1. Humans, and other animals, are able to detect a range of stimuli from the
external environment, some of which are useful for communication
DP1 “identify the role of receptors in detecting stimuli”
 A stimulus is a change in the environment. Examples of stimuli include light,
sound, temperature, pressure, pain and certain chemicals.
 A receptor is a specialised cell that detects a stimulus. As a result a nerve
impulse may be generated or a hormone produced. There is a range of
receptor cells adapted to detecting specific stimuli, e.g. rods and cones in the
eye. Sometimes receptors are distributed all over the body, such as touch
receptors in the skin. In other cases, particular receptors are concentrated in
an organ, such as the eye, or an endocrine gland such as the adrenal gland.
DP2 “explain that the response to a stimulus involves:”
 stimulus
 receptor
 messenger
 response
SC DP1 “identify data sources, gather and process information from
secondary sources to identify the range of senses involved in
communication”
2. Visual communication involves the eye registering changes in the
immediate environment
DP1 “describe the anatomy and function of the human eye, including the:”
 conjunctiva
 cornea
 sclera
 choroid
 retina
 iris
 lens
 aqueous and vitreous humor
 ciliary body
 optic nerve
DP2 “identify the limited range of wavelengths of the electromagnetic
spectrum detected by humans and compare this range with those of other
vertebrates and invertebrates”
 Limit of human wavelength is 380nm to 780nm
 Invertebrates:
Bees can see in UV but humans cannot.
 Vertebrates:
Birds can see in UV but humans cannot.
 UV light
- Vertebrates
- Goldfish, salmon
- Zebra, finches (Birds)
 Infra-red:
- Vertebrate
- Australian Pythons
SC DP1 “plan, choose equipment or resources and perform a first-hand
investigation of a mammalian eye to gather first-hand data to relate
structures to functions”
SC DP2 “use available evidence to suggest reasons for the differences in
range of electromagnetic radiation detected by humans and other animals”
3. The clarity of the signal transferred can affect interpretation of the
intended visual communication
DP1 “identify the conditions under which refraction of light occurs”
 Light rays travel in straight lines. However, if a light ray passes from one
medium to another at an angle other than 90 º, the ray is bent. This
bending, as light passes from one medium to another, is called refraction.
 Refraction of light occurs when light passes from one substance to
another.
DP2 “identify the:”
Cornea, aqueous humor, lens and vitreous humor as refractive media.
DP3 “identify accommodation as the focusing on objects at different
distances, describe its achievement through the change in strength of the
lens and explain its importance”
Accommodation is the focusing of the eye on objects at different distances.
Accommodation is achieved through the change in curvature of the lens, to either
elongated (taut, ligaments rested) or highly convex (slackened, ligaments
contracted). Accommodation is important because it allows the eye to focus on
distant objects then the ability to change focus to a close object very quickly
without straining the eye.
DP4 “compare the change in the refractive power of the lens from rest to
maximum accommodation”
When the lens is rested it has minimum accommodation because it is ready to
look at an object in the distance not needing to bend the light rays. But, when it
needs maximum accommodation it has to look at a near by-object which means
it needs to refract the light rays the most because they are entering at acute
angles.
DP5 “distinguish between myopia and hyperopia and outline how
technologies can be used to correct these conditions”
Feature
Myopia
Hyperopia
Cause of condition
The ciliary muscles do
The ciliary muscles does
not relax enough causing not contract enough,
the lens to be not fully
leaving the lens still
elongated causing too
elongated, causing not
much refraction
enough refraction.
Where image focuses
Too short of the retina
Past the Retina
Which objects focus
Close Objects
Distant Objects
correctly
Diagram of lens used for Concave Lens
Convex Lens
correction
DP6 “explain how the production of two different images of a view can
result in depth perception”
Some animals have forward facing eyes. This means that there is considerable
overlap between the views on the left and the right. Because the two eyes are a
few centimetres apart, each eye sees a slightly different view of an object. The
images formed by each eye are superimposed by the brain, and because each
view is slightly different, objects appear to have depth as well as height and
breadth, that is we see in three dimensions. This is known as stereoscopic or
binocular vision. This type of vision also makes it possible to judge distances of
near objects. Climbing animals such as monkeys and predators such as cats have
forward facing eyes, but grazing animals such as horses have eyes on the side of
the head so they have a wider field of view.
