HSC YEAR 12 BIOLOGY Communications First I would like to say that this document should be used as a guideline in building your own syllabus answers, rather than copied and memorised. The latter strategy will work against you in exams. Identify the role of receptors in detecting stimuli A stimulus is a change in the internal or external environment. Examples include: light, sound, temperature, pressure, pain and certain chemicals (hormone levels). Receptors are range of specialised cells that detect these stimuli and generate nerve impulses to inform the nervous system of their presence, which then carries out appropriate responses. Receptors are distributed all over the body such as pain receptors in the skin. Some receptors are concentrated in an organ such as the cones in the eye. Explain that the response to a stimulus involves: A receptor detects a change and sends a message via messager nerve cells to the brain; the brain then interprets the change and sends a message again via nerve cells to an effector organ to produce a response to counteract the change. This reduces the effect of the stimulus and restores the body back to a stable state. Once this is achieved, the brain sends another message to stop the response. Describe the anatomy and function of the human eye Conjunctiva - A delicate membrane that covers the visible surface of the eye and inside surface of the eyelids. It protects the front of the eye by acting as a shield and reducing friction. Cornea - the relatively thick and transparent frontal part of the eye. It refracts light towards the retina, to assist in forming an image. Sclera - A white, tough coating that continues from the Cornea and covers the entire eyeball except the front. It protects the eye and helps maintain its shape.
Choroid - A thin black pigmented layer containing blood vessels that lie on the inside of the Sclera. Choroid supplies parts of the eye with blood and absorbs scattered light to prevent formation of false images. Retina - The innermost layer of the eye containing photoreceptors and nerve fibres. It receives and converts light into electrical impulses that would travel to the brain via optic nerves. Iris - A pigmented muscular structure in the front of the eye that controls the size of the pupil and thus the amount of light entering the eye (Relaxes to dilate, tighten to contract). Lens - A flexible transparent bioconvex protein disk found behind the pupil. Lens allows the fine focus of light onto the retina. Aqueous and Vitreous humour - Aqueous humor is a clear viscous liquid that fills the front of the eye and supplies nutrients to cornea and lens. Vitreous humour is jelly like substance that fills the back chamber of the eye. Both substances maintain the shape of the eye and help refract light towards the retina. Ciliary Body - Ciliary bodies contain ligament and muscles that connect the Choroid with the lens. The ligament holds the lens in position while the muscles alter the shape of the lens. Optic Nerve - Optic nerves are nerve cells that connect the eye to the brain. Optic nerves carry the electrical impulses produced by the retina to the visual cortex of 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 (doing two dots in one go) Only a limited range of the electromagnetic spectrum known as visible light can be detected by human eyes. This is because most of the light from the sun is in this range, and the selective mechanism of natural selection. The visible light spectrum corresponds to electromagnetic waves with wavelengths between 400nm-700nm. Different wavelengths constitutes for different colours we see, red, orange, yellow, green, blue and violet. Colours not only allow human to distinguish and identify objects but also allows us to assign various attributes to their colourful appearances, e.g. ripen fruit have darker colours compared to fruits that are not ready to eat.
