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 or external environment of an organism. Examples of stimuli include light, sound, temperature, pressure, pain and certain chemicals.

· The role of receptors is to detect stimuli and convert information into electrochemical signals which can be interpreted by the brain

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, receptor, messenger, effector, response

The stimulus-response model is outlined above.

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 the final reaction to the stimulus.

Identify data sources, gather, and process information from secondary sources to identify the range of senses involved in communication

Sense

Analysis and examples of communication

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

· Bioluminescence in fireflies to attract mates

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

· Humpback whales communicate by sound which can travel hundreds of kilometres

Smell (olfactory)

· Chemoreceptors detect chemicals

· Communication via chemical signals

· Many animals rely on smell to find food, find a mate or as a means of identification. Male dogs use smell to mark their territory and detect presence of females on heat

Touch (tactile)

· Mechanoreceptors for touch are abundant under the skin

· Sensory nerve endings in the skin respond to touch

· Herring gull chicks peck at a spot on their mother’s beak to get her to release food

Taste (gestation)

· Chemoreceptors detect chemicals.

· Many animals use taste if they have a poor sense of smell (these two are closely related senses)

· Male elephants taste the urine of female elephants to see if they are fertile

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:

· Humans are able to detect wavelengths in the visible spectrum (400-700nm) to allow for us to distinguish foods and objects within our environment.

· 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

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 cow’s eye and relate structures to functions

Materials:

· Cow’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

Independent variable: shape of the lens

Dependent variable: Distance between screen and the lens required to focus

Controlled variables: light source, screen, distance between light and screen

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

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

· Cones (respond to colour

Cone –responds to colour

Rod

· 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 in distribution, structure and function of the photoreceptor cells in the eye

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

· Contains 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

· Contains 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.

· Energy (ATP) is required to reattach retinal to opsin and to return rhodopsin to the shape that it had before being stimulated by light.

· 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.

· The photosynthetic pigment present in cones is iodopsin, which contains photopsin. There are 3 types of photopsin present in cones:

· Opsin green

· Opsin red

· Opsin blue

· An individual cone contains only one of the three types of photopsins. Each type of photopsin absorbs light in a particular range of wavelengths:

· Blue: short wavelengths

· Green: medium wavelengths

· Red: long wavelengths

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 certain 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 (not colour), they play no role in colour blindness so those who are colour-blind can usually see.

· The 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.

· Colour blindness is more frequent in males than females because it is a sex-linked characteristic; the gene for the red and green cones is located in the X chromosome. Females have two X chromosomes (XX) and males only have one (XY) which means that females need both chromosomes carrying the defective gene to express it while males only need one.

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

Type of photoreceptor

Rods and cones

Reticular/retinal cells in separate ommatidia

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

High visual acuity

Lower visual acuity than mammals but more efficient in detecting movement

Poor visual acuity

· Mammals have a similar eye structure to humans; the major difference within mammal eyes is the presence or absence of cone cells (nocturnal mammals have no cones, so they cannot see colour).

Compound eyes

Worm eye cup

Process and analyse information from secondary sources to describe and analyse the use of colour for communication in animals and relate this to the occurrence of colour vision in animals

Many animals use colour for communication. Colour can be used to enable animals to:

· Find a mate

· Warn off predators

· Find food

Animal

Method

Purpose

Fireflies

Bioluminescence

To attract mates

Blue-ringed octopus

Glowing blue ring around their bodies

Signal an intention to attack

Peacock

Extensive colouring of feathers

Peacocks use colour in courtship behaviour. The male peacock has a bright blue chest to attract and impress the female

Rainbow lorikeets

Bright colours underneath wings/beaks

The lorikeet threaten rivals by opening their wings/beaks to display the warning colours

Red-back spider

Red strip on abdomen

Use as a warning mechanism telling predators that they are poisonous

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 is a useful and versatile form of communication as it does not require contact or closeness between organisms to send and receive messages. Sound can convey very complex messages because it has many features that can be varied (e.g. frequency, loudness, speed, length of sound)

· Sound can be used to communicate both at day and night; and over distances where animals cannot see, smell or touch each other. For example, it can be used to communication in dense forests

· All animals live in environments that transmit sound (solid, liquid, gas mediums – air, water, earth).