SC DP1 “plan, choose equipment or resources and perform a first-hand
investigation to model the process of accommodation by passing rays of
light through convex lenses of different focal lengths”
A biconvex lens is shaped as shown in the diagram below. Convex lenses magnify
images by causing rays of light to converge.
The lens in the human eye is a convex lens. When parallel rays of light are passed
through a convex lens, they will converge at a point, known as the focal point.
The focal length of a lens is the distance of the focal point from the centre of the
lens.
Convex Lens
SC DP2 “analyse information from secondary sources to describe changes
in the shape of the eye’s lens when focusing on near and far objects”
SC DP3 “process and analyse information from secondary sources to
describe cataracts and the technology that can be used to prevent
blindness from cataracts to discuss the implications of this technology for
society”
A cataract is a clouding that develops in the crystalline lens of the eye or in its
envelope, varying in degree from slight to complete opacity and obstructing the
passage of light. Cataracts typically progress slowly to cause vision loss and are
potentially blinding if untreated. The condition usually affects both the eyes, but
almost always one eye is affected earlier than the other.
Cataracts mostly affect the elderly as they are the majority getting cataract
surgeries. There are no known causes of cataracts and research is still going on
to find a cause, but for now they only have suggestions. Such as people who have:





A family history of the eye condition
Diabetes
An injury to the eye
Exposed their eyes to sunlight without protection over a long term
Smoked for a period of time
There are some technologies that can be used to fix this problem. Initially
glasses, strong bifocals, magnification, appropriate lighting or other visual aids
may be able to improve your vision. But, eventually surgery will be the only
option because the cataracts will spread and blindness will eventually occur.
Surgery is only recommended when your cataracts have progressed enough to
seriously impair your vision and affect your daily life. Many people consider poor
vision an inevitable fact of aging, but cataract surgery is a simple, relatively
painless procedure to regain vision.
The most common surgery, is where the surgeon will remove your clouded lens
and in most cases replace it with a clear, plastic intraocular lens (IOL). New IOLs
are being developed all the time to make the surgery less complicated for
surgeons and the lenses more helpful to patients. Presbyopia-correcting IOLs
potentially help you see at all distances, not just one. Another new type of IOL
blocks both ultraviolet and blue light rays, which research indicates may damage
the retina.
Another least commonly used surgery is called Phacoemulsification, which is a
modern cataract surgery in which the eye's internal lens is emulsified with an
ultrasonic handpiece to break up the protein that causes the cataract.
The Fred Hollows Foundation was started by Fred Hollows (1929-1993). Fred
was an eye doctor, a skilled surgeon of international renown, a champion of the
right of all people to good health and a strong advocate for social justice.
The Fred Hollows Foundation was established in 1992 to continue the work of
Professor Fred Hollows.
The Foundation works internationally on comprehensive quality eye care, with a
focus on cataract. In Australia, The Foundation is committed to roles as both
partner and advocate of effective health programs for Indigenous Australians.
4. The light signal reaching the retina is transformed into an electrical
impulse
DP1 “identify photoreceptor cells as:”
Cells containing light sensitive pigments and explain that these cells convert light
images into electrochemical signals that the brain can interpret.
DP2 “describe the differences in distribution, structure and function of the
photoreceptor cells in the human eye”
PhotoDistribution Structure
Pigment
Function
Colour and
receptor
(description
wavelength
Cell
and
of light to
diagram)
which cell
is sensitive
Rods
Evenly
The outer
Rhodospin Responsible Sensitive to
distributed segment is
for most
low-light
across most long and
peripheral
(night
of the
narrow.
vision,
vision)
retina, but
including
are absent
the
from the
detection of
fovea.
movement
Cones
Distributed Have a
Iodopsins
Responsible Less
in groups
shorter
for colour
sensitive to
throughout outer
vision
light, they
the retina,
segment
require
but there
that is conelarger
are fewer
shaped
quantities
around the
of light to
periphery
stimulate
of the
or bleach
retina.
them
DP3 “outline the role of rhodopsins in rods”
 Rhodopsin is a 2 part molecule, containing a protein molecule called opsin
and a light absorbing molecule called retinal.
 The main function of the photochemical pigments rhodopsin is to absorb
light.
 The light activates the retinal which allows the retinal molecule to split
away from the opsin molecule.
