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IP Secondary 4 Biology > Chapter 5 - The Human Eye > Flashcards

Chapter 5 - The Human Eye Flashcards

1
Q

What are sense organs?

A
  • Receptors (receive stimuli from the environment)

- Highly-specialised structures

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2
Q

Structure of the eye:

Description of cornea

A

A dome-shaped transparent layer

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3
Q

Structure of the eye:

Function of cornea

A

Is able to refract light rays into the eye

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4
Q

Structure of the eye:

Description of conjunctiva

A

A mucus membrane, covering the sclera

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5
Q

Structure of the eye:

Function of conjunctiva

A

Secretes mucus to keep the front of the eyeball moist

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6
Q

Structure of the eye:

Description of pupil

A

A hole in the centre of the iris

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7
Q

Structure of the eye:

Function of pupil

A

Allows light to enter the eye

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8
Q

Structure of the eye:

Description of iris

A

A circular sheet of muscles, consisting of two sets of involuntary muscles: circular and radial muscles
Contains a pigment which gives the eye its colour

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9
Q

Structure of the eye:

Function of iris

A

(Function of circular and radial muscles)

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10
Q

Structure of the eye:

Function of eyelid

A

Protects the cornea from mechanical damage
Squinting prevents excessive entry of light
Blinking spreads tears over the eyes so that dust can be wiped off

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11
Q

Structure of the eye:

Function of eyelash

A

Shields the eye from dust particles

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12
Q

Structure of the eye:

Function of tear gland

A

Secretes tears

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13
Q

Structure of the eye:

Function of tears

A

Wash away dust particles
Keep the cornea moist for atmospheric oxygen to dissolve
Lubricate the conjunctiva, reducing friction when the eyelids move

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14
Q

What are the 3 layers in the wall of the eyeball?

A

Sclerotic coat (sclera): outermost layer
Choroid: middle layer
Retina: innermost later

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15
Q

Structure of the eye:

Description of sclera

A

Tough, white outer covering of the eyeball which is continuous with the cornea

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16
Q

Structure of the eye:

Function of sclera

A

Eye muscles attached to this layer facilitates the movement of the eyeball

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17
Q

Structure of the eye:

Description of choroid

A

Black pigmented middle layer

Contains blood vessels

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18
Q

Structure of the eye:

Function of choroid

A

Black: Prevents the internal reflection of light

Blood vessels: Carry oxygen and nutrients to eyeball and remove metabolic waste products from the eyeball

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19
Q

Structure of the eye:

Description of retina

A

Innermost layer of the eye wall
Contains light-sensitive cells known as photoreceptors, which consist ‘rods’ and ‘cones’
Connected to nerve fibres from the optic nerve

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20
Q

Structure of the eye:

Description of cones

A

Photoreceptors in retina

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21
Q

Structure of the eye:

What are the types of cones and what is their function?

A

Three types of cones: red, blue and green
Each type contains a different pigment, which absorbs light of different wavelengths, enabling us to see a variety of colours

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22
Q

Structure of the eye:

Function of cones

A

They enable us to see in bright light

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23
Q

Structure of the eye:

Description of rods

A

Photoreceptors in retina

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24
Q

Structure of the eye:

What pigment is contained in rods and what is its function?

A

Visual purple

It is bleached when exposed to bright light and impulses cannot be sent to the brain

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25
Q

Structure of the eye:

Function of rods

A

They enable us to see in dim light (Rods are stimulated even by very dim light)

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26
Q

What happens in colour blindness?

A

The person is not able to perceive certain colours

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27
Q

Why does colour blindness occur?

A

One or more of the cones (red, blue or green) are missing

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28
Q

Structure of the eye:

Description of fovea

A

A small yellow depression

Contains cones but not rods

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29
Q

Structure of the eye:

Function of fovea

A

It is where images are focused

Enables a person to have detailed colour vision in bright light

30
Q

Structure of the eye:

Description of blind spot

A

Region where the optic nerve leaves the eye

Does not contain photoreceptors, therefore not sensitive to light

31
Q

Structure of the eye:

Function of optic nerve

A

Transmits impulses to the brain when photoreceptors are stimulated

32
Q

Structure of the eye:

Description of lens

A

Transparent, circular and biconvex structure

33
Q

Structure of the eye:

Function of lens

A

Shape or thickness can be changed in order to refract light onto the retina

34
Q

Structure of the eye:

Function of suspensory ligament

A

Attaches the edge of the lens to the ciliary body

35
Q

Structure of the eye:

Function of ciliary body

A

Contains ciliary muscles which control the curvature and thickness of lens

36
Q

Structure of the eye:

Description of aqueous chamber

A

Space between the lens and the cornea

Filled with aqueous humour

37
Q

Structure of the eye:

Description of aqueous humour

A

A transparent, watery fluid in the aqueous chamber

38
Q

Structure of the eye:

Function of aqueous humour

A

Keeps the front of the eyeball firm

Refracts light into the pupil

39
Q

Structure of the eye:

Description of vitreous chamber

A

Space behind the lens

Filled with vitreous humour

40
Q

Structure of the eye:

Description of vitreous humour

A

A transparent, jelly-like substance in the vitreous chamber

41
Q

Structure of the eye:

Function of vitreous humour

A

Keeps eyeball firm

Refracts light onto the retina

42
Q

Test:

Which structure refracts light into the pupil?

