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Chapter 1

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Wilfrid Laurier University
David Smith

A Green Algea  Using light for both energy and information  Eyespot: light sensor  The Sun  The reason there is life on earth Electromagnetic Spectrum  Ranges from gamma rays to radio waves; visible light and the wavelengths used for photosynthesis occupy a narrow band of the spectrum  The longer the wavelength, the lower the energy of the photons it contains. The shorter the wavelength the higher the energy of the photons it contains  What is Light?  Definition of light: Electromagnetic radiation that humans can detect with their eyes  A wave of discrete particles called photons  Wavelength: Distance between two successive peaks  To be used, light energy must be absorbed by molecules called pigments Light Interacting With Matter  Pigment Structure  Conjugated system  Alternating double/single carbon bonds  Delocalization of e- Photosynthesis -> Vision -> Red photosynthetic algea -> Absorption of Light by Chlorophyll  Colour is the result of wavelengths of light that are not absorbed by a pigment  Light as a Source of Energy  Photosynthesis sustains almost all life  Halobacteria also capture light energy  Thrive in salt water habitats that are lethal to most other forms of life.  Species of halobacterium contain a pigment-protein complex called bacteriorhodopsin, which functions as a proton pump. The pigment component of bacteriorhodopsin captures photons of light that provide energy supply needed to pump protons out of the cell.  Resulting in a H + concentration that represents a source of potential energy that is used to generate ATP.  Light as a Source of Information Photoreceptors: basic light-sensing system, found almost universally in all organisms Rhodopsin: Most common photoreceptor in nature  basic vision in animals  also used by many other organisms  a highly conserved photoreceptor  consists as a pigment molecule (retinal) bound to a protein (opsin)  An Eyespot – Sensing Light Without Eyes  Allows sensing of light direction and intensity  Organisms responds by phototaxis…allows the cell to stay in the optimum light environment to maximize light capture for photosynthesis. Photomorphogenesis  The normal developmental process activated when seedlings are exposed to light  In plants, a photoreceptor called phytochrome senses the light environment The Eye  Organ animals use to sense light  Vision o Requires a brain to interpret signals sent from eye -> co- evolved because detailed visual processing occurs in the brain rather than in the eye. Ocellus of Planaria  Simplest eye o Senses light direction and intensity o Photoreceptor cell is a modified nerve cell that contains thousands of individual photoreceptor molecules Compound Eye of the Deer Fly  Brain receives a mosaic image of the world  Extraordinarily adept at detecting movement  Octopus Eye  Eyes with single lenses, “camera eyes”  In a single-lens eye, as light enters through the transparent cornea, a lens concentrates the light and focuses it onto a layer of photoreceptor cells at the back of the eye, the retina. The photoreceptor cells of the retina send inform
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