Diffusion, Facilitated Diffusion, Primary and Secondary Active Transport and Osmosis

Question 1

state what it is meant by the key term ‘diffusion’

Answer 1

diffusion is the net movement of particles from an area of high concentration to an area of low concentration down it’s concentration gradient

Question 2

state what it is meant by the key term ‘flux’

Answer 2

flux is the amount of material crossing a surface per unit of time

Question 3

state what it is meant by the key term ‘net flux’

Answer 3

net flux is the difference between two one way fluxes at any given moment in time

Question 4

state what it is meant by the key term ‘diffusion equilibrium’

Answer 4

diffusion equilibrium is when the two one way fluxes create an even concentration of solute on either side

Question 5

state the 6 diffusion influencers

Answer 5

1. temperature
2. mass of molecule (heavier = slower)
3. the medium molecules are moving in
4. concentration gradient
5. diffusion distance
6. surface area

Question 6

state Fik’s law

Answer 6

net flux = P x S x (Co - Ci)

Question 7

define what it is meant by the key term ‘permeability coefficient’ (P)

Answer 7

permeability coefficient is an experimentally determined number for a particular type of molecule at a given temperature and reflects the ease at which a molecule is able to move through a given membrane

Question 8

what types of molecules can move across a cell membrane by the process of simple diffusion

Answer 8

1. small non-polar molecules

2. non-polar molecules can dissolve in the non-polar regions of the fatty acids

Question 9

what type of proteins are ion channels

Answer 9

ion channels are integral proteins

Question 10

state 3 ways protein channels influence which molecules can diffuse through them

Answer 10

1. the diameter of a protein channel is just wider than that of the solute that can diffuse through it
2. the charged and polar sub-units of the channel protein
3. the number of water molecules associated with the ions

Question 11

define what it is meant by the key term ‘membrane potential’

Answer 11

1. membrane potential is the separation of electrical charge which exists across a plasma membrane (measured in millivolts)
2. membrane potential provides an electrical force that influences the movement of ions across the membrane

Question 12

define what it is meant by the key term ‘electrochemical gradient’

Answer 12

the electrochemical gradient is the concentration and electrical difference between sides of a plasma membrane

Question 13

state what it is meant by the key term ‘channel gating’

Answer 13

channel gating is the process of opening and closing ion channels

Question 14

state the three factors effecting channel protein conformation

Answer 14

1. the binding of specific molecules to channel proteins
2. changes in membrane potential
3. physical deforming of the membrane

Question 15

explain how the binding of specific molecules to channel proteins effects their conformation

Answer 15

1. can directly, or indirectly, produce an allosteric, or covalent, change in the shape of the channel protein - ligand gated channels
2. ligands that influence them often chemical messengers

Question 16

explain how changes in membrane potential influences a channel proteins conformation

Answer 16

changes in membrane potential can cause movement of certain charged regions on a channel protein altering its shape (voltage gated channels)

Question 17

how can physically deforming cell membranes influence the channel proteins conformation

Answer 17

physical deforming/stretching the membranes may effect the conformation of proteins (mechanically gated channels)

Question 18

explain mediated transport systems (4 things)

Answer 18

1. protein carriers/transporters move large and polar molecules across a cell membrane in a process called mediated transport
2. solutes bind to specific site on transporter
3. transporter undergoes conformational change
4. when solute dissociates the transporter returns to original shape

Question 19

state the 3 factors influencing mediated transport flux

Answer 19

1. saturation of solute binding sites
2. number of solute specific transporters in cell membrane
3. rate of the transporter proteins conformational change

Question 20

what are the two types of mediated transport

Answer 20

1. facilitated transport

2. active transport (primary and secondary)

Question 21

state what it is meant by the key term ‘facilitated diffusion’

Answer 21

facilitated diffusion is the net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient via a specific transport/carrier protein

Question 22

state what it is meant by the key term ‘active transport’

Answer 22

active transport is the movement of molecules from an area of low concentration to an area of high concentration against it’s concentration with the use of energy

Question 23

state what it is meant by the key term ‘primary active transport’

