What is communication, types of communication, Barriers in communication
Communication
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Transcript of Communication
Year 12 Biology Notes – 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
Communication is the transfer of information or messages from one organism to another.
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.
The cells of the nervous system are not all the same, some have the role of detecting
changes in the environment and converting information into electrochemical signals for
translation in the brain, these are called receptors.
Stimulus Type of receptor Organ
Light Photoreceptors Eye
Touch Mechanoreceptors Skin
Temperature change Thermoreceptors Skin, hypothalamus
Explain that the response to a stimulus involves:
- Stimulus
Stimulus that reflects changes in the environment
- Receptor
Receptor that detects the stimulus. Each type of sensor is responsible for detecting a
certain type of stimulus.
- Messenger
Messenger that involves receptors that change the energy of the stimulus into an
electrochemical signal that is used to start a nerve impulse. The nerve impulse is the
messenger that is sent via the sensory neuron to the central nervous system (CNS) via
the spinal cord.
- Effector
Simultaneously, while the message is transmitted to the brain the CNS sends a message
via the motor neuron to the effector organ.
Effector that is the organ that receives the message and carries out the response.
- Response
Response is carried out in reaction to the stimulus.
Identify data sources, gather, and process information from secondary sources to identify the
range of senses involved in communication
Sense Explanation
Sight (visual) - Detected by photoreceptors
- Sight is frequently the means by which animals obtain information
about their environment
- Used to measure distance, determine colour and recognise
potential threat
- Facial expression and posture in humans communicate aggression
or affection
Sound (auditory) - Mechanoreceptors respond to mechanical energy and can detect
pressure waves
- Communication by sound
- Many species cannot produce sound or detect a wide range of
sounds frequencies
- Used to attract mates and distress calls to alert others of dangers
Smell (olfactory) - Chemoreceptors detect chemicals
- Communication occurs via chemical signals
- Many animals rely on smell to find food, find a mate or as a means
of identification
Touch (tactile) - Mechanoreceptors for touch are abundant under the skin
- Sensory nerve endings in the skin respond to touch
- Used in avoiding obstacles, fighting, defence mechanisms,
friendship behaviour and courtship
Taste (gestation) - Chemoreceptors detect chemicals
- Many animals use taste if they have a poor sense of smell (these
two are closely related senses)
2. Visual communication involves the eye registering changes in immediate environment
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
The eye functions as a sense organ by detecting light stimuli from the environment and transforming
this information received into
nerve impulses that are carried to
the brain. Humans have two eyes
for binocular vision. Each eye
sees a different image of an
object in the light path. The two
images are fused into one image
in the brain, allowing the
perception of depth.
Associated with the eyeballs are
numerous parts that help
maintain adequate functioning of
the eye. The eyeball is essentially
surrounded by a coat, made up of
three layers of tissue: an inner,
middle and outer layer (see
diagram).
Posterior refers to the back part
of the eye
Anterior refers to the front part of the eye
The outer coat:
The conjunctiva is a thin, transparent membrane that protects the front
of the eye. The membrane helps keep the outer surface of the eyeball
moist.
The sclera is the outmost layer of the eye. It is composed of tough, non-
elastic tissue that protects the inner layers of the eye, and maintains the
shape of the eyeball. It is also the site of attachment for external muscles
of the eye, which enables the eyeball to move in the socket. Towards the back of the eye, the sclera
is opaque (forming the white part of the eye); towards the front, it becomes a transparent structure
called the cornea.
The cornea contains no blood vessels and is complete transparent, allowing light to pass through. Its
curvature helps bend/refract incoming light rays so they converge at the back of the eyeball.
The middle coat:
The choroid layer is located in the middle coat of the eyeball. Most of the blood vessels in the eye
are located in this layer. Posteriorly (towards back of the eye), the choroid layer is black and reduces
scattering and reflection of light within the eye. Anteriorly (towards front of the eye), the choroid
forms the ciliary body and lens. In front of this is the iris.
The ciliary body forms a ‘ring’ around the front of the eye, and contains the circularly arrange ciliary
muscles. The ciliary muscles attach to the lens by suspensory ligaments. The muscles and ligaments
are important in adjusting the curvature of the lens for near and far vision. The ciliary body also
secretes aqueous humour.
Aqueous humour is a transparent, watery liquid found in the anterior part of the eye between the
cornea and the lens. It provides nutrients for the lens and the cornea (both of which do not have
their own blood supply. It also helps refract light.
