Transport Across Cell Membranes

Question 1

Why is the cell membrane called the fluid-mosaic model?

Answer 1

It is fluid because the individual phospholipids can move, giving the membrane flexibility. It is a mosaic because the proteins vary in size and shape, similar to tiles or stones in a mosaic.

Question 2

What elements make up the cell surface membrane?

Answer 2

Phospholipid bilayer, proteins (carrier and channels),cholesterol, glycolipids and glycoproteins.

Question 3

What is the function of cholesterol in the cell membrane?

Answer 3

Reduce movement of the phospholipids and prevent leakages of water and ions in the cell.

Question 4

Name the 2 types of transport proteins found in the cell membrane?

Answer 4

Protein channels and carrier proteins

Question 5

Transport proteins are specific, what does this mean?

Answer 5

They are selective, and only work in the presence of specific ions.

Question 6

What features would you expect to see in cell membranes where rapid diffusion is needed?

Question 7

Define facilitated diffusion?

Answer 7

Movement of charged or larger molecules across the membrane facilitated by proteins within the membrane.

Question 8

Define simple diffusion?

Answer 8

The net movement of molecules or ions from an area of high to low concentration until they are evenly distributed.

Question 9

When does diffusion stop?

Answer 9

Until they are distributed evenly at equilibrium.

Question 10

What characteristics do molecules have t have in order to cross a membrane through simple diffusion?

Answer 10

Small
Non polar

Question 11

What factors will affect the rate of diffusion of oxygen into a cell?

Answer 11

Temperature, concentration gradient, thickness of membrane, surface area

Question 12

Define osmosis?

Answer 12

The net movement of water from an area of high water potential to lower water potential through a selectively permeable membrane.

Question 13

What are the units of water potential?

Answer 13

KPa

Question 14

Describe and explain what would happen to an animal cell places in pure water?

Answer 14

Osmosis will cause water to move into the cell, so the cell swells and can burst in a process called lysis.

Question 15

Define water potential?

Answer 15

Water potential is pressure exerted by water molecules on the membrane. If a solution has a high water potential, it has a high water concentration (not much solute dissolved in it).

Question 16

Describe and explain what happens to an animal cell placed in pure water?

Answer 16

-water will enter the cell through osmosis as the pure water has a higher water potential
-the cell will burst (cytolysis) as it has no cell wall to withstand the force

Question 17

Describe and explain what happens to a plant cell placed in a solution with a very negative water potential?

Answer 17

• water molecules move out of the cell
  -cell shrinks (plasmolyses)

Question 18

What happens to a cell’s water potential if the cell takes in more potassium ions?

Answer 18

-potassium ions are a solute, so are dissolved into the water
-this means that the cells water potential is lowered

Question 19

Define active transport?

Answer 19

The movement of particles from an area of lower concentration to higher concentration, using energy in the form of ATP.

Question 20

Whats the role of ATP in active transport?

Answer 20

Energy is required to make the carrier protein change shape, which allows it to transfer the molecules or ions across the membrane.

Question 21

What 3 features would you expect to see in cells that do a lot of active transport?

Answer 21

-lots of carrier proteins
-lots of ATP
-temperature control