 The activated pigment causes a change in electrical charges of the
membrane of the rod (changing the language of light energy into a type of
language the brain can process which is electrical energy).
 Electrical impulse cannot jump from axon branch to axon branch at the
synapses (which is an insulator) so an chemical, which has to be created
which is called a neurotransmitter chemical to allow the electrical
impulse to keep continuing along the axon, there is a short delay when
this happens (the less stops the quicker the impulse can travel to the
brain).
DP4 “identify that there are three types of cones, each containing a
separate pigment sensitive to either blue, red or green light”
Rhodopsin and other opsins
Because all rods have only one type of pigment, rhodopsin, they are not sensitive
to different colours. Rhodopsin is a broad spectrum pigment. Its peak sensitivity
is in the 500 nm wavelength region of the visible spectrum, but rods do not allow
us to perceive any colour. Vision involving rhodopsin in rods allows us to see in
shades of black, white and grey.
Each cone contains one of three types of iodopsin pigments and is therefore most
sensitive to light in one of three wavelengths. These pigments result in cone cells
being sensitive to:

the short wavelengths of blue light, peak sensitivity being at
approximately 455 nm; or

the medium wavelengths of green light, peak sensitivity being at
approximately 530 nm; or

the long wavelengths of red light, peak sensitivity being at
approximately 625 nm.
However, the sensitivity of a particular cone cell allows it to detect light to some
extent on either side of these peak sensitivities, giving an overlap in some of the
colours detected. 'Red' cones are actually more sensitive to yellow light (560-565
nm) than to red light, but they respond to red light before any of the others do,
therefore behaving as red receptors. Therefore light of a particular wavelength
may stimulate more than one cone. By comparing the rate at which various
receptors respond, as well as the overlap in colours detected, the brain is able to
interpret these signals as intermediate colours. This allows us to 'see' a variety of
colours.
DP5 “explain that colour blindness in humans results from the lack of one
or more of the colour sensitive pigments in the cones”
 Cones detect colour, any defect or damage to the cones will affect the
ability of the eye to perceive colour.
 Humans have three different forms of opsins present in cones, each coded
for by one gene.
 A mutation in a gene that codes for a cone pigment leads to the inability of
this pigment to function correctly. As a result, the person is unable to
perceive colour in the normal trichromatic matter and is said to be either
colour deficient or colour blind, depending on how the mutation affects
the pigment.
 In humans red/green pigments are located on the X chromosome.
Mutations in the gene for the blue cone pigment are extremely rare.
SC DP1 “process and analyse information from secondary sources to
compare and describe the nature of photoreceptor cells in mammals,
insects and in simple light receptors in one other animal”
Animal
No. of eyes Type of
Description of Pigment
Colour
Photoreceptor
Photoreceptor
Vision
cell
cell
Mammal – 2
Rods and Cones Rods for
Rhodospin Yes
Human
peripheral and and
nighttime
Iodopsins
vision. Cones
for colour and
clarity.
Insect –
Each
Ommatidia
Registers
Rhabdom Yes
Fly
compound
vision for a
eye is
different part
made up
of the
of about
environment.
8000 units
The result is
called
an image that
ommatidia
is a pattern of
dots.
SC DP2 “process and analyse information from secondary sources to
describe and analyse the use of colour for communication in animals and
relate this to the occurrence of colour vision in animals”
Many animals use colour to communicate a variety of types of information. The
effectiveness of this communication depends on the animals that they are
sending this information to, having colour vision to detect it. Fish, amphibians,
reptiles and birds have well-developed colour vision, but humans and other
primates are among the minority of mammals that can see colour.
Animals may use colour to signal their availability to mate, to indicate their
suitability as a potential parent, to hide from predators or to warn of their
unpalatability as prey. Some species mimic other unpalatable or poisonous
species by using colour.
Human have 10,000 cones per square millimetre compared to some birds that
have up to 120,000 per square millimetre. Birds who feed in the daylight see
colours very clearly, for example hummingbirds can spot red flowers from over a
kilometre away.
5. Sound is also a very important communication medium for humans and
other animals
DP1 “explain why sound is a useful and versatile form of communication”
 Sound is used for:
- Mating behaviour
- Warning of predators
- Feeding patterns
- Social activities
Survival can depend on the ability to relate to each other, establish territory,
defend territory, obtain food and reproduce.
