(a) (i) Outline the function of the iris in the human eye. A clear, bi-convex disc that focuses light onto the retina
(ii) Explain how humans achieve depth perception.
When eyes face forward, each eye sees an image o an object in the light path The two images are fused into one image in the cerebral cortex of the brain. This fusion into one image is related to the perception of depth. Depth perception is the sense of depth that occurs when objects are viewed with binocular vision. We say that a person has stereoscopic vision; that he/she is viewing the world in three dimensions. Stereoscopic vision depends on the fact that the two eyes are separated horizontally so they have slightly different views of objects located at different distances away. When an object is a slightly different distance away 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 focused and seen to be a different distance from the eye to another objects that is closer to the eye
(b) The diagram below shows the structures of the middle ear
(i) Outline the functions of A, B and C
A: Tympanic membrane (eardrum): Vibrates when sound waves reaches it and transfers mechanical energy into the middle ear
B: Incus (anvil): The incus is the second of the ossicles, three bones in the middle ear which act to transmit sound. Function: Vibrations in the middle ear are received via the tympanic membrane.
C:Stapes (stirrup):Situated between the incus and the inner ear, the stapes transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear.
(ii) During your study of Communication you performed a first hand investigation to identify the relationship between the wavelength and frequency (pitch) of a sound.
Describe how you did this and outline your findings.
We used a CRO (cathode ray oscilloscope) and audio oscillator. After selecting a sine wave output of about 500 Hz on the audio oscillator we connected it directly to the CRO and adjusted the volume until a note could be heard. We then observed and recorded our results of the frequency, wave shape and length and the pitch. We then changed the pitch of the oscillator to about 200 Hz and 1000 Hz and again, recorded the results. We then matched up a tuning fork with its sounding box. We recorded our observations of a small and a large fork.
Amplitude: low volume
Amplitude: High volume
Tuning fork (large)
Tuning fork (small)
(c) Describe and account for the differences between the way humans and one other named species see and hear the world. Outline the adaptive value of these differences.
Type of Eye
Description of photoreceptors
Eye made up of a large number of separate light receptors called ommatidia. They have fewer rods and cones then mammal eyes. The eye forms an image similar to a mosaic. Each ommatidium has its one cornea and lens made up of a crystalline cone. These eyes can have high fluid speed, for detecting movement.
Single lens eye
Have a very complex eye. They can focus and form an image. There are different types of receptors found in the eye. Rods and cones are found in complex eyes. Some are capable of colour vision while others are important in visual accuracy and night vision. By having two eyes information can be gathered about depth perception. Each eye has a single lens.
How they hear
Have hearing organs. Grasshoppers a recovered in auditory hairs that are sensitive to sound waves. These have different lengths and stiffness and respond to vibrations at different