Some animals have receptors cells that detect different ranges of radiations compare to humans, that is, they have visual acurity in other parts of the electromagnetic spectrum. Rattlesnakes can detect infrared radiation, since their prey radiate heat in forms of infrared their vision is a great asset in hunting. Honeybee can detect ultraviolet radiation (300nm to 650nm), allowing them to detect ultraviolet markings on flowers and find pollen. It also allows them to uses polarised light for navigation. As markings on insect look very different under ultraviolet radiation, UV vision is also used for mating. This difference in detection comes about because of differences in the visual pigments found in the photoreceptor cells of these organisms. Also the proportion, distribution and size of rods and cones bring about differences. Identify the conditions under which refraction of light occurs & Identify the cornea, aqueous humor, lens and vitreous humor as refractive media Refraction is the bending of light. It occurs when light passes from one medium to another with a different density at any angle except 90 degrees to its surface. In the eye, the cornea, aqueous humour, lens and vitreous humour act as refractive media. They allow incoming light to be focused on the retina. Identify accommodation as the focusing on objects at different distances, describe its achievement through the change in curvature of the lens and explain its importance & Compare the change in the refractive power of the lens from rest to maximum accommodation & Analyse information from secondary sources to describe changes in the shape of the eyes lens when focusing on near and far objects Light entering the eye from different distances enters at different angles and thus forming different focal lengths. Therefore in order to have clear vision at all distances, the eye must be able to adjust its refractive power, so that the focal point is always rest on the retina regardless of distance. The eye achieves this by altering the shape of the lens. This fine adjustment is known as accommodation. The shape of the lens is controlled by the ciliary muscles. To view distant objects, the ciliary muscle relaxes and pulls on the lens to keep it thin, reducing its refractive power (higher focal length). To view close objects (less than 6m away), the ciliary muscles tighten and contract inwards towards the
lens, allowing it to bulge, increasing its refractive power (less focal length). Accommodation is of major importance in clear vision, if absent, light may converge in front or behind the retina resulting in blurred vision. Distinguish between myopia and hyperopia and outline how technologies can be used to correct these conditions. Hyperopia is long sightedness. People with hyperopia can see distant objects clearly but not close objects. Possible causes are: the eyeball is slightly too short or the lens is too weak, and as a result light from close objects are focused behind the retina resulting in blurred vision. Myopia is short sightedness. People with myopia can see close objects clearly but not distance objects. Possible causes are: the eyeball is elongated or the lens is too strong, light from distance objects are focused in front of the retina, resulting in blurred vision. Technologies such as spectacles and contact lens can be used to correct hyperopia and myopia. Convex lens allows angular light rays (light from close objects) to converge before entering the eye so therefore can be used to correct hyperopia. Concave lens can cause parallel light rays (light from distant objects) to diverge before enter the eye so therefore can be used to correct myopia. The use of contact lens however can cause problems such as decrease in oxygen supply to the eye and the possibility of damage to the eye upon insertion and removal of the contact lens. Over use of contact lens can also risk infections. Surgery that can correct both hyperopia and myopia involves changing the shape and the refractive ability of the cornea by using lasers. A recent development involves the use of contact lenses implanted between the lens and the iris for correction. These technologies are usually very costly, but they come with very high success rates. The quality of life is heavily reduced for those who loses their vision or hearing, it also risks lives in developing countries. Suffers usually loses their jobs and their roles in society and usually fail to contribute. The use of technologies to restore sight and hearing enables suffers to live independently and to live productive lives with less reliance and cost on others. Their quality of life is restored as they are able to read and write, participate in conversations, watch TV and interact with
others. It allows them to work, earn a living and support a family and maintain roles in society. These technologies have increased life expectancy in areas all around the world. Explain how the production of two different images of a view can result in depth perception Depth perception is the ability to judge distances. It is achieved by having 2 forward facing eyes that produces a 3 dimensional vision. The brain interprets the 2 images from each eye by superimposing them to produce a single binocular vision. The brain uses slight differences in 2 images to create a 3D vision that allows us to calculate depth. Depth perception can also be achieved from previous experience of the size of an object, and the parallax effect i.e. when the head is moved, distant objects move less compared to close objects. 