Explain that sound is produced by vibrating objects and that the frequency of the sound is the same as the frequency of the vibration of the source of the sound

Sound is a form of energy caused by a vibrating object (moving back and forth). Sound waves must then have medium to travel through; the medium can be solid, liquid or gas. The vibrating object causes vibrations (of the same frequency) in the medium – compressing surrounding particles, which is subsequently followed by rarefaction (where the particles spread out again). This action results in a compression (longitudinal) wave travelling through the medium.

Frequency refers to the number of wavelengths that pass through a given point per second, and is measured in hertz (Hz). It determines the pitch of the sound.

Note: Lower frequencies (longer wavelengths) travel further, whilst shorter frequencies do not travel as far

Amplitude refers to the maximum displacement of particles (i.e. maximum compression), and determines the loudness of the sound.

Outline the structure of the human larynx and the associated structures that assist the production of sound

The larynx is a complex structure situated in the throat-neck region, which forms part of the trachea. It is made up of cartilage leading from the oral cavity (mouth) to the bronchi/lungs. A major function of the larynx is to produce sound. This is mainly achieved through the two muscular vocal cords/folds (made of elastic fibres) within the cartilage, which move when we speak and breathe. Controlled vibration of these vocal chords produces sounds of different pitch and volume by changing shape.

· Tight, stretched vocal folds (with a smaller gap between the vocal folds) produce a higher pitch

· Looser, relaxed vocal folds(with a larger gap between vocal folds) produce a lower pitch

Overall speech requires many other systems, including:

· The brain

· The mouth (lips, soft palate, tongue)

· Respiratory system (nose, throat and lungs – the muscles to the lungs provide the volume of the sound)

Gather and process information from secondary sources to outline and compare some of the structures used by animals other than humans to produce sound

Structures used to produce sound

Cicada

Muscular action altering the chitinuous membranes (within its abdomen) produces sound, which is then amplified using tympana membranes.

Grasshoppers and crickets

Stridulation – the insect rubs its rear legs on their forewings to generate a sound through friction

Frogs

Male frogs squeeze air through the larynx and over the vocal cords whilst the mouth and nose are closed to produce sound. This sound is then amplified by inflated vocal sacs (membranes of skin under the throat)

Plan and perform a first-hand investigation to gather data to identify the relationship between wavelength, frequency and pitch of a sound

Wavelength refers to the distance from one crest to another (or one trough to another)

Frequency refers to the number of crests that pass a particular point per unit time. It is measured in Hertz (Hz)

The pitch refers to our perception of the sound, and depends on the frequency/wavelength of the sound. A sound wave with a short wavelength will have a high frequency, producing a sound of higher pitch. A sound wave with a longer wavelength will have a low frequency, producing a sound of lower pitch.

Method

1. Place a 30 cm ruler on the end of a table. Ensure that approximately 2/3 of the ruler is hanging off the table

2. Push down on the end of the ruler hanging off the table and release

3. Observe the pitch of the sound and the frequency (through the approximate number of vibrations of the ruler per second)

4. Repeat steps 2 and 3 with a gradually lower proportion of the ruler hanging off

Note: the force upon which you push down on the ruler correlates to the amplitude of the sound produced (more force = higher amplitude = higher volume)

Results

When a larger portion of the ruler was left hanging off, a lower pitch was heard (due to a lower number of vibrations of the ruler, and hence a lower frequency). When a lower portion of the ruler was hanging off, the opposite effect was observed.

6. Animals that produce vibrations also have organs to detect vibrations

Outline and compare the detection of vibrations by insects, fish and mammals

Insects

Some insects have tympanic organs – special structures used to detect vibrations. For example, crickets have tympanic membranes on their legs and abdomen, which vibrate when sound reaches them (acting like eardrums). Sensory cells (mechanoreceptor cells) detect the messages and send it to the brain. This system is more sensitive to high frequency sounds.

On the other hand, mosquitoes have hairs on antennae to detect sound.

