Content: The Eye
Topic: Co-ordination and Response
Contents and instructions:
This eBook contains Revision Notes, Questions and Answers. It is divided into 4 parts:
Part 1 – Basic Structure and Function of the eye
Part 2 – How we control the amount of light that enters the eye
Part 3 – How we focus on near and far objects
Part 4 – A revision game for you to print out and play
Learning Objectives
You need to be able to do:
1. Label and describe what each part of the eye does.
2. Know how the iris changes in bright and dim light
3. Know how the lens changes shape when it focuses on a near or distant object.
4. Be able to describe the changes in 2 and 3, with reference to a reflex arc.
If you are in Singapore use may want to use this links to view your syllabus.
2013 exam - http://www.seab.gov.sg/oLevel/2013Syllabus/5094_2013.pdf, page 15
2014 exam - http://www.seab.gov.sg/oLevel/2014Syllabus/5094_2014.pdf, page 15
© Chad Evans, www.knowneedlah.com , www.facebook.com/KnowNeedLah
Disclaimer: This is an original work researched from various materials including those published by the GCSE and ‘O’ Level
examining boards, the Qualifications and Curriculum Authority and the Departments for Education in England, Wales and Northern
Ireland.
This eBook is written to be accessible and readily comprehensible. It may therefore use terms other than those used by the examining
boards and other authorities. All information has been compiled in good faith by Chad Evans, but to the extent permitted by law, no
warranty is given to its completeness or accuracy or whether it is up-to-date and Chad Evans may not be held responsible for any loss
suffered as a result of the information or anyone acting upon its content. In the event that you are in doubt concerning your GCSE or
‘O’ Levels coursework or examinations we recommend that you seek further advice at your school or examining center.
Although all external links are checked at the time of compilation and on a regular basis, Chad Evans cannot be held responsible for
the validity of any of these links. Chad Evans does not accept responsibility or otherwise endorse any information contained in the
sites linked to from within these pages.
Part 1 – Basic Structure and Function of the eye
The eye is made up of the following parts. When shown a diagram without labels. You
must be able to write down what each one is. You must also know the function of each
part and preferably able to write it down too!
Vitreous
Gel
(humour)
Cornea
Cillary
Body
Iris
Pupil
Lens
{
Retina
Fovea
Suspensory
Ligament
Blind
Spot
Optic
Nerve
Cornea: This is transparent and curved, it bends the light rays towards the lens.
Iris: This is the coloured part of the eye. It contains muscle fibres that change the size of
the iris. This in turn changes the size of the pupil, controlling the amount of light that
enters the eye.
Lens: This focuses the light onto the retina.
Retina: This contains receptors, which detect light and sends electrical impulses towards
the optic nerve. There are two types of receptors, cone cells detect colour and rod cells
detect shades (black and white).
Optic nerve: This carries the electrical nerve impulses from the retina to the brain.
Blind Spot: This is where the optic nerve is joined to the retina, there are no receptors
here, so it can not detect light and therefore images. This is why it is called the blind spot.
Fovea: Has the highest number of receptors (cones), providing the most detailed images
for our sight.
Ciliary body/muscle: This changes the shape of the lens when the eye is focusing of
near or distant objects.
Suspensory Ligaments: These attach the ciliary body/muscle to the lens. They slacken
and tighten, depending on the movement of the ciliary body/muscle.
Vitreous Gel (Humour): Maintains the shape and structure of the eye
Example Questions (Long Answer - easy)
1) The diagram shows a cross section of an eye. Identify the parts A – K in the box
below.
Letter
A
B
C
D
E
F
G
H
I
J
K
Name of Part
Example Questions (Long Answer - easy)
2) The diagram shows a cross section of an eye. The table below state the function of
parts A – K. Write the correct letter next to it function.
