 | Term | Definition |
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Acetyl coenzyme A (Acetyl CoA) |
A key intermediate compound in metabolism; consists of a two-carbon acetyl group covalently bonded to coenzyme A. |
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Adipose tissue |
Tissue in which fat is stored. |
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Adenosine triphosphate (ATP) |
An organic compound containing adenine, ribose, and three phosphate groups; of prime importance for energy transfers in cells. |
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ATP synthase |
Large enzyme complex that catalyzes the formation of ATP from ADP and inorganic phosphate by chemiosmosis; contains a transmembrane channel through which protons diffuse down a concentration gradient; located in the inner mitochondrial membrane, the thylakoid membrane of chloroplasts, and the plasma membrane of bacteria. |
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Aerobic |
Growing or metabolizing only in the presence of molecular oxygen. |
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Aerobic respiration |
Cellular respiration that requires oxygen; the terminal electron acceptor is molecular oxygen. |
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Alcohol fermentation |
Fermentation in which enzymes decarboxylate pyruvate to form a two-carbon compound called acetaldehyde. NADH produced during glycolysis transfers hydrogen atoms to the acetaldehyde, reducing it to ethyl alcohol. |
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Anaerobic |
Growing or metabolizing only in the absence of molecular oxygen. |
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Anaerobic respiration |
Cellular respiration that doesn’t require oxygen; the terminal electron acceptor is an inorganic molecule other than oxygen. |
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Anabolism |
The aspect of metabolism in which simpler substances are combined to form more complex substances, resulting in the storage of energy, the production of new cell materials, and growth. |
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Autotroph |
An organism that synthesizes complex organic compounds from simple inorganic raw materials; also called producer or primary producer. |
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Beta (β) oxidation |
Process by which fatty acids are converted to acetyl CoA before entry into the citric acid cycle. |
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Breathing |
The process of taking air into the lungs and pushing it out again. |
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Carbohydrate |
Compound containing carbon, hydrogen, and oxygen, in the approximate ratio of C:2H:O, e.g., sugars, starch, and cellulose. |
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Catabolism |
The aspect of metabolism in which complex substances are broken down to form simpler substances; catabolic reactions are particularly important in releasing chemical energy stored by the cell. |
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Chemiosmosis |
The diffusion of ions across a membrane (specifically, the generation of ATP by the movement of hydrogen ions across a membrane). |
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Citrate |
A six-carbon organic acid. |
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Citric acid cycle (Tricarboxylic acid [TCA] cycle; Krebs cycle) |
Series of chemical reactions in aerobic respiration in which acetyl coenzyme A is completely degraded to carbon dioxide and water with the release of metabolic energy that is used to produce ATP; also known as the Krebs cycle and the tricarboxylic acid (TCA) cycle. |
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Coenzyme A (CoA) |
An organic cofactor for an enzyme; generally participates in the reaction by transferring some component. Such as electrons or part of a substrate molecule. |
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Deamination |
The removal of an amino group (-NH2) from an amino acid or other organic compound. |
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Decarboxylation |
A reaction in which a molecule of CO2 is removed from a carboxyl group of an organic acid. |
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Dehydrogenation |
A form of oxidation in which hydrogen atoms are removed from a molecule. |
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Electron transport system |
A series of chemical reactions during which hydrogens or their electrons are passed along an electron transport chain from one acceptor molecule to another, with the release of energy. |
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Ethyl alcohol |
A two-carbon alcohol. |
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Facultative anaerobe |
An organism capable of carrying out aerobic respiration but able to switch to fermentation when oxygen is unavailable; e.g., yeast. |
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Fermentation |
An anaerobic process by which ATP is produced by a series of redox reactions in which organic compounds serve both as electron donors and terminal electron acceptors. |
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Glucose |
A hexose aldehyde sugar that is central to many metabolic processes. |
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Glycolysis |
The first stage of cellular respiration, literally the “splitting of sugar.” The metabolic conversion of glucose into pyruvate, accompanied by the production of ATP. |
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Heat |
The total amount of kinetic energy in a sample of a substance. |
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Lactate (lactic acid) fermentation |
Fermentation in which NADH produced during glycolysis transfers hydrogen atoms to private, reducing it to the waste product lactate. |
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Lipid |
Any of a group of organic compounds that are insoluble in water but soluble in nonpolar solvents; lipids serve as energy storage and are important components of cell membranes. |
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NADP+/NADPH |
Oxidized and reduced forms, respectively, of nicotinamide adenine dinucleotide, a coenzyme that transfers electrons (as hydrogen), particularly in catabolic pathways, including cellular respiration. |
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Nitrogen cycle |
The worldwide circulation of nitrogen from the abiotic environment into living things and back into the abiotic environment. |
