BSC2010 BIOLOGICAL SCIENCE I FALL 2012 STUDY GUIDE 12 PHOTOSYNTHESIS Vocabulary Absorption spectrum The range of a pigment s ability to absorb various wavelengths of light Action spectrum A graph that profiles the relationship effectiveness of different wavelengths of radiation in driving a particular process Calvin Cycle The second of two major stages in photosynthesis following the light reaction Involves fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrates Carotenoids An accessory pigment either yellow or orange in the chloroplasts of plants Absorb wavelengths of light that chlorophyll cannot carotenoids broaden the spectrum of colors that can drive photosynthesis Chlorophyll a a photosynthetic pigment that participates directly in the light reactions which convert solar energy to chemical energy Chlorphyll b An accessory photosynthetic pigment that transfers energy to chlorophyll a Chloroplast An organelle found in plants that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water Electromagnetic Spectrum The entire spectrum of electromagnetic radiation ranging in wavelength from less than a nanometer to kilometer Excited state Fluorescence Ground State Light Reactions Granum A stack of membrane bounded thylakoids in the chloroplast functions in the light reactions of photosynthesis Heterotroph An organism that obtains organic food molecules by eating other organisms or substances derived from them Mesophyll Leaf cells specialized for photosynthesis In C3 and Cam plants mesophyll cells are located between the upper and lower epidermis in C4 plants they are located between the bundle sheath cells and the epidermis Photoautotroph An organism that harnesses light energy to drive the synthesis of organic compounds from carbon dioxide Photon A particle of light energy Photosynthesis The conversion of light energy to chemical energy that is stored in sugars or other organic compounds Photosystem A light capturing unit located in the thylakoid membrane of the chloroplast consist of a reaction center complex surrounded by numerous light harvesting complexes There is two photosystems I II Pigment Ribulose bisphosphate Rubisco Ribulose bisphosphate carboxylase The enzyme that catalyzes the first step of the Calvin cycle Stomata A pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant Stroma The dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA involved in the synthesis of organic molecules from carbon dioxide and water Thylakoids A flattened membranous sac inside chloroplast Thylakoids exist in stacks called grana that are interconnected their membranes contain molecular machinery used to convert light energy to chemical energy Visible Spectrum Portion of electromagnetic spectrum that ranges from 380nm to 750nm Concepts and Principles energy Know what photosynthesis is why it is important and the organisms that use it as a source of The process that converts solar energy into chemical energy Directly or indirectly photosynthesis nourishes almost the entire world Used by photoautotrophs Know what photoautotrophs and heterotrophs are Photoautotrophs are self feeders using light as a source of energy to synthesize organic compounds We are heterotrophs consumers who live on compounds produced by other organisms Know what stomata are and their functional significance to the plant Microscopic pore that allows gas exchange between the environment and the interior which consists of incoming CO2 and releasing O2 located on the leaf epidermis outermost layer Know the plant plant cell and chloroplast anatomy depicted in Figure 10 4 and where the different parts of photosynthesis occur in the cell Photosynthesis takes place in chloroplasts chloroplasts are present in all green tissues of a plant but are particularly abundant and active in the mesophyll cells of the leaf Know what the electromagnetic spectrum is and which parts of the spectrum are important to photosynthesis Be able to relate the absorption spectrum of chlorophyll pigments to the action spectrum of photosynthesis Visible light falls within the wavelengths of 380nm and 750nm The action spectrum resembles the absorption spectrum Know the overall reaction of photosynthesis including products and reactants and be able to follow the path of atoms through the process as depicted in Figure 10 5 of each pathway Know the two pathways of photosynthesis where they occur and the reactants and products Light reactions photo take place on the thylakoid membranes Reactants solar energy water and ADP NADP Products O2 ATP NADPH Calvin cycle synthesis takes place in the stroma Reactants CO2 ATP NADPH Products CH20 sugar ADP NADP pigments to harvest light energy Know the pigments that are important for photosynthesis and how chloroplasts use these The pigments important for photosynthesis are chlorophyll a and b and carotenoids Chloroplasts use pigments to absorb light photons and then use these photons to boost an electron from its ground state to an excited state where it has more potential energy thus harvesting light energy Know what a photosystem is the components of a photosystem how energy is transferred from light to the reaction center complex and how photosystem I and II are connected Know where electrons come from to replace those lost to the primary electron acceptors in photosystems I and II There are two photosystems in the chloroplast membrane PS II and PS I connected by an electron transport chain 1 Light energy initates energy transfer chain reaction between pigments until energy is 2 transferred to P680 Instead of becoming excited P680 transfers its electron to the primary electron acceptor in the reaction complex P680 is now positively charged P680 and is a very strong oxidizing reagent 3 Water is split by an enzyme Two of its electrons are donated to the P680 pair restoring them to P680 The oxygen is combined with oxygen from the splitting of another molecule of water to form O2 The H ions are used to help generate a high concentration of H in the thylakoid space The splitting of water is possible because it is coupled to the reduction of the highly unstable pair of P680 molecules 4 The electron picked up by the primary acceptor is passed down an electron transport chain 6 5 The gradual falling of electrons to
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