Biology – 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
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Stimuli are an environmental factor or factors (internal or external) that organisms can detect and
to which they respond, such as light, sound, temperature, pressure, pain and certain chemicals.
A receptor is a specialized cell that detects a stimulus found in the sensory organs. 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 i.e. each different type of receptors are responsible for detecting a certain type of stimulus
e.g. smell, taste, light, temperature and chemicals
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Explain that the response to a stimulus involves: stimulus, receptor, messenger, effector,
response
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Stimulus – a change/s in the environment
Receptors – detects the stimulus ( as stated above different receptors pick up different stimulus)
Messenger – the receptor changes the energy of the stimulus into energy that is used to start a
nerve impulse. The nerve impulse is the messenger ( can be a hormone as well)
Effector – is the organ that receives the message and carries out the response.
2. Visual communication involves the eye registering changes in the immediate
environment
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Describe the anatomy and function of the human eye, including the: – Conjunctiva
Cornea, Sclera, Choroid. Retina Iris, Lens, Aqueous and vitreous humour, Ciliary body,
Optic nerve
STRUCTURE/PART
Conjunctiva - a transparent membrane
Cornea – transparent front window, where light
enters the eyeball
Sclera – the white and tough outer layer of the eye.
Choroid - a sheet of blood vessels underneath the
sclera
Retina – a complex structure of photoreceptors
(rods and cones) at the back of the eye
Iris – the coloured part of the eye, it is a ring of
muscle with a hole in the middle (pupil)
Lens- behind the iris
Aqueous and Vitreous Humour – 2 pressurised
chambers filled with clear jelly
Ciliary Body- an extension of the choroid layer at
the front where it becomes thicker and has smooth
muscles embedded into it
Optic Nerve- contains millions of nerve fibres
ANATOMY & FUNCTION
Aids in protection and helps keep eyeball moist.
It’s the 1st part to focus the light waves.
Helps protects and helps maintain shape of the eye
Carries oxygen and nutrients to the eye and
removes c02 and waste and absorbs light to prevent
internal reflection or scattering
The photoreceptors allow us to see shapes,
movement and colour. Retinal nerves cells convert
incoming light to nerve impulses
Controls the amount of light entering the eye, in
dim light the iris relaxes and pupils dilate, in bright
light the iris tightens and the pupil contracts.
Focuses light on the photoreceptors ( light sensitive
cells) the lens is focused with a circulator and
muscular ring called the Ciliary body.
Gives the eye its shape
contains muscles; supports the lens and alters the
shape of the lens
consists of bundles of sensory neurons; transmits
impulses generated in the retina to the brain
Identify the limited range of wavelengths of the electromagnetic spectrum detected by
humans and compare this range with those of other vertebrates and invertebrates
The electromagnetic spectrum consists if wave varying in length, from less than a nanometre (gamma
rays) to over a km (radio wave) these waves include visible light, infra-red radiation and ultraviolet
radiation. Blue-green light (500 nm) is the most effective wavelengths for humans. Either side of this
wavelength in the red or ultraviolet areas are less effective in humans but are used by other organisms.
The human eye can detect visible light (380 nm to 750nm) and thermoreceptors in the skin detect infra
red radiation (heat), unlike humans though, insects such as bees can detect UV light and some snakes can
detect body heat. But many animals are unable to distinguish different colours
3. The clarity of the signal transferred can affect interpretation of the intended visual
communication
Identify the conditions under which refraction of light occurs
Light is a wave of motion and part of the electromagnetic spectrum, light travels in straight lines, but is
refracted when it moves from one medium to another. Refraction occurs when the wave changes speed
and direction. A ray of light moving into a denser medium is refracted towards the normal while a ray of
light moving into a less dense medium is refracted away from the normal.
Identify the cornea, aqueous humour, lens and vitreous humour as refractive media
When light enters the eye, it’s moving into a denser medium and so the light if refracted towards the
normal.
In the eye, refraction occurs when light passes from the air to the cornea, from the cornea to the aqueous
humor, from the aqueous humor to the lens and from the lens to the vitreous humor. Light spreading out
from one point on an object can therefore be focused on a particular point on the retina.
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 focusing of objects at different distances.