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 & Describe the differences in distribution, structure and function of the photoreceptor cells in the human eye & Outline the role of rhodopsin in rods & Identify that there are three types of cones, each containing a separate pigment sensitive to either blue, red or green light Photoreceptor cells are modified nerve cells containing visual pigments. These cells are capable of detecting and converting light images into electrical impulses that the brain can interpret. There are 2 types of photoreceptor cells: rods and cones. These cells can be found in a thin sheet on the retina of the eye. Rods are about 20 times more numerous than cones. Rods are spread out across the retina but are more densely packed on the periphery of the retina. Rods are long rod shaped cells containing the visual pigments known as rhodopsin. These pigments consist of joining retinal molecule and scotopsin protein. This pigment is sensitive to lower level of light but cannot discriminate between
colours. Therefore rods are responsible for night vision and are capable of detecting fine movement (In a dark room pupils dilate to expose more rods on the periphery of the retina, to establish night vision). Cones are also spread out across the retina but in groups. They are densely packed in the centre of the retina also known as the fovea. Cones are conical cells containing the visual pigment photopsins. This pigment consists of joining retinal molecule and one of the three types of photopsin protein. Each type of photopsin protein absorbs light of different wavelengths i.e. light of different colours, red, green and blue. This allows the visual pigment to discriminate between colours but they only be activated with high intensity light. With their exclusive connection to the brain via the optic nerve, cones allow the brain to interpret images with great detail and in a blend of colour, as long as the required intensity of light is provided. Different cones are stimulated by different colours; the rate and magnitude at which the different cones are stimulated determines the overall colour. For the reasons above, the fovea corresponds to the area with the highest visual acurity. (The visual pigments on these photoreceptor cells work by converting light energy into chemical energy and then to electrical energy, producing nerve impulses that are sent to the brain where they are interpreted as images.) When light energy is absorbed by the visual pigment known as the rhodopsin in rod cells, a series of chemical reactions occur, causing the pigment to undergo a reversible structural change, where the bond between the retinal molecule and its opsin protein is temporarily broken. This generates electrical impulses that are sent to the brain via the optic nerve, where they are interpreted as images. Enzymes convert the pigments back to its original form there is an absence of light energy. Because rhodopsin is highly sensitive to light, the visual pigments are in its excited states most of the daytime and are restored by enzymes at night. Explain that colour blindness in humans results from the lack of one or more of the coloursensitive pigments in the cones Colour blindness in humans result from the lack of one or more photopsins in the cone cells in the retina. The most common is the red green colour blindness. People with this condition cannot distinguish between red and green. This is because either the red or green cods are missing or are not functional. This is an inherited sex-linked disease, which is more common in males.
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 Cataract is the cloudiness or darkening of the lens in the eye that reduces its transparency. It occurs from progressive denaturing and oxidisation of the constituent proteins. The cause of such denaturing includes aging, genetic factors, diseases such as diabetes, injuries to the eye and the use of drugs. In the early stages of cataract, the lens may increase in strength, temporarily curing long sightedness. The yellowing of the lens will reduce perception of blue colours. If cataract is left untreated, blurred vision or and permanent blindness will occur. Cataracts correction surgeries aim to remove the damaged lens by physical operation or by high frequency sound. After removal, an intraocular lens is inserted to permanently replace the lens. Because the intraocular lens is not as flexible as the organic lens, patients usually requires glasses after surgery. Cataracts operation is cheap, simple and has high success rate. The quality of life is heavily reduced for those who loses their vision or hearing, it also risks lives in developing countries. Suffers usually loses their jobs and their role in society and thus affects those around them and the society negatively. The use of technologies to restore sight and hearing enables suffers to live independent and productive lives with less reliance and cost on others. Their quality of life is restored as they are able to read and write, participate in conversations, watch TV and interact with others. It also allows them to work, earn a living and support a family and maintain roles in society. These technologies have increased life expectancy in areas all around the world. 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 The function and nature of photoreceptor cells varies among species. However they all contain basic visual pigments that are capable of absorbing light energy and converting this into electrical impulses that are sent to and interpreted by the brain. Mammals such as humans have complex single lens eye capable of accommodation to produce an images on the retina. The photoreceptors in humans are rods and cones. Rods being sensitive to low intensity light and cones used for colour vision.