Vitreous humour is a clear, jelly-like material filling the remainder of the eyeball. It contains
dissolved nutrients, refracts light, and helps maintain shape of the eyeball.
The lens is a transparent structure made of cells enclosed in a membrane called the lens capsule.
The lens refracts light rays and directs them onto the retina to form a focused image. The lens is
highly elastic – allowing it to change shape (either rounder or flatter). This allows the eye to
accommodate for near and far vision.
The iris is the coloured part of the eye, situated behind the cornea and in front of the lens. It is
surrounded by aqueous humour. The iris is made up of connective tissue and smooth muscles, which
allow it to perform its main function – that is, controlling the size of the pupil. The pupil is an
opening in the iris through which light passes in order to reach the retina at the back of the eye.
The inner coat
The retina contains photoreceptor cells, nerves and blood vessels; the photoreceptor cells (cones-
which respond to colour, and rods – which do not respond to colour) respond to light before
transmitting the information towards the central nervous system.
The fovea is a particularly sensitive area (near the centre) of the retina that focuses images most
sharply. It contains densely packed cone cells, but no rod cells at all. The fovea is the part of the
retina where the greatest detail can be detected
The blind spot is an area of the retina corresponding to the exit point for the optic nerve. Because
there are no rod/cone cells, light cannot be detected in this area.
The optic nerve transmits visual signals from 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
Use available evidence to suggest reasons for the differences in range of electromagnetic radiation
detected by humans and other animals
The electromagnetic spectrum is a major stimulus that impacts on our sense. It is a range of energy
forms that all travel at the speed of light, and in waves. However, electromagnetic waves differ in
wavelength (distance between successive crests of a wave) and frequency (amount of waves passing
through a given point in one second).
Visible light (for humans) lies towards the middle of the electromagnetic spectrum with wavelengths
of 400-700nm. The human eye is limited to the detection of only the wavelengths that lie in this
range; all other forms of electromagnetic radiation cannot be detected by the naked eye.
Most living organisms have a visual range close to that of humans; however, some are very different.
For example:
Honeybees are able to detect wavelengths in the ultraviolet range (300-650 nm). Some
flowers have ultraviolet markings on them which the bees use to find pollen; to guide them
to the nectar of a plant.
Rattle snakes can detect infrared light (400-850 nm), in order to detect prey (heat is emitted
in the form of infrared waves)
Deep sea fish can only detect blue light (450-500 nm); little light penetrates to the depth at
which they live so they use bioluminescence (470 nm) to communicate
The sense receptors possessed by a particular population or species is typically suited to the
environment in which they live. This is because over time, the effectiveness of the organism’s
receptors inevitably impacts their ability to survive and reproduce. In this manner, selecting pressure
causes those with receptors most suited to their environment to survive. The way different
organisms’ senses adapt to their needs is clearly highlighted in the above examples.
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
Aim: To dissect a bull’s eye and relate structures to functions
Materials:
Bull’s eye
Dissecting equipment (sharp scalpel, dissecting scissors, forceps, probe)
Disposable rubber gloves
Dissecting tray
Newspaper
Safety:
Risk Controlling risk
Sharp scalpel/scissors could cut skin Great care must be taken when using scalpel/scissors. Use forceps to hold the eye whilst dissecting to minimise risk of cutting your own fingers.
Entry of infective microbes via any cuts in skin Wear rubber gloves when performing dissection
Method
1. Put on a pair of disposable gloves, collect and eye specimen and place on newspaper on top
of dissecting tray
2. Remove fatty tissue from around the eyeball with the scissors and scalpel
3. Examine the external features of the eye (optic nerve, sclera, cornea, conjunctiva, iris, pupil
etc.)
4. Cut a long around the eyeball parallel to the lens. The clear liquid that escapes is the
aqueous humour. Observe the pupil and iris at the front.
5. Remove the lens. The vitreous humour, which is denser and more jelly like than the aqueous
humour, can also be removed.
6. Clean the lens. Observe words on newspaper with the lens; try squeezing the lens and see
what happens.
7. Rinse the eyeball and examine the retina
8. Wrap the eye and eye parts in newspaper and dispose of them.
9. Place dissecting equipment in disinfectant, and dispose of dissecting gloves
3. The clarity of the signal transferred can affect interpretation of the intended visual
communication
Identify the conditions under which refraction of light occurs
The bending of light is called refraction. Refraction occurs when light travels from one medium to
another of a different density at an angle other than 90 degrees (perpendicular). This is because the
light travelling at differing speeds in the different mediums. If light travels to a more dense medium,
it bends towards the normal; if it enters a less dense medium, it bends away from the normal.