Sound not light dependent
Can travel through solids, liquids and gases.
Most animals can produce and detect sound.
DP2 “explain that sound is produced by vibrating objects and that the
frequency of the sound is the same as the frequency of the vibration of the
source of the sound”
 Sound is a form of energy produced by an object that vibrates, moving
backwards and forwards. The vibrating object causes nearby air
molecules to vibrate back and forth, and these molecules cause others to
vibrate.
 This results in a compression wave travelling through the air.
 The frequency of the vibration of air molecules is the same as the
frequency of the vibrating object.
DP3 “outline the structure of the human larynx and the associated
structures that assist the production of sound”
The frequency of sound generated by the larynx is the same frequency that the
medium vibrates and the same frequency that the ear detects.
The human larynx produces sound by using muscles to change the shape of the
vocal cords or folds and pass air over them to make them vibrate.
The vocal folds are located in the larynx, which is found at the top of the trachea.
It is a tubular organ made of cartilage, held in place by ligaments and muscle.
When the vocal cords are pulled tight, they vibrate at a high frequency and when
there is less tension they vibrate at a lower frequency. Speed of opening and
closing also affects frequency. Vocal cords open and close more frequently for
high pitched voices.
SC DP1 “plan and perform a first-hand investigation to gather data to
identify the relationship between wave-length frequency and pitch of a
sound”
Used the Cathode Ray Oscilloscope (CRO)
SC DP2 “gather and process information from secondary sources to outline
and compare some of the structures used by animals to produce sound”



Adult female mosquitos beat their wings, emitting low-frequency sounds
(200-400 Hz).
Male frogs croak, the sound is generated in their vocal sacs and mouth
cavities.
A snake or a turtle will hiss, a gecko chirp and a crocodile produce a wide
variety of sounds.
6. Animals that produce vibrations also have organs to detect vibrations
DP1 “outline and compare the detection of vibrations by insects, fish and
mammals”
DP2 “describe the anatomy and function of the human ear, including:”
DP3 “outline the role of the Eustachian tube”
The role of the Eustachin tube is to equalise the pressure between the outer ear
and the inner ear. This is so the tympanic membrane remains intact. The tube is
able to do this as it connects the inner ear with the outside air in the pharynx.
Under normal circumstances, the canal of the tube is closed, but yawning,
coughing and swallowing opens the canal briefly and equalises the pressure.
DP4 “outline the path of a sound wave through the external, middle and
inner ear and identify the energy transformations that occur”
DP5 “describe the relationship between the distribution of hair cells in the
organ of Corti and the detection of sounds of different frequencies”
The detection of sounds of different frequencies is made possible by two
features. The first is that vibrations of a certain frequency cause the next
structure to vibrate at the same frequency. The second feature is that the similar
membrane of the organ of corti is made up of fibres or hairs of varying lengths.
Each of these lengths vibrates at a different frequency.
The hair cells are arranged along the basilar membrane from those stimulated by
low frequency at the apex, to those stimulated by high frequency at the base.
DP6 “outline the role of the sound shadow cast by the head in the location
of sound”
Sound waves reach both ears with equal intensity when the sound is directly in
front or behind you. However, mostly sound reaches one ear with greater
intensity then the other. The head casts a shadow which blocks some of the
intensity in the ear furthest from the source, as the sound bends around the
head. The difference in intensity is reflected in the signal that is sent to the brain
via the auditory nerve. This is processed to provide the location of the sound.
SC DP1 “gather, process and analyse information from secondary sources
on the structure of a mammalian ear to relate structures to functions”
SC DP2 “process information from secondary sources to outline the range
of frequencies detected by humans as sound and compare this range with
two other mammals, discussing possible reasons for the differences
identified”
Mammal
Lowest Frequency
Highest Frequency
Detected(Hz)
Detected(Hz)
Human
20
20000
Dolphins
20000
80000
Kangaroo Rat
30
50000
SC DP3 “process information from secondary sources to evaluate a hearing
aid and a cochlear implant in terms of:
 the position and type of energy transfer occurring
 conditions under which the technology will assist hearing
 limitations of each technology
Hearing aids and cochlear implants are both devices designed to improve
deafness. A hearing aid is an electronic, battery-operated device that amplifies
and changes sound to allow for improved communication. Hearing aids receive
sound through a microphone, which then converts the sound energy to electrical
energy. The amplifier increases the loudness of the signals and then converts the
electrical energy back to sound. This sound leaves the hearing aid through a
speaker which directs the sound down the auditory canal. Most hearing aids are
placed in or near the external auditory canal.