The simplest photoreceptor cells are found in cup eye of the flatworm. These photoreceptor cells do not form an image and can only detect the presence of light with no colour. These worms use this for directional information. Insects such as bees have compound eyes with thousands of light detecting units called ommatidium. Each ommatidium has its own lens to focus light onto photoreceptor cells. This allows insects photoreceptor cells to detect fine movements accurately in large field of vision. The photoreceptor cells in insects can recover from their structural changes rapidly. This allow them to detect up to 300 flashes per second, enabling them to see even when flying at speed. Bee's photoreceptor cells also allow them to view UV light for identifying flower patterns. 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 While most vertebrates have very good colour vision, most mammals do not as they are nocturnal, with the exception of primates. Occurrence of colour vision depends on the presence of cone receptors cells. Colour is usually used by animals for protection, mating, aggression and for finding food. Primates have three types of cones cells present in its retina for colour vision. Humans have very high concentrations of cones in the fovea of the eye. Thus humans have strong colour vision that allows humans to clearly distinguish between objects. Other primates such as baboons use colour as part of sexual behaviour. They display bright bands of colours when they are sexually mature. Primates also eat fruit, by detecting the colour of the fruit, primates can identify whether the fruit is ripe. Animals such as octopuses and chameleons have pigment cells that allow them to be camouflage against their environment, abusing the colour visions of predators for its survival. Octopuses can also use this colour change to attract preys and to show alarm. This clearly displays a relationship between colour vision and colour communication in animals.
This is again supported by the fact that nocturnal life style required minimal colour differentiation thus nocturnal animals very high concentrations of rods rather than cones and do not have strong colour vision. Also invertebrates such as insect do not detect colour because of their distinctive need for detection of subtle movements rather than distinguishing between objects. Explain why sound is a useful and versatile form of communication Sound is a very versatile and useful form of communication because: 1. Sound has many features that can be varied, e.g. pitch, loudness, speed and length. This allows sound to communicate complex information. 2. Sound is useful in both day and night. It travels over long distances and in many different range of mediums (such as air and water), and diffract around corners. Therefore the sender does not need to be visible to the receiver. The nature of sound waves also allows the source of the sound to be determined by using sound shadows. 3. Sound can be readily produced by vibrations with little effort while carrying large amount of information. Sound is used for mating, defensive purposes and warnings of danger. 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 created by vibration of objects such as air and water particles. This vibration results in a mechanical longitudinal wave that can be detected by various mechanisms. Unlike EMR sound cannot travel through a vacuum. The frequency of sound is the same as frequency of the vibrating object.
Outline the structure of the human larynx and the associated structures that assist the production of sound Human sound production is carried out by the larynx situated in the front of the neck. It consists of a ring of cartilage containing two elastic fibres called vocal cords. Controlled vibrations of these two vocal cords while changing their tension (higher the tension, higher the pitch), oscillates the air particles pushed up by the lungs, creating sounds of varying pitch. The brain assist in speech creation by determining and instructing which kind of sound is to be produced. The sound produced by the larynx is finetuned by the tongue, hard and soft palate, the teeth and the lips to meets the speech demands of the human language. The loudness of the sound is proportional to the amount of air pushed up from the lungs. Outline and compare the detection of vibrations by insects, fish and mammals Mammals have evolved to have very versatile hearing systems. Their sensory organs are sensitive to sound energies well below the threshold for other organisms. Humans are able to detect sounds between 0.02 khz to 20 khz. However the human ear is most sensitive to sounds of 2-4 khz. This corresponds to the speech band. This is driven by the social demand and the need of language in a human life. Other mammals such as dolphins and bats can detect sounds of much higher frequencies. This is because of their need for echolocation, in which very high frequency pulses of sound are emitted. The pulses will be refracted and reflected by objects in its path. These disturbed pulses can be analysed by the organism to determine an object's size, position and movement. This enables them to avoid or seek the object out. The kangaroo rat can detect sounds of very low frequencies 0.125 with great detail, such as those made by its predators such as the wing beat of an owl or the rustle of a snake.
