Communication

1) Humans and other animals are able to detect a range of stimuli from the external environment, some of which are useful for communication.

Identify the role of receptors in detecting stimuli.

A stimulus is a change in the internal and external environment of an organism. Examples of stimuli include light, sound, temperature, pressure, pain and certain chemicals.

Living organisms detect stimuli using receptors. A receptor is a specialised sensory cell in a sense organ. As a result of detecting the stimulus, a nerve impulse may be generated or a hormone may be produced.

Sometimes receptors consist of single cells scattered over the body, such as touch receptors in skin. However, in many organisms receptors have become concentrated in particular areas to form sense organs (e.g. eyes, ears, or an endocrine gland such as the adrenal gland).

There is a range of receptor cells adapted to detecting specific stimuli, e.g. rods and cones in the eye. Receptors are commonly classed according to the type of energy to which they respond:

Stimulus Sense organ Sensory receptors Function SenseLight Eye Photoreceptors: rods and

cones in the retina of the eyeDetect light, colour and movement.

Sight

Sound Ear Mechanoreceptors: hair cells in Organ of Corti

Detect sound waves

Hearing

Chemical Tongue Chemoreceptors: taste buds Detect dissolved molecules

Taste

Chemical Nose Chemoreceptors: in nasal passages

Detect molecules in the air

Smell

Pressure Skin Mechanoreceptors: in skin Detect pressure on skin

Touch

There are several other receptors:A nociceptor sends signals that cause the perception of pain in response to

potentially damaging stimuli. They are sensitised by prostaglandins (fatty acids) and are desensitised by aspirin.

A thermoreceptor responds to changes in temperature. In the mammalian peripheral nervous system, there are receptors that respond to both heat and cold.

An electromagnetic receptor responds to light, magnetism and electricity. A photoreceptor is a specialised type of neuron that is capable of phototransduction (the conversion of a light signal to an electrical signal).

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Explain that the response to a stimulus involves: stimulus, receptor, messenger, effector, response.

Stimuli Receptors Messengers CNS Effectors Response

In order that a stimulus may produce a response, a receptor must detect the stimulus. A message must then be passed to a messenger, which may be a nerve or a hormone. The messenger then passes information through the central nervous system to an effector, which may be a gland or a muscle, which responds to the information.

For example, a bright light causes someone to close their eyes. The light receptor cells are able to pass on this information to messengers (nerve cells), which convey the information to the central nervous system. Other nerves then convey the information back to an effector such as a muscle or a gland that produces a response to the stimulus. Thus the muscles in the eye will cause the eye to close.

This is known as the stimulus-response model and is outlined below:

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Identify the range of senses involved in communication.

The senses are valuable characteristics for detecting changes in our environment and then registering sensations. They help us to survive and are also a means of communication to other organisms.

Senses Human examples Other animal examplesSight (visual) Facial expression signal

emotions including aggression● Bioluminescence in fireflies to attract mates.

● Female chimpanzees have a coloured rump to show when they are ready for mating.

● Blue-ringed octopus signal an intention to attack by glowing blue rings on their bodies.

Smell (olfactory)

Not so important in humans, human females may change

their menstrual cycle because of olfactory information

● Animals release pheromones to make their presence known.

● Male mice will mate immediately when they smell a receptive female.

Hearing (auditory)

Language used extensively to convey information, used as a

warning signal.

● Crickets use sound as a warning and to attract mates.

● Some moths can hear the ultrasonic calls of bats and can avoid being eaten.

● Frogs use sound for mating calls. ● Dolphins use echolocation.

Touch (tactile) Used in group bonding and in mating. Also used aggressively

● Seagull chicks get their mothers to release food by pecking on their beaks.

● Bees dance to communicate the location of food.Taste Five types of tastes:

Salty, Sour, Sweet, Bitter, Umami (Glutamate)

Some butterflies such as the Monarch butterfly have a bitter taste to communicate that they are poisonous

Touch as a method of communication:Shaking hands in humans is a gesture of greeting. Gestures of comfort such as hugging in humans and touching hands in chimpanzees are recognised examples of how touch is used as a form of communication. Touch may be used by many animals in courtship behaviour also. In some amphibian species (e.g. frogs), the male strokes the female during mating to stimulate her to release eggs.

Taste as a form of communication:Animals that have a poor sense of smell may rely more on taste as a form of communication. For example, after passing faeces male chameleons rubs his cloaca on branches to mark his territory. Other chameleons lick the branches of trees and shrubs to detect whether the territory is occupied. This makes up for the chameleon’s poorly developed sense of taste.

Smell as a form of communication:Animals such as dogs and mice rely to a large extent on their sense of smell to recognise trails and territory, locate food, recognise others, and find a receptive mate. Ants release pheromones which are an important form of communication between ants, attracting each other and marking out pathways to food.

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2) Visual communication involves the eye registering changes in the immediate environment.

Describe the anatomy and function of the human eye.

Structure Anatomy and FunctionConjunctiva Continuation of the epidermis of the skin. It protects the cornea

at the front of the eyeball from friction.Cornea Transparent to light. It refracts light to help form an image on

the retina.Sclera The white of the eye: a tough coat of fibres. It protects the

eyeball against mechanical damage and helps to maintain the shape of the eyeball.

