Plants absorbing light, phytochrome and also rhodopsin

Question 1

What controls the growth response of a plant?

Answer 1

Auxin, IAA (Indocleatic acid)

Question 2

How does IAA stimulate phototropic response?

Answer 2

IAA produced in tip of shoots
They accumulate in shaded side, stimulate cell elongation
Causing shoot to grow towards light source

Question 3

What is a phytochrome and what forms can they exist in?

Answer 3

Light sensitive pigment in plants
.Pr (red), the inactive form
.Pfr (far red), the active form

Question 4

State the time of the day when each form of phytochrome is most abundant:

Answer 4

In sunlight - Levels of Pfr rise
In darkness - Levels of Pr rise, no red light available in the dark, Pfr converted to Pr

Question 5

What does Pfr do ?

Answer 5

-Binds to protein receptors in target cells
-Activates signal molecules which activates transcription factors
-Proteins produced will have different metabolic activities in response to light, e.g. flowering

Question 6

Name of light pigment in animals and location?

Answer 6

Rhodopsin which is located in outer segment

Question 7

Describe how light causes a change in voltage across rod cell?

Answer 7

1)Light absorbed by rhodopsin
2)Rhodopsin converted to opsin and retinal
3)Opsin binds to cell surface membrane and sodium ion channels close
4)Sodium ions pumped out of cell and reduced influx of sodium ions cause hyperpolarization

Question 8

Suggest what happens to rod cells in presence of darkness when recovering from bleaching (5 marks):

Answer 8

1)Opsin disconnects from rod cell surface membrane
2)Rhodopsin reformed from opsin and retinal
3)Na+ channels open and sodium ions diffuse back into cell
4)Depolarization that stimulates release of inhibitory neurotransmitter (glutamate)