9.5 Option - 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
Students learn to:
· Identify the role of receptors in detecting stimuli:
- A stimuli is any change in the internal and external environment of an organism
- This stimuli is picked by the organisms receptors
- In the most simple form a receptor in organisms consists of single cells scattered around the body
- In many organisms receptors have become more concentrated in particular areas to from sensory organs, which contain non-sensory tissue and sensory cells. E.g. The eye
· Explain that the response to a stimulus involves:
- Stimulus: Any change in the internal or external environment of an organism
- Receptor: The receptor detects this change, and sends messages to the brain or CNS by impulses in the nerve
- Messenger: These impulses then trigger the CNS or brain to process the information and trigger new impulses
- Effectors: These new impulses are transmitted to the effectors for it to produce a response
- Response: A response is produced in response to the stimulus
Students:
· Identify data sources, gather and process information from secondary sources to identify the range of senses involved in communication:
- Sight: Sight is a common form of communication, many animals have dangerous looking colours so as to detour predators
- Sound: This is a common form of communication, many animals use different sounds for different situations, such as danger
- Touch: Touch can be used as communication in such forms as comforting gestures. For example humans hug to comfort or show affection
- Taste: Chameleons use taste to identify if a territory is occupied. As chameleons rub their cloaca on branches to mark there territory. Chameleons have a very poor sense of smell
- Smell: Young babies are known to be capable of identifying their mother, by their smell
2. Visual communication involves the eye registering changes in the immediate environment
Students learn to:
· Describe the anatomy and function of the human eye, including the:
- Conjunctiva: Thin transparent membrane that is there to protect the exposed areas of the eye
- Cornea: Transparent, and allows light to enter as well as helping bend or refract it. Has many nerves and is sensitive to touch and pain
- Sclera: Outermost layer of the eye at the back, opaque in colour forming the ‘white’. Tough non-elastic tissue protecting the delicate inner layers, helps maintain shape as well as allowing a place for the attachment of muscles for movement
- Choroid: Middle of the eye containing most of the blood vessels. Posterior black to reduce scattering and reflecting of light within the eye. Anterior continues to form the ciliary body and lens
- Retina: Lines the posterior two thirds of the eye and is thin and delicate. Contains several layers of nerve cells. Contains photoreceptors, rods and cones.
- Iris: Consists of connective tissue and smooth muscles. These muscles are arranged circular and radially and control the size of the pupil
- Lens: Refracts light rays and directs them onto the retina. It is highly elastic allowing it to change shape to accommodate to different distances
- Aqueous Humor: Watery fluid in the anterior section of the eye, between the cornea and lens. It has a composition similar to blood plasma and provides nutrients for the lens and cornea
- Vitreous Humor: Jelly like material filing the remainder of the eye, behind the lens and enclosed by the retina. Contains dissolved nutrients, refracts light and helps maintain the shape of the eye
- Ciliary body: Produces aqueous humor, as well as this it controls the ciliary muscle which changes the shape of the lens by controlling the suspensory ligaments
- Optic nerve: Carries information from the eye to the brain changing light energy into nerve impulses
· 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: Detect range lengths of 380nm to 760nm
- Invertebrates: Many insects (honeybees) can detect wavelengths in the ultraviolet UV range of the spectrum. Their light sensitive cells can detect shorter wavelengths present in the UV range. They are unable to detect some of the longer wavelengths in the red part of the spectrum, they see red as black. Therefore bees do not have a wider spectrum, but rather a different range
- Vertebrates: Many birds are able to detect light in to the UV range of the spectrum. In addition to this birds tend to be able to detect light most efficiently in the red. Therefore they have a wider range of detection
Students:
· Plan, choose equipment or resources and perform a first-hand investigation of a mammalian eye to gather first-hand data to relate structures to functions:
- After removing the fatty tissue from the eye
- Made an incision behind the cornea, and in front of the lens
- Aqueous humor escapes, then studied the anterior section of the eye. Observing the pupil and the iris
- Removed the lens and the vitreous humor and examined the lens
- Observed print through the lens, whilst squeezing it to observe what happens
- Examined the retina
· Use available evidence to suggest reasons for the differences in range of electromagnetic radiation detected by humans and other animals:
- Different animals require vision in different areas of the spectrum. This allows them to live appropriately in their habitats
- For example; Honey bees are able to detect light into the UV range. This is beneficial as many flowers have UV patterns, this helps direct bees to the pollen and nectar in the centre of the flower
3. The clarity of the signal transferred can affect interpretation of the intended visual communication
Students learn to:
· Identify the conditions under which refraction of light occurs:
- As light moves through a medium of a different density, the speed at which its travelling changes
- Because of the light slowing down or speeding up, the light rays are bent or refracted
- When light is passed through a biconvex lens, the rays are refracted towards a central point, known as the focal point
· Identify the cornea, aqueous humor, lens and vitreous humor as refractive media:
- The density of the cornea, aqueous humor, lens and vitreous humor are close to that of water
- They all refract light
- The greatest amount of refraction occurs when light hits the cornea, as the density between the air before it and the cornea are of extreme differences
· Identify accommodation as the focusing on objects at different distances, describe its achievement through the curvature of the lens and explain its importance:
- This is the ability of the eye to focus on objects of varying distances
