Depth perception depends on binocular vision, where the field of view of each eye overlaps – allowing each eye to observe the same object simultaneously. The images formed by each eye are superimposed by the brain, and because each view is slightly different, it allows us to see it in When objects are close enough, we are also able to judge its distance from us. Stereoscopic vision refers to vision where the same object is viewed from slightly different angles – creating an impression of depth. Predators also have stereoscopic vision (eyes at front of the head) to allow them to estimate distances from prey. Tree-dwelling primates have it to allow them to estimate depth when moving from branch to branch. Animals that are likely to be preyed upon, however, usually have eyes placed on each side of the head – allowing for a wider total visual field at the expense of losing the ability to judge distances. Plan, 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 the process of accommodation by passing rays of light through convex lenses of differing lengths Independent variable: shape of the lens Dependent variable: Distance between screen and the lens required to focus Controlled variables: light source, screen, distance between light and screen Equipment: Two convex lenses of different shape (one thin, one thick) Lens holder Sheet of white paper clipped on solid support (acts as a screen where the object is focused) Candle as a source of light Method: Darken the room and set up thin lens holder as Move the lens forwards and backwards to find a position that produces a clear, focused image of the light source on screen. Measure and record the distance of the screen from the lens Keep the lens holder the same distance, and change the lens to the thick lens. Observe the screen and not the appearance of the image Repeat 2-3 for the thick lens Results: The thicker lens (one with more curvature) had a smaller focal length (was closer to the screen). The thinner lens (one will less curvature) had a longer focal length (held further from the screen) Analyse information from secondary sources to describe changes in the shape of the eye’s lens when focusing on near and far objects
As rod cells detect light (not colour), they play no role in colour blindness so those who are colour-blind can usually see. The most common type of colour blindness is red-green (people with the condition perceive red and green as the same colour), where the cones most receptive to red light and green light are missing. Colour blindness is more frequent in than females because it is a sex-linked characteristic; the gene for the red and green cones is located in the X chromosome. Females have two X chromosomes (XX) and males only have one (XY) which means that females need both chromosomes carrying the defective gene to express it while males only need one. 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 Mammal: Human Insect: Dragonfly Flatworm: Planarian Worm Type of photoreceptor Rods and cones Reticular/retinal cells in separate ommatidia Eye cups Type of image Image on retina is inverted and diminished Mosaic image of large visual field, can see in colour (if formed) is unclear and not inverted – gives information about light intensity and direction Similarity in photoreceptors Detects - rhodopsin Detects light - rhodopsin Detects light - rhodopsin Difference in photoreceptor Has higher resolving power and greater visual acuity Is made up of many called ommatidia (each has its own cornea and transparent crystalline cone which acts as lens) pointing in different direction. Can be more efficient detecting colour than mammals and fast movement. Has photoreceptor cells than insect or mammals and has poor visual acuity and no colour vision. Two eye spots (Ocelli) are used to detect light and move away from it. Structure that refracts light Cornea, aqueous humour, lens (changes curvature), vitreous humour Cornea, lens (fixed, cannot accommodate) No refraction Sensitivity to Rhodopsin is a photosensitive pigment Greater – detects light, UV as well as visible light Highly sensitive Visual acuity High visual acuity Lower visual acuity than mammals but more efficient in detecting movement Poor visual acuity Mammals have a similar eye structure to humans; the major difference within mammal eyes is the presence or absence of cone cells (nocturnal mammals have no cones, so they cannot see colour).