Fish

Fish have internal ears and a lateral line system along the sides of their body.

The line system consists of a long fluid-filled canal (lateral line canal) which runs underneath the skin on the side of the fish. There are pores (openings) at regular intervals joining the canals to the outside. Any disturbance in the water causes vibrations in the fluid, which is then detected by the neuromasts via the receptor hair cells on their ends. The hair cells project into the canal fluid, thus allowing it to detect vibrations. Once the hair cells are stimulated, nerve impulses are then sent to the brain.

The line system detects the fish’s own movement through the water, the direction/speed of the current, any vibrations or pressure waves from moving objects (e.g. predators) and low-frequency sounds.

Fish also have inner ears near the brain. Vibrations are conducted through the skeleton and the air-filled swim bladder (in the abdomen) through to the inner ear. Hair cells in the semicircular canals (in the inner ears) vibrate in response and send a message to the brain.

Mammals

The detection of vibrations in mammals occurs through organs known as ears.

Vibrations are detected by hair cells in internal structures as a result of vibration of membranes and their amplification from the outside through to the inner ear.

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

The outer ear

The outer ear consists of the pinna and an ear canal which ends in a membrane called the eardrum.

The pinna refers to the outer part of the ear visible on the side of one’s head. It consist of numerous grooves; folds of skin over cartilage. Its function is to collect sound waves and direct them into the ear.

The sound waves travel along the ear canal (external auditory meatus) until it reaches the tympanic membrane (ear drum). The ear drum is a flexible membrane that stretches tightly across the passage of the canal. It vibrates when sound waves reach it, and transfers the mechanical energy into the middle ear.

The middle ear

The middle ear consists of three tiny bones (ossicles), the oval/round window and the Eustachian tube (which connects with the back of the nose and throat)

The ear ossicles (note MIS) consist of three tiny, movable bones: the malleus (hammer), incus (anvil) and the stapes (stirrups). When the eardrums vibrate, the ossicles vibrate, in turn amplifying the sound and conducting it to the oval window.

The oval window is a flexible region that joins the ossicles of the middle ear to the cochlea in the inner ear. The oval window is directly connected to the stapes, allowing it to fulfil its function of: picking up vibrations from the ossicles and passing them into the fluid in the cochlea.

The round window is a flexible membrane between the cochlea and middle ear, situated just below the oval window. When the stapes pushes into the oval window, the round window bulges outwards and acts as a ‘pressure release valve’ (adjusting pressure differences to allow for fluid movement within the cochlea). This is important because the fluid movement is required for the hair cells within the cochlea to be stimulated (and hence cause hearing).

The inner ear

The inner ear consists of a series of bony canals and chambers that are filled with fluid. From here, nerve fibres join up to form the auditory nerve, which transmit impulses to the auditory cortex of the brain.

The cochlea is a coiled up system of three tubular chambers filled with fluid. It has the appearance of the snail shell. Its function is to change mechanical energy into electrochemical energy.

The organ of Corti is a structure within the cochlea (in the cochlear duct – on the basilar membrane) that contains millions of receptor hair cells that convert vibrations (fluid movements) into electrochemical signals (nerve impulses). The hair cells synapse onto sensory neurones, which collect into the auditory nerve.

The auditory nerve is a nerve that travels from the ear to the brain. Its function is to essentially transmit electrochemical signals to the brain.

Outline the role of the Eustachian tube

The Eustachian tube connects the middle ear to the throat/nose. The main role of the Eustachian tube is to equalise the pressure between the outer and inner ear, so that the eardrum can vibrate efficiently. The Eustachian tube executes its function by connecting the middle ear to an air-filled space (pharynx in the throat). The tube is usually closed, but is opened by yawning or swallowing.

Outline the path of a sound wave through the external, middle and inner ear and identify the energy transformations that occur

In air, sound travels in a longitudinal (compressional) wave. It consists of a series of compressions and decompressions of particles in the air, caused by a vibration at the source.

Sound waves firstly travel into the ear canal and reach the tympanic membrane (ear drum) – causing vibration of the ear drum at the same frequency as the entering sound waves. In this way, sound energy is converted to mechanical energy (movement of the tympanic membrane). Subsequently, the ear ossicles also vibrate.

