responses to stimuli

Question 1

role of sodium ions in role of mammalian rod cell

Answer 1

Na+ pumped out of rod cell
in the light, sodium ions do not move back into rod cell
in the dark, sodium ions can move back into rod cell
in the dark, the rod cell is depolarised
in the light the rod cell is hyperpolarised

Question 2

explain how IAA affects the growth of the coleoptile

Answer 2

IAA diffuses from tip of coleoptile
therefore can be taken up by cells in zone of elongation
causes cells to elongate
leads to lowering of pH in the cellulose cell wall
therefore causes the coleoptile to grow towards the light

Question 3

explain the effect of increasing light intensity on the current produced by a rod cell

Answer 3

increasing light intensity decreases the current
because the rhodopsin is broken down
therefore more opsin binds to the channel protein in the outer segment
sodium gated voltage channels close
reducing the influx of sodium ions/ making membranes impermeable to sodium ions

Question 4

describe the role of IAA in the phototropic response of plants

Answer 4

IAA produced in the tip of the shoot
accumulates on the dark side of the shoot
stimulates cell elongation
causing the shoot to grow towards the light source

Question 5

how does IAA work

Answer 5

causes cell elongation
by ‘loosening’ cell walls/ makes them more plastic
cell walls take in water by osmosis and elongate
protons pumped into cell wall from cytoplasm disrupt the bonds between cellulose molecules- allowing cell wall to be stretched

Question 6

rod cells

Answer 6

contain light-sensitive pigment (rhodopsin)
- absorbs light energy and subsequently splits into cis-retinal and opsin
only produce monochromatic vision

Question 7

rod cells in dark

Answer 7

rods arent stimulated
sodium ions diffuse into cell through open sodium ion channels
sodium ions simultaneously actively pumped out of cell
inside of cell is slightly depolarised
enables release of glutamate
so no information is transmitted to brain

Question 8

glutamate

Answer 8

inhibits neurones which connect rod cells to the optic nerve

Question 9

rod cells in light

Answer 9

rhodopsin splits into cis-retinal and opsin
opsin binds to membrane of cells so sodium ion channels close
membrane becomes hyperpolarised so no transmitters are released into synaptic cleft
an AP can form and is transmitted to the brain via optic nerve

Question 10

cone cells

Answer 10

can only work in bright condition
less sensitive than rod cells
involved in colour vision