Choroid A membrane containing pigment and blood vessels. It nourishes the retina and prevents internal reflection as it is black and

absorbs light.Retina Contains light-sensitive receptor cells connected to sensory

neurons. The retina detects light.Iris A pigmented muscular structure that contracts and dilates to

adjust the amount of light entering the eye.Lens A flexible, transparent structure which allows light to enter the

back of the eye. It refracts light to allow fine focusing of an image onto the retina.

Aqueous humour A watery fluid that helps to maintain the shape of the eye.Vitreous humour A jelly-like fluid that helps to maintain the shape of the eye.

Ciliary body Contains muscles. It supports the lens and alters the shape of the lens.

Optic nerve Consists of bundles of sensory neurons. It transmits impulses generated in the retina to the brain.

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Identify the limited range of wavelengths of the electromagnetic spectrum detected by humans and compare this range with those of other vertebrates and invertebrates.

Humans use the sense of sight to interpret much of the world around them. What we see is called “light”. However, humans only see a small part of the entire “electromagnetic spectrum.” Humans can see only the wavelengths of electromagnetic radiation between about 380 and 760 nanometres because our eyes do not have detectors for wavelengths of energy less than 380 or greater than 760 nanometres. Thus we cannot “see” other types of energy such as gamma or radio waves. Rattlesnakes, however, can detect electromagnetic radiation in the infrared range and use this ability to find prey.

Type of animal

Name of animal

Part of electromagnetic spectrum detected

Wavelengths detected

Vertebrate Human Visible 700-400 nmRattlesnake Infra-red and visible 850-480 nm

Japanese dace fish

Ultraviolet and visible As low as 360 nm

Invertebrate Honeybee Ultraviolet and visible 700-300 nmMantis shrimp

Ultraviolet and visible 640-400 nm

Nocturnal animals such as the rattlesnake are better hunters during the night because their prey cannot see them; however the snake is able to detect the prey’s body heat as infrared.

Similarly, deep-sea angler fish have no available light and use bioluminescence to attract prey.

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Perform a first-hand investigation of a mammalian eye to gather data to relate structures to functions.

We dissected a sheep’s eye to observe the structures of a mammalian eye.

S AFE W ORK P RACTICES :

Worked on newspaper inside a tray to prevent the displacement of any parts of the eye.

Disposed of sharp items (scalpels, tweezers and scissors) in a sharps deposit box.

Disposed of eye and materials by wrapping them in newspaper and placing in the bin.

We minimised hazards by wearing safety equipment: gloves, goggles and aprons. Rings and watches were removed to prevent tearing the gloves. Long hair was tied back to prevent cross-contamination.

Suggest reasons for the differences in range of electromagnetic radiation detected by humans and other animals.

Humans see only a limited range of the electromagnetic spectrum because it is all that is necessary to their survival.

Other animals have different needs to humans and thus they have adapted to suit these requirements. Snakes hunt at night for food, thus they are able to detect the infrared body heat of their prey even though they cannot see the prey visibly.

Ocean-dwelling organisms such as species of coral reef fish and some crustaceans are able to detect UV light. This can enhance the image that the organisms see, creating more contrast and thus allowing the organism to see more detail as necessary.

As humans do not hunt for prey at night nor live underwater, we do not have the need to see UV or infrared light.

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3) The clarity of the signal transferred can affect interpretation of the visual communication.

Identify the conditions under which refraction of light occurs.

In order to be seen an object reflects light, generates its own light or transmits light to our eyes. When light moves from one substance or medium to another, it is bent, or refracted. The speed at which the light is travelling also changes.

The movement of light through a denser medium is slower and is thus refracted to a greater degree.

When light is passed through a biconvex lens [shaped like ()], the rays are refracted toward a central point known as the focal point. The rays then cross over and diverge from that point. If a screen is placed in the pathway of the diverging rays, the resulting image is upside down or inverted.

Identify the cornea, aqueous humor, lens and vitreous humor as refractive media.

The density of the cornea, aqueous humor, lens and vitreous humor are similar to each other and all refract light that passes through the eye. The refractive power of air – through which light travels to reach the eyes of terrestrial mammals – is lower than the refractive power of parts of the eye. Therefore, the greatest degree of refraction in the human eye occurs when light moves into the cornea, since the change in refractive power is at its greatest point: the greater the difference in the refractive power of two media, the more the light is refracted when it passes from one medium to the other.

The lens is able to refract light to a greater or lesser degree by altering its shape. This is termed accommodation and is useful in allowing the eye to adjust for near or distant vision. The overall shape of the lens (its degree of curvature) determines the degree to which light can be refracted.

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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 term used to describe the focusing of objects at different distances, brought about by changing the convexity of the lens and, as a result, its refractive power. This change in the shape of the lens results from the action of the ciliary muscles, which in turn affect the tension of the suspensory ligaments that hold the lens.

Distant Vision – when the eye is looking at distant objects, light reaches the eyes in parallel rays. This light is focused on the retina by the lens in its resting state. The lens is quite flat and at its lowest strength or refractive power. This means that there is very little refraction or bending of light as it passes through the lens. The ciliary muscles are relaxed and tension in the attachments from the lens to the ciliary body keep the lens thin.