Function of Part
Carries impulses from the retina to the brain
Transparent and curved, bends light towards the lens
Contains receptors which respond to light by producing electrical
nerve impulses
An area of the retina with the most receptors
Changes the shape of the lens
Focuses light onto the retina
Attach the ciliary body to the lens, they slacken and tighten
Muscle fibers which can change the size of the pupil
An area of the retina with no receptors
A transparent liquid that helps maintain the shape of the eye
Surrounded by the iris, which changes the shape of the aperture, to
regulate the amount of light entering the eye
Letter
Example Questions (Long Answer - moderate)
3) The diagram shows a cross section of an eye. In the table below state the function of
parts A – K
Letter
A
B
C
D
E
F
G
H
I
J
K
Function of Part
Example Questions (Long Answer - challenging)
4) The diagram shows a cross section of an eye. In the table below identify the parts of
the eye and state their function, for parts A – K.
Letter
A
B
C
D
E
F
G
H
I
J
K
Name of Part
Function of Part
Answer Sheet: Part 1(Long answers)
1)
Letter
A
B
C
D
E
F
G
H
I
J
K
Function of Part
Suspensory Ligaments
Ciliary body/muscle
Blind Spot
Optic Nerve
Pupil
Lens
Iris
Cornea
Fovea
Vitreous gel/humour
Retina
2)
Function of Part
Carries impulses from the retina to the brain
Transparent and curved, bends light towards the lens
Contains receptors which respond to light by producing electrical
nerve impulses
An area of the retina with the most receptors
Changes the shape of the lens
Focuses light onto the retina
Attach the ciliary body to the lens, they slacken and tighten
Muscle fibers which can change the size of the pupil
An area of the retina with no receptors
A transparent liquid that helps maintain the shape of the eye
Surrounded by the iris, which changes the shape of the aperture, to
regulate the amount of light entering the eye
Letter
D
H
K
I
B
F
A
G
C
J
E
3) & 4)
Letter Function of
Part
A
Suspensory
Ligaments
B
Ciliary
body/muscle
C
Blind Spot
D
Optic Nerve
E
Pupil
F
G
H
I
J
K
Lens
Iris
Cornea
Fovea
Vitreous
gel/humour
Retina
Function of Part
Attach the ciliary body to the lens, they slacken and
tighten
Changes the shape of the lens
An area of the retina with no receptors
Carries impulses from the retina to the brain
Surrounded by the iris, which changes the shape of
the aperture, to regulate the amount of light entering
the eye
Focuses light onto the retina
Muscle fibers which can change the size of the pupil
Transparent and curved, bends light towards the lens
An area of the retina with the most receptors
A transparent liquid that helps maintain the shape of
the eye
Contains receptors which respond to light by
producing electrical nerve impulses
Part 2 – How we control the amount of light that enters the eye
The Iris consists of two types of muscle. These muscles contract or relax, which changes
the size of the pupil. It is important to remember that it is the iris that controls the amount
of light entering the eye, not the pupil. The pupil, is just a hole, it only appears black. Just
like when you put a hole is a box, it appears black, but there is not actually anything
there. The two types of muscle that the iris is made up of are circular muscle and radial
muscle.
Dim Light
Radial muscle contracts
Circular muscles relax
Increased pupil size
Bright Light
Radial muscles relax
Circular muscle contracts
Decreased pupil size
It is sometimes hard to visualize. Try to think of the circular muscle working in the same
way as your lips. When you contract the muscles in your lips, your mouth gets smaller,
when they relax it gets bigger. Then think of the radial muscle being like your bicep,
When it is relaxed it is long and thin, but when you contract your bicep, it becomes short
and fat, which pulls your arm towards you. In the eye when the radial muscles contracts,
it becomes short and thick, pulling the circular muscle towards itself, opening up the
pupil.
This is what happens when you relate it to a reflex arc.
In Bright Light
Increased light is detected by the retina (receptor). The retina sends electrical impulses
along the optic nerve (sensory neurone) to the central nervous system (and brain). The
brain sends impulses along a motor neurone to the circular muscle in the iris (the
effector). The circular muscle contracts (radial muscle relaxes), the size of the pupil
decreases. Reducing the amount of light that enters the eye.