As the ear ossicles vibrate, they transfer the vibrations to the oval window which is pushed inwards onto the cochlea. This creates a pressure wave in the fluids of the cochlea. As the wave travels through the fluids, the round window membrane is pushed in the opposite direction. The fluid pressure waves push into the cochlear duct, and onto the membranes close to the organ of Corti. This movement of the membranes bend the cochlear hair cells. This stimulates nerve impulses in the neurones that lead to the auditory nerve. Hence mechanical energy is converted into electrochemical energy (nerve impulses). The impulses travel along the auditory nerve to the brain, where it is interpreted as sound.

Describe the relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies

There are thin fibres of varying lengths spread within the basilar membrane on the organ of Corti. Vibrations of different frequencies travel different distances through the fluids of the cochlea, before causing the fibres of the membrane to vibrate. Hence, each length of fibre vibrates at a different frequency.

High frequency sounds cause the short fibres in the front part of the membrane (near the oval window) to vibrate. Lower frequency sounds cause the longer fibres towards the end of the basilar membrane (see right)

When a particular fibre is stimulated (vibrated), its associated hair cell is bent. This then causes the cell to send an electrochemical impulse along the auditory nerve to the brain. The nerve impulses travel to different areas of the auditory cortex in the brain, depending on where the nerve impulse is generated on the basilar membrane. In this way, sound of different frequencies will activate different sets of hair cells that send the signal to a distinct area of the brain – causing us to perceive sound of a particular ‘pitch’.

Outline the role of the sound shadow cast by the head in the location of the sound

The location of our ears on either side of our head helps us perceive the direction from which a sound is sourced from. Sound waves coming directly in front, behind or above the head will cause both ears to receive the sound waves equally. However, sound coming from the one side reaches the ear corresponding to that side but is blocked by the head in reaching the other ear. This creates a sound shadow for the ear furthest from the sound source (receiving a reduction in amplitude).

The receptors in the ear closer to the sound will detect it more intensely (and also earlier). The differences in perception by each ear due to the sound shadow enable the brain to then interpret the direction of a sound.

Gather, process and analyse information from secondary sources on the structure of the mammalian ear to relate structures to functions

Structure

Description of Anatomy

Function

Pinna

Large fleshy external part of the ear

Collects sound and channels it into the ear

Tympanic membrane

The eardrum – membrane that stretches across the ear canal

Vibrates when sound reaches it and transfers mechanical energy into middle ear

Ear ossicles

Three tiny bones: malleus, incus, stapes

Amplify the vibrations from tympanic membrane

Oval window

Region linking the ossicles (middle ear) to the cochlea (in inner ear)

Picks up vibrations from ossicles and passes them into cochlear fluid

Round window

Membrane between cochlea and middle ear beneath oval window

Bulges outwards to allow release of pressure caused by vibration of stapes onto the oval window

Cochlea

Circular fluid filled chamber

Changes mechanical energy into electrochemical

Organ of Corti

Structure within cochlea

Contains hair cells that transfer the vibrations into electrochemical signals

Auditory nerve

Nerve travelling from the ear to the brain

Transmits electrochemical signals to the brain

Process information from secondary sources to outline the range of frequencies detected by humans as sound and compare this range with two other mammals, discussing possible reasons for the differences identified

Mammal

Hearing range (Hz)

Reason

Human

16 – 20,000

This hearing range encompasses the normal range projected by human voice (1000 – 3000Hz), of which our ear is most sesntivie to.

Mouse

1000 – 123,000

Mice communicate using high frequency noise, and are able to produce sounds out of predators’ frequency ranges. Hence they can alert other mice of danger without alerting the predator to their presence.

Bat

1000 – 120,000

Bats produce frequencies up to 120,000 Hz for echolocation, where they listen to the echoes of their calls in order to navigate and locate food. This is important as bats are nocturnal mammals, thus they often find food in complete darkness.

