Organisms Respond to Changes in their Internal and External Environments - Receptors, Retina

Question 1

Where are photoreceptors found?

Answer 1

• In the retina of eyes

Question 2

What type of stimuli do photoreceptors detect?

Answer 2

• Light

Question 3

Which part of the eye does light enter through?

Answer 3

• Pupil

Question 4

How is the amount of light that enters the eye controlled?

Answer 4

• By the muscles of the iris

Question 5

How are light rays focused onto the retina?

Answer 5

• The cornea and lens focus light rays onto the retina

Question 6

Name the area of the retina where there are many photoreceptors

Answer 6

• Fovea

Question 7

How do nerve impulses from photoreceptors reach the brain?

Answer 7

• Nerve impulses from photoreceptor cells are carried from the retina, along the optic nerve to the brain

Question 8

What is the optic nerve?

Answer 8

• A bundle of neurones

Question 9

Why is the area where the optic nerve is located, called the blind spot?

Answer 9

• No photoreceptor cells there, so it’s not sensitive to light

Question 10

What are the two types of photoreceptors in the human eye?

Answer 10

• Rods

- Cones

Question 11

Where are rods mainly found?

Answer 11

• In the peripheral parts of the retina

Question 12

Where are cones mainly found?

Answer 12

• Concentrated in the fovea

Question 13

Explain what happens when photoreceptors detect light

Answer 13

• Light-sensitive pigments in the photoreceptors absorb light
• Light bleaches the pigments, causing a chemical change and increasing membrane permeability to sodium ions
• Generator potential is created
• If reaches threshold, bipolar neurones connect photoreceptors to optic nerve which takes impulses to brain

Question 14

What type of neurones connect photoreceptors to the optic nerve?

Answer 14

• Bipolar neurones

Question 15

What type of pigments do rods contain?

Answer 15

• Rhodopsin

Question 16

What does rhodopsin break down into during bleaching?

Answer 16

• Pigment called retinal

- Protein called opsin

Question 17

What type of information do rods provide? What is this type of vision called?

Answer 17

• Information in black and white

- Monochromatic vision

Question 18

What type of pigments do cones contain?

Answer 18

• Red-sensitive pigment
• Green-sensitive pigment
• Blue-sensitive pigment

Question 19

What type of information do cones provide? What is this type of vision called?

Answer 19

• Information in colour

- Trichromatic vision

Question 20

Define the term visual sensitivity

Answer 20

• Ability to detect low levels of light

Question 21

Do rod cells have a high or low visual sensitivity?

Answer 21

• High visual sensitivity

Question 22

Explain why rod cells have high visual sensitivity

Answer 22

• Many rod cells join one bipolar neurone

- Weaker generator potentials combine to reach the threshold and trigger an action potential

Question 23

Do cone cells have a high or low visual sensitivity?

Answer 23

• Low visual sensitivity

Question 24

Explain why cone cells have a low visual sensitivity

Answer 24

• One cone cell joins one bipolar neurone

- Takes more light to reach the threshold and trigger an action potential

Question 25

Define the term visual acuity

Answer 25

• The ability to tell apart points that are close together

Question 26

Do rod cells have a high or low visual acuity?

Answer 26

• Low visual acuity

Question 27

Explain why rod cells have a low visual acuity

Answer 27

• Many rods join the same bipolar neurone

- Light from two points close together cannot be told apart

Question 28

Do cone cells have a high or low visual acuity?

Answer 28

• High visual acuity

Question 29

Explain why cone cells have a high visual acuity

Answer 29

• Cones joins one bipolar neurone
• When light from two points hit two cones, two action potentials go to the brain
• So two close points can be distinguished as two separate points