Identify the cornea, aqueous humour, lens and vitreous humour as refractive media
Light refraction occurs at each boundary
between the cornea, aqueous humour, lens and
vitreous humour due to their varying densities.
The refraction is essential to form a clear image
on the retina.
Refraction occurs when light passes from the air
into the denser material of the cornea. When
the light then passes into less dense aqueous
humour, it is refracted again. The same thing
occurs when the light passes through the denser
lens, and then finally through the vitreous
humour.
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 refers to the focusing of objects at different distances.
A convex lens is one that is thicker in the middle,
thinner on the outside. It causes light to converge. The
lenses in our eyes are convex.
A concave lens is one that is thinner in the middle,
thicker on the outside. It causes light to diverge.
Most of the refraction occurs when light passes
through the cornea; however fine focusing is achieved
through the lens. The lens is attached via suspensory
ligaments in the middle of a ring of muscle called
suspensory ligaments. The contraction or relaxation of the ciliary muscles in the ciliary body causes
the shape of the lens to change, and hence alters the focal length/distance.
If we wish to see a close object, the ciliary body contracts, the suspensory ligaments
become loose, and the lens becomes more rounded in shape.
If we wish to see a distant object, the ciliary body relaxes; the suspensory ligaments
become tighter and pull on the lens. The lens gets flatter in shape, giving a clear image of
the object.
This ability to make the lens just the right thickness in order to see objects at different distances is
called the power of accommodation.
Focusing is the result of accommodation. It is essential for an image to be focused to achieve clear
vision. In this way, accommodation allows organisms to see both near and far objects clearly. This is
important for many organisms to be able to detect predators, food sources etc.
Compare the change in the refractive power of the lens from rest to maximum accommodation
Maximum accommodation (in terms of the ciliary muscles)
occurs when focusing on very close objects and the lens is
rounded in shape.
Relaxed/rest state occurs when looking at distant objects, and
the lens is flatter in shape.
Refractive power is basically the degree to which the lens
bends/refracts light. It is inversely proportional to the focal
length of the lens, and is measured by the unit dioptre.
When the eye is looking at close objects, the light rays tend to
diverge as they reach the eye. For proper focusing, the refractive power of the lens must be
increased, by making the lens more convex (rounded).
When the eye is looking at distant objects, light reaches the eyes in almost parallel rays. This light is
focused on the retina when the lens has little refractive power (i.e. when it is quite flat). A minimal
amount of refraction or bending of light occurs when it passes through the lens as it is not required.
Lens Maximum accommodation Rest
Shape Bulges/round Thin/flat
Distance from object Near Distant
Refractive power High (approx. 67 dioptres) Lower (20-34 dioptres)
Distinguish between myopia and hyperopia and outline how
technologies can be used to correct these conditions
Myopia, or short sightedness, is when it is possible to see near
objects clearly, but more distant objects are blurred and
indistinct. It occurs when the distance between the lens and the
retina is too great (i.e. the eyeball is too long) or when the lens
cannot get thin enough to focus distant objects correctly (instead,
the image is focused in front of the retina).
Myopia can be corrected by wearing glasses with concave lenses (thinner middle, thicker ends –
diverges light). They spread the light rays out before entering the eye; allowing the lens to focus
them correctly.
Hyperopia, or long sightedness, is when it is possible to see distant
objects clearly, but near objects are blurred and indistinct. It occurs
when the distance between the lens and the retina is too short (i.e.
eyeball is too short) or when the lens cannot get fat enough to focus
near objects correctly (instead, the image is focused on an imagery
spot behind the retina).
Hyperopia can be corrected by wearing glasses with convex lenses.
These bend the light rays in a bit extra to allow them to focus on the
retina.
Other corrective technologies
Laser surgery can also be used treat myopia and hyperopia. The
treatment involves reshaping the curvature of the cornea. A thin flap or
corneal tissue is cut, folded back, and a laser beam is applied to the
exposed corneal tissue (reshaping the layers underneath to treat
refractive error). When the laser is finished, the flap is returned.
Contact lenses are similar to spectacle lenses (either concave or convex). However, they are
designed to model the curvature of the eyeball, and sit directly on the surface on the eye – just
covering the cornea.
Explain how the production of two different images of a view can result in a depth perception
Depth perception depends on binocular vision, where the field of view of each eye overlaps –
allowing each eye to observe the same object simultaneously. The images formed by each eye are
superimposed by the brain, and because each view is slightly different, it allows us to see it in three-
dimensions. When objects are close enough, we are also able to judge its distance from us.
