PHOTOSYNTHESIS IN HIGHER PLANTS
Important Terms:
· Absorption Spectrum:A curve showing the amount of different wavelengths of light absorbed by a substance.
· Action Spectrum:A curve depicting the relative rates of photosynthesis at different wavelengths of light.
· Accessory Pigments:The pigments which handover the energy absorbed by them to the chlorophyll.
· CAM Plants:Refers to the succulent and some other plants which show crassulacean acid metabolism.
· Chemosynthesis:The process of carbohydrate synthesis in which the organisms use chemical reactions to obtain energy from inorganic compounds.
· Fluorescence: A property of emission of radiations absorbed by a substance.
· Photocentre:(also known as reaction centre) Refers to a primary pigment (chlorophyll) molecule where light energy is converted into chemical or electron energy.
· Photolysis: Light dependent splitting of water molecule in the chloroplasts.
· Photon:A tiny particle of light containing energy called quantum (hv).
· Photophosphorylation:A light driven or energized synthesis of ATP from ADP and inorganic phosphate.
· Photosystem:Light harvesting systems of pigment molecules present in thylakoids of the chloroplast. They are photosystem I and photosystem II.
· Photosynthetically Active Radiation (PAR): The visible spectrum of light between 400 nm to 700 nm which can be absorbed by the chlorophyll molecules.
· Photosynthetic Carbon Oxidation Cycle: Photorespiration or C2 cycle. Light dependent utilization of O2 and release of CO2 by the photosynthetic organs of a plant.
· Photosynthetic Carbon Reduction Cycle: C3 cycle.
· Phosphorescence:Delayed emission of long wave radiations from an irradiated and activated substance.
· Primary Pigments:Photosynthetic pigments, which convert light energy into chemical or electron energy.
· Quantum Yield:Number of oxygen molecules released per photon or quantum of light. Its value is 1/8 to 1/10 (evolution of one molecule of O2 requires 8-10 quanta).
ADDITIONAL INFORMATION
· Photosynthesisis an oxidation reduction process where water is oxidized to O2 and CO2 is reduced to (CH2O)n.
· The Redox Potential of H2O/O2 is + 0.8V and that of CO2/(CH2O)n is -0.4V. The difference is 1.2 V per electron transferred. Redox potential is the tendency of the system (atom/molecule) to give or take up electrons. The symbol used to express the standard redox potential at pH 7 is E0. The compound having low redox potential tend to lose electrons and those having high redox potential gain electrons.
· Herbicides such as CMU ( 3 p.chlorophenyl 1,1 dimethyl urea) and DCMC (3,4- Dichlorophenyl 1,1 dimethyl urea) block electron transport between quinone (Q) to plastoquinone (PQ), during non-cyclic electron transport.
· Quantum Yield: Number of oxygen molecules released per photon or quantum of light is called quantum yield. Its value is 1/8 to 1/10 (10-12.5%). In other words, evolution of one molecule of oxygen or consumption/ fixation of one molecule of CO2 requires 8-10 quanta. The number of light quanta used for producing one molecule of O2 or fixation of one molecule of CO2is called quantum requirement.
· Chemical Coupling Hypothesis: Synthesis of ATP is connected to liberation of energy while electrons pass down hill over the electron transport chain.
· Chemi-Osmotic Hypothesis (Mitchell 1961): There is accumulation of protons which pass through membrane bases ATPase (for coupling factor, elementary particle) catalyzing synthesis of ATP from ADP and inorganic phosphate.
· P-protein: It is synthesized in companion cells ( absent in gymnosperms). In sieve tube cells it has a role as defence against phloem feeding insects and sealing of damaged sieve tubes by plugging sieve plates.
· Thylakoid Reactions: Reactions of photochemical phase as they occur over the thylakoids.
· Stroma Reactions: Reactions of biosynthetic phase, as they occur in stroma.
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