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BIOL 1000 (389)

Unit 1 Textbook Notes.docx

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York University
BIOL 1000
Julie Clark

Chapter 1 Light and Life 9272011 12800 PM 11 The Physical Nature of Light Light serves two important functions for life on Earth 1 Source of energy that sustains all life 2 Provides organisms with information about the physical world11a What is lightReason for life on earth has to do with distance from earth and sunSun converts 4 million tonnes of matter into energy every second which is given off as electromagnetic radiation which travels at the speed of light and reaches earthLight is defined as the portion of the electromagnetic spectrum that is visible which spans wavelengths from 400nm to 700nmLight behaves as a stream of energy particles whose packets of energy are called photonsEach photon contains a specific amount of energy the amount which is inversely related to its wavelength11b Light interacts with matterLight is able to interact with and change matter which allow light to be used by living thingsWhen photons hit and object three possibilities 1 Can be reflected off object 2 Transmitted through object 3 Absorbed by objectFor most objects all three processes occurFor light to be used by organism photons must be absorbedPigment molecule which absorbs light absorb at different wavelengthsIn order to absorb light pigments contain region where carbon atoms are covalently bonded with alternative single and double bonds called conjugated system11c Why chlorophyll a is greenLight is absorbed when energy of photon is transferred to an electron of the pigment moleculeWhen an electron absorbs energy it moves to a higher energy levelFor chlorophyll electron can exist in only two excited statesLower state is achieved by chlorophyll absorbing red photon and higher state achieved by absorbing blue photonIn order for light to be absorbed by pigments energy of photon must match energy difference between 0 and excited stateChlorophyll a is green because it cannot absorb photons of green light and reflects it 12 Light as a Source of EnergyAfter an electron is raised to a higher state it can be used to do workEx transporting NADPH Can also be used to synthesize other moleculesEx lipids proteins and nucleic acids13 Light as a Source of Information13a Rhodoposin a highly conserved photoreceptorPhotoreceptor basic light sensing system most common is rhodopsinRhodopsin molecules contain opsin which binds retinal single pigment moleculeAbsorption of light causes retinal pigment to chance shape which triggers alternation to opsin protein electrical signals to brain 13b Sensing light without eyesMany organisms are able to sense light without eyes sometimes by using an eye spotEyespot located within chloroplast which allows cell to sense light direction and intensityPositive phototaxis organism moving towards lightNegative phototaxis organism moving away from lightAllows organism to stay in optimum light environment maximizing efficiency of photosynthesis
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