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Communication
1) Humans and other animals are able to detect a range of stimuli from
the external environment, some of which are useful for communication.
 Identify the role of receptors in detecting stimuli.
A stimulus is a change in the internal and external environment of an organism.
Examples of stimuli include light, sound, temperature, pressure, pain and certain
chemicals.
Living organisms detect stimuli using receptors. A receptor is a specialised
sensory cell in a sense organ. As a result of detecting the stimulus, a nerve impulse may
be generated or a hormone may be produced.
Sometimes receptors consist of single cells scattered over the body, such as touch
receptors in skin. However, in many organisms receptors have become concentrated in
particular areas to form sense organs (e.g. eyes, ears, or an endocrine gland such as the
adrenal gland).
There is a range of receptor cells adapted to detecting specific stimuli, e.g. rods
and cones in the eye. Receptors are commonly classed according to the type of energy to
which they respond:
Stimulus
Light
Sense organ
Eye
Sensory receptors
Photoreceptors: rods and
cones in the retina of the eye
Sound
Ear
Chemical
Tongue
Mechanoreceptors: hair cells
in Organ of Corti
Chemoreceptors: taste buds
Chemical
Nose
Pressure
Skin
Chemoreceptors: in nasal
passages
Mechanoreceptors: in skin
Function
Detect light,
colour and
movement.
Detect sound
waves
Detect dissolved
molecules
Detect molecules
in the air
Detect pressure
on skin
Sense
Sight
Hearing
Taste
Smell
Touch
There are several other receptors:
A nociceptor sends signals that cause the perception of pain in response to
potentially damaging stimuli. They are sensitised by prostaglandins (fatty acids) and are
desensitised by aspirin.
A thermoreceptor responds to changes in temperature. In the mammalian
peripheral nervous system, there are receptors that respond to both heat and cold.
An electromagnetic receptor responds to light, magnetism and electricity. A
photoreceptor is a specialised type of neuron that is capable of phototransduction (the
conversion of a light signal to an electrical signal).
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 Explain that the response to a stimulus involves: stimulus, receptor, messenger,
effector, response.
Stimuli  Receptors  Messengers  CNS  Effectors  Response
In order that a stimulus may produce a response, a receptor must detect the
stimulus. A message must then be passed to a messenger, which may be a nerve or a
hormone. The messenger then passes information through the central nervous system to
an effector, which may be a gland or a muscle, which responds to the information.
For example, a bright light causes someone to close their eyes. The light receptor
cells are able to pass on this information to messengers (nerve cells), which convey the
information to the central nervous system. Other nerves then convey the information back
to an effector such as a muscle or a gland that produces a response to the stimulus. Thus
the muscles in the eye will cause the eye to close.
This is known as the stimulus-response model and is outlined below:
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 Identify the range of senses involved in communication.
The senses are valuable characteristics for detecting changes in our environment and then
registering sensations. They help us to survive and are also a means of communication to
other organisms.
Senses
Sight (visual)
Smell
(olfactory)
Hearing
(auditory)
Touch (tactile)
Taste
Human examples
Facial expression signal
emotions including aggression
Other animal examples
● Bioluminescence in fireflies to attract mates.
● Female chimpanzees have a coloured rump to show
when they are ready for mating.
● Blue-ringed octopus signal an intention to attack by
glowing blue rings on their bodies.
Not so important in humans,
● Animals release pheromones to make their presence
human females may change
known.
their menstrual cycle because ● Male mice will mate immediately when they smell a
of olfactory information
receptive female.
Language used extensively to
● Crickets use sound as a warning and to attract
convey information, used as a
mates.
warning signal.
● Some moths can hear the ultrasonic calls of bats and
can avoid being eaten.
● Frogs use sound for mating calls.
● Dolphins use echolocation.
Used in group bonding and in
● Seagull chicks get their mothers to release food by
mating. Also used aggressively
pecking on their beaks.
● Bees dance to communicate the location of food.
Five types of tastes:
Some butterflies such as the Monarch butterfly have a
Salty, Sour, Sweet, Bitter, Umami
bitter taste to communicate that they are poisonous
(Glutamate)
Touch as a method of communication:
Shaking hands in humans is a gesture of greeting. Gestures of comfort such as hugging in
humans and touching hands in chimpanzees are recognised examples of how touch is
used as a form of communication. Touch may be used by many animals in courtship
behaviour also. In some amphibian species (e.g. frogs), the male strokes the female
during mating to stimulate her to release eggs.
Taste as a form of communication:
Animals that have a poor sense of smell may rely more on taste as a form of
communication. For example, after passing faeces male chameleons rubs his cloaca on
branches to mark his territory. Other chameleons lick the branches of trees and shrubs to
detect whether the territory is occupied. This makes up for the chameleon’s poorly
developed sense of taste.
Smell as a form of communication:
Animals such as dogs and mice rely to a large extent on their sense of smell to recognise
trails and territory, locate food, recognise others, and find a receptive mate. Ants release
pheromones which are an important form of communication between ants, attracting
each other and marking out pathways to food.
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2) Visual communication involves the eye registering changes in the
immediate environment.
 Describe the anatomy and function of the human eye.
