Ch7: Photosynthesis, Light, And Life

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chlorophyll

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[Gk. chloros, green, + phyllon, leaf] The green pigment of plant cells; the receptor of light energy in photosynthesis; also found in algae and photosynthetic bacteria

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absorption spectrum

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The spectrum of light waves absorbed by a particular pigment

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C4 plants

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Plants in which the first product of CO2 fixation is a four-carbon compound (oxaloacetate); both the Calvin cycle (C3 pathway) and the C4 pathway are employed by C4 plants

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Hill reaction

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The evolution of oxygen and photoreduction of an artificial electron acceptor by a chloroplast preparation in the absence of carbon dioxide

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carotene

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[L. carota, carrot] A yellow or orange pigment belonging to the carotenoid group

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accessory pigment

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A pigment that captures light energy and transfers it to chlorophyll a

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carotenoids

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A class of fat-soluble pigments that includes the carotenes (yellow and orange pigments) and the xanthophylls (yellow pigments); found in chloroplasts and chromoplasts of plants. Carotenoids act as accessory pigments in photosynthesis

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action spectrum

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The spectrum of light waves that elicits a particular reaction

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antenna complex

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The portion of a photosystem that consists of pigment molecules (antenna pigments) that gather light and "funnel" it to the reaction center

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C4 pathway

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The set of reactions through which CO2 is fixed to the compound phosphoenolpyruvate (PEP) to yield oxaloacetate, a four-carbon compound

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carbon-fixation reactions

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In photosynthetic cells, the light-independent enzymatic reactions concerned with the synthesis of glucose from CO2, ATP, and NADPH. Also called light-independent reactions and dark reactions

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ATP synthase

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An enzyme complex that forms ATP from ADP and phosphate during oxidative phosphorylation in the inner mitochondrial membrane

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C3 pathway

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See Calvin cycle

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crassulacean acid metabolism (CAM)

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A variant of the C4 pathway; the enzyme PEP (phosphoenolpyruvate) carboxylase fixes CO2 into C4 compounds at night, then during the daytime, the fixed CO2 is transferred to the ribulose bisphosphate of the Calvin cycle in the same cell; characteristic of most succulent plants, such as cacti

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Calvin cycle

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The series of enzymatically mediated photosynthetic reactions during which CO2 is reduced to glyceraldehyde 3-phosphate (3-phosphoglyceraldehyde) and the CO2 acceptor, ribulose 1,5-bisphosphate, is regenerated. For every three molecules of CO2 entering the cycle, a net gain of one molecule of glyceraldehyde 3-phosphate results

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photosynthesis

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[Gk. photos, light, + syn, together + tithenai, to place] Conversion of light energy to chemical energy; the production of carbohydrates from carbon dioxide and water in the presence of chlorophyll by using light energy

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resonance energy transfer

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The transfer of light energy from an excited chlorophyll molecule to a neighboring chlorophyll molecule, exciting the second molecule and allowing the first one to return to its ground state

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phycobilins

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A group of water-soluble accessory pigments, including phycocyanins and phycoerythrins, found in the red algae and cyanobacteria

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electromagnetic spectrum

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The entire spectrum of radiation, which ranges in wavelength from less than a nanometer to more than a kilometer

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light reactions

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The reactions of photosynthesis that require light and cannot occur in the dark. Also called light-dependent reactions and energy-transduction reactions

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pigment

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A substance that absorbs light, often selectively

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xanthophyll

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[Gk. xanthos, yellowish-brown, + phyllon, leaf] A yellow chloroplast pigment; a member of the carotenoid class

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noncyclic electron flow

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The light-induced flow of electrons from water to NADP+ in oxygen-evolving photosynthesis; it involves both Photosystems I and II

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ferredoxin

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An electron-transferring protein of high iron content; some ferredoxins are involved in photosynthesis

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photophosphorylation

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[Gk. photos, light, + phosphoros, bringing light] Formation of ATP in the chloroplast during photosynthesis

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cyclic electron flow

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In chloroplasts, the light-induced flow of electrons originating from and returning to Photosystem I

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photon

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[Gk. photos, light]: The elementary particle of light

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photolysis

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The light-dependent oxidative splitting of water molecules that takes place in Photosystem II of the light reactions of photosynthesis

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photorespiration

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The oxygenase activity of Rubisco combined with the salvage pathway, consuming O2 and releasing CO2; occurs when Rubisco binds O2 instead of CO2

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cytochrome

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[Gk. kytos, container, + chroma, color] Heme proteins serving as electron carriers in respiration and photosynthesis

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Kranz anatomy

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[Ger. Kranz, wreath] The wreathlike arrangement of mesophyll cells around a layer of large bundle-sheath cells, forming two concentric layers around the vascular bundle; typically found in the leaves of C4 plants

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photosystem

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A discrete unit of organization of chlorophyll and other pigment molecules embedded in the thylakoids of chloroplasts and involved in the light-dependent reactions of photosynthesis

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Rubisco

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RuBP carboxylase/oxygenase, the enzyme that catalyzes the initial reaction of the Calvin cycle, involving the fixation of carbon dioxide to ribulose 1,5-bisphosphate (RuBP)

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reaction center

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The complex of proteins and chlorophyll molecules of a photosystem, capable of converting light energy to chemical energy in the photochemical reaction

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sucrose

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A disaccharide (glucose plus fructose) found in many plants; the primary form in which sugar produced by photosynthesis is translocated

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starch

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[M.E. sterchen, to stiffen] A complex, insoluble carbohydrate; the chief food storage substance of plants; composed of a thousand or more glucose units