is a hypotonic solution?

Answer 16

When a cell is placed in a solution with a higher water potential compared to the lower water potential within the cell

Question 17

What is a hypertonic solution?

Answer 17

When a cell is placed in a solution with a lower water potential compared to the higher water potential within the cell

Question 18

What is facilitated diffusion?

Answer 18

Some molecules are two big or polar therefore they cant pass through the bilayer.
Carrier and channel proteins use a passive process to move particles down a concentration gradient

Question 19

How do carrier proteins work?

Answer 19

A large molecule attaches to a carrier proteins in the membrane
The protein then changes shape
This releases the molecule on the opposite side of the membrane

Question 20

How do channel proteins work?

Answer 20

They form pores in the membrane, this allows for smaller ions and polar molecules to diffuse through

Question 21

What is active transport?

Answer 21

This is an active process which uses ATP. A carrier protein, the protein changes shape and this moves molecules across the membrane. ATP is used to move the solute against a concentration gradient

Question 22

What is endocytosis and how does it work?

Answer 22

1. It transports molecules that are two large to be transported using carrier proteins.
2. Endocytosis is entering the cell
3. The cells membrane surrounds the cell, the membrane then pinches off to form a vesicle.
4. Lysosomes are then injected into the cell breaking down the substance

Question 23

What is exocytosis and how does it work?

Answer 23

1. It transports molecules that are two large to be transported using carrier proteins.
2. Exocytosis is leaving the cell
3. The golgi apparatus packages the molecules into vesicles and then they move towards the plasma membrane
4. The vesicles fuse with the membrane and then release the contents to the outside of the cell