Above: The object is far away and the biconvex lens is elongated to slightly converge rays. The light rays are almost parallel.

Near Vision – when the eye is looking at close objects (less than 6m away), the light rays tend to diverge as they reach the eye. This means that the refractive power of the lens must be increased, achieved by the lens becoming more convex: bulging outwards. The contracting of the ciliary muscles causes the bulging of the lens, hence the image is focused on the retina.

Above: the light rays diverge from the close object. Highly rounded biconvex lens converge light rays – the focal length is longer.

Accommodation is important to allow clear vision. If the lens could not change curvature, the image would not be focused properly, resulting in a blurred image and hampering visual communication.

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

For distant vision the curvature of the lens must be relatively flat. When the ciliary muscles are relaxed they hold the suspensory ligaments taut, pulling on the lens and keeping it relatively flat (elongated lens) and allowing the image of distant objects to be focused on the retina, as light rays from distant objects tend to be parallel. Light rays are not greatly refracted when the lens is elongated, or slightly convex.

For near vision the curvature of the lens must be increased; a thicker lens has greater refractive power and a shorter focal length. The ciliary muscles thus contract, causing the suspensory ligaments to slacken. As a result, the lens becomes rounder (its curvature increases), known as a highly convex lens, refracting the light to a greater degree and allowing a focused image to fall on the retina.

Therefore, the refractive power of the lens changes from low (flatter lens) when at rest, to high (rounder lens) at maximum accommodation.

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

When the eyes face forward, each eye sees an image of an object in the light path. The two images are fused into one image in the cerebral cortex of the brain (called fusion).

Depth perception is the sense of depth that occurs when objects are viewed with binocular vision, dependent on the fact that a person has stereoscopic vision – that is, they view the world in three dimensions. The person’s eyes are separated and thus have slightly different views of objects located different distances away. When an object is a slightly different distance from each eye, it is imaged by each eye at a different distance from each fovea. This gives the perception of depth as this image is fused and seen to be a different distance from the eye to another object that is closer to the eye. The two objects are focused in different places on the retina and thus are seen as two images in their respective positions so there is depth to the picture that is perceived.

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

The eyes vary in shape and size from person to person, and these are often hereditary. If the cornea or lens is not the right shape, or the eyeball is too elongated or too round, the ability of the eye to refract light and focus it accurately onto the retina is affected. If light is not accurately transmitted it can result in the weakening of clarity of sight. Difficulties in seeing are called visual defects and include myopia (short-sightedness) and hyperopia (long-sightedness). They are not usually due to disease but as a result of how the body grows.

Myopia is when a person can see near objects clearly but distant objects appear blurred. Light from distant objects is brought into focus at a point in front of the retina surface as a result of an elongated eyeball. Myopia can be corrected with concave lenses in spectacles or contact lenses. The concave lens diverge the light before it reaches the eyes so that the objects in the light path are brought into focus on the retina.

Hyperopia results from a short eyeball or poor accommodation ability in the lens. It is the condition in which a person can see distant objects clearly but closer objects appear blurred. Close objects are focused behind the retina and thus are not clear. Hyperopia can be corrected with spectacles or contact lenses with convergent lenses, so the light is converged more strongly for close vision.

Other technologies to correct these visual defects include:

- Radial keratectomy: Fine surgical instruments shave small amounts off the corneal surface, thus refractive power is altered

- Photo-refractive keratectomy: involves the removal of the epithelium (outer membrane) and the surface of the cornea. The laser is used to shape the uppermost surface of the cornea.

- Laser surgery: lasers are used to shave the corneal surface, thus refractive power is altered.

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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.

A cataract is any clouding or opacity of the crystalline lens of the eye. They develop slowly and are more common in older people as they may be caused by general wear and tear as well as UV light exposure, metabolic disorders and smoking.

At present, the only effective treatment for cataracts is surgery, involving the removal of clouded lens or parts of it. The lens is then either replaced with artificial lens or sight is corrected with eyeglasses or contact lenses.

There are different types of cataract surgery:

Phacoemulsification: Removes the cataract but leaves most of the lens capsule in place. A small incision (3mm) is made where the cornea and conjunctiva meet and a thin probe is inserted, which transmits ultrasound waves to break up the cataract and suction out the fragments. The lens capsule remains in place to provide support for lens implants.

Extracapsular Cataract Extraction: Used when the cataract has advanced to a stage where phacoemulsification cannot break up the clouded lens. A larger incision (10mm) is required where the cornea and sclera meet. The nucleus of the lens capsule is removed in one piece and the soft lens cortex is vacuumed out, leaving the capsule in place. A clear artificial lens, called an intraocular lens (IOL), is then implanted into the empty lens capsule.

Intracapsular Cataract Extraction: Involves the removal of the entire cataract and surrounding capsule. An incision is made in the upper part of the eye and the cornea is folded back. A freezing probe freezes the lens and capsule to make extraction easier and to minimise bleeding during the surgery.