In the Dark
Decreased light is detected by the retina (receptor). The retina sends electrical impulses
along the optic nerve (sensory neurone) to the central nervous system (and brain). The
brain sends impulses along a motor neurone to the radial muscle in the iris (the effector).
The radial muscle contracts (circular muscle relaxes), the size of the pupil increases.
Increasing the amount of light that enters the eye.
Example Questions (Multiple Choice)
1) Mark wakes up in a dark room and turns on the light (bright light). Which row in the
table is the correct line to show the changes that take place in the iris?
A
B
C
D
Diameter of the
Pupil
Radial muscles of the
iris
Circular muscles of the iris
Increases
Decreases
Increases
Decreases
Relax
Relax
Contract
Contract
Contract
Contract
Relax
Relax
2) Mark plans to goes to sleep, when he turns off the light (bright light) and makes the
room dark. Which row in the table is the correct line to show the changes that take place
in the iris?
A
B
C
D
Diameter of the
Pupil
Radial muscles of the
iris
Circular muscles of the iris
Increases
Decreases
Increases
Decreases
Relax
Relax
Contract
Contract
Contract
Contract
Relax
Relax
3) The list below shows the events when a person turns on a light in a dark room, but in
the incorrect order. In which order should the events occur?
1 the pupil diameter decreases
2 more light strikes the retina
3 nerve impulses are sent along the optic nerve
4 the circular muscles of the iris contract and the radial muscles relax
A
B
C
D
1, 2, 3, 4
4, 3, 2, 1
2, 3, 4, 1
3, 2, 1, 4
4) The list below shows the events when a person turns off a light in a bright room, but in
the incorrect order. In which order should the events occur?
1 nerve impulses are sent along the optic nerve
2 less light strikes the retina
3 the pupil diameter increases
4 the circular muscles of the iris relax and the radial muscles contract
A
B
C
D
1, 2, 3, 4
4, 3, 2, 1
2, 1, 4, 3
3, 2, 1, 4
Example Questions (Long Answer – Challenging)
1) The diagram shows the cross section of an eye.
a) Which structure is mainly responsible for preventing light damaging the retina, by
changing it shape in order change the amount of light entering the eye (provide letter and
name)?
___________________________________
b) A person is sat on a train (light), the train then enters a tunnel (dark), before leaving
the tunnel and returning back into sunlight (light) again. Explain the changes in the pupil
with reference to your knowledge of the reflex arc.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
Answer Sheet: Part 2 (Multiple Choice)
1) B
2) C
3) C
4) C
Answer Sheet: Part 2 (Long answers)
1)
a) Iris (G)
b) On entering the tunnel decreased light is detected by the retina (receptor). The retina
sends electrical impulses along the optic nerve (sensory neurone) to the central nervous
system (and brain). The brain sends impulses along a motor neurone to the radial muscle
in the iris (the effector). The radial muscle contracts (circular muscle relaxes), the size of
the pupil increases. Increasing the amount of light that enters the eye.
On leaving the tunnel increased light is detected by the retina (receptor). The retina
sends electrical impulses along the optic nerve (sensory neurone) to the central nervous
system (and brain). The brain sends impulses along a motor neurone to the circular
muscle in the iris (the effector). The circular muscle contracts (radial muscle relaxes), the
size of the pupil decreases. Reducing the amount of light that enters the eye.
TIP
Sometimes it helps to sketch out a diagram or the reflex arc before writing, so you don’t
miss out any of the stages.
The reflex Arc
Stimulus => Receptor => Sensory Neurone => Central Nervous System => Motor Neurone => Effector
Part 3 – How we focus on near and far objects
The lens shape is controlled by the ciliary body/muscle.
Focusing on a near object
The ciliary body/ muscles contract. The Lens becomes thicker. The Light rays are bent
much more towards the retina.
