1.4

Question 1

Define diffusion

Answer 1

The passive movement of particles from an area of high concentration to low concentration (down a concentration gradient)

Question 2

Explain the structure and function of potassium channels for facilitated diffusion in axons.

Answer 2

Structure:
integral membrane proteins
consists of 4 symmetrical units
narrow pore that only lets K+ ions through
a protein subunit is attached to the channel
amino acids lining the pore are hydrophilic

1) resting axon: potassium channels are voltage gated, the inside of axons is more negative compared to the outside
2) action potential: during an impulse, the inside becomes more positive, allowing K+ ions to rapidly diffuse out the cell
2) refractory period: after a short amount of time, the extra subunit moves into the channel blocking any K+ ions from diffusing out the cell, the subunit will move once the axon rests.

Question 3

Define osmosis

Answer 3

The passive movement of water molecules across a semi-permeable membrane from an area of high water concentration to low water concentration

Question 4

What is a hypotonic solution?

Answer 4

When the concentration of a solute is greater inside a cell compared to the outside (it gains water, it swells and eventually bursts)

Question 5

What is a hypertonic solution?

Answer 5

When the concentration of a solute is greater outside the cell compared to inside the cell (loses water - cells shrivel & shrink)

Question 6

What is an isotonic solution? And why is it important for medical procedures?

Answer 6

When the concentration of a solute is at equilibrium with the concentration outside the cell. (no NET movement of water)

Because an isotonic solution prevents too much water from entering or exiting the cells by osmosis & damaging the tissues or organs

Question 7

Outline active transport:

Answer 7

1) particle collide with the pump
2) protein pump is activated by ATP & uses the energy release to change shape
3) the particle being transported is released on the other side of membrane
4) ADP + Pi are released from the protein pump causing it to revert to its original shape, ready to receive another particle

Question 8

Explain the structure and function of sodium–potassium pumps for active transport:

Answer 8

• 3 Na+ ions collide with the pump and attach to its binding sites
• Pump is activated from the breakdown of ATP, Pi attaches to the pump & energy released induces shape change
• 3 Na+ ions are released on the outside of the axon
• 2 K+ ions collide with the pump and attach to its binding sites
• Pi is released, inducing a shape change
• 2 K+ ions are released on the inside of the axon

Question 9

Outline Endocytosis:

Answer 9

It is the bulk transport of material into the cell

1) the plasma membrane is pinched inwards
2) this forms a vesicle which is cut off and enters the cytoplasm

Question 10

Outline Exocytosis:

Answer 10

It is the bulk transport of materials out of the cell

1) substances produced by the cell are packaged in vesicle
2) it fuses to the plasma membrane and releases contents outside the cell