Unit 1.4d(ii)

Question 1

What two types of photoreceptor cells are found within the eyes retina?

Answer 1

Rod cells and cone cells

Question 2

Do rod cells work in bright or dim lights?

Answer 2

Dim

Question 3

Do rod calls have colour perception?

Answer 3

No

Question 4

Do cone cells work in bright or dim light?

Answer 4

Bright light

Question 5

Are done cell responsible for colour perception?

Answer 5

Yes, they’re responsible for colour vision

Question 6

What are photoreceptors in the eye made of?

Answer 6

They are made of retinal and opsin

Question 7

What is retinal?

Answer 7

It’s a light sensitive molecule

Question 8

What is opsin?

Answer 8

Opsin us a membrane protein

Question 9

What is the retinal, opsin complex called in rod cells?

Answer 9

Rhodopsin

Question 10

Firstly what happens when the retinal in a rod cell absorbs 1 photon of light?

Answer 10

The rhodopsin change’s conformation to become photo excited

Question 11

What does photo excited rhodopsin activate?

Answer 11

It’s activates hundreds of transducin molecules (a G-protein)

Question 12

What does each transducin activate?

Answer 12

One PDE enzyme

Question 13

What does PDE stand for?

Answer 13

Phosphodiesterase

Question 14

What does PDE catalyse?

Answer 14

The hydrolysis, so therefore the breakdown, of cGMP molecules

Question 15

What does cGMP stand for?

Answer 15

Cyclic GMP

Question 16

What causes the ion channels in the rod cells membrane to close?

Answer 16

The reduction in cGMP concentration

Question 17

What is prevented when the rod cells ion channel close?

Answer 17

The inward leak of positive ions stops causing the membrane potential to increase

Question 18

What’s it called when the membrane potential increases?

Answer 18

Hyper-polarisation (as the charge increases)

Question 19

What does the hyper polarisation of the rod cell trigger?

Answer 19

It triggers a nerve impulse in the retina’s neuron

Question 20

So how are rod cells able to respond in low light intensities?

Answer 20

They have high degrees of amplification

Question 21

What causes the production of different photo receptor cells in proteins?

Answer 21

Different opsins combine with retinal

Question 22

What are the specific wavelengths that that proteins have sensitivity for?

Answer 22

Red, green, blue, ultraviolet