Biological membranes - Diffusion

Question 1

define diffusion

Answer 1

the net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration (down the concentration gradient)

Question 2

why is diffusion passive

Answer 2

the cell does not use energy - molecules have their own kinetic energy

Question 3

why do we say net movement

Answer 3

the molecules move randomly - some will move in the other direction

Question 4

when does diffusion stop

Answer 4

diffusion will continue until an equilibrium is reached (molecules are evenly spread out and no net movement from either side)

Question 5

give the six factors affecting the rate of diffusion

Answer 5

temperature, surface area, concentration gradient, stirring/moving, diffusion distance, type of molecule

Question 6

what is the effect of temperature on the rate of diffusion

Answer 6

increased temperature leads to increased kinetic energy of molecules, so increased rate of diffusion as particles move quicker

Question 7

what is the effect of surface area on the rate of diffusion

Answer 7

increased surface area increases the rate of diffusion as more particles can diffuse across at any one time

Question 8

what is the effect of concentration gradient on the rate of diffusion

Answer 8

increased concentration gradient increases the rate of diffusion

Question 9

what is the effect of stirring/moving on the rate of diffusion

Answer 9

increased stirring, increases kinetic energy which increases the rate of diffusion

Question 10

what is the effect of diffusion distance on the rate of diffusion

Answer 10

decreased diffusion distance increases the rate of diffusion as molecules don’t have to travel as far

Question 11

what is the effect of type of molecule on the rate of diffusion

Answer 11

larger molecules need more energy - decreased rate of diffusion
non-polar molecules increased rate of diffusion because they can dissolve in the bilayer

Question 12

define simple diffusion

Answer 12

the net movement of molecules directly through the phospholipid bilayer between phospholipids down the concentration gradient

Question 13

give examples of molecules that use simple diffusion

Answer 13

small molecules:
carbon dioxide
water
oxygen
non-polar molecules:
dissolve in the hydrophobic region of the phospholipid bilayer e.g steroids, fat-soluble vitamins

Question 14

define facilitated diffusion

Answer 14

passive movement of molecules or ions through a channel protein or carrier protein from a higher to a lower concentration

Question 15

which molecules travel through channel proteins

Answer 15

specific for certain ions e.g sodium ion channels

Question 16

describe how channel proteins work and why they are needed

Answer 16

ions are charged and therefore need transport proteins
channel proteins have a hydrophilic lining
channels can sometime be gated (open or closed)

Question 17

what are aquaporins

Answer 17

special channel proteins which allow water to diffuse across membranes more quickly

Question 18

which molecules travel through carrier proteins

Answer 18

for specific, large, polar molecules e.g glucose, amino acids

Question 19

how do carrier proteins work

Answer 19

when one specific molecule binds to the protein, it changes shape and allows the molecule across the membrane

Question 20

which part of the phospholipid does cholesterol bind to

Answer 20

fatty-acid tails

Question 21

give two changes to cell surface membrane that could result in a greater glucose uptake

Answer 21

more carrier proteins, greater surface area

Question 22

how would vitamin D, a fat soluble vitamin, travel through the bilayer

Answer 22

non-polar, so can dissolve in bilayer and pass through it directly