Accommodation is the ability of the lens to change shape and focus light from objects at a range of
distances. If the lens becomes more rounded (greater curvature) it refracts light to a greater extent and
close objects can be focused. If the lens becomes less rounded (less curvature) it refracts light less and
distant objects can be focused.
The Ciliary muscles are responsible for adjusting the shape of the lens. When they relax, the lens is less
rounded. When they contract, the lens becomes more rounded.
Compare the change in the refractive power of the lens from rest to maximum
accommodation
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When the eye is accommodated it focuses on close objects.
In the eye at rest (unaccommodated) the lens is flattened because it is subjected to tension by the
suspensory ligaments. The focal length of the lens is long and so distant objects are in focus.
When accommodation occurs the ring of ciliary muscles contract, the tension in the suspensory
ligaments is reduced and the lens bulges due to its natural elasticity. The refractive power of the
lens increases therefore shortening the focal length
The lens in the eye changes shape to focus the image from objects
At rest the lens in flattened and thin, Ciliary muscles relaxed and suspensory ligaments are taunt
The focus is in the distance and focal length long (refractive power low)
At maximum accommodation the lens becomes more rounded, Ciliary muscles contract and the
suspensory ligaments are relaxed
The focal length is shorter and close objects are in focus
Distinguish between myopia and hyperopia and outline how technologies can be
used to correct these conditions
Myopia – is also known as short sightedness, where objects in the distance appear to be
blurred, while those up close can be seen clearly. This occurs when the lens is too thick and
the curvature is too great or the eyeball is elongated causing the image to fall short, forming
in front of the retina instead of on it. The usual cause of myopia is that the eyeball is too long.
Some forms of myopia improve with age.
Hyperopia- is also known as long/far sightedness, where objects up close appear blurred and
distanced objects can be clearly seen it occurs if the lens is too thin and the curvature is too
slight or the eyeball is too short which causes the image to form behind the retina instead of
on it. The usual cause of hyperopia is that the eyeball is too short or that the lens gradually
hardens with age, reducing its power of accommodation.
With both these conditions, they can be both correct in a number of ways including:
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Glasses/spectacles
Contact lenses
Surgery
In myopia, concave lenses can be worn for distance viewing. These lenses cause parallel rays
to diverge slightly before they enter the eye so that the lens can focus them on the retina.
In hyperopia, convex lenses can be worn for viewing close objects. These lenses cause
parallel light rays to converge slightly before entering the eye so that the lens can then
converge the rays to a point on the retina.
Refractive surgery may also be used to treat both myopia and hyperopia. A thin flap of the cornea is cut
and folded back. A laser is used to reshape the cornea to a more suitable shape. The fold of skin is then
folded back into place.
Explain how the production of two different images of a view can result in depth
perception
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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.
Binocular vision occurs when both eyes are focused on the same visual field. The brain then
compares these 2 images, which are slightly different and the final interpretation gives distance,
depth, height and width of vision or stereoscopic vision.
Most predators have binocular vision so they can see more sharply, therefore increases their
chances of catching prey.
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
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Photoreceptor cells are those containing light sensitive pigments, which have the ability to
convert light images into electrochemical signals the brain can interpret. An electrochemical
signal consists of a wave of sodium and potassium ions which move across the cell membrane of
the neurone.
There are 2 types of photoreceptors: rods and cones, both contain photosensitive chemical
substances that undergo reactions when they absorb light energy.
Describe the differences in distribution, structure and function of the photoreceptor cells in
the human eye
Distribution – rods are found near the periphery of the retina while cones are in the more central
locations
Structure – shapes of the photoreceptor cells differs as naming implies – rods and cones
Function – rods detect shape and movement in dim light, cones detect colour and work in bright light for
fine detail.
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Rods are long rod-shaped cells, which are sensitive to low levels of light but are unable to
discriminate between colours. The image formed by the brain using information form rod cells
lacks detail. Rods are linked in groups to single neurones. Rods are found mainly around the
periphery of the retina and there are none at the fovea. They are more suitable for night vision.
When the pupil is dilated more rods will be exposed. Rods also detect movement very well.
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Cones are conical cells which contain a pigment which is only sensitive to high intensities of light
but exist in three different forms so that these cells can distinguish between colours. They have
extensive nerve connections with the brain and produce a more detailed image. The number of
cones increases towards the centre of the back of the retina. At the centre of the retina is a small
area, known as the fovea, which has densely packed cones only. The fovea corresponds to the
region of maximum visual acuity.