Process information from secondary sources to evaluate a hearing aid and a cochlear implant in terms of: the position and type of energy transfer occurring, conditions under which the technology will assist hearing, limitations of each technology

Hearing aid

Cochlear implant

Description

Hearing aids are battery operated devices that are designed to amplify the sound entering the outer ear. They can be removed at any time

Cochlear implants are battery operated devices used to replace a damaged cochlear, which functions to convert vibrations into electrochemical energy to be sent along the auditory nerve.

Position

Worn externally; inside the external auditory canal

Worn both internally and externally:

· Headset (microphone and coil) worn outside ear

· Speech processor also outside ear

· Implant (receiver package and electrodes) which is surgically placed inside the skull and inner ear (cochlea). The receiver is inserted into a bone behind the ear, and the coil is threaded through the cochlea.

Type of energy transfer

Sound Electrical Sound

(Microphone, amplifier, speaker)

SoundElectricalElectrochemical

Description of energy transfer

The aid receives sound energy through a microphone, which converts it into electrical energy. The amplifier increases the volume (amplitude) of the sound and converts the electrical energy back to sound. The sound is then directed in the auditory canal via a speaker on the aid.

Sound waves are picked up by a microphone and converted into an electrical code by the speech processor. Connecting cables then transfer the electrical signals to the implanted cochlear. The implant then uses the electrical pulses to stimulate the cochlear nerves – creating electrochemical messages that are sent along the auditory nerve.

Conditions under which it will assist

Hearing aids only work if the inner ear is intact and functioning normally (i.e. no nerve damage/defect; patient must have residual hearing). For example, if cochlea is damaged, the aid wouldn’t work as it only amplifies the sound reaching the inner ear. However, it will assist if there is a ruptured ear drum, or damaged ossicle.

Cochlear implants are used where permanent damage/defect has occurred to the inner ear. It bypasses damaged parts of the inner ear and electronically stimulates the auditory nerve. However, the implants will not work if the auditory nerve is damaged.

Limitations

· Some higher sound frequencies cannot be detected with the aid

· Loud noises are annoying for users/ difficulty in hearing with background noises

· Does not assist when there is damage to inner ear; quality depends on residual hearing

· Advantages: non-invasive, no side effects, relatively inexpensive, can be used at any age.

· Expensive in comparison to hearing aids

· Requires surgery – carries risk and has side effects

· The sounds created by the implant are different to normal hearing (patients usually have approx. 80% speech recognition), which takes time to learn. Works best if implanted before the age of five.

· Same issue as hearing aid with background noises

· Required to adjust programming for different situations (e.g. conversation, watching television)

· Recipient required to wear permanent device (sound processor) attached to skull, which is a hindrance

Future/

improvement

The detection of more high frequency sounds could be a potential source of research and improvement.

Cochlear implants cannot help if auditory nerve is damaged; this could be a potential area of research. As well, the limitations could be a source of improvement, for example, having more electrodes to improve range and quality of hearing.

Hearing aid:

Cochlear implant

7. Signals from the eye and ear are transmitted as electrochemical changes in the membranes of the optic and auditory nerve

Identify that a nerve is a bundle of neuronal fibres

The units that make up the nervous system are the nerve cells (also known as neurones). There are three types of neurones

· Sensory neurones which transmit electrochemical impulses from sense organs to other neurones in the CNS

· Motor neurones which transmit electrochemical impulses from the CNS to muscles/glands

· Connector neurones, which connect sensory neurones to motor neurones (in brain/spinal cord)

Each neurone has three parts:

· A cell body containing the nucleus (forms grey matter of the CNS)

· One or more branching extensions called dendrites, which conduct nerve impulses towards the cell body. In sensory neurones, there is a single elongated dendrite called a Dendron

· One single long extension called an axon (forms white matter of the CNS), conducting nerve impulses away from the cell body.

Dendrites and axons are collectively referred to as neuronal fibres. They consist of fluid-filled tubes and are often surrounded by a fatty, insulating cover called the myelin sheath. The cell body of a neurone is usually located in the CNS (brain or spinal cord), whilst the axon and dendrites usually extend towards a sensory or effector organ. In this way, nerves can stretch over a long distances (e.g. from base of spine to foot). The neuronal fibres (sensory or motor fibres) are gathered into bundles, which are known as nerves. The bundle is held together by a connective tissue sheath.

