9- detection of light by mammals

Question 1

rods

Answer 1

Rods contain a light-sensitive pigment called rhodopsin. Rhodopsin absorbs light energy and subsequently splits into opsin and trans-retinal.

Question 2

rods in the dark

Answer 2

• Na+ ions diffuse in through Na+ ion channels, and are pumped out by active transport.
• The inside of the cell is only slightly more negative. The membrane is depolarised.
• Glutamate is released. It inhibits neurons connecting the rods to the optic nerve.
• No visual information is transmitted to the brain.

Question 3

rods in the light

Answer 3

• Rhodopsin is bleached into opsin and trans-retinal.
• Opsin triggers the closing of Na+ ion channels.
• The interior becomes more negative than usual. The cell becomes hyperpolarized.
• Less glutamate is released.
• Depolarisation in the bipolar cell triggers an action potential.
• The action potential crosses the synapse to the sensory neuron.
• Sensory neurons form the optic nerve, which transmits signals to the brain.

Question 4

resynthesis of rhodopsin

Answer 4

• Rods are inactive until rhodopsin is resynthesized.
• ATP is required to convert trans-retinal to cos-retinal and rejoin it to opsin to form rhodopsin.

Question 5

receptors

Answer 5

Cells specialised for detection of stimuli.

Question 6

photoreceptors- rods

Answer 6

• Produce monochromatic vision / vision in dim conditions with less detail.
• More sensitive - dim light is sufficient for them to work.
• Has a summation effect.

Question 7

photoreceptors- cones

Answer 7

• Produce colour vision / high visual acuity with greater detail.
• Less sensitive - can only work in bright conditions.
• No summation effect, making them less sensitive.