diffusion

Question 1

diffusion is an example of…

Answer 1

passive transport - energy comes from natural inbuilt motion of particles - no ATP required.

Question 2

what is simple diffusion?

Answer 2

the passive net movement of molecules from an area of high concentration to an area of low concentration until there is no net movement/equilibrium has been reached.

Question 3

which molecules can simply diffuse through the phospholipid bilayer?

Answer 3

small, non-polar molecules e.g. carbon dioxide, oxygen and lipid-based hormones (steroids)

Question 4

what is facilitated diffusion?

Answer 4

the passive movement of large molecules from an area of high concentration to an area of low concentration via transmembrane transport proteins until there is no net movement/equilibrium has been reached.

Question 5

why can some molecules not simply diffuse through the phospholipid bilayer?

Answer 5

charged ions and polar molecules e.g. glucose - cannot simply diffuse because of the hydrophobic nature of fatty acid tails of phospholipids.

Question 6

what are the similarities and differences between simple diffusion and facilitated diffusion?

Answer 6

similarities:
1. both passive forms of transport - don’t require ATP.
2. molecules move DOWN the conc. gradient.

differences:
1. facilitated diffusion requires transport proteins.

Question 7

name the two types of proteins involved in facilitated diffusion.

Answer 7

protein channels

carrier proteins

Question 8

describe how protein channels transport polar-molecules across the membrane

Answer 8

• proteins that form water-filled hydrophilic channels across the membrane.
• channels are selective - only allow specific water-soluble ions to pass through - controls entry and exit of specific ions.
• ions bind with protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other side.

Question 9

describe how carrier proteins transport polar-molecules across the membrane

Answer 9

• molecules such as glucose specific to that protein - bind to protein.
• it changes shape in a way which means that the molecule is released to the inside of the membrane.
• no external energy required - only kinetic energy of molecules themselves.

Question 10

what is the formula for determining the rate of diffusion (Fick’s law)?

Answer 10

(surface area x concentration gradient) / diffusion distance

Question 11

what are the units of the rate of diffusion?

Answer 11

mol/s

Question 12

what are the factors affecting the rate of diffusion?

Answer 12

concentration gradient - large for max. diff
diffusion distance - short for max.diff
temperature
no. of carrier proteins

Question 13

name two exchange surfaces in living organisms?

Answer 13

alveoli

villi

Question 14

where does diffusion take place in living organisms?

Answer 14

1. alveoli - exchanging oxygen and carbon dioxide
2. villi - exchange soluble molecules into the blood
3. leaf (stomata) - carbon dioxide and oxygen
4. roots - water