A

Cornea

43
Q

Test:

Which structure protects the eyeball against mechanical injury?

A

Sclera

44
Q

Test:

Which structure prevents internal reflection of light within the eye?

A

Choroid

45
Q

Test:

Which structure controls the curvature and thickness of the lens?

A

Ciliary muscles

46
Q

Test:

Which structure controls size of the pupil?

A

Iris

47
Q

Test:

Which structure focuses light onto the retina?

A

Lens

48
Q

Test:

Which structure is a light-sensitive layer where images are formed?

A

Retina

49
Q

Test:

Which structure is where most of the light is focused, where vision is sharpest?

A

Fovea

50
Q

Test:

Which structure is the point where optic nerve leaves the eye?

A

Blind spot

51
Q

What are the muscles controlling the iris?

A

Circular muscles

Radial muscles

52
Q

Describe the muscles controlling the iris

A

Involuntary

Antagonistic

53
Q

How does the iris control the amount of light entering the eyes in bright light?

A

The circular muscles contract
The radial muscles relax
The pupil constricts, reducing the amount of light that enters the eye

54
Q

How does the iris control the amount of light entering the eyes in dim light?

A

The circular muscles relax
The radial muscles contract
The pupil dilates, increasing the amount of light that enters the eye

55
Q

What is the pupil reflex?

A

It is a reflex action in response to changes in light intensity

56
Q

What is the function of the pupil reflex?

A

It protects the eye from excessive light exposure, which could damage the retina

57
Q

The reflex arc of the pupil reflex

A

Stimulus (change in light intensity) → receptor (retina) → sensory neurone in optic nerve → brain → motor neurone → effector (iris)

58
Q

How is an image formed on the retina?

describe the entire process

A
  1. Light rays are refracted when it passes through the cornea and aqueous humour
  2. Light rays are further refracted when they pass through the lens
  3. Image on the retina either stimulates the rods or cones, depending on the intensity of light
59
Q

What is the nature of the image formed on the retina?

A

Vertically inverted
Laterally inverted
Smaller than the object

60
Q

How is the image formed in the brain?

describe the entire process

A
  1. Inverted image is formed on the retina
  2. Light-sensitive cells (rods & cones) are stimulated
  3. Nerve impulses generated are transmitted through the optic nerve
  4. Nerve impulses reach the optic centre of the brain
  5. The brain interprets the information and forms an upright image
61
Q

What is the role of the brain in vision?

A

The brain has a corrective function
- The image is upside down within the retina, but the brain makes it upright
The brain can integrate information from the overlapping visual fields of both eyes
- It interprets them as one image

62
Q

What happens when the blind has his sight restored?

A

Objects appear upside down to him at first

His brain has to learn how to correct the images that fall on the retina

63
Q

What is focusing?

A

(also known as accommodation)

The lens of the eye is adjusted so that clear images of objects at different distances are formed on the retina

64
Q

What is being adjusted in focusing?

A

The curvature or thickness of the lens is adjusted

65
Q

A more curved (convex) lens causes a ________ degree of ‘bending’
This is called a ________ angle of refraction

A

greater

greater

66
Q

Light rays from a near object are ________

A ________ angle of refraction is needed to bring them into focus

A

divergent

greater

67
Q

Light rays from a distant object are ________

A ________ angle of refraction is needed to bring them into focus

A

parallel

smaller

68
Q

How does the eye focus on nearby objects?

describe the 1st half of the process

A
  1. Ciliary muscles contract, relaxing their pull on suspensory ligaments
  2. Suspensory ligaments slacken, relaxing their pull on the lens
  3. Lens becomes thicker and more convex, decreasing the focal length
69
Q

How does the eye focus on distant objects?

describe the 1st half of the process

A
  1. Ciliary muscles relax, pulling on the suspensory ligaments
  2. Suspensory ligaments become taut, pulling on the edge of the lens
  3. Lens becomes thinner and less convex, increasing the focal length
70
Q

How does the eye focus on nearby/distant objects?

describe the 2nd half of the process

A
  1. Light rays are sharply focused on the retina stimulating the photoreceptors
  2. Nerve impulses produced are transmitted to the brain via the optic nerve
  3. The brain interprets the impulses and the persons sees the nearby/distant object

IP Secondary 4 Biology (6 decks)

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