Stereoscopic vision refers to vision where the same object is viewed from slightly different angles –
creating an impression of depth. Predators also have stereoscopic vision (eyes at front of the head)
to allow them to estimate distances from prey. Tree-dwelling primates have it to allow them to
estimate depth when moving from branch to branch. Animals that are likely to be preyed upon,
however, usually have eyes placed on each side of the head – allowing for a wider total visual field at
the expense of losing the ability to judge distances.
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
Aim: To model the process of accommodation by passing rays of light through convex lenses of
differing lengths
Equipment:
Two convex lenses of different shape (one thin, one thick)
Lens holder
Sheet of white paper clipped on solid support (acts as a screen where the object is focused)
Candle as a source of light
Variables:
Independent variable: shape of the lens
Dependent: Distance between the screen and the lens
Control: Light source, screen and distance between the light and screen
Method:
1. Darken the room and set up thin lens holder as above
2. Move the lens forwards and backwards to find a position that produces a clear, focused
image of the light source on screen.
3. Measure and record the distance of the screen from the lens
4. Keep the lens holder the same distance, and change the lens to the thick lens. Observe the
screen and not the appearance of the image
5. Repeat steps 2-3 for the thick lens
Results: The thicker lens (one with more curvature) had a smaller focal length (was closer to the
screen). The thinner lens (one will less curvature) had a longer focal length (held further from the
screen)
Analyse information from secondary sources to describe changes in the shape of the eye’s lens
when focusing on near and far objects
When a person is looking at something close, the ciliary body contracts, the ligaments
loosen, and the lens becomes rounded. Accommodation and refractive power of the lens are
at a maximum.
When a person is looking at something distant, the ciliary muscles relax, the ligaments
tighten, and the lens becomes flatter and thinner. The muscles are in a relaxed state, and
refractive power is minimal.
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
Cataracts are a condition where the lens grows cloudy and eventually becomes opaque. When part
or the whole of the lens becomes opaque, the transmission of light through the eye is obstructed,
causing both near and far objects to become blurred. Cataracts mostly develop slowly as a result of
aging. The development of cataracts is often linked to eye injury, extended exposure of the eyes to
the sun’s UV light, excessive smoking, radiation and particular diseases (e.g. diabetes).
When the presence of cataracts begins to interfere with daily activities and the quality of one’s life,
treatment by means of surgery is the only option
Technologies used
Today, cataract surgery involves IOL implantation – that is, replacing the cloudy lens with a
plastic/silicone intraocular lens (lens within the eye), similar in shape to a natural human lens.
The most common technique (phacoemulsification) involves making a 3mm incision where the
cornea meets the sclera, and small, vibrating probe is inserted into the eye. This probe breaks up the
lens into small particles, which are then suctioned out using an aspirator. The artificial lens is then
inserted into the space left in the existing lens capsule. The incision in the eye may be so small that
no stiches are needed.
Implications
The cataract surgery takes very little time, is performed under local anaesthetic, and can be done
anywhere. It has revolutionised the treatment of cataracts so that people who are cataract blind,
can now see. The implications of cataract surgery are huge; regaining sight often increases an
individual’s life span, and allows older people to live more independent and active lives, thus
reducing the financial burden required to look after the elderly.
This safe, precise and successful technique has been made available to thousands of people in
developing countries through groups like the Fred Hollows Foundation, which send teams to those
isolated and poor communities to perform cataract surgery. As such, the surgery was made available
to those who could not previously afford them.
4. The light signal reaching the retina is transformed into an electrical impulse
Identify photoreceptors cells as those containing light sensitive pigments and explain that these
cells convert light images into electrochemical signals that the brain can interpret
The retina is a thin sheet of cells that contain photoreceptor cells.
Photoreceptor cells are those containing light sensitive pigments and these cells convert
light into electrochemical signals that the brain can interpret.
There are two types of photoreceptor cells in the retina:
Rods and cones contain photosensitive chemical substances that undergo chemical reactions
when they absorb light energy.
When the rods and cones are stimulated by light, electrochemical signals are transmitted
through successive neurones on the retina and finally into the optic nerve and then to the
cerebral cortex in the brain.
Describe the differences distribution, structure and function of the photoreceptor cells in the eye
Rod Cone
Feature Rods Cones
Distribution - 125 million in the human retina - Spread across the retina but
more dense around the edges of the retina (periphery)
- none in the fovea
- 6-7 million in the human retina - Located mostly on the fovea (centre)
of the retina and a small depression in the centre of the macula lutea at the back of the eyeball.
