Photosynthesis

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Photosynthesis

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the complex biological process that converts the energy of light into chemical energy stored in glucose and other organic molecules; occurs in plants, algae, and some bacteria

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autotrophs

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any organism that can synthesize reduced organic compounds from simple inorganic sources such as carbon dioxide and methane; most plants and some bacteria and archaea are autotrophs

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heterotrophs

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any organism that cannot synthesize reduced organic compounds from inorganic sources and that must obtain them by eating other organisms; some bacteria, archaea, and virtually all fungi and animals are heterotrophs

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Calvin Cycle

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a set of light-independent ractions that use NADPH and ATP formed in the light-dependent reactions to drive the fixation of atmospheric carbon dioxide and reduction of the fixed carbon, ultimately producing sugars

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NADP+/NADPH

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a nonprotein electron carrier that is reduced during the light-dependent reactions in photosynthesis and extensively used in biosynthetic reactions

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chloroplasts

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a chlorophyll-containing organelle, bounded by a double membrane, in which photosynthesis occurs; found in plants and photosynthetic protists; also the location of amino acid, fatty acid, purine, and pyrimidine synthesis

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thylakoids

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a flattened, membrane-bound vesicle inside a plant chloroplast that functions in converting light energy to chemical energy; a stack of thylakoids is a granum

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Grana(granum)

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in chloroplasts, a stack of flattened, membrane-bound vesicles (thylakoids) where the light reactions of photosynthesis occur

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lumen

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the interior space of any hollow structure(rough ER) or organ (stomach)

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stroma

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the fluid matrix of a chloroplast in which the thylakoids are embedded; site where the Calvin cycle reactions occur

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pigments

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any molecule that absorbs certain wavelengths of visible light and reflects or transmits other wavelengths

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wavelength

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the distance between two succesive crests in any regular wave, such as light waves, sound waves, or waves in water

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electromagentic spectrum

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the entire range of wavelengths of radiation extending from short wavelengths (high energy) to long wavelengths (low energy); includes gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves (from short to long wavelengths)

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visible light

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the range of wavelengths of electromagentic radiation that humans can see, from about 400 to 700 nanometers

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photons

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a discrete packet of light energy; a particle of light

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absorption spectrum

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the amount of light of different wavelengths absorbed by a pigment; usually depicted as a graph of light absorbed versus wavelength

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chlorophyll

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any of several closely related green pigments, found in chloroplasts and photosynthesis and photosynthetic protists, that absorb light during photosynthesis

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caretenoids

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any of a class of accessory pigments, found in chloroplasts, that absorb wavelengths of light not absorbed by chlorophyll; typically appear yellow, orange, or red

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action spectrum

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the relative effectiveness of different wavelengths of light in driving a light-dependent process such as photosynthesis; usually depicted as a graph of some measure of the process versus wavelength

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fluorescence

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the spontaneous emission of light from an excited electron falling back to its normal (ground) state

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photosystem

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one of two types of units,consisting of a central reaction center surrounded by antenna complexes, that is responsible for the light-dependent reactions of photosynthesis

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antenna complex

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part of a photosystem, containing an array of chlorophyll molecules and accesosry pigments, that receive energy from light and directs the energy to a central reaction center during photosynthesis

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reaction center

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centrally located component of a photosystem containing proteins and a pair of specialized chlorophyll molecules; is surrounded by antenna complexes and receives excited electrons from them

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photosystem II

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a photosystem that contains a pair of P700 chlorophyll molecules and uses absorbed light energy to split water into protons and oxygen and to produce ATP

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photosystem I

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a photosystem that contains a pair of P700 chlorophyll molecules and uses absorbed light energy to produce NADPH

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pheophytin

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in photosystem II, a molecule that accepts excited electrons from a reaction center chlorophyll and passes them to an electron transport chain

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plastoguinone

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a nonprotein electron carrier in the choloroplast electron transport chain; receives excited electrons from pheophytin and passes them to more electronegative molecules in the chain; also carries protons to the lumen side of the thylakoid membrane, generating a proton-motive force