- The grater the distance, the smaller the curvature of the lens. This is done by:
. The cilliary muscles relax, and pull back
. As this happens they tighten the suspensory ligaments
. This stretches and elongates the lens, allowing for a slighter curve
- The closer the distance the greater the curve of the lens must be to allow for quicker diffraction. This is done by:
. The cilliary muscles contract and stretch out
. This causes the suspensory ligaments to slacken
. The lens becomes more rounded allowing for greater curve of the lens
· Compare the change in the refractive power of the lens from the rest to maximum accommodation:
- The thinner the lens, or less curvature, that is when at rest, the less refractive power
- When at maximum accommodation, the refractive power of the lens increases
- Therefore, the refractive power of the lens from rest to maximum accommodation is of a greater refractive power
· Distinguish between myopia and hyperopia and outline how technologies can be used to correct these conditions:
- Myopia is the eyes inability to focus on distant objects, as the focal length is to short meaning the image falls short of the retina
- Myopia is caused by: Eyeball too elongated in shape, refractive power of the cornea is inadequate or the lens may not become flat enough
- Hyperopia is the eyes inability to focus on short distances, as the focal length is too long and the image does not converge quick enough for the retina
- Hyperopia is caused by: Eyeball to rounded or short, lens is to flat and cannot change enough
- Both hyperopia and myopia are easily corrected through the use of spectacles, and in more recent time’s contact lenses. As well as this there are now permanent corrections through the use of laser eye surgery
- Spectacles for myopia are concave, and hyperopia are convex
· Explain how the production of two different images of a view can result in depth perception:
- This is the ability to accurately judge the distance of an object
- Human eyes are spaced apart, they therefore take in the same image at two slightly different angles
- The two images are directed to the brain where they are put together and any missing information is filled in. Allowing you to see the image in 3D
- This is called binocular or stereoscopic vision
Students:
· Plan and choose equipment or resources and perform a first-hand investigation to model the process of accommodation by passing rays of light through convex lenses of different focal lengths:
- Aim: To model accommodation by passing rays of light through convex lenses of different densities, to observe the focal length
- Ray box, multiple slit slides, biconvex lenses of different densities and power pack
- Placing the first convex lens 6 cm from the ray box, and measured the focal length of the light that passes through the lens. Then did so for the second lens
- Results showed that the greater the density of an object, and the greater the curvature, the greater the refractive power and therefore shorter focal length
· Analyse information from secondary sources to describe changes in the shape of the eye’s lens when focusing on near and far objects:
- Far objects: Lens elongates (becomes longer and thinner) The ciliary muscles relax, causing the suspensory ligaments to tighten. Refractive power decreases
- Near objects: Lens becomes thicker and curvature increases. The ciliary muscles contract, causing the suspensory ligaments to shorten and slacken. Refractive power increases
· 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:
- Cloudy opaque film build up over the lens of the eye
- Decreases visual clarity, reduces light availability to the eye
- Opaque covering can eventually lead to blindness, even with capable photoreceptors
- Cure: Surgical removal of the lens by making an incision on the eye ball. This lens is then replaced with a plastic intraocular lens (IOL)
- This has major implications on society, as half of the worlds blind population is bind due to cataracts. Many of whom are from third world countries
4. The light signal reaching the retina is transformed into an electrical impulse
Students learn to:
· Identify photoreceptors 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:
Photoreceptor / Structure / Distribution / Number / Function (pigment)Cone / Cone shaped, broader than rods
Contain idopsins / Distributed in groups throughout the retina, concentrated in macula. There are fewer around the periphery / 6 to 7 million cones / Work better in bright light cones distinguish colour
One cone for blue, one for green, one for red.
The idopsin for each colour is different
Rod / Rods are long and narrow
Contain Rhodospin / Evenly distributed across the retina. Absent from the fovea / 125 million rods / Work better in dim light Higher sensitivity than cones
· Outline the role of rhodopsin in rods:
- Rhodopsin is made up of two parts, a retinal molecule that is derived from vitamin A and a protein called opsin
- Light strikes the rhodopsin pigment, and it changes from a resting state to an excited state. This is due to the activation of the retinal
- When the retinal becomes activated, the rhodopsin splits into an opsin part and a free retinal part. Rhodopsin is said to be bleached
- The activated pigment causes a change in electrical charges of the membrane of the cone
- This starts an electrical impulse triggering the release of neurotransmitter
- The neurotransmitter then stimulates the bipolar cell, triggering an impulse (electrochemical signal)
- The bipolar cell transmits the electrochemical signal to the ganglion cells which in turn carry it to the brain
- Rhodopsin is then regenerated to be used again
· Identify that there are three types of cones, each containing a separate pigment sensitive to either blue, red or green light:
- Cones allow us to see in colours. This is due to the cone cells containing one of three different pigments
- This makes each more sensitive to light in one of three wavelengths:
1. Short wavelengths of ‘blue light’ 455nm
2. Medium wavelengths of ‘green light’ 530nm
3. Long wavelengths of ‘red light’ 625 nm
- The sensitivity of cones also allows it to detect light to some extent of either side of their peak sensitivities. This allows for an overlap in some colours, and therefore allows for the cones to detect a range of colours from the spectrum
· Explain that colour blindness in humans results from the lack of one or more of the colour-sensitive pigments in the cones:
- The cones have three different types of pigment, to detect different colours