Conjunctiva

Cornea

Sclera

Choroid

Retina

Iris

Lens

Aqueous and vitreous humour

Ciliary body

Optic nerve

The eye including the sclera, choroid, retina, fovea, optic nerve, conjunctiva, iris, cornea, lens, pupil, aqueous humour, ciliary body and vitreous humour

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 (EM) is a term used to describe different types of radiation. This radiation travels in the form of waves, known as transverse waves. The waves are able to travel in a vacuum and carry energy. The electromagnetic spectrum is a range of energy forms which travels at the speed of light. These energy forms vary in wavelengths and frequencies depending on the type of animal. Humans detect visible light which ranges 400 – 700nm. Snakes use infrared light to detect preys and avoid predators.

Use available evidence to suggest reasons for the differences in range of electromagnetic radiation detected by human and other animals

Many organisms live in different niches. These niches produce different obstacles in which the organism must adapt to survive, thus, the necessity to detect predators and preys within their environment are significant. Electric eels emit an electric field within their environment. Any disturbances within their environment such as a prey are detected by the electric eel. The eels use this form of electromagnetic radiation as vision within their water environment, but develop a poor vision landscape.

Snakes use infrared light to detect predators and their prey. This is due to the fact that snakes are largely found on the ground and in the bushland. Snakes rarely use normal vision due to the lack of peripheral vision they have. Australian pythons have heat-sensitive pits in their skin that enable them to detect infrared radiation so it is easier to see their prey.

A python has air holes known as heat-sensitive pits enabling them to detect infrared radiation

The platypus has electromagnetic receptors in its bills. This helps the platypus to detect prey which produces an electric field. They use these receptors as vision within a water environment, which is considered to be poor.

The platypus has electromagnetic receptors in its bills to detect its prey

Humans use two single eyes to detect visible light. Humans have many photoreceptor cells of different pigments which added various colours of the spectrum which are transformed into electrochemical signals for the brain to interpret.

Identify conditions under which refraction of light occurs

Refraction is the bending of light when it passes from one medium to another due to the different speeds in the different Medias. Light is refracted in the eye when it passes from air into dense material of the cornea; this then reaches into the aqueous humour, lens and vitreous humour. Enabling light to be focused onto the retina and interpreted into the brain. Refraction occur when the wave changes speed and direction.

The clip is a demonstration of refraction from one medium to another due to the differences in medias.

http://www.youtube.com/watch?v=DtDaQPbKV9s&feature=related

Distortion of the pencils due to the bending of light as it passes from one medium to another due to the different speeds in the different medias

Identify the cornea, aqueous humour, lens and vitreous humour as refractive media

The cornea has a density close to that of water. The light then passes from the cornea into the aqueous humour. It proceeds to being refracted again when the light passes from the aqueous humour into the denser lens. This provides the extra refraction which is required to focus (converge or bring together) the rays of light onto the retina called the ‘focal point’. The focal point is the point which the object is being focused upon, the focal length is the distance between the focal point and the centre of the lens. The aqueous and the vitreous humours have only a minimal refractive effect on the light passing through the eye; nonetheless they maintain a role in the refractive media.

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. It is the ability of the eye to focus the light onto the retina to determine the resolution of an image. The contraction or relaxing of the ciliary muscles in the Ciliary body causes the shape of the lens to change, thus altering the focal length of the lens. The image on the retina is thus inverted, and can be compared to the actual object.

In relation to distant objects, approximately six metres from the eye, the light rays require less bending by the lens which allows the choroid to expand and put tension on the ligaments. The lens is pulled into a more flat shape. The thicker the lens, the more sharply the light is bent. The lens becomes nearly spherical as it focuses on more nearer objects. If objects are closer approximately within six metres, the Ciliary muscles contract, pulling the border of the choroid of the eye towards the lens which therefore causes the ligaments to relax. Using this reduced tension, the elastic lens becomes thicker and rounder.

The refractive power of the lens is determined by the shape of the eye. A short thick lens will be able to refract more than a long thin lens and shorten the focal length of the eye. Therefore, light rays from near objects will require more refraction and a shorter focal length is necessary for it to be focused on the retina in comparison to distant objects.

The video outlines the process of accommodation as the focusing on objects at different distances

http://www.youtube.com/watch?v=p_xLO7yxgOk&feature=related

Accommodation in distant objects and close objects

Long distance:

When an object is closer than 6m the need for refraction is more necessary. The Ciliary muscles contract which makes the lens shorter and thicker, shortening its focal length.