Neurone bundle (nerve)

Perform a first-hand investigation using stained prepared slides and/or electron micrographs to gather information about the structure of neurones/nerves

Myelin sheath/axon electron micrograph

(20,000x)

Electron micrograph of three neurones in human brain

Electron micrograph – sensory neurone in retina

(500x)

Identify neurones as nerve cells that are the transmitters of signals by electrochemical changes in their membranes

Within a neurone, the myelin sheath has small gaps called the nodes of Ranvier. The ion channels that function in the action potential are concentrated in the node regions of the axons. Also, extracellular fluid is only in contact with the neuronal membrane at these nodes. The action potential jumps from node to node, skipping the insulated regions of the membrane between each node.

Nerve impulses are electrical signals produced by the plasma membrane of a nerve cell. Basically, when the cell is at rest, a potential difference (difference in electrical charge) exists across the membrane. The side of the membrane exposed to the cytoplasm is negative, whilst the side exposed to the extracellular fluid is positive. The differences on either side of the membrane result in a cellular voltage (difference in potential energy), which is known as the resting membrane potential. This potential measures to be about 70 millivolts, expressed as -70 mV (indicating the inside of the membrane as negative). Thus, the membrane is known to be polarised.

At resting state, there is a higher concentration of sodium ions in the extraceullar fluid and a higher concentration of potassium inside the cell membrane. The ion channels (which are selectively permeable to Na+, K+, Cl- ) are closed – and the ratio of Na+ within the cell is maintained via the Na+/K+ exchange pump (where Na+ is actively transported out).

Depolarisation and action potential

A cell membrane’s potential can change in response to appropriate stimulations. When the cell membrane of a neuron is stimulated (e.g. light at sensory receptor), the sodium channels open and subsequently, Na+ ions diffuse into the cell, causing depolarisation (a positive shift from membrane potential; e.g. from -70mV to -40mV). If the depolarisation is strong enough, it generates a nerve impulse or action potential.

The change in voltage causes the potassium channels to open, so K+ ions diffuse outside to restore the potential difference. Meanwhile, the sodium channels close. This process is called repolarisation. The original distribution of the K+ and Na+ ions is restored via the Na+/K+ exchange pump, causing the cell membrane to return to its resting potential. This is known as the refractory period, a brief moment where another action potential cannot be generated

Transmitting action potentials

The action potential is propagated along the whole neurone as the inward flow of the Na+ affects the permeability of the next region of membrane and it too depolarises – creating a ‘domino effect’, ultimately resulting in a wave of ionic changes moving along the whole neurone. Note that the movement occurs in one direction only.

Furthermore, action potentials are transmitted from neurone to neuron across synapses, which are gaps between end of an axon (of one cell) and the dendrites of the next receiving neurone. Basically neurotransmitter chemicals diffuse across the gap from one neurone to the membrane of another – causing an electrical response

Define the term ‘threshold and explain why not all stimuli generate an action potential

Present information from secondary sources to graphically represent a typical action potential

The threshold refers to the amount of positive charge in a membrane pontetial required before an action potential is produced. The threshold is typically at least 15 mV more positive than resting potential (-70 mV).

The action potential is an ‘all-or-none’ response; either the level of stimulation is below the threshold and nothing happens, or it reaches the threshold and an action potential is generated.

Note that an action potential does not vary in size. If a stimulus is very strong, the rate at which action potentials are generated increases, causing an increase in the number of cells to respond.

Furthermore, if a cell is within its refractory period, an action potential cannot be produced, until the previous one is complete.

Identify the areas of the cerebrum involved in the perception and interpretation of light and sound

The cerebrum forms a large portion of the brain, and it controls thinking, foresight, movements and sensation. The cerebrum is separated into two hemispheres – the left hemisphere controls the right side of the body whilst the right hemisphere controls the left side of the body. The two halves connect and communicate via bundles of nerve fibres that make up the corpus callosum. The cerebrum’s folded surface layer is called the cerebral cortex.