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Cones are more suitable for day vision. In bright light, when the pupil is contracted, it will be
mainly the cones that are activated. As cones require light of high intensity to stimulate them, it
follows that we cannot see colours in poor light. They are also sensitive to 3 colours – red, blue
and green long wavelength cones detect red, middle detects green and short detects blue.
Visual acuity is dependent on the number of cone cells per unit area. The more there are the
greater the number of impulses which will pass to the brain and the more detailed the image.
Outline the role of rhodopsins in rods
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Rhodopsin is a type of light sensitive pigment found in rods; they are synthesized from vitamin
A, and are sensitive to blue-green light. Rhodopsin is highly light sensitive; Therefore Rods are
specialized for night vision. When Rhodopsin absorbs a sufficient amount of light energy it splits
into 2 parts and changes shape and begins a series of chemical reactions. These reaction produce
generator potential, which starts a nervous impulse this reaction of light 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.
identify that there are three types of cones, each containing a separate pigment sensitive to
either blue, red or green light
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As cones require light of high intensity to stimulate them, it follows that we cannot see colours in
poor light. They are also sensitive to 3 colours – red, blue and green long wavelength cones detect
red, middle detects green and short detects blue. Each type of cone contains a different light
sensitive pigment (erythrolabe in red cones, chlorolabe in green cones and cyanolabe in blue
cones)
The cones contain three different photopigments. The trichromatic theory of colour vision suggests that
each is sensitive to a different range of wavelengths, corresponding to the three primary colours red, blue
and green. The sensitivity of these photopigments is broad enough to allow them to cover the full
spectrum of visible light. Each pigment is thought to be located in different cones, and different colours
are perceived in the brain from the sensory input from combinations of the three cone types. Thus the
brain builds up a colour picture according to the number of impulses received from the three types of
cones
Explain that colour blindness in human results from the lack of one or more of the coloursensitive pigments in the cones
As human eyes have 3 colour sensitive pigments, Colour blindness occurs in humans as a result from
malfunctioning or absence of one or more colour sensitive pigments found in the cones which can cause a
number of problems in identifying various colours and shades. Complete inability to distinguish colours is
rare. The most common form of colour blindness is the failure to discriminate between red and green or
red-green colour blindness. Colour blindness is due to a recessive gene on the X chromosome.
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
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Many animals use sound to communicate with each other. Sound is a versatile form of
communication because animals can vary the nature of the sounds they produce. For example,
animals may produce sounds of varying pitch and loudness to communicate different information.
As it travels easily and quickly over short distances in the air and it is versatile as a range of
sounds in pitch and loudness can give different meanings to different sounds or similar sounds.
Sound is also useful both day and night. It travels over long distances and can go around corners.
The sender does not have to be visible to the receiver.
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
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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.
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. It is the cavity in the throat that
holds the vocal cords. The vocal cord consists of 2 membranes running from back to front, connected
with cartilage, which a removed inwards and outwards by muscle. The vocal cords allow humans to make
sounds that are modified by the tongue, lips, nose and mouth. Inside the larynx are the vocal cords, which
consist of muscles which can adjust pitch by altering their position and tension. Together, the larynx,
tongue and hard and soft palate make speech possible. When air passes over the vocal cords in the larynx,
they produce sounds that can be altered by the tongue, together with the hard and soft palate, the teeth and
the lips. In the larynx, when breath passes through them, the opening between the two membranes passes
through of the vocal cords opens and closes rapidly so that the vibrating membranes produce sounds.
Higher pitched voices open and close more frequently- at a higher frequency. The tightness of the vocal
cords also influence pitch
6. Animals that produce vibrations also have organs to detect vibrations
Outline and compare the detection of vibrations by insects, fish and mammals
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Many insects have a pair of membranes, called the tympanic membranes, located on the abdomen
or legs. The tympanic membranes act in a similar way to eardrums by vibrating when sound
waves reach them. Sensory cells called mechanoreceptor cells detect the vibrations and send a
message to the brain.
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Many insects also have hairs on the exterior of the body which vibrate in response to sound
waves of specific frequencies, depending on the stiffness and length of the hairs. The hairs are
often tuned to frequencies of sounds produced by the same or other species. These hairs may be
used to detect mates or predators.