This technology is one of the greatest successes in medicine and surgery, as the removal of cataracts was previously very painful and required a long recovery period. Advancements in treatment have eliminated sutures, anaesthetic, and injections, thus surgery is safer, quicker and is easier to recover from. Modern surgery is also 90% successful in restoring vision.

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Perform a first-hand investigation to model the process of accommodation by passing rays of light through convex lenses of different focal lengths.

Normal Sight:

Myopia:

The focal length is too short and the focus needs to be moved.

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4) The light signal reaching the retina is transformed into an electrical impulse.

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.

The innermost coat of the eyeball, the retina, is a thin sheet of cells about one tenth of a millimetre thick. It consists of several layers of nerve cells, one of which is the layer of visual receptors – the rods and cones. Of all nerve cells in the retina, only the rods and cones respond directly to light, hence the name photoreceptors.

The rods and cones are the last layer of cells in the retina that light reaches. The photoreceptors generate impulses which travel along the various neurone layers of the retina to the optic nerve, which carries signals to the brain.

There are five main layers of nerve cells (neurones) that are diretly involved in the transmission of impulses in the retina:

Photoreceptor Cell Layer: the rods and cones that, when stimulated by light, perform 3 main functions – 1) absorb light energy (involving visual pigments)

2) convert light energy into electrochemical energy, generating a nerve impulse3) transmit the impulse towards the bipolar layer.

Horizontal Cell Layer: occurs at the junction between photoreceptors and bipolar cells. They connect one group of rod and cone cells with another and then link them to bipolar cells.

Bipolar Cell Layer: these sensory neurones receive electrochemical signals from the rods and cones and transmit the signal to the next layer.

Amacrine Cell Layer: occurs at the junction between bipolar and ganglion cells.

Ganglion Cell Layer: these neurones receive electrochemical signals from the bipolar cells. The distal end of ganglion cells is extended into long processes that go on to form the fibres of the optic nerve. These neurones are responsible for carrying signals from the retina to the brain.

Studies suggest that horizontal and amacrine cells are involved in processing, or “summarising” incoming visual information.

Most of the interpretation of visual stimuli occurs in the brain, based on variables such as: strength of light depth perception no. of rods/cones stimulated Describe the differences in distribution, structure and function of the photoreceptor cells in the human eye.

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Both rods and cones are elongated cells that contain an outer segment (closer to the choroid layer) joined to an inner segment that leads to the conducting part of the cell. The conducting part of the cell comprises a cell body containing the nucleus and an extension (or process) called the foot. This process conducts impulses to the next layer of neutrones in the retina.

Rods and cones contain visual pigments – chemical substances that absorb light energy. These pigments are stacked in layers of flat membranes in the outer segment of each photoreceptor.

Rhodopsin is the only pigment present in rods, thus rods can only detect black and white light. Cones contain iodopsins, of which there are 3 types, each sensitive to different wavelengths, and thus cones are responsible for colour vision. The role of visual pigments is to absorb light energy, which the rod or cone cell then converts to an electrochemical signal the brain can interpret.

Rods are evenly distributed across most of the retina, but are absent from the fovea. As a result, rods are responsible for most peripheral vision, including the detection of movement. They are extremely sensitive to light, responding best to low light intensities. They are used for night vision and to detect light and shadow contrasts.

Cones are distributed in groups throughout the retina, mostly being concentrated in the macula (yellow spot), an area of the retina that gives the central 10° of vision. The fovea is a small pit in the middle of the macula that contains densely packed cones only. They are less sensitive to light than rods, functioning best in high intensity light, giving daytime vision.

Outline the role of rhodopsin in rods.

Rhodopsins are light-sensitive pigments, which consist of two molecules bonded together: opsin and retinal. When light enters a rod cell, it splits rhodopsin molecules into its two components. This reaction results in an impulse in the neurone attached to the rod or cone. The two products slowly recombine, ready to be split again by more light. This is known as the visual cycle.

The main function of the photochemical rhodopsin is to absorb light in order to set off a series of biochemical steps to carry a signal to the brain.

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

Each cone contains one of three types of iodopsin pigments and is therefore most sensitive to light in one of three wavelengths. These pigments result in cone cells being sensitive to:

The short wavelengths of blue light, peak sensitivity being approx 455nm The medium wavelengths of green light, peak sensitivity at approx 530nm The long wavelengths or red light, peak sensitivity being at approx 625nm

‘Red’ cones are actually more sensitive to yellow light (560-565nm) than to red light, but they respond to red light before any of the others do, therefore behaving as red receptors.

By comparing the rate at which various receptors respond, as well as the overlap in colours detected, the brain is able to interpret these signals as intermediate colours.

Explain that colour blindness in humans results from the lack of one or more of the colour-sensitive pigments in the cones.

Because cones detect colour, any defect or damage to the cones will affect the ability or the eye to perceive colour.

Humans have three different forms of opsins present in cones, each coded for by one gene. A mutation in a gene that codes for a cone pigment leads to the inability of this pigment to function correctly. As a result, the person is unable to perceive colour in the normal trichromatic manner and is said to be either colour deficient or colour blind, depending on how the mutation affects the pigment.

In humans, the genes coding for red and green pigments are located on the X chromosome while the gene for blue pigment is found on Chromosome Seven (not a sex chromosome, thus it is extremely rare).