The hemispheres are divided into four lobes:

· Frontal lobe – contains Broca’s area which controls muscles of speech and articulation of words

· Temporal lobe – Responsible for hearing, memory processing and integration of hearing and vision. Includes the Wenicke’s area which controls interpretation of language.

· Parietal lobe – used for interpreting written language

· Occipital lobe – processes visual information. It receives and interprets information from retinas.

Other important areas of the brain include:

· Cerebellum – plays an important role in motor control; contributes to the coordination (but not initiation) of movement

· Medulla oblongata - located at the base of the brain just above the spinal cord; deals with involuntary functions of breathing, heart rate and blood pressure

Perception of light

Optic nerves are the sensory nerves of vision. Fibres form from the retina of the eye, passing through the skull via an opening in the eye socket. The optic nerves from each of the eye cross over to provide each visual cortex with the same image, although each eye receives the image at a slightly different angle. A visual cortex lies in the occipital lobe of each cerebral hemisphere.

Perception of sound

Auditory nerves arise from the cochlea and equilibrium (vestibule) apparatus within the inner ear. The two divisions merge to form one nerve known as the vestibulocochlear nerve. It runs from the organ of Corti to the auditory cortex, located in the temporal lobe of each cerebral hemisphere.

Explain, using specific examples, the importance of correct interpretation of sensory signals by the brain for the coordination of animal behaviour

Sense organs detect changes in the environment and send information to the brain. The brain then interprets the information and sends an impulse to the effector organ (e.g. muscle). Hence, it is essential for the brain to correctly interpret signals from the sense organ, in order for our effector organs to apply an appropriate response.

For example, walking involves several receptors such as the eyes, gravity receptors in the ears, pressure sensors in the feet and position receptors in the joints. These receptors send signals to the brain. The brain must then correctly interpret signals received, and send appropriate messages to the muscles to co-ordinate the process of walking.

The importance of the brain in the coordination of animal behaviour is further highlighted when parts of it are damaged:

· Multiple sclerosis (MS) is an autoimmune system in which the immune system attacks the body’s own myelin protein. The myelin sheaths in the CNS are gradually destroyed. As the insulating layer becomes non-functional, the impulses are short-circuited and eventually conduction of impulses ceases. Because the brain can no longer correctly interpret signals, this causes symptoms like: weakness in muscles, clumsiness, visual disturbances (even blindness)

· Alcohol and sedatives can impair transmission of nerve impulses by reducing the plasma membrane’s permeability to sodium ions. AS a result, the brain is unable to correctly interpret sensory signals, causing poor co-ordination of movements, lack of concentration, blurred vision, slurred speech

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

Aim: To gather information to distinguish the cerebrum, cerebellum and medulla oblongata and locate the regions involved in speech, sight and sound perception

Equipment:

· Sheep Brain

· Scalpel and tweezers

· Rubber Gloves

· Newspaper

Safety

Risk

Containing risk

There is a hazard using the scalpels. The blades are extremely sharp and may cause injury.

Use extreme care when handling the scalpel blades.

Pathogen contamination from organic remains

Remains should be wrapped in newspaper and then given to the laboratory technician for safe disposal.

Wipe down bench and disinfect after dissection.

Method:

1. Examine the sheep brain externally noting the appearance and location of the cerebrum, cerebellum and medulla oblongata.

1. Make a biological drawing of the external parts of the brain and labelling the parts.

1. Cut the brain in half lengthways and identify the areas for speech, sight and sound perception.

1. Make a biological drawing of the cross-section labelling that you can identify for speech, sight and sound perception

Results:

Part of Brain

Description

Cerebrum

· Front part of the brain

· Folded

· Forms majority of the brain structure

· Separated into 2 hemispheres

Cerebellum

· Located underneath cerebrum

· Highly folded

· Back of the brain

· Smaller than cerebrum

Medulla oblongata

· Base of the brain just above the spinal cord; not folded and is the smallest of the major brain components

· Found between pons and spinal cord

· White matter outside and grey matter outside

White matter is composed mainly of myelinated axons. Grey matter is composed mainly of cell bodies.