Close distance:

When an object is more than 6m distant, the light that is reaching the eye are almost parallel, therefore the refraction is less intense. The Ciliary muscles remain relaxed; therefore the lens will become long and thin.

• Compare the change in the refractive power of the lens from rest to maximum accommodation.

The change in the refractive power of the lens is closely related to accommodation. For far objects, the refraction level or bending of light which passes through the lens is not as strict. The Ciliary muscles are relaxed and the tension in the attachments from the lens are thing and the lens is flat or at its lowest refractive power. As the eye concentrates on the closer objects, the light rays diverge; therefore the refractive power is at its strongest point and at its maximum accommodation.

The refractive power of the lens is measured in diopters. When an object is brought closer to the eye, the focal length must be changed for the image to be clear on the fovea of the retina. For instance, an object that is 1 metre away from the eye, it must have a focal length of 60 diopters for the image to be seen clearly. As a person’s eye gets older by age, the lens becomes more rigid and loses the ability of its flexibility therefore, its ability to change its shape fluently (1.5 diopters). In comparison to a baby, who starts with a total accommodation power of approximately 15 diopters.

• Distinguish between myopia and hyperopia and outline how technologies can be used to correct these conditions

Myopia:

A clip identifying a technology ‘corneal refractive’ to correct myopia

http://www.youtube.com/watch?v=XbzC1LG8Xoo

Hyperopia:

Different corrective technologies available

http://www.youtube.com/watch?v=GmbPWoLvEjQ

Corrective measures to assist in accommodation

• Explain how the production of two different images of a view can result in depth perception.

Depth perception is the ability to accurately judge the distances of different objects. Depth perception is due to the formation of two different images of a view of objects that are different distances away from the eye. The two images are fused into one image in the cerebral cortex of the brain. Humans obtain stereoscopic vision which thus depends on the way two eyes are separated horizontally. These will therefore the views of objects are located in different distances. When an object is different in distance, the apperception of depth occurs.

This is a binocular or stereoscopic vision

Each of the eyes take the object from a different angle. As the two images combine it creates one depth and dimension

• 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.

Photoreceptor cells are neurons modified so that they are sensitive to light. Thus, they are the containing light sensitive pigments which convert light images into electrochemical signals that the brain can interpret. There are two different photoreceptors within the eye; rods and cones. Cones enable animals to perceive colours whereas the rods enable light and peripheral vision.

Photoreceptor cells containing light sensitive pigments

Describe the differences in distribution, structure and function of the photoreceptor cells in the human eye.

The retina is a thin layer that contains the photoreceptor cells. There are light sensitive cells which are activated by light energy to produce an electrochemical signal which therefore travels along the neurons which is then linked to the brain. In the retina, there are two types of photoreceptor cells; rods and cones. Both of these are modified neurons.

The rods are long-rod shaped cells which are sensitive to low levels of light; unfortunately they are unable to discriminate colours. They are mainly used for night vision as they are responsive to various light intensities. Cones are cells which contain pigment; they are responsible for the colour vision during the daytime. They are also used for clarifying images.

Cones are suitable for day time, cones need a high intensity of light to distinguish a coloured image. If it is night then the visual representation is mainly a blue-green light, this is due to the lack of light passing through the retina.

Structure of the rods and cones

Outline the role of rhodopsin in rods.

Rhodospin is the light absorbing pigment in the rods. In this way the light images formed on the retina are converted into electrochemical signals for the brain to interpret. As rhodospin absorbs light, it changes its shape causing a decrease in the amount of inhibitory neurotransmitters in the synpases between photoreceptor cells and bipolar cells. Rhodospins allow the ability to see shades of grey, black and white. There is only one type of rod and their rhodospin which are sensitive to blue –green light.

As light hits the rhodospin it causes a chemical change which creates decomposition. The active rhodospin changes the charge of rod cell and creates an electric current along the cell. This electric message is sent along the rod to the ganglion, which is connected to the optic nerve. The optic nerve sends the message to the visual cortex so light will be interpreted into an image.

Demonstrates the light energy which passes through the rhodospin allowing the changes in membrane permeability which alternatively implements action potentials

Identify that there are three types of cones, each containing a separate pigment sensitive to either blue, red or green light

There are three types of cones, each containing a separate pigment sensitive to either blue, red or green light. There are molecules called photospins and they are involved in the colour vision. Each of the separate pigments differs in wavelengths of light that they absorb.