Describe the anatomy and function of the human ear & Outline the role of the Eustachian tube & Outline the path of a sound wave through the external, middle and inner ear and identify the energy transformations that occur & Describe the relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies The Eustachian tube connects the middle ear to the nose and throat passages. The tube opens when we yawn or chew to allow air from the two air filled spaces to enter the middle ear. This equalises the air pressure on either side of the tympanic membrane. This maintains accurate vibration of the eardrum and also provides protection by holding it in place and preventing any excessive bludging of the eardrum. In the outer ear, sound waves collected by the pinna travel down the ear canal to the typanic membrane. The membrane is vibrated by the sound waves and thus converts sound energy into kinetic energy. In the middle ear, the ossicles mallus, incus and stapes receive, intensify and transmit the vibration from the typanic membrane to the oval window. The oval window immersed in cochlea fluid, vibrates creating fluid motion in the cochlea of the inner ear. This kinetic motion is converted into electrical energy by the mechnoreceptor hair cells found on the organ of corti in the cochlea. These electrical impulses are sent to the brain via auditory nerves. The organ of corti runs along the length of the cochlea. The organ of corti consists of the basilar membrane, hair cells and tectorial membrane. When the bascilar membrane vibrates, it pushes hair cells against the tectorial membrane. This contact causes the hair cells to send an electrical impulse to the auditory nerve. The hair cells in the initial part of the basilar membrane are stimulated by high frequency sounds as it travels short distances. The hair cells at the end part of the membrane are stimulated by low frequency sounds as it travels further. The nerve impulses generated from different lengths of the organ of corti stimulates different auditory regions in the brain, this allows us to perceive sounds of different pitch.
Outline the role of the sound shadow cast by the head in the location of sound Sound shadow refers to the region which does not receive direct sound as the head is blocking the vibration. The difference in loudness and time of arrival of sound in each ear allows us to determine which ear the sound entered first. With this, the source of the sound can be easily located. If there is no difference in arrival time and loudness, the head needs to be turned in order to determine the source. Gather and process information from secondary sources to outline and compare some of the structures used by animals other than humans to produce sound Animals use a range of structures to produce sounds. Grasshoppers and crickets rub the pegs on their hind legs against the ridges on their wings to create sounds. This is called stridulation. Frogs squeezes their lungs to puff up their air sacs under their throat while shutting their nostrils and mouth. This air is released over their vocal cords to produce a croaking noise. Fish rub bones or teeth against each other and can also vibrate their swim bladders to create sound. Bats produce very high frequency soundwaves from their larynx. 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 Insects, mammals, fish all have analogous structures that contain mechnoreceptors cells that convert sound energy into electrical impulses interpreted as sounds by the brain. Insects such as caterpillars have fine long hairs on the exterior body that response to low frequency sounds. Grasshoppers have tympanic membranes wrapped over air chambers found on their bodies. The membrane picks up sound vibrations and transfers them to the mechnoreceptors within the air chamber.
Fish have lateral line systems that run along the length of their bodies. The system contains neuromasts that response to vibrations in the water. Fish also have an inner ear system that contains mechnoreceptors stimulated by vibrations in the water. Fish also have swim bladders that transfer water vibration to the inner ear. Mammals such as humans have outer ears that funnel sound waves down the ear canal. The sound waves cause vibrations in the tympanic membrane, followed by the ossicles, oval window and the cochlea. The mechnoreceptors in the cochlea known as hair cells convert this vibration into electrical impulses sent to the brain via the auditory nerve. Process information from secondary sources to evaluate a hearing aid and a cochlear implant Hearing aids are devices attached to the pinna of the ear. The device picks up sounds from the environment and converts them into electrical impulses. An amplifier microphone converts these impulses into a louder version of the original sound. Hair cells in the inner ear convert this louder sound into impulses which are interpreted by the brain. Energy transfer in the hearing aid: sound energy > electrical energy > sound energy (louder). Hearing aids help those with damage in the outer and middle ear, i.e. damage to the eardrum and or the ossicles resulting in poor transfer of sound energy. The user must have some residual hearing ability, i.e. it does not assist those with damage to hair cells or auditory nerve. Limitation includes: - Some sound frequencies cannot be detected, causing distortion. - Feedback. - Non selective amplification, all sounds including loud noises are amplified this can be annoying. - Picking up individual sounds in a crowd can be difficult. - Battery may run out. Advantages: - Relativity cheap. - Easy to wear and operate.