Structure
Conjunctiva
Cornea
Sclera
Choroid
Retina
Iris
Lens
Aqueous humour
Vitreous humour
Ciliary body
Optic nerve
Anatomy and Function
Continuation of the epidermis of the skin. It protects the cornea
at the front of the eyeball from friction.
Transparent to light. It refracts light to help form an image on
the retina.
The white of the eye: a tough coat of fibres. It protects the
eyeball against mechanical damage and helps to maintain the
shape of the eyeball.
A membrane containing pigment and blood vessels. It nourishes
the retina and prevents internal reflection as it is black and
absorbs light.
Contains light-sensitive receptor cells connected to sensory
neurons. The retina detects light.
A pigmented muscular structure that contracts and dilates to
adjust the amount of light entering the eye.
A flexible, transparent structure which allows light to enter the
back of the eye. It refracts light to allow fine focusing of an
image onto the retina.
A watery fluid that helps to maintain the shape of the eye.
A jelly-like fluid that helps to maintain the shape of the eye.
Contains muscles. It supports the lens and alters the shape of the
lens.
Consists of bundles of sensory neurons. It transmits impulses
generated in the retina to the brain.
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 Identify the limited range of wavelengths of the electromagnetic spectrum detected by
humans and compare this range with those of other vertebrates and invertebrates.
Humans use the sense of sight to interpret much of the world around them. What we see
is called “light”. However, humans only see a small part of the entire “electromagnetic
spectrum.” Humans can see only the wavelengths of electromagnetic radiation between
about 380 and 760 nanometres because our eyes do not have detectors for wavelengths of
energy less than 380 or greater than 760 nanometres. Thus we cannot “see” other types of
energy such as gamma or radio waves. Rattlesnakes, however, can detect
electromagnetic radiation in the infrared range and use this ability to find prey.
Type of
animal
Vertebrate
Invertebrate
Name of
animal
Human
Rattlesnake
Japanese
dace fish
Honeybee
Mantis
shrimp
Part of electromagnetic
spectrum detected
Visible
Infra-red and visible
Ultraviolet and visible
Wavelengths detected
Ultraviolet and visible
Ultraviolet and visible
700-300 nm
640-400 nm
700-400 nm
850-480 nm
As low as 360 nm
Nocturnal animals such as the rattlesnake are better hunters during the night
because their prey cannot see them; however the snake is able to detect the prey’s body
heat as infrared.
Similarly, deep-sea angler fish have no available light and use bioluminescence to
attract prey.
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 Perform a first-hand investigation of a mammalian eye to gather data to relate
structures to functions.
We dissected a sheep’s eye to observe the structures of a mammalian eye.
SAFE WORK PRACTICES:
 Worked on newspaper inside a tray to prevent the displacement of any parts of the eye.
 Disposed of sharp items (scalpels, tweezers and scissors) in a sharps deposit box.
 Disposed of eye and materials by wrapping them in newspaper and placing in the bin.
 We minimised hazards by wearing safety equipment: gloves, goggles and aprons.
Rings and watches were removed to prevent tearing the gloves. Long hair was tied back
to prevent cross-contamination.
 Suggest reasons for the differences in range of electromagnetic radiation detected by
humans and other animals.
Humans see only a limited range of the electromagnetic spectrum because it is all that is
necessary to their survival.
Other animals have different needs to humans and thus they have adapted to suit these
requirements. Snakes hunt at night for food, thus they are able to detect the infrared body
heat of their prey even though they cannot see the prey visibly.
Ocean-dwelling organisms such as species of coral reef fish and some crustaceans are
able to detect UV light. This can enhance the image that the organisms see, creating more
contrast and thus allowing the organism to see more detail as necessary.
As humans do not hunt for prey at night nor live underwater, we do not have the need to
see UV or infrared light.
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3) The clarity of the signal transferred can affect interpretation of the
visual communication.
 Identify the conditions under which refraction of light occurs.
In order to be seen an object reflects light, generates its own light or transmits
light to our eyes. When light moves from one substance or medium to another, it is bent,
or refracted. The speed at which the light is travelling also changes.
The movement of light through a denser medium is slower and is thus refracted to
a greater degree.
When light is passed through a biconvex lens [shaped like ()], the rays are
refracted toward a central point known as the focal point. The rays then cross over and
diverge from that point. If a screen is placed in the pathway of the diverging rays, the
resulting image is upside down or inverted.
 Identify the cornea, aqueous humor, lens and vitreous humor as refractive media.
The density of the cornea, aqueous humor, lens and vitreous humor are similar to
each other and all refract light that passes through the eye. The refractive power of air –
through which light travels to reach the eyes of terrestrial mammals – is lower than the
refractive power of parts of the eye. Therefore, the greatest degree of refraction in the
human eye occurs when light moves into the cornea, since the change in refractive power
is at its greatest point: the greater the difference in the refractive power of two media, the
more the light is refracted when it passes from one medium to the other.
The lens is able to refract light to a greater or lesser degree by altering its shape.
This is termed accommodation and is useful in allowing the eye to adjust for near or
distant vision. The overall shape of the lens (its degree of curvature) determines the
degree to which light can be refracted.
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 Identify accommodation as the focusing on objects at different distances, describe its
achievement through the change in curvature of the lens and explain its importance.
