Diffusion and Osmosis

Question 1

What are factors that affect the rate of diffusion

Answer 1

• concentration gradient
• length of diffusion pathway
• temperature
• surface area to volume ratio

Question 2

What is diffusion?

Answer 2

the net movement of molecules/ions from a region of higher concentration to a region of lower concentration (until they are evenly distributed)

Question 3

What is facilitated diffusion?

Answer 3

diffusion that only occurs in specific protein channels or carrier proteins

Question 4

Explain why facilitated diffusion is a passive process?

Answer 4

There is no ATP from respiration used in the process, the only energy used is the built-in (kinetic) energy of the molecules themselves

Question 5

What is osmosis?

Answer 5

the movement of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane

Question 6

What is meant by the term ‘water potential’?

Answer 6

a measure of the pressure caused by water molecules, and the likelihood of them moving

Question 7

What is the water potential of pure water (at standard conditions)?

Answer 7

0 kPa

Question 8

What happens to water potential if a solute is added?

Answer 8

It decreases

Question 9

What happens if the water potential outside of an animal cell increases too much?

Answer 9

the cell will gain water by osmosis and will eventually burst

Question 10

What is a selectively permeable membrane?

Answer 10

a membrane that is permeable to water molecules (and few other smaller molecules) but not to larger molecules

Question 11

How might a cell be adapted to increase the rate of osmosis?

Answer 11

Larger surface area would increase the rate of osmosis

Question 12

Explain how K+ ions are involved in the opening of stomata

Answer 12

• K+ ion concentration in guard cells increases
• lowers water potential inside guard cell
• water moves from higher water potential into the lower water potential outside of the cell, by osmosis
• cells become turgid and change shape, opening the stomata

Question 13

What substances are transported across membranes by facilitated diffusion?

Answer 13

larger molecules, water soluble molecules, polar molecules

Question 14

What substances are transported across membranes by simple diffusion?

Answer 14

small molecules, non-polar molecules, lipid soluble molecules

Question 15

How and why do hydrophobic compounds enter through cell membranes?

Answer 15

lipid soluble so can cross the phospholipid bi-layer

Question 16

Describe the difference between carrier and channel proteins

Answer 16

carrier- when a molecule binds a conformational change occurs
channel- hydrophilic channels that open to allow specific ions to diffuse through