Transport Across the Membrane

Question 1

Why is the cell membrane described as a fluid-mosaic?

Answer 1

Fluid because the phospholipids are constantly moving. Mosaic because all the proteins in the membrane create a mosaic pattern.

Question 2

What are the main components of the cell membrane?

Answer 2

phospholipids
cholesterol
glycoproteins and glycolipids
other proteins like carrier and channel proteins.

Question 3

What do channel and carrier proteins do?

Answer 3

They allow large molecules and ions to pass through the membrane.

Question 4

What does cholesterol do?

Answer 4

It controls the fluidity of the membrane.

Question 5

How does cholesterol control the fluidity of the membrane?

Answer 5

When the temperature increases, the cholesterol binds to the hydrophobic tails of the phospholipids causing them to pack closely together so the membrane does not become too fluid. When it is cold it lies between the phospholipids molecules so the membrane doesn’t freeze and crack.

Question 6

What is diffusion?

Answer 6

The net movement of particles from an area of high concentration to an area of low concentration.

Question 7

What substances move across the membrane via diffusion?

Answer 7

small, lipid-soluble substances

Question 8

Why does diffusion decrease over time?

Answer 8

As diffusion happens, the concentration gradient decreases meaning the rate of diffusion decreases over time.

Question 9

What three factors affect the rate of diffusion?

Answer 9

1. Concentration gradient
2. The thickness of the membrane
3. The surface area of the mebrane

Question 10

How does the concentration gradient affect the rate of diffusion?

Answer 10

The higher the concentration gradient, the higher the rate of diffusion.

Question 11

How does the thickness of the membrane affect the rate of diffusion?

Answer 11

The thicker the membrane, the lower the rate of diffusion as the diffusion distance increases.

Question 12

How does the surface area of the membrane affect the rate of diffusion?

Answer 12

The higher the surface is, the higher the rate of diffusion.

Question 13

What is facilitated diffusion?

Answer 13

The movement large particles and ions down a concentration gradient using channel and carrier proteins.

Question 14

How do carrier proteins move large molecules across the membrane?

Answer 14

A large molecule attaches to one end of the channel protein. The protein changes shape which allows the large molecule to move into the opposite side of the membrane.

Question 15

How do channel proteins move charged molecules across the membrane?

Answer 15

They form pores in the membrane, which allow charged particles to diffuse down a concentration gradient.

Question 16

What factors affect the rate of facilitated diffusion?

Answer 16

The concentration gradient and the number of channel and carrier proteins.

Question 17

What is osmosis?

Answer 17

The net movement of water from an area of high water potential to an area of low water potential across a semi-permeable membrane.

Question 18

What is water potential?

Answer 18

The tendency of water to move out of solution.

Question 19

What does isotonic mean?

Answer 19

The water potential inside the cell is the same as the solution it is placed in.

Question 20

What does hypertonic mean?

Answer 20

The water potential outside the cell is less than inside the cell.

Question 21

What happens if you place a plant cell in a hypertonic solution?

Answer 21

Water moves out of the cell via osmosis and the cell becomes flaccid.

Question 22

What happens if you place an animal cell in a hypertonic solution?

Answer 22

Water moves out of the cell via osmosis and the cell shrivels up and die.

Question 23

What does hypotonic mean?

Answer 23

The water potential inside the cell is less than outside the cell.

Question 24

What happens if you place an animal cell in a hypotonic solution?

Answer 24

Water moves into the cell via osmosis causing it to swell and burst.

Question 25

What happens if you place a plant cell in a hypotonic solution?

Answer 25

Water moves into the cell via osmosis causing it to become turgid. It doesn’t burst due to the presence of a cell wall.

Question 26

What factors affect the rate of osmosis?

Answer 26

the same as diffusion.

Question 27

What is active transport?

Answer 27

the movement of particles from an area of low concentration to an area of high concentration using energy released by ATP and carrier proteins.

Question 28

What is co-transport?

Answer 28

The movement of two substances across a membrane together.

Question 29

Describe the movement of glucose through the wall of the ileum using co-transport.

Answer 29

1. Sodium ions are actively transported from the epithelial cells to the blood via the sodium-potassium pump.
2. The concentration of sodium ions is higher in the ileum compared to the inside of the epithelial cells meaning they move down into the cells.
3. The sodium ions also bring glucose across the cell membrane via a co-transport protein.
4. The glucose then moves into the blood via facilitated diffusion.