1.4 - Membrane Transport

Question 1

Define simple diffusion

Answer 1

The passive movement of particles from an area of high concentration to low concentration using existing kinetic energy

Question 2

Define osmosis

Answer 2

The passive movement of water molecules from an area of low solute concentration to high solute concentration across a partially permeable membrane using attraction between solute particles and water

Question 3

Define active transport

Answer 3

the movement of particles against the concentration gradient using energy from ATP and carriers in the membrane

Question 4

Define facilitated diffusion

Answer 4

substances that cannot pass through the phospholipid bilayer have to pass through integral protein channels that have a hydrophilic core

Question 5

Simple diffusion (3)

Answer 5

• substances such as O2, CO2, H2O, lipids, steroids, hormones
• passive: no energy from ATP used
• EG: alveolar surface of lung (O2, CO2)

Question 6

Facilitated diffusion using carriers (2)

Answer 6

• lipid-insoluble molecules

- EG: glucose into red blood cells

Question 7

Facilitated diffusion using channels (3)

Answer 7

• small polar molecules and ions diffuse aided with channel proteins
• these create hydrophilic pores to allow channel-mediated facilitated diffusion
• EG: Na+ entering nerve cells

Question 8

Osmosis (3)

Answer 8

• passive: no energy
• can move by simple or facilitated diffusion
• EG: water in roots

Question 9

Give two examples of active transport and state what type of pumps they are

Answer 9

• sodium-potassium pump in neurons: symport

- sodium-chlorine pump in kidneys: antiport

Question 10

What is required by active transport?

Answer 10

An integral protein transporter in the membrane

Question 11

Give the steps of active transport (6)

Answer 11

1. ATP binds to a transport protein
   2a) Enzyme breaks covalent bond on one of the phosphates
   2b) Molecule or ion binds to transport protein
2. The split releases enough energy to change the shape of the pump so that it opens outward
   4a) Molecule or ion released
   4b) Phosphate is released and process starts again

Question 12

Exocytosis and endocytosis (4)

Answer 12

• types of active transport
• plasma membrane folds around a substance to transport it across the cell
• works due to the fluidity of the membrane
• vesicular transport/cytosis

Question 13

Define exocytosis

Answer 13

The transportation of large materials or materials in bulk OUT OF a cell

Question 14

What are the steps of exocytosis? (5)

Answer 14

1. Materials needed are made in the ribosomes
2. Then processed and packaged by the golgi apparatus
3. These vesicles then move along the cytoplasm
4. Fuse with the plasma membrane
5. Materials are released

Question 15

Give two examples of exocytosis

Answer 15

1. Digestive enzymes

2. How nerve cells release neurotransmitters

Question 16

Define endocytosis

Answer 16

The transportation of large materials or materials in bulk INTO a cell

Question 17

What are the different types of endocytosis? (3)

Answer 17

Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

Question 18

What are the steps of pinocytosis? (3)

Answer 18

1. Part of the plasma membrane is pulled inwards
2. Droplet of fluid becomes enclosed once vesicles bud off
3. This then waves through the cytoplasm

Question 19

Define hypertonic

Answer 19

A solution that has a higher osmolarity than another

Question 20

Define isotonic

Answer 20

A solution that has the same osmolarity as another

Question 21

Define hypotonic

Answer 21

A solution that has a lower osmolarity than another

Question 22

Define osmolarity

Answer 22

A measure of the solute concentration in a solution

Question 23

What type of solution must organs and tissues be kept in and why? (5)

Answer 23

• isotonic
• red blood cells have no cell wall
• they will wrinkle if placed in a hypertonic solution
• they will burst if placed in a hypotonic solution
• will stay the same in an isotonic solution

Question 24

Who proposed the fluid-mosaic model and when?

Answer 24

Singer and Nicholson

1972

Question 25

How was the fluid-mosaic model supported? (2)

Answer 25

• observations from electron microscope

- proteins were present on surface of phospholipids bilayer but not as a continuous layer

Question 26

Who proposed the sandwich model and when?

Answer 26

Davison and Danielli

1935

Question 27

Describe the sandwich model (2)

Answer 27

• phospholipid bilayer in the centre

- proteins coat both surfaces forming a ‘sandwich’

Question 28

Give evidence for the sandwich model (3)

Answer 28

• 1959
• using electron micrograph and potassium permanganate.
• stain showed two dark lines and a pale line in between.

Question 29

Name 3 problems with the sandwich model

Answer 29

• proteins would be exposed to hydrophilic surfaces on both sides which is unstable
• lipid soluble substances would not pass through
• membranes are bifacial (have different inner and outer surfaces)