B9.2 - Sense Organs - The eye

Question 1

what is the eye a type of?

Answer 1

the eye is a type of sensory organ in the body

Question 2

what specialised cells do eyes contain?

Answer 2

contains specialised light receptors

Question 3

what are light receptors?

Answer 3

light receptors are a type of sensory receptor that is sensitive to light intensity and colour

Question 4

what are the two types of light receptors?

Answer 4

rod cells and cone cells

Question 5

what are rod cells?

Answer 5

sensitive to light of low intensities. More sensitive to light than cone cells. Don’t detect colour

Question 6

what are cone cells?

Answer 6

sensitive to colour and light at high intensities

Question 7

what do eyes enable us to do?

Answer 7

eyes enable us to detect changes in the strength and colours of light in our surroundings

Question 8

how many cone cells do an eye have?

Answer 8

human eyes have 3 cone cells each sensitive to a different range of colours

Question 9

what do light receptors contain?

Answer 9

light receptors cells have a nucleus, cytoplasm and a cell membrane.

Question 10

what are the different parts of the eye?

Answer 10

cornea
Pupil 
iris
Lens 
Retina 
Optic nerve
Suspensory ligaments 
Ciliary muscles 
Sclera

Question 11

Cornea: What is the structure and the function?

Answer 11

structure:

• Transparent layer at the front of the eye.
• Has no blood vessels

function:
- Refracts/ bends light as it enters the eye

Question 12

Pupil: What is the structure and the function?

Answer 12

structure:
- Hole in the center of the iris

function:
- Enables light to enter the eye

Question 13

Iris: What is the structure and the function?

Answer 13

structure:
- Coloured part of the eye that contains muscles

function:
- Controls the diameter of the pupil

Question 14

Lens: What is the structure and the function?

Answer 14

structure:
- Transparent disc behind the pupil and the iris

function:
- Can change shape.
- Forces light onto the retina as it enters the eye

Question 15

Retina: What is the structure and the function?

Answer 15

structure:

• The area at the back of the eye which contains cone and rod light receptors
• Region known as the fovea in the retina which only has cone cells.

function:
- Senses light

Question 16

Optic Nerve: What is the structure and the function?

Answer 16

structure:
- Bundle of nerve fibres

function:
- Sends nerve impulses from the retina to the brain

Question 17

Suspensory ligaments: What is the structure and the function?

Answer 17

structure:
- Attachment between the lens and the ciliary muscles

function:
- Keeps the lens in place and allows its shape to be changed by ciliary muscles

Question 18

Ciliary muscles: What is the structure and the function?

Answer 18

structure:
- Small muscles attached to the suspensory ligaments

function:
- Alters the shape of the lens

Question 19

Sclera: What is the structure and the function?

Answer 19

structure:
- White, opaque outer layer of the eye

function:
- Protects the eye

Question 20

what happens in bright/ high intensity light conditions?

Answer 20

→ can cause damage to your retina
→ pupils constrict to make it smaller
→ this means less light gets in so there is no damage to the retina

Question 21

what happens in low light conditions

Answer 21

→ no damage/ threat to the retina
→ pupils dilate (become larger)
→ allows more light into the retina so we can have clearer sight to see in the dark

Question 22

what’s an antagonistic pair?

Answer 22

when one does an action, the other does the opposite

Question 23

what are the two types of muscles that make up the iris?

Answer 23

→ circular muscles (inside)

→ radial muscles (outside)

Question 24

what happens to the circular muscles and radial muscles in bright light?

Answer 24

In bright light, circular muscles contract making pupils smaller and radial muscles relax

Question 25

what happens to the circular muscles and radial muscles in low light?

Answer 25

In less light, circular muscles relax and radial muscles contract to make pupils larger

Question 26

what is accommodation?

Answer 26

the reflex that changes the refractive power of the lens

This allows us to see both near and distant objects.

Question 27

how does the eye focus on near objects ?

Answer 27

→ ciliary muscles contracts inwards towards the lens
→ because it is closer to the lens the sensory ligaments become loose/ slacken
→ lens is free to return to fatter shape
→ can then refract light more strongly

Question 28

how does the eye focus on distant objects?

Answer 28

→ light is not needed to be refracted as strongly
→ lens doesn’t need to do much since cornea has already refracted light
→ to reduce the refractive power of the lens it needs to be stretched out for the surface to be less curved.
→ ciliary muscles relaxed
→ moves away from the lens and pulls on the suspensory ligaments taut
→ stretches the lens out

Question 29

what happens when a ciliary muscle contracts?

Answer 29

when ciliary muscles contract it moves inwards towards the lens

Question 30

what is a specific about sensory ligaments?

Answer 30

Sensory ligaments are not a muscle so it cannot be contracted or the opposite it can only slacken or become taut.