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Lecture 2

Lecture 2 Light.docx

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Western University
Biology 1002B

Lecture 2 OutcomesRelationship between excited states of a pigment and its absorption fluorescence emission spectra Redorange light 625nm700nm shows a good rate of photosynthesis however the best rate of photosynthesis is seen with violetblue light 400nm525nm Red has a higher emission than blue fluorescence shifted to the longer wavelength because some energyis lost as heat sub level of excited stateSo absorption characteristics reflect the excited state of the pigment however after the blue photon of light is absorbed it is quickly lost as heat to be brought down to the red state and even more heat is lost until it returns to the ground reflecting a photon of light that is darker in redAn absorption spectrum is a graph showing the percentage of light absorbed by pigments within the chloroplast for each wavelength of lightAn example is the absorption spectrum of chlorophyll a and b The best absorption is seen with violetblue light There is also good absorption with redorange light However most of the greenyellow light is reflected and therefore not absorbed This wavelength of light shows the least absorption Region of the electromagnetic spectrum known as visible lightlight absorbs visible light not UV or radio waveschlorophyl absorbs all lights except for greengreen is either transmitted through the pigment or lost as reflected lightchlorophyll best absorbs light at the wavelength corresponding to the ultraviolet red is also goodRelationship between wavelength and energy content of a photon inverse relationship between the length of the wavelength and the energy contentthe longer the wavelength the lower the energy content of the wavelength Molecular characteristic of visible pigments that make them able to absorb lightPigments are able to absorb light due to a conjugated system of altercation between double and single bondthese bonds contain non boding pi electrons that trap the light and are not involved in bonding with the exception of retinol Relationship between pigments and associated proteinPigments are not free floating systems in our cells rather they are attached to associated proteinsduring isolation of the pigment you have to be careful of not completely removing the pigmentproteins are coloured because they are non covalently attached to the pigmentsFour fates of the excited state of chlorophyll resulting from absorption of photons
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