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Noncyclic electron transport |
In photosynthesis, the linear flow of electrons through Photosystems I and II; results in the formation of ATP (by chemiosmosis), NADPH, and O2. Compare with cyclic electron transport. |
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Oxaloacetate |
Four-carbon compound; important intermediate in the citric acid cycle and in the C4 and CAM pathways of carbon fixation in photosynthesis. |
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Oxidation |
The loss of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule. |
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Oxidative phosphorylation |
The production of ATP using energy derived from the transfer of electrons in the electron transport system of mitochondria; occurs by chemiosmosis. |
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Phosphorylation |
The addition of a phosphate group to an organic molecule in order to produce an organic phosphate. |
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Pyruvate |
The three-carbon end product of glycolysis. |
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Reduction |
The gain of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule. |
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Respiration |
Cellular respiration is the process by which cells generate ATP through a series of redox reactions. In aerobic respiration the terminal electron acceptor is molecular oxygen; in anaerobic respiration the terminal acceptor is an inorganic molecule other than oxygen. |
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Specific immune responses |
Defense mechanisms that target specific macromolecules associated with a pathogen. Includes cell-mediated immunity and antibody-mediated immunity. Also known as acquired or adaptive immune responses. |
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Substrate-level phosphorylation |
A type of chemical reaction that results in the formation of ATP by the direct transfer of a phosphate group to ADP from a reactive intermediate. |
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Yeast |
A unicellular fungus (ascomycete) that reproduces asexually by budding or fission and sexually by ascospores. |
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absorption spectrum |
A graph of the amount of light at specific wavelengths that has been absorbed as light passes through a substance. Each type of molecule has a characteristic this. |
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action spectrum |
A graph of the effectiveness of light at specific wavelengths in promoting a light-requiring reaction. |
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antenna complex |
The currently accepted arrangement of chlorophyll, accessory pigment molecules, and pigment-binding proteins into light-gathering units in the thylakoid membranes of photoautotrophic eukaryotes. |
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autotroph |
An organism that synthesizes complex organic compounds from simple inorganic raw materials; also called producer or primary producer. |
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bundle sheath cell |
Tightly packed cells that form a sheath around the veins of a leaf. |
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C3 plant |
Plant that uses three-carbon PGA as the first intermediate for carbon fixation. |
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C4 plant |
Plant that fixes carbon initially by the Hatch-Slack pathway, in which the reaction of CO2 with phosphoenolpyruvate is catalyzed by PEP carboxylase in leaf mesophyll cells; the products are transferred to the bundle sheath cells, where the Calvin cycle takes place. |
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Calvin cycle |
Cyclic series of reactions in the chloroplast stroma in photosynthesis; fixes carbon dioxide and produces carbohydrate. |
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CAM plant |
Plant that carries out crassulacean acid metabolism; carbon is initially fixed into organic acids at night in the reaction of CO2 and phosphoenolpyruvate, catalyzed by PEP carboxylase; during the day the acids break down to yield CO2, which enters the Calvin cycle. |
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carbon fixation reactions |
Reduction reactions of photosynthesis in which carbon from carbon dioxide becomes incorporated into organic molecules, leading to the production of carbohydrate; requires ATP and NADPH. |
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carotenoids |
A group of yellow to orange plant pigments synthesized from isoprene subunits; include carotenes and xanthophylls. |
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chemoautotroph |
Organism that obtains energy from inorganic compounds and synthesizes organic compounds from inorganic raw materials; includes some bacteria. |
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chemoheterotroph |
Organism that uses organic compounds as a source of energy and carbon; includes animals, fungi, and many bacteria. |
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chemotroph |
Organism that uses organic compounds or inorganic substances, such as iron, nitrate, ammonia, or sulfur, as sources of energy. |
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chlorophyll |
A group of light-trapping green pigments found in most photosynthetic organisms. |
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chlorophyll-binding proteins |
About 15 different proteins associated with chlorophyll molecules in the thylakoid membrane. |
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chloroplasts |
Membranous organelles that are the sites of photosynthesis in eukaryotes; occur in some plant and algal cells. |
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cyanobacteria |
Prokaryotic photosynthetic microorganisms that possess chlorophyll and produce oxygen during photosynthesis. Formerly known as blue-green algae. |
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fluorescence |
The emission of light of a longer wavelength (lower energy) than the light originally absorbed. |
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glyceraldehyde-3-phosphate (G3P) |
Phosphorylated 3-carbon compound that is an important intermediate in glycolysis and in the Calvin cycle. |
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granum |
A stack of thylakoids within a chloroplast. |
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ground state |