Focusing on a distant object
The ciliary muscles relax. The Lens becomes thinner. The Light rays are not bent as
much towards the retina.
Example Questions (Multiple Choice)
1) The cilliary body changes the shape of the lens in the eye. Which row in the table is
the correct line when the eye is focused on a distant object?
A
B
C
D
Shape of lens
Slightly curved
Slightly curved
Very curved
Very curved
Cillary body
Contracted
Relaxed
Contracted
Relaxed
2) The cilliary body changes the shape of the lens in the eye. Which row in the table is
the correct line when the eye is focused on a near object?
A
B
C
D
Shape of lens
Slightly curved
Slightly curved
Very curved
Very curved
Cillary body
Contracted
Relaxed
Contracted
Relaxed
3) Katie was watching a mosquito in her room. The graph below shows the changes in
the curvature of the lens in the eye. At which point on the graph (A, B, C or D) was the
mosquito closest (near object) to Katie.
4) Katie was watching a mosquito in her room. The graph below shows the changes in
the curvature of the lens in the eye. At which point on the graph (A, B, C or D) was the
mosquito furthest away (distant object) to Katie.
5) The diagram shows the cross section of an eye.
Which row in the table is the correct line to show which structures are receptors and
which are effectors?
A
B
C
D
Receptors
I and C
I and K
C and K
F and I
Effectors
B and G
B and G
A and E
A and G
6) Susan is waiting for a bus. She sees the bus in the distance and then looks at her
watch for 5 seconds, then back at the approaching bus. Which row shows the correct
sequence to show the changes in the shape of the lens.
7) Susan late for her bus. She sees the bus pull away from the bus stop, just as she
arrives. Which row shows the correct sequence to show the changes in the shape of the
lens, as she watches the bus slowly move away from her.
Example Questions (Long Answer – Challenging)
1) The diagram shows the cross section of an eye.
a) Which structures is mainly responsible for changing the shape of the lens, to focus
images onto the retina (provide letter and name)?
___________________________________
b) Katy is standing at the finishing line of the 100m track on sports day. She watches her
friend run in the race. Explain the changes in eye, between when her friend stood at the
start of the race and crossed the finishing line.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
Answer Sheet: Part 3 (Multiple Choice)
1) B
2) C
3) D
4) C
5) B
6) C
Answer Sheet: Part 3 (Long answers)
1)
a) Ciliary body/muscles (B)
b) When Katy is focused on her friend in the distance, the ciliary muscles relax. The Lens
becomes thinner. The Light rays are not bent as much towards the retina.
When Katy is focused on her friend at the finish line, the ciliary muscles contract. The
Lens becomes thicker. The Light rays are bent much more towards the retina.
Part 4 – Revision Game (Biominos)
From the table below cut out “strips”, so they look like dominos (Biominos). DO NOT cut
down the middle! Then shuffle the strips (as they are in the correct order, you may want
to get someone to cut them for you, so you do not cheat). Starting from the “Biomino”
with the word START, try to form a long line, until you reach the word FINISH. If you get
stuck half way, you can always begin from the end and try to meet in the middle!
START
Chad Evans
www.knowneelah.com
Iris
Controls the amount of
light entering the eye
In ‘Bright Light’
The circular muscle
contracts and the radial
muscles relax
Fovea
Has the largest number
of cone cells
In ‘the dark’
The circular muscles
relax and the radial
muscles contract
The Pupil
Not “a real thing”,
merely an apature (hole)
Retina
Contains receptors that
send electrical impulses
along the optic nerve
When you focus on a
‘near object’
The lens is short and
thick
Examples of receptors
in the eye
Fovea and Retina
When you focus on a
‘distant object’
The lens is long and thin
Vitrious Humour (Gel)
Maintains the shape of
the eye
Examples of effectors
in the eye
Cilliary body and iris
Finish!
Good Luck in your
Exams!