Things to Think About Today Light waves travel in straight lines until they meet matter Then, light is reflected, absorbed, refracted Why do animals have eyes? How did eyes evolve? What are the parts of the eye and how do they work to bend light
Light Energy Meets Matter Reflected Refracted (Bent) Absorbed
Light waves travel in straight lines until they meet matter Some matter ( lenses) focus rays and bend them in defined ways Pin activity=Boxes with solutions/laser pointer, ray box Ray boxes with lenses, gelatin lenses
Convex Lenses Magnifying Lenses are Convex lenses
Eyes: Detect and Focus Light Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons In higher organisms the eye is a complex optical system which: –collects light from the surrounding environment – regulates its intensity through a diaphragm – focuses it through an adjustable assembly of lenses to form an image –converts the image into a set of electrical signals –transmits these signals to the brain, through complex neural pathways that connect the eye, via the optic nerve, to the visual cortex and other areas of the brain.
3 types of eyes have evolved Single centered lens –Advanced mollusks (octopus), spiders,vertebrates Many tiny lenses –Arthropods (trilobites) –Ex. Ants (50 images) Horsefly (7,000 images) Dragonfly (30,000 images) Hole without lens –snakes
Functions of Parts of the Eye Eyelid- protection of eye from injury Pupil- hole in the center of the iris that lets light in –Appears black because the eye tissue absorbs most of the light Sclera-tough outer layer –collagen and elastin Iris-colored area surrounding pupil –Composed of smooth muscle
Rod and Cone Cells Rod Cells- numerous ( 130 million in each eye –Responsible for Twilight vision, Gray shades –Very sensitive to light –Found on outside of retina Cone Cells- – less numerous ( 7 million) –Responsible for –Ability to see Color –Found in center of the retina (macula)
Hyperopia- Far-sighted Image is focused behind the eyeball Cornea is flatter, eye is shorter, focusing power is weaker Young people can “accommodate” by changing shape of eye= As people get older, lens get harder and can’t be bent. Lasix surgery changes shape of cornea –http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0004853/
Bird Vision How do nocturnal birds see? –Rod cells are very sensitive in low light Humans have around 200,000/mm 2, some owls have over a million/mm 2 –Birds also have larger pupils which let more light in What about day foragers –Have more cones than humans –May have more than one fovea area of sharpness)
Ruminant Pupils Slit-like in bright light, circular in dim light Gives permanent wide- angle vision whether in dim or bright light -makes watching for predators more efficient.
Making the connection between physical science and biology Light travels in straight lines Light bends when it meets matter Lenses are matter that bend light How animals see Eye diseases Do you need light to see? Ray box Bending Experiment Play with Lenses Eye Dissection Annenberg video
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