Accommodation is the term used to describe the focusing of objects at different
distances, brought about by changing the convexity of the lens and, as a result, its
refractive power. This change in the shape of the lens results from the action of the ciliary
muscles, which in turn affect the tension of the suspensory ligaments that hold the lens.
Distant Vision – when the eye is looking at distant objects, light reaches the eyes
in parallel rays. This light is focused on the retina by the lens in its resting state. The lens
is quite flat and at its lowest strength or refractive power. This means that there is very
little refraction or bending of light as it passes through the lens. The ciliary muscles are
relaxed and tension in the attachments from the lens to the ciliary body keep the lens thin.
Above: The object is far away and the biconvex lens is elongated to slightly converge
rays. The light rays are almost parallel.
Near Vision – when the eye is looking at close objects (less than 6m away), the
light rays tend to diverge as they reach the eye. This means that the refractive power of
the lens must be increased, achieved by the lens becoming more convex: bulging
outwards. The contracting of the ciliary muscles causes the bulging of the lens, hence the
image is focused on the retina.
Above: the light rays diverge from the close object. Highly rounded biconvex lens
converge light rays – the focal length is longer.
Accommodation is important to allow clear vision. If the lens could not change
curvature, the image would not be focused properly, resulting in a blurred image and
hampering visual communication.
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 Compare the change in the refractive power of the lens from the rest to maximise
accommodation.
For distant vision the curvature of the lens must be relatively flat. When the
ciliary muscles are relaxed they hold the suspensory ligaments taut, pulling on the lens
and keeping it relatively flat (elongated lens) and allowing the image of distant objects to
be focused on the retina, as light rays from distant objects tend to be parallel. Light rays
are not greatly refracted when the lens is elongated, or slightly convex.
For near vision the curvature of the lens must be increased; a thicker lens has
greater refractive power and a shorter focal length. The ciliary muscles thus contract,
causing the suspensory ligaments to slacken. As a result, the lens becomes rounder (its
curvature increases), known as a highly convex lens, refracting the light to a greater
degree and allowing a focused image to fall on the retina.
Therefore, the refractive power of the lens changes from low (flatter lens) when at
rest, to high (rounder lens) at maximum accommodation.
 Explain how the production of two different images of a view can result in depth
perception.
When the eyes face forward, each eye sees an image of an object in the light path.
The two images are fused into one image in the cerebral cortex of the brain (called
fusion).
Depth perception is the sense of depth that occurs when objects are viewed with
binocular vision, dependent on the fact that a person has stereoscopic vision – that is,
they view the world in three dimensions. The person’s eyes are separated and thus have
slightly different views of objects located different distances away. When an object is a
slightly different distance from each eye, it is imaged by each eye at a different distance
from each fovea. This gives the perception of depth as this image is fused and seen to be
a different distance from the eye to another object that is closer to the eye. The two
objects are focused in different places on the retina and thus are seen as two images in
their respective positions so there is depth to the picture that is perceived.
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 Distinguish between myopia and hyperopia and outline how technologies can be used
to correct these conditions.
The eyes vary in shape and size from person to person, and these are often
hereditary. If the cornea or lens is not the right shape, or the eyeball is too elongated or
too round, the ability of the eye to refract light and focus it accurately onto the retina is
affected. If light is not accurately transmitted it can result in the weakening of clarity of
sight. Difficulties in seeing are called visual defects and include myopia (shortsightedness) and hyperopia (long-sightedness). They are not usually due to disease but
as a result of how the body grows.
Myopia is when a person can see near objects clearly but distant objects appear
blurred. Light from distant objects is brought into focus at a point in front of the retina
surface as a result of an elongated eyeball. Myopia can be corrected with concave lenses
in spectacles or contact lenses. The concave lens diverge the light before it reaches the
eyes so that the objects in the light path are brought into focus on the retina.
Hyperopia results from a short eyeball or poor accommodation ability in the lens.
It is the condition in which a person can see distant objects clearly but closer objects
appear blurred. Close objects are focused behind the retina and thus are not clear.
Hyperopia can be corrected with spectacles or contact lenses with convergent lenses, so
the light is converged more strongly for close vision.
Other technologies to correct these visual defects include:
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Radial keratectomy: Fine surgical instruments shave small amounts off the
corneal surface, thus refractive power is altered
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Photo-refractive keratectomy: involves the removal of the epithelium (outer
membrane) and the surface of the cornea. The laser is used to shape the
uppermost surface of the cornea.
-
Laser surgery: lasers are used to shave the corneal surface, thus refractive power
is altered.
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 Process and analyse information from secondary sources to describe cataracts and the
technology that can be used to prevent blindness from cataracts and discuss the
implications of this technology for society.
A cataract is any clouding or opacity of the crystalline lens of the eye. They
develop slowly and are more common in older people as they may be caused by general
wear and tear as well as UV light exposure, metabolic disorders and smoking.
At present, the only effective treatment for cataracts is surgery, involving the
removal of clouded lens or parts of it. The lens is then either replaced with artificial lens
or sight is corrected with eyeglasses or contact lenses.
There are different types of cataract surgery:
 Phacoemulsification: Removes the cataract but leaves most of the lens capsule
in place. A small incision (3mm) is made where the cornea and conjunctiva meet and a
thin probe is inserted, which transmits ultrasound waves to break up the cataract and
suction out the fragments. The lens capsule remains in place to provide support for lens
implants.
