topic 2 - exchange across cell membrane - diffusion

Question 1

what is diffusion

Answer 1

the net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration

Question 2

what way will the molecules and net movement diffuse

Answer 2

molecules will diffuse both ways, but the net movement will be to the area of lower concentration - this continues until particles are evenly distributed throughout the liquid or gas

Question 3

what is the concentration gradient

Answer 3

the path from an area of higher concentration to an area of lower concentration - particles diffuse down the concentration gradient

Question 4

is diffusion a passive process, what does this mean

Answer 4

diffusion is a passive process - no energy is needed for it to occur

Question 5

why can oxygen and carbon dioxide diffuse easily through cell membranes

Answer 5

because they’re small so they can pass through spaces between the phospholipids - they’re also non polar which makes them soluble in lipids, so they can dissolve in the hydrophobic bilayer

Question 6

what is simple diffusion

Answer 6

a form of diffusion that does not require the assistance of membrane proteins - when molecules diffuse directly through a cell membrane

Question 7

why would charged particles diffuse slowly

Answer 7

because they’re water soluble and the centre of the bilayer is hydrophobic

Question 8

what is facilitated diffusion

Answer 8

the passive movement of substances across a plasma membrane by diffusing through carrier proteins or channel proteins located in the plasma membrane

Question 9

how do carrier proteins affect facilitated diffusion

Answer 9

carrier proteins move large molecules across membranes, down their concentration gradient - different carrier proteins facilitate the diffusion of different molecules

Question 10

explain the three steps to facilitated diffusion

Answer 10

(1) a large molecule attaches to a carrier protein in the membrane
(2) the protein changes shape
(3) this releases the molecule on the opposite side of the membrane

Question 11

how do channel proteins affect facilitated diffusion

Answer 11

channel proteins form pores in the membrane for charged particles to diffuse through (down their concentration gradient) - different channel proteins facilitate the diffusion of different particles

Question 12

what are three factors that simple diffusion depends on

Answer 12

(1) the concentration gradient
(2) the thickness of the exchange surface
(3) the surface area

Question 13

how does simple diffusion depend on the concentration gradient

Answer 13

the higher it is, the faster the rate of diffusion - as diffusion takes place the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium - meaning diffusion slows down over time

Question 14

how does simple diffusion depends on the thickness gradient

Answer 14

the thinner the exchange surface, the faster the rate of diffusion

Question 15

how does simple diffusion depend on the surface area

Answer 15

the larger the surface area, the faster the rate of diffusion

Question 16

what are microvilli

Answer 16

small finger-like projections that are located on the outermost part of epithelial cells that extend from villi - formed by the cell surface membrane folding up on itself

Question 17

how do microvilli increase rate of diffusion

Answer 17

they give the cell a larger surface area - meaning that more particles can be exchanged in the same amount of time - increasing rate of diffusion

Question 18

what are two factors that facilitated diffusion depends on

Answer 18

(1) concentration gradient
(2) number of channel pr carrier proteins

Question 19

how does facilitated diffusion depend on the concentration gradient

Answer 19

the higher the concentration gradient, the faster the rate of facilitated diffusion - as equilibrium is reached, the rate of facilitated diffusion will level off

Question 20

how does facilitated diffusion depend on the number of channel or carrier proteins

Answer 20

once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient - so the greater the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion

Question 21

what are aquaporins

Answer 21

special channel proteins that allow the facilitated diffusion of water through cell membranes

Question 22

how does having more channel proteins increases rate of facilitated diffusion

Answer 22

aquaporins allow cells to reabsorb a lot of the water that would otherwise be excreted by the body