A person that is deemed to be ‘colour blind’ is not truly colour blind but is usually able to see only two of the three primary colours of light. As they are unable to detect one of the colours that normal trichromats can, they perceive colour differently and interpret all colours based on combinations of the two primary colours that they are able to see.

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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.

‘Eyes’ in animals range from really simple structures to extremely complex ones. Simple eyes are made up of single photoreceptors cells whose function is limited to distinguish light from dark. Complex eyes form a refraction and focusing system involving lenses, specialised areas of acuity, and receptors that can distinguish between a variety of colours.

Mammals, including humans, have evolved complex single-lens eyes. The retina of complex eyes contains rods and cones, which contain the visual pigments that absorb light. This initiates changes in the transmission of neurotransmitters that pass messages across synapses. These changes pass via bipolar cells to ganglion cells, which transmit a nerve impulse via the optic nerve to the brain.

Depending on the photoreceptors which are found within the eye, the ability to detect colour may vary. For example, humans have three types of cones and are able to detect three types of colour: blue, red and green. However, dogs have only two types of cones, lacking the red photoreceptor, and therefore are unable to detect red-green light.

Another type of eye is the compound eye, found in insects. A compound eye contains thousands of light-detecting units called ommatidia. Each ommatidium has its own lens, which focuses light onto light-absorbing pigments. Altered pigments initiate a nerve impulse that is transmitted to nerve fibres (axons) which are continuous with the receptor cells.

Each ommatidium registers visions from a different part of the environment, resulting in an image that is a pattern of dots. Visual pigments can return to their original state very quickly, meaning they can absorb more light at a faster rate.

The bee, for example, is able to detect three colours: blue, green and ultraviolet light. It cannot see red light.

One of the simplest light receptor arrangements is in the planarian worm (or the flat worm). The structure is called an eye cup, which holds cells containing photoreceptors. When these photoreceptors are stimulated by light, they alter so that a nerve impulse is sent to the brain. There are two eye cups, thus when the brain registers light intensity and direction (it cannot form an image) the animal moves around and away from the light source, towards and area of low light intensity.

The flat worm cannot detect any colour, only directional information.

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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.

Colour plays an extremely important role in communication for many animals, including humans. Three forms of colour communication include:

A form of passing on information – Colours are commonly used in species as a form of information, assisting other animals (both the same and different species) to understand what is being expressed. Animals which use this form of communication include:

Humans: for colour-coding objects, and types of information such as targets and dangerous objects.

Blue-ringed octopus: alters its colour when readying itself for an attack, and also to warn its prey.

Food recognition: used by many animals to determine food supplies, particularly birds and insects, who use the colour of flowers to identify pollen levels.

Courtship and mating – Colours are often used by many species to signal when they are ready for mating, as well as in the attraction of a mate. Examples include:

Male satin bowerbird: constructs a nest of grass and twigs, decorated with flowers and shiny objects, particularly blue objects. When a female is attracted to the nest, the male completes the mating ritual with a dance.

Male frigate bird: puffs up his red neck pouch in an attempt to attract females Male angler fish: are brightly coloured to attract females.

Defence mechanism – Many creatures use colour as some form of defence mechanism. Examples include:

Camouflage: involves an animal becoming almost indistinguishable from their surroundings, such as the chameleon (which has the ability to alter its colour) and the peppered moth (which has evolved to become almost invisible in the London smog).

Warning mechanisms: involves colours being displayed when an animals feels threatened. An example is the peacock which not only uses its vibrant tail to attract a mate, but also to signal when it feels threatened, warning other peacocks.

Many animals use colour to communicate a variety of types of information. The effectiveness of this communication depends on the animals that they are sending this information to, having colour vision to detect it. Fish, amphibians, reptiles and birds have well-developed colour vision, but humans and other primates are among the minority of mammals that can see colour.

Animals may use colour to signal their availability to mate, to indicate their suitability as a potential parent, to hide from predators or to warn of their unpalatability as prey. Some species mimic other unpalatable or poisonous species by using colour.

Humans have 10,000 cones per square millimetre compared to some birds that have up to 120,000 per square millimetre. Birds who feed in the daylight see colours

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very clearly, for example hummingbirds can spot red flowers from over a kilometre away.

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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 bends around objects and travels around corners. It can travel through substances, solids, liquids and gases. Whatever the habitat, an animals is always surrounded by a sound-transmitting medium.

Sound enables animals to communicate without being in visual or direct contact. When visual, tactile and olfactory senses are impaired or absent, sound can be used as the primary method of communication. A variety of sounds may be produced by varying the pitch, loudness and tone. A complete message can be conveyed quickly. Sound, particularly low-frequency sounds, will also travel long distances.

Toothed whales and bats use a form of sound communication called echolocation, whereby the animal emits sounds and listens for the echo to come back to them. This type of SONAR (Sound Navigation Ranging) works well even in complete darkness. By this process, killer whales are able to judge distance, direction, size, shape and speed of objects in water.

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 originates when something vibrates rapidly enough to organise the movement of molecules, so as to send a compression wave through a medium. The wave can only travel through media which contain particles that can be compressed (compression) and spread (rarefaction). The particles move backwards and forwards in the same direction as the flow of energy. It is energy that is transferred, not molecules.

