Plasma Membranes

Question 1

Define compartmentalisation

Answer 1

Seperate membrane bound areas in a cell

Question 2

What is the basic structure of all membranes called?

Answer 2

Plasma membrane

Question 3

What are membranes formed from?

Answer 3

Phospholipid bilayer

Question 4

Who proposed the Fluid Mosaic Model?

Answer 4

Singer and Nicholson in 1972

Question 5

Why is it called a fluic mosaic model?

Answer 5

Phospholipids are free to move (fluid) and proteins embedded in the surface are like the tiles of a mosaic

Question 6

Define an intrinsic protein

Answer 6

Proteins embedded through both layers of the membrane.

Question 7

Give an example of an intrinsic protein

Answer 7

A channel/carrier protein

Question 8

What is an extrinstic protein?

Answer 8

A protein embedded on only one layer of the bilayer.

Question 9

How do glycoproteins and glycolipids act?

Answer 9

As cell receptors, involved in cell signalling

Question 10

State some factors that affect membrane structure.

Answer 10

Temperature, Solvents

Question 11

How does temperature affect membranes?

Answer 11

Increased temperature means that phospholipids have an increased kinetic energy. If temperature continues to increase it will break down completely. It will also denature embedded proteins.

Question 12

How do solvents affect membranes?

Answer 12

Organic less polar than water or non polar solvents dissolve membranes.

Question 13

Define passive transport

Answer 13

Transport of substances utilising energy form the natural movement of particles from another source.

Question 14

Define active transport.

Answer 14

Transport of substances utilising energy from ATP to move particles against their natural motion.

Question 15

Define diffusion.

Answer 15

The net movement of particles from a region of high concentration to a region of low concentration.

Question 16

Define equilibrium

Answer 16

A balance in concentrations.

Question 17

Why does diffusion happen?

Answer 17

Particles have kinetic energy so are constantly moving, and uneven distribution eventually becomes even.

Question 18

Why is diffusion faster over smaller distances?

Answer 18

Particles constantly collide, slowing down net movement

Question 19

What defines simple diffusion?

Answer 19

Diffusion in the absence of a membrane or barrier

Question 20

State two factors which affect the rate of diffusion across a membrane.

Answer 20

Surface area- the larger the exchange surface, the higher the rate of diffusion. Thickness of membrane- the thinner the exchange surface, the higher the rate of diffusion.

Question 21

Define faciliated diffusion.

Answer 21

When molecules diffuse across a membrane through by protein channels.

Question 22

Why are membranes with protein channels selectively permeable?

Answer 22

Because protein channels are usually specific to one ion or molecule.

Question 23

How does a carrier protein function?

Answer 23

1. Molecule binds to external receptors
2. ATP binds to protein and is hydrolysed
3. Binding of Pi changes the shape of the protein, opening it to the inside
4. Pi is released and reforms ATP
5. Carrier protein returns to it’s original shape.

Question 24

Define bulk transport.

Answer 24

When large molecules like enzymes and hormones are transported across the membrane using parts of the membrane called vesicles.

Question 25

What is endocytosis?

Answer 25

Bulk transport into cells. Phagocytosis is solids and Pinocytosis is liquids.

Question 26

What is exocytosis?

Answer 26

The reverse of endocytosis- the movement of substances out of the cell

Question 27

Define osmosis.

Answer 27

The movement of water molecules from an area of high concentration to an area of low concentration.

Question 28

Define water potential.

Answer 28

Pressure exerted by water molecules as they collide with walls of their container and eachother.

Question 29

What is the water potential of pure water?

Answer 29

0kPa

Question 30

What is the pressure of water in a closed system called?

Answer 30

Hydrostatic pressure

Question 31

Describe cytolysis

Answer 31

Animal cells cannot take the increased pressure of water and the cell bursts.

Question 32

Describe crenation.

Answer 32

The tendency of animal cells to ’pucker’ when placed in a solution of lower water potential.

Question 33

What is pressure against plant call walls called?

Answer 33

Turgor

Question 34

What happens when a plant cell is placed a solution of lower water potential.

Answer 34

Water leaves the cell and the protoplast pulls away from the cell wall. The cell is plasmolysed.