4.2 Diffusion and Osmosis

Question 1

Diffusion definition

Answer 1

net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed

Question 2

3 factors of diffusion

Answer 2

1. particles are constantly in motion due to kinetic energy they possess
2. motion is random, with no set pattern
3. particles are constantly bouncing off one another as well as off other objects

Question 3

simple diffusion

Answer 3

passive
energy comes from natural inbuilt motion of particles

Question 4

facilitated diffusion

Answer 4

facilitates movement of charged ions and polar molecules through transmembrane channels and carriers that span the membranes
- hydrophobic tails of phospholipids mean csm isn’t permeable

passive- relies on inbuilt motion of molecules

occurs at specific point on plasma membrane where there are special protein molecules(protein channels and carrier proteins)

Question 5

protein channel

Answer 5

form water-filled hydrophilic channels across membrane

selective- only opens in presence of specific water-soluble ions so they can pass through

ions bind with proteins, causing it to change tertiary structure in a way that close it to one side of the membrane and opens it to other side, bringing the molecule across

Question 6

carrier protein

Answer 6

span plasma membrane

when molecule specific to protein is present it binds with protein

causes protein to change shape in way that molecule is released to inside of membrane

Question 7

osmosis

Answer 7

passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane

Question 8

water potential

Answer 8

Greek letter psi Ψ
measured in KPa
pressure created by water molecules

Question 9

what is pure water’s water potential under rtp 25°C and rp 100KPa

Answer 9

0

Question 10

4 rules of water potential

Answer 10

1. addition of solute to pure water reduces wpt
2. water potential of solution must always be negative
3. more solute is added, the lower is water potential
4. water will move by osmosis to a region of higher wpt to one of lower wtp(less negative) until a dynamic equilibrium is reached(isotonic)

Question 11

omosis in red blood cells

Answer 11

rbc live in blood plasma which has same water potential so no water is gained(haemolysis- csm bursts) or lost(shrinks and dies)

Question 12

osmosis in plant cells

Answer 12

plant cells are normally permanently bathed in pure water, and so water enters via osmosis
protoplast swells and presses on cell wall, causing a pressure build up that resist entry of further water
cells is turgid

Question 13

incipient plasmolysis

Answer 13

if plant cell is placed in solution with lower wtp, water leaves

volume of cell decreases and protoplast no longer pressed on cell wall

further loss will cause cell contents to shrink and protoplast to pull away from cell wall(plasmolysis)