Blue region = 420nm

Green region = 530nm

Red region = 560nm

Wavelengths of each of the photosensitive pigments in cone cells absorb

• Explain that colour blindness in human’s results from the lack of one or more of the colour-sensitive pigments in the cones.

Colour blindness occurs when individuals are unable to distinguish certain colours. It is caused by a sex linked genetic deficiency, which affects more males (approximately 10% of the population) than females (1% of the population). There are three types of colour blindness: red-green(protanopia and deuteranopia), blue-yellow(tritan) and the rarest black and white pigments present in vision. The total colour blindness in which there are no cones is extremely rare; the individual is only able to observe with black and white vision.

Consists of the Protanopia, Tritanopia and Deuteranopia

Explain why sound is a useful and versatile form of communication.

Sound is the ability of individuals to communicate with each other. Therefore, it is essential as it is required for survival. This does not depend on light and therefore can operate 24 hours a day. Sound can travel through solids as well as liquids and gases which further emphasises the versatility. This means that it can be used in dense environment such as forests. Human speech is the most sophisticated form of sound as is the sole basis of language upon most of our civilisation depends on it.

The use of sound can also act as a direction shadow which enables humans to hear without directly seeing the object. When an object vibrates it produces a series of disturbances in the particles surrounding it, thus, the energy which is created by the vibrations travel outwards three dimensionally from the source of the sound as a compression wave. It allows sound to move further apart, known as rarefaction.

Sound can be manipulated easily, this is essential for animals as they are able to change the pitch or amplitude of a sound to send different messages. Sound is also useful for animals searching for prey. Overall, the utilisation of sound can easily be detected through a sense of vibrations allowing a form of communication.

Demonstrates a human speaking, it is essential for the communication of civilisation

This animation shows how the use of sound was able to identify a bird whilst not being able to see it visually.

http://www.youtube.com/watch?v=XLdwW9kJN_g

• 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 backwards or forwards. These vibrate that are set up have the same frequency in the medium through which the sound is passing. The mediums which are detected by the structure such as the ear are converted into sound for the brain to interpret. This is seen through the clip http://www.youtube.com/watch?v=zAVOOy_O-Lw&feature=related

For example, if a tuning fork vibrates at 256 hertz, it sets up the air particles vibrating at 256 hertz. Thus, the 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 sound.

The wavelength shows that the same frequency sound that started is sent to the ear at the same frequency

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 in front of the fourth, 5^th and 6^th cervical structures. It forms the top part of the trachea. The larynx is a tubular organ made of cartilage allowing it to surround and protect the vocal folds. The larynx surround a narrow opening in the trachea called the glottis.  When air is exhaled, it rushes by a pair of vocal cords in the larynx which produces sound when voluntary muscles in the voice box are tensed, which therefore stretches the cords so they vibrate.

The structure of the whole tract. All of these structures are responsible for producing different qualities of sound

High pitched sounds result when the cords are stretched tightly and vibrate rapidly. The vocal folds open and close more frequently if it is a high pitched sound; low pitched sounds comes from less tense cords vibrating slowly. By looking down into the larynx, the positioning of the vocal folds in order to produce sound is different.

As the positioning of the vocal folds change, the frequency of the sound waves also changes. These results in high pitched frequencies to become more tensed and low pitched to become less tensed.

Looking down on the larynx identifying the result of different frequencies due to the different tensions of the larynx

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

Insect:

Insects use mechanoreceptors to identify vibrations on the ground

Mammal:

Humans use ears to detect sound. Consisting of three main segments

Fish

Fish use swim bladders to send the signals on to the ear where the hair cells detect and send it to the brain for it to interpret

• 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

This animation displays the structure of the ear:

http://www.youtube.com/watch?v=7a2aoZeZhZ8

Structure of the ear, including the outer, middle and inner ear

Outline the role of the Eustachian tube.

The Eustachian tube is a long narrow tube that opens in the middle ear which leads to the pharynx. The main role of the Eustachian tube is to equalise the pressure between the outer and inner ear, this aids the tympanic membrane as it is not forced into a position it would usually not occupy. The inner ear can maintain the same pressure as the outer ear due to the equalisation. The tympanic membrane stays in its usual position and the ear is able to hear normally again.

The Eustachian tube opens during swallowing, sneezing and yawning. When the Eustachian tube is patent it allows the ventilation of the middle ear and equalisation of the middle ear and atmospheric pressure. The Eustachian tube also protects the middle ear from nasopharyngeal secretions and sound.