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photophosphorylation

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production of ATP molecules using the energy released as light-excited electrons flow through an electron transport chain during photosynthesis; involves generation of a proton-motive force during electron transport and its use to drive ATP synthesis

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oxygenic

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any process or reaction that produces oxygen; photosynthesis in plants, algae, and cyanobacteria, which involves photosystem II, is oxygenic

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anoxygenic

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any process or reaction that does not produce oxygen; photosynthesis in purple sulfur and purple nonsulfur bacteria, which does not involve photosystem II, is anoxygenic

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ferredoxin

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in photosynthetic organisms, an iron-and sulfur-containing protein in the ETC of photosystem I; can transfer electrons to the enzyme NADP+ reductase, which catalyzes formation of NADPH

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Z scheme

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path of electron flow in which electrons pass from photosystem II to photosystem I and ultimately to NADP+ during the light-dependent reactions of photosynthesis

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plastocyanin

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a small protein that shuttles electrons from photosystem II to photosystem I during photosynthesis

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cyclic photophosphorylation

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path of electron flow during the light-dependent reactions of photosynthesis in which photosystem I transfers excited electrons back to the ETC of photosystem II, rather than to NADP+

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carbon fixation

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the addition of carbon dioxide to an organic compound; a redox reaction where the carbon atoms in carbon dioxide is reduced

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ribulose bisphosphate (RuBP)

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a 5-Carbon compound that combines with carbon dioxide in the first step of the Calvin cycle during photosynthesis

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glyceraldehyde-3-phosphate

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the phosphorylated 3-carbon compound formed as the result of carbon fixation in the first step of the Calvin cycle

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rubisco

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the enzyme that catalyzes the first step of the Calvin cycle during photosynthesis: the addition of a molecule of carbon dioxide to ribulose bisphosphate

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maladaptive

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a trait that lowers fitness

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photorespiration

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a series of light-driven chemical reactions that consumes oxygen and releases carbon dioxide, basically reversing photosynthesis; usually occurs when there are high O2 and low carbon dioxide concentrations inside plant cells, often in bright, hot, dry, environments when stomata must be kept closed

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guard cells

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one of two specialized, crescent-shaped cells forming the border of a plant stoma; can change shape to open or close the stoma

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stoma (stomata)

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generally, a pore or opening; in plants, a microscopic pore on the surface of a leaf or stem through which gas exchange occurs

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C3 photosynthesis

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the most common form of photosynthesis in which atmospheric carbon dioxide is used to from 3-phosphoglycerate, a 3-carbon sugar

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C4 photosynthesis

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a variant type of photosynthesis in which atmospheric carbon dioxide is first fixed into 4C sugars, rather than the 3C sugars of classic C3 photosynthesis; enhances photosynthetic efficiency in hot, dry environments, by reducing loss of oxygen due to photorespiration

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PEP carboxylase

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an enzyme that catalyzes addition of carbon dioxide to phosphoenol pyruvate, a 3C compound, forming a 4C organic acid; found in mesophyll cells of plants that perform C4 photosynthesis

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mesophyll cells

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a type of cell, found near the surfaces of plant leaves, that is specialized for the light-dependent reactions of photosynthesis

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bundle-sheath cells

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a type of cell found around the vascular tissue (veins) of plant leaves

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vascular tissue

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in plants, tissue that transports water, nutrients and sugars; made up of the complex tissues xylem and phloem, each of which contains several cell types

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crassulacean acid metabolism (CAM)

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a variant type of photosynthesis in which carbon dioxide is stored in organic acids at night when stomata are open and then released to feed the Calvin cycle during the day when stomata are closed; helps reduce water loss and oxygen loss by photorespiration in hot, dry environments

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starch

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a mixture of two storage polysaccharides, amylose and amylopectin, both formed from alpha-glucose monomers; amylopectin is branched, and amylose is unbranched; the major form of stored carbohydrates in plants