The frequency of the vibration of the medium molecules is the same as the frequency of the vibrating object.

The frequency of vibrations is the number of waves which pass a given point in one second, expressed in cycles per second (one cycle being called a hertz, Hz). Low-frequency sounds have long wavelengths while high-frequency sounds have short wavelengths.

The amplitude of a sound wave is the maximum distance that a particle moves from its original position. The amplitude determines the volume of a sound.

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

The larynx, or voice box, lies directly below the tongue and soft palate. Inside the larynx are the vocal cords, which consist of muscles that can adjust pitch by altering their position and tension.

When air passes over the vocal cords in the larynx, they produce sounds that can be altered by the tongue, as well as with the hard and soft palate, teeth, and lips.

Diaphragm action pushes air from the lungs through the vocal folds, producing a periodic train of air pulses. This pulse train is shaped by the resonances of the vocal tract. The basic resonances, called vocal formants, can be changed by the action of the articulators to produce distinguishable voice sounds.

Together, the larynx, tongue, and hard and soft palate make speech possible.

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

Equipment: Cathode Ray Oscilloscope (CRO) Audio Oscilloscope

Method: Audio oscilloscope produces sounds of different frequencies (pitch). The frequency is measured in hertz.

The CRO displays the sound waves on a screen. The wavelength can be measured on the screen.

Results:Frequency (Hz) Pitch Wavelength (cm)

5 No sound heard 1 40050 Low sound 140500 Medium sound 14

5 000 High sound 1.450 000 No sound heard 0.14

Conclusion: The lower the frequency, the longer the wavelength and the lower the pitch of sound. The higher the frequency, the shorter the wavelength and a high pitch sound.

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

Insects: Orthopterans (meaning ‘straight wings’) include grasshoppers, locusts

and crickets. Usually it is only the males that produce sound in order to attract females. They do this by rubbing parts of their body together:

Grasshoppers and locusts scrape a row of pegs on their back legs along the hard edges of their front legs.

Crickets produce sounds by lifting the wing covers to 45° and rubbing the front of one wing cover (plectrum) over the rough area of the other wing (file). This is called stridulation.

Male cicadas have a pair of ribbed membranes called tymbals at the base of their abdomen. Muscles attached to the tymbals contract, causing them to buckle and produce a pulse of sound.

Fish: When catfish are alarmed or travelling in a shoal, they vibrate a bone

against their swim bladder, producing a noise similar to a giant aerator bubbler on a fish tank.

Birds: A bird’s sound producing organ is called the syrinx, situated at the base

of the trachea where it splits into the two bronchi. Elastic membranes of connective tissue inside the syrinx open and close as the bird exhales. The pressure of the air entering the syrinx, the size of the syrinx, and the elasticity of the folds determine how the sound is produced.

Some birds are mute, for example storks, pelicans and vultures.

Mammals:

The dolphin’s larynx does not possess vocal cords, and current research suggests that all of the clicks, grunts, squeaks and whistles are produced in the tissue complex of the nasal region. Sound results from movements of air in the trachea and nasal sacs, as well as the release of air from the blowhole.

The eastern horseshoe bat emits high-pitched echolocation calls through its nose and appears to use a nose leaf, a horseshoe-shaped fleshy area around its nose, to direct the sound.

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

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

INSECTS: The tactile bristles on an insect’s exoskeleton and on its antennae respond to low frequency vibrations, though many insects possess more specialised structures for hearing.

Orthopterans (such as crickets) have a tympanum or ear on each leg just below the knee. The tympanum is a cavity containing no fluid, enclosed by an eardrum on the outer side and a pressure release valve on the other. Nerve fibres are connected to the eardrum and pick up vibrations directly. Female crickets are deaf to some frequencies and sometimes rely on smells given off by males.

Cicadas possess a pair of large tympana connected to an auditory organ at the base of their abdomen. When a male cicada sings (as females don’t), he crinkles his tympana to prevent deafening himself.

FISH: The hearing abilities of fish vary between species. All fish have a lateral line, a pair of sensory canals, which run the length of each side of the animal. Pressure waves in the surrounding ocean distort the sensory cells in the canals, sending a message to the nerves.

Some fish actually perceive sound waves by possessing an inner ear containing an otolith (ear stone) which is lined with hair cells. Auditory nerves detect the differences in vibrations between the hair cells and the otolith and send a message to the brain.

Fish also have an air-filled swim bladder, located in the abdomen, which vibrates in response to sound or vibrations.

MAMMALS: Killer whales have an acute sense of hearing. Sound is received by the lower jawbone, which contains a fat-filled cavity extending back to the auditory bulla. Sound waves are received and conducted through the lower jaw, middle ear, inner ear and the auditory nerve to the auditory cortex of the brain.

Dolphins close their ear canals when diving. They detect vibrations through special organs in the head and some low frequency sounds through the stomach.