 Extracapsular Cataract Extraction: Used when the cataract has advanced to
a stage where phacoemulsification cannot break up the clouded lens. A larger incision
(10mm) is required where the cornea and sclera meet. The nucleus of the lens capsule is
removed in one piece and the soft lens cortex is vacuumed out, leaving the capsule in
place. A clear artificial lens, called an intraocular lens (IOL), is then implanted into the
empty lens capsule.
 Intracapsular Cataract Extraction: Involves the removal of the entire
cataract and surrounding capsule. An incision is made in the upper part of the eye and the
cornea is folded back. A freezing probe freezes the lens and capsule to make extraction
easier and to minimise bleeding during the surgery.
This technology is one of the greatest successes in medicine and surgery, as the
removal of cataracts was previously very painful and required a long recovery period.
Advancements in treatment have eliminated sutures, anaesthetic, and injections, thus
surgery is safer, quicker and is easier to recover from. Modern surgery is also 90%
successful in restoring vision.
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 Perform a first-hand investigation to model the process of accommodation by passing
rays of light through convex lenses of different focal lengths.
Normal Sight:
Myopia:
The focal length is too short and the focus needs to be moved.
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4) The light signal reaching the retina is transformed into an electrical
impulse.
 Identify photoreceptor cells as those containing light sensitive pigments and explain
that these cells convert light images into electrochemical signals that the brain can
interpret.
The innermost coat of the eyeball, the retina, is a thin sheet of cells about one
tenth of a millimetre thick. It consists of several layers of nerve cells, one of which is the
layer of visual receptors – the rods and cones. Of all nerve cells in the retina, only the
rods and cones respond directly to light, hence the name photoreceptors.
The rods and cones are the last layer of cells in the retina that light reaches. The
photoreceptors generate impulses which travel along the various neurone layers of the
retina to the optic nerve, which carries signals to the brain.
There are five main layers of nerve cells (neurones) that are diretly involved in the
transmission of impulses in the retina:
 Photoreceptor Cell Layer: the rods and cones that, when stimulated by light,
perform 3 main functions – 1) absorb light energy (involving visual pigments)
2) convert light energy into electrochemical energy,
generating a nerve impulse
3) transmit the impulse towards the bipolar layer.
 Horizontal Cell Layer: occurs at the junction between photoreceptors and
bipolar cells. They connect one group of rod and cone cells with another and then link
them to bipolar cells.
 Bipolar Cell Layer: these sensory neurones receive electrochemical signals
from the rods and cones and transmit the signal to the next layer.
 Amacrine Cell Layer: occurs at the junction between bipolar and ganglion
cells.
 Ganglion Cell Layer: these neurones receive electrochemical signals from the
bipolar cells. The distal end of ganglion cells is extended into long processes that go on to
form the fibres of the optic nerve. These neurones are responsible for carrying signals
from the retina to the brain.
Studies suggest that horizontal and amacrine cells are involved in processing, or
“summarising” incoming visual information.
Most of the interpretation of visual stimuli occurs in the brain, based on variables
such as:
strength of light
depth perception
no. of rods/cones stimulated
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 Describe the differences in distribution, structure and function of the photoreceptor
cells in the human eye.
Both rods and cones are elongated cells that contain an outer segment (closer to
the choroid layer) joined to an inner segment that leads to the conducting part of the cell.
The conducting part of the cell comprises a cell body containing the nucleus and an
extension (or process) called the foot. This process conducts impulses to the next layer of
neutrones in the retina.
Rods and cones contain visual pigments – chemical substances that absorb light
energy. These pigments are stacked in layers of flat membranes in the outer segment of
each photoreceptor.
Rhodopsin is the only pigment present in rods, thus rods can only detect black and
white light. Cones contain iodopsins, of which there are 3 types, each sensitive to
different wavelengths, and thus cones are responsible for colour vision. The role of visual
pigments is to absorb light energy, which the rod or cone cell then converts to an
electrochemical signal the brain can interpret.
Rods are evenly distributed across most of the retina, but are absent from the
fovea. As a result, rods are responsible for most peripheral vision, including the detection
of movement. They are extremely sensitive to light, responding best to low light
intensities. They are used for night vision and to detect light and shadow contrasts.
Cones are distributed in groups throughout the retina, mostly being concentrated
in the macula (yellow spot), an area of the retina that gives the central 10° of vision. The
fovea is a small pit in the middle of the macula that contains densely packed cones only.
They are less sensitive to light than rods, functioning best in high intensity light, giving
daytime vision.
 Outline the role of rhodopsin in rods.
Rhodopsins are light-sensitive pigments, which consist of two molecules bonded
together: opsin and retinal. When light enters a rod cell, it splits rhodopsin molecules
into its two components. This reaction results in an impulse in the neurone attached to
the rod or cone. The two products slowly recombine, ready to be split again by more
light. This is known as the visual cycle.
The main function of the photochemical rhodopsin is to absorb light in order to
set off a series of biochemical steps to carry a signal to the brain.
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 Identify that there are three types of cones, each containing a separate pigment
sensitive to either blue, red or green light.