The lowest energy state of an atom. |
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heterotroph |
An organism that cannot synthesize its own food from inorganic raw materials and therefore must obtain energy and body-building materials from other organisms. Also called consumer. |
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light-dependent reactions |
Reactions of photosynthesis in which light energy absorbed by chlorophyll is used to synthesize ATP and usually NADPH. Includes cyclic electron transport and noncyclic electron transport. |
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mesophyll |
Photosynthetic tissue in the interior of a leaf; sometimes differentiated into palisade mesophyll and spongy mesophyll. |
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noncyclic electron transport |
In photosynthesis, the linear flow of electrons through Photosystems I and II; results in the formation of ATP (by chemiosmosis), NADPH, and O2. |
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nucleoside triphosphate |
Molecule consisting of a nitrogenous base, a pentose sugar, and three phosphate groups. |
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P680 |
Chlorophyll a molecules that serve as the reaction center of Photosystem II, transferring photoexcited electrons to a primary acceptor; named by their absorption peak at 680 nm. |
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P700 |
Chlorophyll a molecules that serve as the reaction center of Photosystem I, transferring photoexcited electrons to a primary acceptor; named by their absorption peak at 700 nm. |
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phosphoenolpyruvate (PEP) |
Three-carbon phosphorylated compound that is an important intermediate in glycolysis and is a reactant in the initial carbon fixation step in C4 and CAM photosynthesis. |
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phosphoglycerate (PGA) |
Phosphorylated three-carbon compound that is an important metabolic intermediate. |
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photoautotroph |
An organism that obtains energy from light and synthesizes organic compounds from inorganic raw materials; includes plants, algae, and some bacteria. |
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photoheterotroph |
An organism that is able to carry out photosynthesis to obtain energy but is unable to fix carbon dioxide and therefore requires organic compounds as a carbon source; includes some bacteria. |
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photolysis |
The photochemical splitting of water in the light-dependent reactions of photosynthesis, catalyzed by a specific enzyme. |
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photophosphorylation |
The production of ATP in photosynthesis. |
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photorespiration |
The process that reduces the efficiency of photosynthesis in C3 plants during hot spells in summer; consumes oxygen and produces carbon dioxide through the degradation of Calvin cycle intermediates. |
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photosynthesis |
The biological process that captures light energy and transforms it into the chemical energy of organic molecules (e.g., carbohydrates), which are manufactured from carbon dioxide and water; performed by plants, algae, and certain bacteria. |
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photosystem |
One of two photosynthetic units, consisting of chlorophyll molecules, accessory pigments, proteins, and associated electron acceptors, responsible for capturing light energy and transferring excited electrons; photosystem I best absorbs and uses light of about 700 nm, whereas photosystem II best absorbs and uses light of about 680 nm. |
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phototroph |
An organism that obtains energy for growth from sunlight. |
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pigment |
A substance that selectively absorbs light of different wavelengths. |
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reaction center |
The portion of a photosystem that includes chlorophyll a molecules capable of transferring electrons to a primary electron acceptor, which is the first of several electron acceptors in a series; the reaction center of Photosystem I is P700 and of Photosystem II is P680. |
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redox reaction |
The chemical reaction in which one or more electrons are transferred from one substance (the substance that becomes oxidized) to another (the substance that becomes reduced). |
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ribulose bisphosphate (RuBP) |
A five-carbon phosphorylated compound with a high energy potential that reacts with carbon dioxide in the initial step of the Calvin cycle. |
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Rubisco |
The common name of ribulose bisphosphate carboxylase, the enzyme that catalyzes the reaction of carbon dioxide with ribulose bisphosphate in the Calvin cycle. |
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stomata |
Small pores located in the epidermis of plants that provide for gas exchange for photosynthesis; each stoma is flanked by two guard cells, which are responsible for its opening and closing. |
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stroma |
A fluid space of the chloroplast, enclosed by the chloroplast inner membrane and surrounding the thylakoids; site of the reactions of the Calvin cycle. |
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thylakoids |
An interconnected system of flattened, saclike membranous structures inside the chloroplast; the thylakoid membranes contain chlorophyll and the electron transport chain and enclose a compartment, the thylakoid lumen. |
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thylakoid lumen |
A fluid-filled interior space enclosed by the thylakoid membrane. |
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cyclic electron transport |
In photosynthesis, the cyclic flow of electrons through Photosystem I; ATP is formed by chemiosmosis, but no photolysis of water occurs, and O2 and NADPH are not produced. |
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PEP carboxylase |
An enzyme that catalyzes the reaction by which CO2 reacts with PEP to form oxaloacetate. |
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CAM pathway (crassulacean acid metabolism) |
A special carbon fixation pathway for plants living in very dry (xeric) conditions. |