Insects Fish MammalsStructures used to detect vibrations

Tympanic membranes, sensory

hairs

Lateral line, inner ear, swim bladder

Cochlea

Receptor cells Mechanoreceptor cells

Hair cells in the inner ear,

neuromasts in lateral line

Hair cells in Organ of Corti

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● Describe the anatomy and function of the human ear, including: pinna, tympanic membrane, ear ossicles, oval window, round window, cochlea, organ of Corti, and the auditory nerve.

Structure Anatomy FunctionPinna Large, fleshy external part of the

earCollects sounds and channels it to the ear

Tympanic membrane The eardrum – a membrane that stretches across the ear canal

Vibrates when sound waves reach it and transfers

mechanical energy into the middle ear.

Ear ossicles Three tiny bones: hammer, stirrup and anvil

Amplify the vibrations from the tympanic membrane

Oval window Region that links the ossicles of the middle ear to the cochlea in the

inner ear.

Picks up the vibrations from the ossicles and passes them

on to the fluid in the cochlea

Round window Membrane between cochlea and middle ear

Bulges outwards to allow pressure differences in the

cochleaCochlea Circular chamber filled with fluid Changes mechanical energy

into electrochemical energyOrgan of Corti A structure within the cochlea Location of the hair cells

that transfer vibrations into electromagnetic signals

Auditory nerve The nerve that travels from the ear to the brain

Transmits electrochemical signals to the brain.

Eustachian tube Connects the middle ear with the throat. It is usually kept closed but opens when we swallow or yawn.

As air can pass through the opening, the pressure

between the middle ear and the atmosphere can be

equalised.

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● Outline the role of the Eustachian tube.

The Eustachian tube connects the middle ear with the throat. Usually this opening is kept closed, but it opens when we swallow or yawn.

By permitting air to leave or enter the middle ear, the tube equalises air pressure on either side of the eardrum.

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

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● Describe the relationship between the distribution of hair cells in the Organ of Corti and the detection of sounds of different frequencies.

Passing along the length of the cochlea is a ribbon-like structure, the organ of Corti. 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. Vibrations received at the oval window are transmitted through the fluids of the cochlea causing the transverse fibres of the membrane to vibrate at certain places according to the frequency.

High frequency sounds cause the short fibres of the front part of the membrane to vibrate and low frequency sounds stimulate the longer fibres towards the far end.

As the basilar membrane vibrates, the hairs of the hair cells are pushed against the tectorial membrane. This causes the hair cells to send an electrochemical impulse along the auditory nerve to the brain.

The region of the basilar membrane vibrating the most at any instant sends the most impulses along the auditory nerve.

The actual perception of pitch depends on the mapping of the brain. Nerves from particular parts of the organ of Corti stimulate specific auditory regions of the cerebral cortex of the brain. When a particular part of the cortex is stimulated, we perceive a sound of a particular pitch.

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

- Many animals can use their two ears to judge the position from which a sound comes. They can move each ear independently until each ear receives the maximum sound.

- Humans cannot move their ears, but can locate the direction of a sound nevertheless. This is because the sound is heard more loudly by the ear nearest to it and also fractionally earlier.

- The pinna is mostly skin and cartilage with some muscles attached to the back, which is what allows some animals to "wiggle" their ears.

- The brain uses reflections from the twists and folds of the pinna to determine the direction of sounds. Sounds coming from the front and sides become enhanced as they are directed into the auditory canal while sounds from behind are reduced. This helps an animal to hear what they are looking at while reducing some of the distracting background noise.

When sound waves are coming from directly in front, behind or above the head, both ears receive the sound waves equally and the sound will be the same for both ears. When sound is coming from one side, the receptors in the ear closest to the sound will be stimulated slightly earlier and also more intensely (because the sound energy is less dissipated). The brain then locates the sound as coming from one side of the body. The head is said to cast a sonic shadow on the sound coming into an ear from the opposite side of the body.

● Process information 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.

The range of frequencies that can be detected by humans is 20-23,000 Hz.

Mammal Lowest Frequency Detected (Hz)

Highest Frequency Detected (Hz)

Human 20 23 000Dog 67 45 000

Whale 1 000 123 000Mouse 1 000 91 000

The sound frequencies differ amongst these animals due to the different sounds that need to be recognised in order for these organisms to survive and communicate in their respective environments.

Whales and mice make high-pitched noises to communicate to one another, and hence need to be able to detect high frequency noises. The dog has more sensitive hearing than a human as dogs, in the past, required acute hearing in order to capture prey and avoid predators.

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

Hearing aids and cochlear implants are both devices designed to improve deafness.A hearing aid is an electronic, battery-operated device that amplifies and changes sound to allow for improved communication. Hearing aids receive sound through a microphone, which then converts the sound energy to electrical energy. The amplifier increases the loudness of the signals and then converts the electrical energy back to sound. This sound leaves the hearing aid through a speaker which directs the sound down the auditory canal. Most hearing aids are placed in or near the external auditory canal.

Hearing aids are particularly useful in improving the hearing and speech comprehension of people with sensorineural hearing loss. Sensorineural hearing loss develops when the auditory nerve or hair cells in the inner ear are damaged by aging, noise, illness, injury, infection, head trauma, toxic medications, or an inherited condition. Hearing aids will not restore normal hearing or eliminate background noise.

