receptors, again

Question 1

what do photoreceptors do

Answer 1

Photoreceptors Convert Light into an Electrical Impulse

Question 2

what is step 1 of converting light into an electric impulse

Answer 2

Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments

Question 3

what is step 2 of converting light into an electric impulse

Answer 3

Light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions

Question 4

what is step 3 of converting light into an electric impulse

Answer 4

A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone.

Question 5

what is step 4 of converting light into an electric impulse

Answer 5

Bipolar neurones connect photoreceptors to the op tic nerve, which takes impulses to the brain

Question 6

what are the two types of photoreceptors in the human eye

Answer 6

rods and cones

Question 7

where are rods mainly found

Answer 7

Rods are mainly found in the peripheral parts of the retina, and cones are found packed together in the fovea.

Question 8

what do rods and cones contain differently

Answer 8

Rods and cones contain different optical pigments making them sensitive to different wavelengths of light.

Question 9

what is the difference in vision between rods and cones

Answer 9

Rods only give information in black and white (monochromatic vision), but cones give
information in colour (trichromatic vision).

Question 10

how many different types of cones are there

Answer 10

There are three types of cones, each containing
a different optical pigment — red-sensitive, green-sensitive and blue-sensitive.
When they’re stimulated in different pro portions you see different colours.

Question 11

out of rods and cones which is more sensitive and which lets you see more detail

Answer 11

Rods are More Sensitive, but Cones let you See More Detail

Question 12

why are rods so sensitive

Answer 12

Rods are very sensitive to light (they fire action potentials
in dim light). This is because many rods join one
neurone, so many we a k generator potentials combine
to reach the threshold and trigger an action potential.

Question 13

why are cones less sensitive

Answer 13

Cones are less sensitive than rods (they only fire action
potentials in bright light). This is because one cone
joins one neurone, so it takes more light to reach
the threshold and trigger an action potential.

Question 14

what is visual acuity

Answer 14

y (the ability to tell apart points that are close together)

Question 15

why do rods have low visual acuity

Answer 15

Rods give low visual acuity because many rods
join the same neurone, which means light from
two points close together can’t be told apart.

Question 16

why do cones give high visual acuity

Answer 16

Cones give high visual acuity because cones are
close together and one co ne joins one neurone.
W hen light from two points hits two cones,
two action potentials (one from each cone) go
to the brain — so you can distinguish two points
that are close together as two separate points