Shows the location of the eustachian tube within the ear

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

The external ear:

When the sound energy in a sound wave hits the pinna, the pinna then collects and channels the vibrations down into the ear canal. The sound energy then moves down the end of the tympanic membrane causing a vibration. The sound energy is thus transformed into a mechanical energy of the tympanic membrane.

The middle ear:

As vibrations are transformed from the tympanic membrane it proceeds to the oval window. As they vibrate the three main bones: malleus, incus and stapes behave like a lever. This reduces the amount of amplitude of sound on the tympanic membrane to avoid the damage to the eardrums. It also increases the force of the vibrations on the oval window creating an improved quality of low frequencies. It is then transferred into the round window.

The inner ear:

The pressure wave in the cochlear fluid passes the vestibular canal and back. The fluid pressure waves push onto the cochlearduct and on the membranes close to the ‘Organ of Corti’. The movement of membranes bends the cochlear hair cells stimulating the nerve cells. The sound energy travelling through the air is converted from mechanical energy into electrical energy in the solids and liquids of the ear structures. The message is then sent, via the auditory nerve, to the brain where it is interpreted.

The hair cells detect low frequency sound waves; the high frequency sound waves are detected by the outer hair cells

Outlines the steps in the sound waves through the external, middle and inner ear

• 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 stretches the length of the cochlea. This has three main components: the basilar membrane, hair cells and the tectorial membrane. The basilar membrane is composed of transverse fibres of varying lengths. The vibrations which are received at the oval window are transmitted to the fluid of the cochlea, the cochlea nerve fibres are coiled around the base of hair cells. This causes the vibrations at certain places according to the frequency. As the basilar membrane vibrates, the hair cells which are responsible for the detection in certain frequencies are pushed against the tectorial membrane causing the hair cells to send electrochemical impulses along the auditory nerve for the brain to interpret. Each of the hair cells have a different length detecting different frequencies.

APEX of OCC = Low

BAST of OCC = High

http://www.neurophys.wisc.edu/animations/cochlmtn.mov

The animation shows the detection of sound by the organ of Corti.

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

The sound shadows (or sonic shadow) are a phenomenon caused by the obstruction or absorption of a sound wave by an object in its path. This means that when a sound vibration strikes the closest ear, the intensity is much stronger than the one further away, this is due to the fact that the head blocks some of the intensity of the sound – this needs to be refracted or bent around the head.

Humans are not able to move their ears, this is due to the pinna, which consists mainly of skin and cartilage and muscles. For other animals such as rabbits locate the direction of sound by comparing the sound intensities between the two ears. They are able to move their ear accordingly to distinguish the detection of sound.

The sound shadow: illustrates that the head acts as a shadow whereby the closest ear hears more of the sound

Bibliography:

Websites

http://www.visionrx.com/library/enc/enc_conjuctiva.asp

http://library.thinkquest.org/28030/ana/int.htm

http://www.macula.org/anatomy/retinaframe.html

http://www.macula.org/anatomy/eyeframe.html

http://www.bcm.edu/oto/grand/71196.html

http://www.virtualmedicalcentre.com/anatomy.asp?sid=29&page=1

http://www.virtualmedicalcentre.com/anatomy.asp?sid=29&page=2

http://www.gooddive.com/scuba-diving-glossary/images/ear-eustachian-tube.jpg

http://insects.about.com/od/morphology/f/hearing.htm

http://www.rci.rutgers.edu/~uzwiak/AnatPhys/ChemicalSomaticSenses_files/image020.jpg

http://www.american-hearing.org/images/master-ear.jpg

http://www.pskf.ca/sd/images/dcp_4970.jpg

http://startproducingmusic.com/wp-content/uploads/2008/08/wavelength-cycles-frequency.jpg

http://www.colblindor.com/2007/04/17/deuteranopia-red-green-color-blindness/

http://www.colblindor.com/2006/05/08/tritanopia-blue-yellow-color-blindness/

http://www.colblindor.com/2006/11/16/protanopia-red-green-color-blindness/

http://cas.bellarmine.edu/tietjen/Laboratories/Eye07.gif

http://library.thinkquest.org/5053/Australia/Platypus_J01.jpg

Biology Textbooks

Biology Sixth Edition published 2002 By Campbell Reece

NSW Biology published 2007 By Carolyn Jeffery, Pauline Ross

Biology in Context(The Spectrum of Life) Second Edition By Peter Aubusson, Eileen Kennedy, Peter Hickman