Hearing aids are particularly useful in improving the hearing and speech
comprehension of people with sensorineural hearing loss. Sensorineural hearing
loss develops when the auditory nerve or hair cells in the inner ear are damaged
by aging, noise, illness, injury, infection, head trauma, toxic medications, or an
inherited condition. Hearing aids will not restore normal hearing or eliminate
background noise.
A cochlear implant is a small, complex electronic device that can help to provide
a sense of sound to a person who is profoundly deaf or severely hard of hearing.
It bypasses damaged parts of the inner ear and electronically stimulates the
auditory nerve. Part of the device is surgically implanted in the skull behind the
ear and tiny electrode wires are inserted into the cochlea. The other part of the
device is external and has a microphone, a speech processor (to convert sound
into electrical impulses), and connecting cables. An implant does not restore or
create normal hearing. Instead, it can give a deaf person a useful auditory
understanding of the environment and help him or her to understand speech.
Unlike a hearing aid which amplifies sound, cochlear implants compensate for
damaged or non-working parts of the inner ear. It electronically finds useful
sounds and then sends them to the brain.
A person with a cochlear implant must learn to interpret the sounds created by
an implant. This process takes time and practice. The person may also have to
use the implant in conjunction with lip reading. It has been shown that
individuals who receive the implant after they have learnt to speak perform
better than those who have never spoken. The implant is also very expensive.
7. Signals from the eye and ear are transmitted as electro-chemical changes in
the membranes of the optic and auditory nerves
DP1 “identify that a nerve is a bundle of neuronal fibres”
DP2 “identify neurones as nerve cells that are the transmitters of signals by
electro-chemical changes in their membranes”
DP3 “define the term threshold and explain why not all stimuli generate an
action potential”
Resting Potential
– No impulse generated
– -70 mV
Action Potential
- An impulse has been generated
- +34 mV
Threshold
- Minimum amount of change in charge needed to generate the impulse
- -50 mV
 When a neurone fires it is known as the 'all or none' response or the 'all
or nothing' response. The reaction either occurs at the maximum or
does not fire at all.
 The point of excitation that causes the neurone to fire is called the
threshold of reaction.
 The intensity of the stimulus is recorded by the firing of all neurones not
in a greater or lesser action potential of an individual cell.
DP4 “identify those areas of the cerebrum involved in the perception and
interpretation of light and sound”
DP5 “explain, using specific examples, the importance of correct
interpretation of signals by the brain for the coordination of animal
behaviour”
The environment in which an organism lives is constantly changing. Sense
organs such as the ear and the eye detect these changes and send information to
the brain. The brain then interprets the information and sends an impulse to an
effector organ such as a muscle. It is essential that the brain interpret signals
from the sense organs correctly. The cerebral cortex is the most important
association centre of the brain. Information comes to this area from our senses
and the brain sorts it out in the light of past experiences. As a result, motor
impulses are sent along the nerves to cause an appropriate action to take place.
For example, the eyes and ears, receptors in muscles and tendons, pressure
sensors on the feet all provide signals about the position of the body in space.
The cerebrum of the brain interprets all of these signals and sends messages to
various effectors to balance the body in space.
Walking involves several receptors, including the eyes, gravity receptors in the
ears, pressure sensors in the feet and position receptors in the joints. These
receptors are connected to the brain by neurones and the brain interprets the
signals it receives. The brain sends messages to the muscles and other effectors
to coordinate the process of walking. The importance of the brain in the
coordination of animal behaviour is highlighted when parts of it are damaged.
The paralysis that follows a stroke, or the shaking movements of people with
Parkinson’s disease, are signs of damage to the brain. In people with these
conditions, muscular contractions are no longer coordinated by the brain.
SC DP1 “perform a first-hand investigation using stained prepared slides
and/or electron micrographs to gather information about neurones and
nerves”
SC DP2 “perform a first-hand investigation to examine an appropriate
mammalian brain or model of a human brain to gather information to
distinguish the cerebrum, cerebellum and medulla oblongata and locate
the regions involved in speech, sight and sound perception”
SC DP3 “present information from secondary sources to graphically
represent a typical action potential”