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 approx 455nm
 The medium wavelengths of green light, peak sensitivity at approx 530nm
 The long wavelengths or red light, peak sensitivity being at approx 625nm
‘Red’ cones are actually more sensitive to yellow light (560-565nm) than to red
light, but they respond to red light before any of the others do, therefore behaving as red
receptors.
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.
 Explain that colour blindness in humans results from the lack of one or more of the
colour-sensitive pigments in the cones.
Because cones detect colour, any defect or damage to the cones will affect the
ability or 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 manner and is said to be either colour deficient or colour blind,
depending on how the mutation affects the pigment.
In humans, the genes coding for red and green pigments are located on the X
chromosome while the gene for blue pigment is found on Chromosome Seven (not a sex
chromosome, thus it is extremely rare).
A person that is deemed to be ‘colour blind’ is not truly colour blind but is usually
able to see only two of the three primary colours of light. As they are unable to detect one
of the colours that normal trichromats can, they perceive colour differently and interpret
all colours based on combinations of the two primary colours that they are able to see.
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 Process and analyse information from secondary sources to compare and describe the
nature and functioning of photoreceptor cells in mammals, insects and in one other
animal.
‘Eyes’ in animals range from really simple structures to extremely complex ones.
Simple eyes are made up of single photoreceptors cells whose function is limited to
distinguish light from dark. Complex eyes form a refraction and focusing system
involving lenses, specialised areas of acuity, and receptors that can distinguish between a
variety of colours.
Mammals, including humans, have evolved complex single-lens eyes. The retina
of complex eyes contains rods and cones, which contain the visual pigments that absorb
light. This initiates changes in the transmission of neurotransmitters that pass messages
across synapses. These changes pass via bipolar cells to ganglion cells, which transmit a
nerve impulse via the optic nerve to the brain.
Depending on the photoreceptors which are found within the eye, the ability to
detect colour may vary. For example, humans have three types of cones and are able to
detect three types of colour: blue, red and green. However, dogs have only two types of
cones, lacking the red photoreceptor, and therefore are unable to detect red-green light.
Another type of eye is the compound eye, found in insects. A compound eye
contains thousands of light-detecting units called ommatidia. Each ommatidium has its
own lens, which focuses light onto light-absorbing pigments. Altered pigments initiate a
nerve impulse that is transmitted to nerve fibres (axons) which are continuous with the
receptor cells.
Each ommatidium registers visions from a different part of the environment,
resulting in an image that is a pattern of dots. Visual pigments can return to their original
state very quickly, meaning they can absorb more light at a faster rate.
The bee, for example, is able to detect three colours: blue, green and ultraviolet
light. It cannot see red light.
One of the simplest light receptor arrangements is in the planarian worm (or the
flat worm). The structure is called an eye cup, which holds cells containing
photoreceptors. When these photoreceptors are stimulated by light, they alter so that a
nerve impulse is sent to the brain. There are two eye cups, thus when the brain registers
light intensity and direction (it cannot form an image) the animal moves around and away
from the light source, towards and area of low light intensity.
The flat worm cannot detect any colour, only directional information.
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 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.
Colour plays an extremely important role in communication for many animals,
including humans. Three forms of colour communication include:
A form of passing on information – Colours are commonly used in species as a
form of information, assisting other animals (both the same and different species) to
understand what is being expressed. Animals which use this form of communication
include:
 Humans: for colour-coding objects, and types of information such as targets
and dangerous objects.
 Blue-ringed octopus: alters its colour when readying itself for an attack, and
also to warn its prey.
 Food recognition: used by many animals to determine food supplies,
particularly birds and insects, who use the colour of flowers to identify pollen levels.
Courtship and mating – Colours are often used by many species to signal when
they are ready for mating, as well as in the attraction of a mate. Examples include:
 Male satin bowerbird: constructs a nest of grass and twigs, decorated with
flowers and shiny objects, particularly blue objects. When a female is attracted to the nest,
the male completes the mating ritual with a dance.
 Male frigate bird: puffs up his red neck pouch in an attempt to attract females
 Male angler fish: are brightly coloured to attract females.
Defence mechanism – Many creatures use colour as some form of defence
mechanism. Examples include:
 Camouflage: involves an animal becoming almost indistinguishable from their
surroundings, such as the chameleon (which has the ability to alter its colour) and the
peppered moth (which has evolved to become almost invisible in the London smog).
 Warning mechanisms: involves colours being displayed when an animals
feels threatened. An example is the peacock which not only uses its vibrant tail to attract
a mate, but also to signal when it feels threatened, warning other peacocks.
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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.
Humans 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.
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5) Sound is also a very important communication medium for humans
and other animals.
 Explain why sound is a useful and versatile form of communication.
Sound bends around objects and travels around corners. It can travel through
substances, solids, liquids and gases. Whatever the habitat, an animals is always
surrounded by a sound-transmitting medium.
Sound enables animals to communicate without being in visual or direct contact.
When visual, tactile and olfactory senses are impaired or absent, sound can be used as the
primary method of communication. A variety of sounds may be produced by varying the
pitch, loudness and tone. A complete message can be conveyed quickly. Sound,
particularly low-frequency sounds, will also travel long distances.