A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. It bypasses damaged parts of the inner ear and electronically stimulates the auditory nerve. Part of the device is surgically implanted in the skull behind the ear and tiny electrode wires are inserted into the cochlea. The other part of the device is external and has a microphone, a speech processor (to convert sound into electrical impulses), and connecting cables.

An implant does not restore or create normal hearing. Instead, it can give a deaf person a useful auditory understanding of the environment and help him or her to understand speech. Unlike a hearing aid which amplifies sound, cochlear implants compensate for damaged or non-working parts of the inner ear. It electronically finds useful sounds and then sends them to the brain. The person may also have to use the implant in conjunction with lip reading.

Hearing Aid Cochlea Implant

Position and type of energy transfer occurring

Sound Electrical Sound

Sound Electrical sound?

Conditions under which technology assists hearing

Sensorineural hearing loss Damaged or non-working parts of inner ear

Will not restore normal hearing or eliminate

Doesn’t restore hearing, very expensive (minimum

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Limitations background noise $US45,000)

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

● Identify that a nerve is a bundle of neuronal fibres.

A nerve is a bundle of axons or neuronal fibres bound together like wires in a cable. A neuron is a nerve cell, typically consisting of:

A cell body Dendrites (a branched protoplasmic extension of a nerve cell that conducts

impulses from adjacent cells inward toward the cell body.) An axon (the long, hairlike extension of a nerve cell that carries a message to a

nearby nerve cell) An insulating myelin sheath (that covers the axon and helps to increase the

speed by which information travels along the nerve).

The direction of a nerve impulse is: dendrites cell body nerve fibre axons.

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

A neurone is a nerve cell that transmits a signal or impulse from one part of the body to another. Neurons send messages electrochemically, meaning that chemicals cause an electrical signal.

A nerve impulse can be detected as a change in voltage. The impulse is transmitted as a wave of electrical changes that travel along the cell membrane of the neurone. The electrical changes are caused as sodium ions move into the neurone, thus the signal is described as an electrochemical impulse.

Action potentials are caused by an exchange of ions across the neuron membrane. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Sodium has a positive charge, so the neuron becomes more positive and becomes depolarised.

It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarisation. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (repolarisation), actually goes past -70 mV (hyperpolarisation) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.

After the signal has been transmitted, potassium ions move to the outside of the cell to restore the original charge of the neurone.

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

Threshold is the amount of positive charge in membrane potential which is required before an action potential is produced.

The point of excitation that causes the neurone to fire is called the threshold of reaction.

Each stimulus produces either a full action potential or none at all (known as “All or Nothing”). Each action potential is a separate event; therefore a cell cannot produce another action potential until the previous one is complete.

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

The functional areas of the cerebrum, and the regions involved in speech, sight and sound perception:

The Cerebrum: is divided into two hemispheres, the left and right. Each hemisphere receives impulses from and exerts control over the opposite side of the body. Each hemisphere is divided into five different lobes:

Frontal Insular Occipital Parietal Temporal

The cerebrum’s surface is drawn up into folds called convolutions, tripling the brain’s surface area. Most activity occurs on the outside surface and fit into three general categories:

Motor (movement) Sensory (senses) Associative (this cortex accounts for about 95% of the cerebral cortex and is the

site of reasoning and logic)

Light: The optic nerves are the sensory nerves of vision. Optic nerves from each of the eyes partly cross over to form the optic chiasma, providing each visual cortex with the same image as viewed by both eyes (thought from a slightly different angle). Impulses are received from the retina via the optic nerve.

Sound: The auditory nerves arise from the cochlea and vestibule apparatus within the inner ear. The auditory cortex is found on the temporal nerve of each cerebral hemisphere. Different sites on this cortex receive and interpret different sound frequencies.

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

The environment in which an organism lives is constantly changing. Sense organs such as the ear and the eye detect these changes and send information to the brain. The brain then interprets the information and sends an impulse to an effector organ such as a muscle. It is essential that the brain interpret signals from the sense organs correctly so that the organism can react appropriately.

The cerebral cortex is the most important association centre of the brain. Information comes to this area from our senses and the brain sorts it out in the light of past experiences. As a result, motor impulses are sent along the nerves to cause an appropriate action to take place.

For example, the eyes and ears, receptors in muscles and tendons, pressure sensors on the feet all provide signals about the position of the body in space. The cerebrum of the brain interprets all of these signals and sends messages to various effectors to balance the body in space.

Walking involves several receptors, including the eyes, gravity receptors in the ears, pressure sensors in the feet and position receptors in the joints. These receptors are connected to the brain by neurones and the brain interprets the signals it receives. The brain sends messages to the muscles and other effectors to coordinate the process of walking.

The importance of the brain in the coordination of animal behaviour is highlighted when parts of it are damaged. The paralysis that follows a stroke, or the shaking movements of people with Parkinson’s disease, are signs of damage to the brain. In people with these conditions, muscular contractions are no longer coordinated by the brain.

● Perform a first-hand investigation using prepared stained slides to gather information about the structure of neurones and nerves.

1) Set up a light microscope and a number of slides, e.g. spinal chord, neurone.2) Observe neurones and nerve cells, drawing a diagram of each.

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● 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.

● Present information to graphically represent a typical action potential.

When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire.

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