- In the fovea each cone cell is connected to one nerve cell to give the greatest acuity
Structure - Elongated - Narrower, longer and straighter - Both contain visual pigments
(rhodopsins) in stacks of disc-shaped membrane at one end of the cell. The other end connects to a nerve cell
- Elongated - Conical - Shorter - Both contain visual pigments
(photopsins) in stacks of disc-shaped membrane at one end of the cell. The other end connects to a nerve cell
Function - In low light conditions the pupil dilates, allowing light to fall on the rods
- So in low light levels, our vision is more ‘grainy’ and we cannot discriminate colour.
- Best in dim light, do not distinguish colour (discriminates between shades of light and dark), used for night vision
- More sensitive to light - Sensitive to movement - Formation of images
- In bright light the pupil is contracted and most light falls on the cones
- This means that in bright light we can see detailed, coloured images
- Require more light than rods to be stimulated
- Day vision, colour vision and visual tasks requiring visual acuity (e.g. reading)
- Formation of images
Outline the role of rhodopsin in rods
Rod cells contain a photosensitive pigment that absorbs light waves called rhodopsin which
is made of up of the protein opsin in loose chemical combination with a pigment called
retinal.
When light strikes a rod cell it stimulates a response, the retinal changes shape and loses its
attachment to the opsin molecule and splits rhodopsin molecules into its components.
Rhodopsin allows seeing the shades of grey, black and white.
Identify that there are three types of cones, each containing separate pigment to either blue, red
or green light
There are three types of cones in the human eye, each containing a pigment sensitive to
either blue, red or green light.
Because three photopigments are used to interpret colour by the various cone cells, humans
possess trichromatic vision.
There are three types of cones, each with its own kind of opsin associated with retinal.
These molecules are called photopsins and they are involved in colour vision, there are 3
types of photopsin present in these cones (each one having only one type of photopsin):
- Opsin blue short wavelengths (maximum at 420 nm)
- Opsin green medium wavelengths (maximum at 530 nm)
- Opsin red Long wavelengths (maximum at 560 nm)
Explain that colour blindness in humans results from the lack of one or more of the colour-
sensitive pigments in the cones
Colour blindness is the inability to see colour, there are a range of colour blindness
conditions from only a slight difficulty distinguishing different shades of the same colour to
the rare inability to distinguish any colours.
Colour blindness in humans results from the lack of one or more of the colour-sensitive
pigments in the cones, people who are colour blind still see some colour.
As rod cells detect light, they play no role in colour blindness so those who are colour blind
can usually see.
Most common type of colour blindness is red-green (people with the condition perceive red
and green as the same colour), where the cones most receptive to red light and green light
are missing.
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
Mammal: Human Insect: Dragonfly Flatworm: Planarian Worm
Diagram of photoreceptor
Type of photoreceptor
Single eye lens Compound eyes Eye cups
Type of image Image on retina is inverted and diminished
Mosaic image of large visual field, can see in colour
Image (if formed) is unclear and not inverted – gives information about light intensity and direction
Similarity in photoreceptors
Detects light - rhodopsin Detects light - rhodopsin Detects light - rhodopsin
Difference in photoreceptor
Has higher resolving power and greater visual acuity
Is made up of many units called ommatidia (each has its own cornea and transparent crystalline cone which acts as lens) pointing in different direction. Can be more efficient detecting colour than mammals and fast movement.
Has fewer photoreceptor cells than insect or mammals and has poor visual acuity and no colour vision. Two eye spots (Ocelli) are used to detect light and move away from it.
Structure that refracts light
Cornea, aqueous humour, lens (changes curvature), vitreous humour
Cornea, lens (fixed, cannot accommodate)
No refraction
Sensitivity to light
Rhodopsin is a photosensitive pigment
Greater – detects light, UV as well as visible light
Highly sensitive
Visual acuity (vision)
High visual acuity Lower visual acuity than mammals but more efficient in detecting movement
Poor visual acuity
Ocelli
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
Animal Method Purpose
Blue-ringed octopus Glowing blue ring around their bodies
Signal an intention to attack
Rainbow lorikeets Warning mechanism by opening their wings
Bright underneath colours are used to threaten off rival male
Red Black Spider Warning mechanism highlighting their poisonous nature
Have a warning red strip on their abdomen to ward off predators or things looking to eat it
Primates Looking at colour of food Use colour to determine whether food is ripe and good to eat