Toothed whales and bats use a form of sound communication called echolocation,
whereby the animal emits sounds and listens for the echo to come back to them. This type
of SONAR (Sound Navigation Ranging) works well even in complete darkness. By this
process, killer whales are able to judge distance, direction, size, shape and speed of
objects in water.
 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 originates when something vibrates rapidly enough to organise the
movement of molecules, so as to send a compression wave through a medium. The wave
can only travel through media which contain particles that can be compressed
(compression) and spread (rarefaction). The particles move backwards and forwards in
the same direction as the flow of energy. It is energy that is transferred, not molecules.
The frequency of the vibration of the medium molecules is the same as the
frequency of the vibrating object.
The frequency of vibrations is the number of waves which pass a given point in
one second, expressed in cycles per second (one cycle being called a hertz, Hz). Lowfrequency sounds have long wavelengths while high-frequency sounds have short
wavelengths.
The amplitude of a sound wave is the maximum distance that a particle moves
from its original position. The amplitude determines the volume of a sound.
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 Outline the structure of the human larynx and the associated structures that assist the
production of sound.
The larynx, or voice box, lies directly below the tongue and soft palate. Inside the
larynx are the vocal cords, which consist of muscles that can adjust pitch by altering their
position and tension.
When air passes over the vocal cords in the larynx, they produce sounds that can
be altered by the tongue, as well as with the hard and soft palate, teeth, and lips.
Diaphragm action pushes air from the lungs through the vocal folds, producing a
periodic train of air pulses. This pulse train is shaped by the resonances of the vocal tract.
The basic resonances, called vocal formants, can be changed by the action of the
articulators to produce distinguishable voice sounds.
Together, the larynx, tongue, and hard and soft palate make speech possible.
 Perform a first-hand investigation to gather data to identify the relationship between
wavelength, frequency, and pitch of a sound.
Equipment:
Method:
 Cathode Ray Oscilloscope (CRO)
 Audio Oscilloscope
 Audio oscilloscope produces sounds of different frequencies (pitch).
The frequency is measured in hertz.
 The CRO displays the sound waves on a screen. The wavelength can be
measured on the screen.
Results:
Frequency (Hz)
5
50
500
5 000
50 000
Pitch
No sound heard
Low sound
Medium sound
High sound
No sound heard
Wavelength (cm)
1 400
140
14
1.4
0.14
20
Conclusion: The lower the frequency, the longer the wavelength and the lower the
pitch of sound. The higher the frequency, the shorter the wavelength and a high pitch
sound.
 Gather and process information to outline and compare some of the structures used by
animals other than humans to produce sound.
Insects:
 Orthopterans (meaning ‘straight wings’) include grasshoppers, locusts
and crickets. Usually it is only the males that produce sound in order to attract females.
They do this by rubbing parts of their body together:
 Grasshoppers and locusts scrape a row of pegs on their back legs along
the hard edges of their front legs.
 Crickets produce sounds by lifting the wing covers to 45° and rubbing
the front of one wing cover (plectrum) over the rough area of the other wing (file). This
is called stridulation.
 Male cicadas have a pair of ribbed membranes called tymbals at the
base of their abdomen. Muscles attached to the tymbals contract, causing them to buckle
and produce a pulse of sound.
Fish:
 When catfish are alarmed or travelling in a shoal, they vibrate a bone
against their swim bladder, producing a noise similar to a giant aerator bubbler on a fish
tank.
Birds:
 A bird’s sound producing organ is called the syrinx, situated at the base
of the trachea where it splits into the two bronchi. Elastic membranes of connective tissue
inside the syrinx open and close as the bird exhales. The pressure of the air entering the
syrinx, the size of the syrinx, and the elasticity of the folds determine how the sound is
produced.
 Some birds are mute, for example storks, pelicans and vultures.
Mammals:
 The dolphin’s larynx does not possess vocal cords, and current research
suggests that all of the clicks, grunts, squeaks and whistles are produced in the tissue
complex of the nasal region. Sound results from movements of air in the trachea and
nasal sacs, as well as the release of air from the blowhole.
 The eastern horseshoe bat emits high-pitched echolocation calls through
its nose and appears to use a nose leaf, a horseshoe-shaped fleshy area around its nose, to
direct the sound.
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6) Animals that produce vibrations also have organs to detect vibrations.
● Outline and compare the detection of vibrations by insects, fish and mammals.
INSECTS: The tactile bristles on an insect’s exoskeleton and on its antennae
respond to low frequency vibrations, though many insects possess more specialised
structures for hearing.
Orthopterans (such as crickets) have a tympanum or ear on each leg just below
the knee. The tympanum is a cavity containing no fluid, enclosed by an eardrum on the
outer side and a pressure release valve on the other. Nerve fibres are connected to the
eardrum and pick up vibrations directly. Female crickets are deaf to some frequencies and
sometimes rely on smells given off by males.
Cicadas possess a pair of large tympana connected to an auditory organ at the
base of their abdomen. When a male cicada sings (as females don’t), he crinkles his
tympana to prevent deafening himself.
FISH: The hearing abilities of fish vary between species. All fish have a lateral
line, a pair of sensory canals, which run the length of each side of the animal. Pressure
waves in the surrounding ocean distort the sensory cells in the canals, sending a message
to the nerves.
Some fish actually perceive sound waves by possessing an inner ear containing an
otolith (ear stone) which is lined with hair cells. Auditory nerves detect the differences in
vibrations between the hair cells and the otolith and send a message to the brain.