Answer 23

primary active transport is the direct use of ATP to move molecules across a cell membrane from an area of low concentration to an area of high concentration against it’s concentration gradient

Question 24

explain primary active transport (2 things)

Answer 24

1. transporters are enzymes (ATPase) which hydrolysis ATP into ADP + Pi and then phosphorylate themselves
2. phosphorylation of transporters is a type of covalent modulation that changes the conformational shape of the transporter and the affinity of the transporters binding site

Question 25

state what it is meant by the key term ‘secondary active transport’

Answer 25

1. secondary active transport is the movement of an ion down it’s electrochemical gradient and the movement of another molecule against it’s concentration gradient
2. can be either co-transport of counter-transport

Question 26

explain secondary active transport (4 things)

Answer 26

1. transporters have 2 binding sites and binding of ions to their specific site cause conformational shape change
2. uses stored energy from the electrochemical gradient
3. maintenance of electrochemical energy is sustained via primary active transport making the electrochemical gradient
4. ion goes down concentration gradient and solute goes against concentration gradient

Question 27

what mediates the movement of water into and out of cells

Answer 27

aquaporins are the mediators that regulate the movement of water into and out of cells

Question 28

state what it is meant by the key term ‘osmosis’

Answer 28

osmosis is the net flux of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane

Question 29

state what it is meant by the key term ‘osmolarity’

Answer 29

1. osmolarity is the total concentration of solute particles present in a solution, regardless of their chemical composition
2. the higher the osmolarity, the lower the water potential

Question 30

state what it is meant by the key term ‘semi-permeable membrane’

Answer 30

a semi-permeable membrane is a membrane which is permeable to water but is not permeable to salts

Question 31

state what it is meant by the key term ‘osmotic pressure’

Answer 31

1. when a solution containing solutes is separated from pure water by a semi-permeable membrane, the pressure that must be applied to the solution to prevent the net flow of water is known as the osmotic pressure
2. greater osmolarity of solution the greater the osmotic pressure
3. the lower the water potential, the higher the osmotic pressure

Question 32

state what it is meant by the key term ‘non-penetrating solutes’

Answer 32

non-penetrating solutes are substances that are not able to cross the cell membrane (do not penetrate through the lipid bilayer)

Question 33

what are sodium and chloride ions categorised as, and why (in relation to osmosis)

Answer 33

1. non-penetrating solutes
2. get pumped back out of the cell Into the extracellular fluid as quick as they diffuse into the cell due to the electrical repulsion generated by membrane potential and secondary transporters

Question 34

what are potassium ions categorised as, and why (in relation to osmosis)

Answer 34

1. potassium diffuses out of cell via protein channels but are pumped back in
2. therefore are intra cellular non-membrane penetrable substances

Question 35

state what it is meant by the key term isotonic

Answer 35

a solution that does not cause a change in cell volume as contains 300 mOsmol/L of non-penetrating membrane solutes, regardless of the concentration of membrane penetrating solutes present

Question 36

state what it is meant by the key term ‘hypertonic’

Answer 36

a solution that causes cells to shrink, contains greater than 300 mOsmol/L of non-penetrating solutes, regardless of the concentration of membrane penetrating solutes present

Question 37

state what it is meant by the key term ‘hypotonic’

Answer 37

a solution that causes cells to swell, contains less than 300 mOsmol/L non-membrane penetrating solutes, regardless of the concentration of membrane-penetrating solutes present

Question 38

state what it is meant by the key term ‘isoosmotic’

Answer 38

solution containing 300 mOsmol/L solute, regardless of it’s composition of non-membrane penetrating and membrane penetrating solutes present

Question 39

state what it is meant by the key term ‘hyperosmotic’

Answer 39

solution containing greater than 300 mOsmol/L solute, regardless of its composition of non-membrane penetrating and membrane penetrating solutes present

Question 40

state what it is meant by the key term ‘hypo osmotic ‘

Answer 40

solution containing less than 300 mOsmol/L solute, regardless of its composition of non-membrane penetrating solutes and membrane penetrating solutes present