rhodpsin and phytochromes

Question 1

components of a rod cell

Answer 1

inner segment with the nucleus and mitochondria and outer segment with membranes containing the purple pigment rhodopsin

Question 2

benefits of having membranes in the outer segment

Answer 2

increases surface area for light to be absorbed

Question 3

which direction does light travel through a rod cell

Answer 3

from the inner segment to outer segment

Question 4

how do Na+ move in and out of the rod cell in total darkness

Answer 4

1. Na+ diffuse into the outer segment through open cation channels
2. and then move down the concentration gradient
3. Na+ move out the inner segment by being actively pumped out causing the membrane to become slightly depolarised
4. this triggers neurotransmitters to be released
5. the inhibitory synapses between the rod cell and bipolar cell allows the neurotransmitters to bind to the bipolar cell preventing in depolarising

Question 5

how do Na+ move in and out of the rod cell when light is present

Answer 5

1. rhodopsin in the outer segment absorbs light and breaks in down into retinal and opsin
2. opsin closes the cation channels so no Na+ enter the cell
3. Na+ are actively pumped out causing the membrane to become hyperpolorised so no transmitter is released
4. bipolar nerone is depooriesed and relaseases neortransmitter
5. 5. this depoliriesed the ganglion cell which sends an action potential to the occiptial lobe of the brain

Question 6

what happens when rhodopsin absorbs light

Answer 6

rhodopsin spilts into opsin and retinal so light can no longer be absorbed which is known as bleaching as the products of colourless. this process then leads to a nerve impulse

Question 7

what happens after rhodopsin absorbs light

Answer 7

re-synthesis of rhodopsin occurs before the rod cell can be activated again, it requires ATP and it takes longer than splitting the rhodopsin

Question 8

what speeds up re-synthesis of rhodopsin

Answer 8

the lower the light intensity

Question 9

what happens to the eye in bright light

Answer 9

nearly all the rhodopsin has been bleached and the eye is light adapted

Question 10

what happens to the eye when moving from bright light to dim light

Answer 10

very little can be seen as there is not enough rhodopsin present as opsin and retinal are still recombining , after 5 min half of the rhodopsin is regenerated and after 30 mins the eye can see very well ad is dark adapted

Question 11

benefits to flowering at the right time of the year

Answer 11

• flowers produced when insects available to pollinate
• day lengths reflect the seasons which is more reliable than the temperature

Question 12

similarities between phytochromes (plants) and rhodopsin (eye)

Answer 12

• both light sensitive
• both made up of a protein and non protein component
• they change shape in response to light
• both allow the organisms to detect light