- No surgery is required. Cochlea implants consist of an external microphone positioned behind the ear that receives sound energy and sent it to a speech processor located on the belt. The processor selects relevant sounds and converts them into radio waves. These radio waves are picked up by a receiver surgically implanted beneath the skin just outside of the skull. The receiver converts these radio signals into electrical impulses that directly stimulate the auditory nerve. Energy transfer in the cochlea implant: sound energy>electromagnetic (radio waves)>electrical energy. Cochlea implants are helps those who are profoundly deaf with damage in the inner ear, i.e. hair cell damage. However a functional auditory nerve is still needed. Limitations include: - Some sound frequencies cannot be detected, causing distortion. - Feedback. - Relativity expensive. - Risks in surgery. - The need to carry the speech processor. Identify that a nerve is a bundle of neuronal fibres & Identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes & Define the term threshold and explain why not all stimuli generate an action potential A nerve is a bundle of axons or nerve fibres bound together. A neurone is a nerve cell. Neurones conduct electrical messages, also known as nerve impulses, from one part of the body to another. This generation of electrical impulses is known as action potential.
Initially neurones actively pump put positive sodium ions, keeping a higher concentration of negative potassium ions on the inside of the neurone. Thus the inside of the cell is negative relative to the outside. This is the polarised resting potential of -70mV. When the neurone is stimulated either by a stimulus or neurotransmitters, the membrane of the cell becomes permeable to sodium ions, allowing them to rush into the cell. This depolarises the cell, making the inside positive. If this depolarisation creates a potential difference of +15mV or greater, an impulse will flow down the axon to the synaptic nob of the cell due to cycles of depolarisation/repolarisation. This is the action potential. Threshold refers to the minimum strength of a stimulus needed to initiate an action potential. When the strength is below the threshold, not enough sodium ions move into the cell and depolarisation creates a potential difference of less than +15mV therefore will not generate an electrical impulse. Each stimulus either produce a full or no potential. The cell can only produce another potential once the first one is complete. When an electrical impulse reaches the synaptic nob, neurotransmitter is released from the terminal, and it passes the synapse to the dendrites of the next cell causing a new electrical impulse in the next cell Eye dissection prac Equipment: bull or sheep eye, scalpel, dissection scissors, disposable gloves, probe, forceps, newspaper, dissecting tray Safety: care with sharp objects, make use of forceps to hold the eye when cutting, and dispose of the eye and gloves after practical Method: 1. Put on gloves, place eye on the tray. 2. cut away any fatty tissue around the eye 3. Examine external feature of the eye - Conjunctiva, initial membrane covering the front of the eye - Cornea, the transparent hard covering of the eye - Optic nerve at the rear of the eye
- Sclera, the tough outer white covering - Iris - Pupil, the dark opening - Any muscles attached to the eye 4. Cut the eye in half; examine the liquid released (aqueous humour) 5. Remove the lens, try reading newsprint with it, and observe the effect of gently squeeze it. 6. Examine the jelly like substance behind the lens (vitreous humour) 7. Rinse the eye and examine the retina 8. Wrap all eye parts in newspaper and dispose of it 9. Dispose of gloves Modelling accommodation prac Equipment: light box, thick convex lens, thin convex lens, pencil, paper, power pack. Method: 1. On a piece of paper, draw a semicircle as the location of the retina. 2. Darken the room; collect the light box to the power pack. 3. Turn on the light box and place it some distance away from the paper 4. Adjust the light box so that 3 parallel lines are emitted 5. Use the thin convex lens in attempt to focus the 3 rays onto the "retina" 6. Replace the thin convex lens with the thick one. 7. Note any changes to the focal point 8. Adjust the distance between the lens and retina, in attempt to focus the rays back onto the retina. 9. Determine which size lens is used to focus distant and close objects Limitations: lens does not change shape, instead is replaced, many more rays than 3, other refractive medias in the eye. 2010 k02033 (from Bored of Studies forum). All Syllabus dot points are taken from the Board of studies USW and are copyrighted by the Board of studies USW. This material may not be reproduced in any form unless you agree: to use the material for information purposes only not to make any charges for providing the material to acknowledge that the material is provided by the original authors