Fish also have an air-filled swim bladder, located in the abdomen, which vibrates
in response to sound or vibrations.
MAMMALS: Killer whales have an acute sense of hearing. Sound is received by
the lower jawbone, which contains a fat-filled cavity extending back to the auditory
bulla. Sound waves are received and conducted through the lower jaw, middle ear, inner
ear and the auditory nerve to the auditory cortex of the brain.
Dolphins close their ear canals when diving. They detect vibrations through
special organs in the head and some low frequency sounds through the stomach.
Structures used to
detect vibrations
Receptor cells
Insects
Tympanic
membranes, sensory
hairs
Mechanoreceptor
cells
Fish
Lateral line, inner
ear, swim bladder
Mammals
Cochlea
Hair cells in the
inner ear,
neuromasts in
lateral line
Hair cells in Organ
of Corti
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● Describe the anatomy and function of the human ear, including: pinna, tympanic
membrane, ear ossicles, oval window, round window, cochlea, organ of Corti, and the
auditory nerve.
Structure
Pinna
Anatomy
Large, fleshy external part of the
ear
The eardrum – a membrane that
stretches across the ear canal
Function
Collects sounds and
channels it to the ear
Tympanic membrane
Vibrates when sound waves
reach it and transfers
mechanical energy into the
middle ear.
Ear ossicles
Three tiny bones: hammer, stirrup Amplify the vibrations from
and anvil
the tympanic membrane
Oval window
Region that links the ossicles of the Picks up the vibrations from
middle ear to the cochlea in the
the ossicles and passes them
inner ear.
on to the fluid in the
cochlea
Round window
Membrane between cochlea and
Bulges outwards to allow
middle ear
pressure differences in the
cochlea
Cochlea
Circular chamber filled with fluid Changes mechanical energy
into electrochemical energy
Organ of Corti
A structure within the cochlea
Location of the hair cells
that transfer vibrations into
electromagnetic signals
Auditory nerve
The nerve that travels from the ear
Transmits electrochemical
to the brain
signals to the brain.
Eustachian tube
Connects the middle ear with the
As air can pass through the
throat. It is usually kept closed but
opening, the pressure
opens when we swallow or yawn. between the middle ear and
the atmosphere can be
equalised.
23
● Outline the role of the Eustachian tube.
The Eustachian tube connects the middle ear with the throat. Usually this opening
is kept closed, but it opens when we swallow or yawn.
By permitting air to leave or enter the middle ear, the tube equalises air pressure
on either side of the eardrum.
● Outline the path of a sound wave through the external, middle and inner ear and
identify the energy transformations that occur.
24
● Describe the relationship between the distribution of hair cells in the Organ of Corti
and the detection of sounds of different frequencies.

Passing along the length of the cochlea is a ribbon-like structure, the organ of
Corti. This has three main components: the basilar membrane, hair cells and the
tectorial membrane.

The basilar membrane is composed of transverse fibres of varying lengths.
Vibrations received at the oval window are transmitted through the fluids of the
cochlea causing the transverse fibres of the membrane to vibrate at certain places
according to the frequency.

High frequency sounds cause the short fibres of the front part of the membrane to
vibrate and low frequency sounds stimulate the longer fibres towards the far end.

As the basilar membrane vibrates, the hairs of the hair cells are pushed against the
tectorial membrane. This causes the hair cells to send an electrochemical impulse
along the auditory nerve to the brain.

The region of the basilar membrane vibrating the most at any instant sends the
most impulses along the auditory nerve.

The actual perception of pitch depends on the mapping of the brain. Nerves from
particular parts of the organ of Corti stimulate specific auditory regions of the
cerebral cortex of the brain. When a particular part of the cortex is stimulated, we
perceive a sound of a particular pitch.
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● Outline the role of the sound shadow cast by the head in the location of sound.
-
-
-
Many animals can use their two ears to judge the position from which a sound
comes. They can move each ear independently until each ear receives the
maximum sound.
Humans cannot move their ears, but can locate the direction of a sound
nevertheless. This is because the sound is heard more loudly by the ear nearest
to it and also fractionally earlier.
The pinna is mostly skin and cartilage with some muscles attached to the back,
which is what allows some animals to "wiggle" their ears.
The brain uses reflections from the twists and folds of the pinna to determine
the direction of sounds. Sounds coming from the front and sides become
enhanced as they are directed into the auditory canal while sounds from
behind are reduced. This helps an animal to hear what they are looking at
while reducing some of the distracting background noise.
When sound waves are coming from directly in front, behind or above the head,
both ears receive the sound waves equally and the sound will be the same for both ears.
When sound is coming from one side, the receptors in the ear closest to the sound will be
stimulated slightly earlier and also more intensely (because the sound energy is less
dissipated). The brain then locates the sound as coming from one side of the body. The
head is said to cast a sonic shadow on the sound coming into an ear from the opposite
side of the body.
● Process information 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.
The range of frequencies that can be detected by humans is 20-23,000 Hz.
