An Overview of PhotosynthesisPhotosynthesis–Is the process of using sunlight to produce carbohydrate –Requires sunlight, carbon dioxide, and water –Produces oxygen as a by-product The overall reaction when glucose is the carbohydrate:6 CO26 H2O light energy C6H12O66 O2Photosynthesis contrasts with cellular respiration–Photosynthesis is endergonic–Reduces CO2to sugar–Cellular respiration is exergonic–Oxidizes sugar to CO2Photosynthesis: Two Linked Sets of ReactionsLight-dependent reactions–Produce O2from H2OCalvin cycle reactions–Produce sugar from CO2The reactions are linked by electrons–Released in the light-dependent reactions –When water is split to form oxygen gas–Then transferred to the electron carrier NADP+, forming NADPHThe Calvin cycle then uses –These electrons –The potential energy in ATP –To reduce CO2to make sugarsThe Structure of the ChloroplastPhotosynthesis occurs in the chloroplastsof green plants, algae, and other photosyntheticorganismsChloroplasts are surrounded by two membranesThylakoids–Internal membranes of chloroplasts that form flattened, vesicle-like structures –Form stacks called grana–Thylakoid membranes contain large quantities of pigments–The most common pigment is chlorophyllStroma–Fluid-filled space between the thylakoids and the inner membrane The Nature of Light EnergyElectromagnetic radiation is a form of energyLight–Is a type of energy electromagnetic radiation –Acts both particle-like and wave-likePhotons
–As a particle, light exists in discrete packets –As a wave, light can be characterized by its wavelength–The distance between two successive wave crests The Electromagnetic SpectrumThe electromagneticspectrum–The range of wavelengths of electromagnetic radiation Visible light–Electromagnetic radiation that humans can see Each photon and wavelength has a specific amount of energy The energy of a photon of light is inversely proportional to its wavelength Shorter wavelengths such as ultraviolet light –Have more energy than longer wavelengths –Such as infrared light
Photosynthetic Pigments Absorb LightPhotons may be absorbed, transmitted, or reflected when they strike an objectPigmentsare –Molecules that absorb only certain wavelengths of light There are two major classes of pigment in plant leaves: 1. The chlorophylls(chlorophyll aand chlorophyll b) –Absorb red and blue light –Reflect and transmit green light 2. The carotenoids–Absorb blue and green light –Reflect and transmit yellow, orange, and red lightEach Pigment Has a Specific Absorption SpectrumAbsorption spectrum –Is a graph to study pigments –Plots the wavelength of light absorbed by pigment moleculesAn action spectrum –Shows the rate of photosynthesis vs. wavelength
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