Diffusion

Question 1

Diffusion definition

Answer 1

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration

Question 2

What is the net movement of particles?

Answer 2

Molecules will diffuse both ways but net movement will be to an area of lower concentration. This continues until particles are evenly distributed

Question 3

What is a concentration gradient and what kind of process is diffusion?

Answer 3

• the path from an area of higher concentration to an area of lower concentration. Particles diffuse down a conc gradient
• passive process no energy is needed for it to happen

Question 4

How do particles diffuse?

Answer 4

Across cell membranes, as long as they can move freely through the membrane
E.g. oxygen and CO2 diffuse easily through cell membranes because they’re small (can pass through the spaces between the phospholipids), they are also non-polar and so soluble in lipids so they can dissolve in the hydrophobic phospholipid bilayer

Question 5

What is simple diffusion?

Answer 5

When molecules dissolve directly through a cell membrane

Question 6

What is facilitated diffusion?

Answer 6

Diffusion using carrier proteins or channel proteins to allow larger molecules to diffuse
Like diffusion, it moves from a higher to lower concentration (down conc gradient) and is a passive process

Question 7

What molecules benefit from facilitated diffusion?

Answer 7

Some larger molecules (e.g. amino acids and glucose) would diffuse extremely slowly through phospholipid bilayer due to size
Charged particles e.g. ions and polar molecules would also diffuse slowly, because they are water soluble and the center of the bilayer is hydrophobic

Question 8

How do carrier proteins move molecules across membranes?

Answer 8

• large molecule attaches to carrier protein (in membrane)
• protein changes shape
• molecule released on opposite side of the membrane

Question 9

How do channel proteins move molecules across a membrane?

Answer 9

• form pores in membrane for charged particles to diffuse through
• different channel proteins facilitate different charged particles

Question 10

What factors affect simple diffusion?

Answer 10

• concentration gradient
• thickness of exchange area
• surface area

Question 11

What factors affect facilitated diffusion?

Answer 11

• concentration gradient
• number of channel or carrier proteins

Question 12

Permeability of cell membrane experiment

Answer 12

• beetroot cells contain a coloured pigment that leaks out
• use a scalpel to cut 5 equal size pieces of beetroot (cork borer)
• rinse to remove pigment released from cutting
• add to various test tubes with same volume of water
• place each in water bath at different temperature for the same amount of time
• remove beetroot
• use colorimeter to get quantitative measurement
• more pigment released = higher permeability

Question 13

Explain permeability of cell membrane experiment

Answer 13

Temperatures below 0
- phospholipids have little energy
- but channel and carrier proteins may deform (increasing permeability)
Temperatures 0-45
- phospholipids can move (partially permeable)
- as temp increases phospholipids move more (KE) and increased permeability
Temperatures above 45
- bilayer starts to melt and membrane becomes more permeable
- channel proteins deform and can’t control what enters or leaves the cell