Mammal
Human
Dog
Whale
Mouse
Lowest Frequency
Detected (Hz)
20
67
1 000
1 000
Highest Frequency
Detected (Hz)
23 000
45 000
123 000
91 000
The sound frequencies differ amongst these animals due to the different sounds
that need to be recognised in order for these organisms to survive and communicate in
their respective environments.
Whales and mice make high-pitched noises to communicate to one another, and
hence need to be able to detect high frequency noises. The dog has more sensitive
hearing than a human as dogs, in the past, required acute hearing in order to capture prey
and avoid predators.
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● Process information to evaluate a hearing aid and cochlea implant in terms of: the
position and type of energy transfer occurring, conditions under which the technology
will assist hearing, and the 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. The person may also have to use the
implant in conjunction with lip reading.
Hearing Aid
Cochlea Implant
Position and type of
energy transfer occurring
Sound  Electrical 
Sound
Sound  Electrical 
sound?
Conditions under which
technology assists hearing
Sensorineural hearing loss
Damaged or non-working
parts of inner ear
Will not restore normal
hearing or eliminate
background noise
Doesn’t restore hearing,
very expensive (minimum
$US45,000)
Limitations
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7) Signals from the eye and ear are transmitted as electrochemical
changes in the membranes of the optic and auditory nerves.
● Identify that a nerve is a bundle of neuronal fibres.
A nerve is a bundle of axons or neuronal fibres bound together like wires in a
cable. A neuron is a nerve cell, typically consisting of:
 A cell body
 Dendrites (a branched protoplasmic extension of a nerve cell that conducts
impulses from adjacent cells inward toward the cell body.)
 An axon (the long, hairlike extension of a nerve cell that carries a message to a
nearby nerve cell)
 An insulating myelin sheath (that covers the axon and helps to increase the
speed by which information travels along the nerve).
The direction of a nerve impulse is: dendrites  cell body  nerve fibre  axons.
● Identify neurones as nerve cells that are the transmitters of signals by electrochemical
changes in their membranes.
A neurone is a nerve cell that transmits a signal or impulse from one part of the
body to another. Neurons send messages electrochemically, meaning that chemicals
cause an electrical signal.
A nerve impulse can be detected as a change in voltage. The impulse is transmitted as
a wave of electrical changes that travel along the cell membrane of the neurone.
The electrical changes are caused as sodium ions move into the neurone, thus the signal is
described as an electrochemical impulse.
Action potentials are caused by an exchange of ions across the neuron membrane.
A stimulus first causes sodium channels to open. Because there are many more sodium
ions on the outside, and the inside of the neuron is negative relative to the outside,
sodium ions rush into the neuron. Sodium has a positive charge, so the neuron becomes
more positive and becomes depolarised.
It takes longer for potassium channels to open. When they do open, potassium
rushes out of the cell, reversing the depolarisation. Also at about this time, sodium
channels start to close. This causes the action potential to go back toward -70 mV
(repolarisation), actually goes past -70 mV (hyperpolarisation) because the potassium
channels stay open a bit too long. Gradually, the ion concentrations go back to resting
levels and the cell returns to -70 mV.
After the signal has been transmitted, potassium ions move to the outside of the
cell to restore the original charge of the neurone.
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● Define the term ‘threshold’ and explain why not all stimuli generate an action potential.
Threshold is the amount of positive charge in membrane potential which is
required before an action potential is produced.
The point of excitation that causes the neurone to fire is called the threshold of
reaction.
Each stimulus produces either a full action potential or none at all (known as “All
or Nothing”). Each action potential is a separate event; therefore a cell cannot produce
another action potential until the previous one is complete.
● Identify those areas of the cerebrum involved in the perception and interpretation of
light and sound.
The functional areas of the cerebrum, and the regions involved in speech, sight
and sound perception:
The Cerebrum: is divided into two hemispheres, the left and right. Each
hemisphere receives impulses from and exerts control over the opposite side of the body.
Each hemisphere is divided into five different lobes:
 Frontal
 Insular
 Occipital  Parietal
 Temporal
The cerebrum’s surface is drawn up into folds called convolutions, tripling the
brain’s surface area. Most activity occurs on the outside surface and fit into three general
categories:
 Motor (movement)
 Sensory (senses)
 Associative (this cortex accounts for about 95% of the cerebral cortex and is
the site of reasoning and logic)
Light: The optic nerves are the sensory nerves of vision. Optic nerves from each
of the eyes partly cross over to form the optic chiasma, providing each visual cortex with
the same image as viewed by both eyes (thought from a slightly different angle).
Impulses are received from the retina via the optic nerve.
Sound: The auditory nerves arise from the cochlea and vestibule apparatus
within the inner ear. The auditory cortex is found on the temporal nerve of each cerebral
hemisphere. Different sites on this cortex receive and interpret different sound
frequencies.
29
● Explain, using specific examples, the importance of correct interpretation of sensory
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 so
that the organism can react appropriately.
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.
● Perform a first-hand investigation using prepared stained slides to gather information
about the structure of neurones and nerves.
1) Set up a light microscope and a number of slides, e.g. spinal chord, neurone.
2) Observe neurones and nerve cells, drawing a diagram of each.
30
● 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.
● Present information to graphically represent a typical action potential.
When the depolarization reaches about -55 mV a neuron will fire an action
potential. This is the threshold. If the neuron does not reach this critical threshold level,
then no action potential will fire.
31