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Fish do not have external ears, but have internal ears located near the brain. There is no eardrum
or cochlea, but the semicircular canals are present. Vibrations of water caused by sound waves
are conducted through the skeleton of the head to the inner ear. Hair cells in the semicircular
canals vibrate in response and send a message to the brain.
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Fish also detect low
frequency vibrations
with the lateral line
system. This consists
of a long fluid-filled
canal which runs just
under the skin down
each side of the fish.
There are pores at
frequent intervals
which connect the
canals to the exterior.
Vibrations in the surrounding water are transmitted to the fluid in the canals, and are detected by
groups of sensitive cells called neuromasts. These neuromasts have hairs which project into the
canal fluid and detect vibrations by a mechanism similar to that used in the cochlea of the
mammalian ear. Messages from the neuromasts are sent to the brain.
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Fish also have an air-filled swim bladder, located in the abdomen, which vibrates in response to
sound or vibrations. Some fish have a series of bones which conduct vibrations from the swim
bladder to the inner ear.
Characteristic
Similarity- hairs
Insect
Long hairs on antennae
Difference –
complexity of hearing
organ
Simple receptor cell at
base of antennae
Fish
Hairs of receptors cells
in lateral line vibrate
Receptor cells form
lateral line along side of
fish. Some fish also
have inner ear near
brain
Mammal
Hair of receptor cell in
organ of Corti vibrate
Receptor cells in
complex organ change
to sound wave to
mechanical vibration to
pressure waves
Describe the anatomy and function of the human ear, including: pinna, tympanic
membrane, ear ossicles, oval window, round window, cochlea, organ of Corti, auditory
nerve
Outline the role of the Eustachian tube
The Eustachian tube connects the middle ear to the pharynx (behind the mouth, in the throat). This tube is
usually closed but can be opened by yawning or swallowing. Its role is to equalize the pressure on both
sides of the ear drum.
Air can pass through this opening, thus equalising the pressure between the middle ear and the
atmosphere.
Outline the path of a sound wave through the external, middle and inner ear and identify
the energy transformations that occur
The sound waves collected by the pinna enters and travels down the ear canal to the tympanic membrane,
which converts the energy into mechanical energy when the tympanic membrane vibrates with the same
frequency as the sound. The ear ossicles of the middle ear transmit the mechanical movements to the oval
window, which in turn vibrates, causing pressure waves in the fluid in the cochlea.
Describe the relationship between the distribution of hair cells in the organ of Corti and the
detection of sounds of different frequencies
The organ of Corti contains sensory hair cells, which detect loudness by the amount of bending of the
hair, the larger the vibration in the fluid the more bending. Pitch is determined by the particular hair cells
stimulated and the region of the organ of Corti stimulated, high frequencies stimulate the region near the
oval window and low frequencies towards the apical end. Perception of pitch is determined by the brain
and how it interprets the signals.
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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.
Outline the role of the sound shadow cast by the head in the location of sound
Sound shadow or sonic shadow, occurs when the position of the head blocks the sound reaching the ear,
therefore one ear receives less sound than the other. As many animals use this to determine the direction
of sound using the difference in the loudness and time of arrive of the sound reaching each ear, the brain
interprets these differences to work out the location of the sound.
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
Neurones or nerve cells are the functional unit of the nervous system; they are specialised cells that
transmit signals from one location in the body to another by electrochemical changes in their membranes.
Therefore a nerve is a bundle of neuronal fibres
Identify neurones as nerve cells that are the transmitters of signals by electro-chemical
changes in their membranes
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A neurone is a nerve cell that transmits a signal or impulse from one part of the body to another.
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.
After the signal has been transmitted, potassium ions move to the outside of the cell to restore the
original charge of the neurone.
Define the term ‘threshold’ and explain why not all stimuli generate an action potential
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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.
A threshold is the minimum stimulus required to generate a response in a nerve cell.
Identify those areas of the cerebrum involved in the perception and interpretation of light
and sound
Explain, using specific examples, the importance of correct interpretation of sensory
signals by the brain for the coordination of animal behaviour
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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.
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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.
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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.
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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.
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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, is signs of damage to the brain. In people with these conditions, muscular
contractions are no longer coordinated by the brain.