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AGECO 121 Plant Stress: It’s Not Easy Being GreenFall 2015Study Guide and Summary for Exam #1The following is a summary of many of the major points for Section 1 of this course. It may be to a plant’s advantage to inhabit and be adapted to a “stressful” environment if it reducescompetition with other plants/animals. An advantage that plants have over animals is that plants make their own food by photosynthesis.The basic reaction of photosynthesis in chemical symbols: CO2+ H2O => CH2O + O2Basic photosynthetic reaction in words: Carbon dioxide and water are consumed and sugar andoxygen created.The oxygen (O2) gas released by photosynthesis comes from the splitting of water (H2O) molecules. The CO2absorbed during photosynthesis ends up initially in the form of a 3-carbon sugar-acid calledPGA.Can you think of 10 ways that you use or depend on photosynthesis? How about 20 ways? 30ways?? More???Plants are greenbecause they contain large amounts of chlorophyllChlorophyll appears green to our eyes because it is a pigment that absorbs the blue and red part ofthe spectrum and mostly reflects and transmits the green and yellow colors. A light absorption spectrumfor chlorophyllis a graph of relative light absorbing effectiveness ofchlorophyll at each wavelength (color) of light.
An action spectrumfor photosynthesis is a graph of relative photosynthetic activity （amount ofoxygen released）at each wavelength (color) of light.The action spectrumfor photosynthesis tells you which colors of light are responsible for poweringphotosynthesis.The similarityof the photosynthesis action spectrum with the chlorophyll light absorption spectrumindicates that chlorophyll is likely the major light-absorbing pigment for photosynthesis.Measurable products of photosynthesisinclude oxygen (O2) gas, sugar, and “biomass” (body weight)of the plant.Chloroplastsare self-contained “organelles” of plant cells. They are bordered by a membraneenvelope and contain a complex stacked membrane structure inside where the light absorption andphotosynthetic reactions occur.You should know the typical structure of a leaf in cross-section and what are the functions of thedifferent cell types and structures. (这个自己记一下然后背)C3 plants are called C3 plants because the first detectable product of photosynthesis is a 3-carbonsugar acid called PGA.Rubisco is an enzyme.Enzymes facilitate chemical reactions that would otherwise not proceed very well, if at all.Rubisco converts CO2into sugar. RUBISCO attaches CO2to existing sugar molecules to make thembigger, and thereby creates more sugar (captured energy) for the plant.
Living things on earth are “carbon-based” because all the major bio-molecules (DNA,carbohydrates, proteins, and fats) contain a “backbone” of carbon atoms. Carbon atoms are the“girders” upon which life forms are constructed.