Membrane transport

Question 1

What is meant by “selectively permeable” when applied to the plasma membrane?

Answer 1

The membrane allows some molecules to pass through but not others.

Question 2

What properties influence whether a molecule can permeate the plasma membrane unassisted? (2)

Answer 2

• Solubility of the particles in lipid

- Size of the particle

Question 3

What are the two methods of unassisted transport?

Answer 3

-Diffusion down a concentration gradient

And/Or

-Movement along an electrical gradient

Question 4

When does diffusion cease?

Answer 4

When dynamic equilibrium (no net movement of molecules) is reached.

Question 5

What is Fick’s law used to determine?

Answer 5

The rate of net diffusion across a membrane.

Question 6

What are the 4 factors that influence the rate of net diffusion used in Fick’s law?

Answer 6

• Magnitude of the concentration gradient
• Surface area of the membrane where diffusion is taking place
• Lipid solubility of the substance
• Molecular wight of the substance (Smaller easier to diffuse)
• Distance through which diffusion must take place.

Question 7

What is an electrical gradient?

Answer 7

A difference in electrical charge between two areas.

Question 8

What is a cation?

Answer 8

A positively charged ion.

Question 9

What is osmosis?

Answer 9

The net diffusion of water down it’s own concentration gradient.

Question 10

What feature of a cell membrane allows water (which should have poor permeability of the membrane due to it’s low solubility in water) to pass through readily?

Answer 10

Aquaporins, protein channels that allow water to pass in and out.

Question 11

What is osmolarity?

Answer 11

The concentration of osmotically active particles present in a solution.

Question 12

What is tonicity?

Answer 12

The effect that a solution has on cell volume

Question 13

What is meant by isotonic?

Answer 13

A solution that contains an equal solute concentration to the cell, therefore does not affect cell volume.

Question 14

What is meant by hypertonic?

Answer 14

A solution that contains a solute concentration greater than that of the cell, hence causes cell to shrink.

Question 15

What is meant by hypotonic?

Answer 15

A solution that contains a solute concentration less than that of inside the cell, causing the cells to swell (and eventually burst)

Question 16

Describe carrier mediated transport.

Answer 16

A substance binds onto a specific carrier which undergoes a conformational change to transport the substance.

Question 17

What 3 characteristics determine the kind and amount of material transferred across the membrane? Describe these characteristics.

Answer 17

• Specificity- Each carrier is specialised to carry a specific substance or a few closely related compounds.
• Saturation- When all carrier proteins are occupied by substance, the transport rate can no longer increase.
• Competition- When the presence of one substance diminished the rate of transport of another.

Question 18

What two forms does carrier mediated transport take?

Answer 18

• Facilitated diffusion (Not requiring energy)

- Active transport (requires energy)

Question 19

Describe facilitated diffusion.

Answer 19

A carrier is used to assist the transfer of a substance across the membrane down the concentration gradient.

Question 20

Describe active transport.

Answer 20

A carrier expends energy to transfer a substance against a concentration gradient.

Question 21

What are the two forms of active transport?

Answer 21

• Primary

- Secondary

Question 22

Describe primary active transport.

Answer 22

Energy is directly required to move a substance against it’s concentration gradient.

Question 23

Describe secondary active transport.

Answer 23

• Energy is required but not used directly to produce “uphill” movement.
• The carrier does not split ATP, moves molecule uphill using a second hand energy stored in the form of an ion concentration gradient.

Question 24

What is another name for the NA+K+ ATPase?

Answer 24

Sodium potassium pump

Question 25

What is the ratio of transport in the sodium potassium pump?

Answer 25

-3 Na+ out for every 2 K+ into the cell.

Question 26

What are the three important roles of sodium potassium pumps?

Answer 26

• Establish Na+ and K+ concentration gradients across plasma membranes.
• Regulates cell volume by controlling solute concentration inside cells.
• The energy used to drive the pump indirectly serves as the energy source for secondary active transport.

Question 27

What are the two mechanisms that secondary active transport occurs by?

Answer 27

Symport

Antiport

Question 28

Describe symport.

Answer 28

The solute and Na+ move in the same direction.

Question 29

Describe antiport.

Answer 29

The solute and Na+ move in the opposite direction to each other

Question 30

What is endocytosis?

Answer 30

The pinching off of membrane to engulf a substance from the extracellular matrix.

Question 31

What is exocytosis?

Answer 31

The release of contents from the intracellular matrix into the extracellular matrix.