Diffusion

Question 1

Define diffusion

Answer 1

Net movement of molecules or ions from a region of high concentration to a region of low concentration.

• think “concentration gradient”
• ions, small molecules such as O₂, CO₂,

Question 3

What are carrier proteins?

Answer 3

These proteins play a role in facilitated diffusion.

The incoming ion or molecule touches the carrier protein, which then changes shape to permit the crossing.

Question 4

Define facilitated diffusion

Answer 4

1. Hydrophillic molecules and ‘any old ions’ larger than CO₂ cannot cross the cell membrane, so they need help (facilitation)
2. They pass through water filled pores within channel proteins that span the membranes
3. Each channel protein only lets in a specific molecule - the ‘door’ needs opening with a key which can be the shape of the required molecule
4. Or in the case of gated channels a signal from a hormone or a change in potential difference (volts)

Question 5

Define osmosis

Answer 5

The net movement of water molecules from a solution with a lower concentration of a solute (and high concentration of water) to a higher concentration of solute (and low concentration of water) across a partially permeable membrane.

Osmosis continues until the concentrations are equal - “isotonic”

(ōsmos - Gk for push)

TIDBIT:

Water can bond with the solute, but where’s there’s more water molecules, the surplus will be free to move through a membrain.

Question 6

Define active transport

Answer 6

When substances move against a concentration gradient (with the use of energy and assistant proteins)

Question 8

Is diffusion active or passive?

Answer 8

Passive - no energy is required for transportation (like rolling a ball down a hill)

Question 11

For active transport, where does the energy come from?

Answer 11

ATP

adenosine triphosphate

Question 12

Name some examples of where active transport takes place (3pts)

Answer 12

1. ions across epithelial cells
2. plant cell roots
3. muscle cells
4. nerve cells
5. also between mitochondria and cytoplasm

Question 13

Explain how energy is given off in the ATP process

Answer 13

ATP - adenosine Triphosphate is formed during cellular respiration (breakdown of carbohydrates and fats)

1. Basically, a phosphate group is removed from adenosine tri-phosphate to create adenosine di-phosphate (ADP)
2. This requires a small amount of energy but once the bond is broken, the phosphate group in ADP becomes hydrated and the resulting water-phosphate bonds gives off a lot of energy.

Question 14

What are ‘pumps’?

Answer 14

Another word for active transport proteins