Print › AP Biology Unit 4 Key Terms

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.
Acetyl coenzyme A (Acetyl CoA): A key intermediate compound in metabolism; consists of a two-carbon acetyl group covalently bonded to coenzyme A.
action spectrum: A graph of the effectiveness of light at specific wavelengths in promoting a light-requiring reaction.
Adenosine triphosphate (ATP): An organic compound containing adenine, ribose, and three phosphate groups; of prime importance for energy transfers in cells.
Adipose tissue: Tissue in which fat is stored.
Aerobic: Growing or metabolizing only in the presence of molecular oxygen.
Aerobic respiration: Cellular respiration that requires oxygen; the terminal electron acceptor is molecular oxygen.
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.
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.
Anaerobic: Growing or metabolizing only in the absence of molecular oxygen.
Anaerobic respiration: Cellular respiration that doesn’t require oxygen; the terminal electron acceptor is an inorganic molecule other than oxygen.
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.
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.
Autotroph: An organism that synthesizes complex organic compounds from simple inorganic raw materials; also called producer or primary producer.
autotroph: An organism that synthesizes complex organic compounds from simple inorganic raw materials; also called producer or primary producer.
Beta (β) oxidation: Process by which fatty acids are converted to acetyl CoA before entry into the citric acid cycle.
Breathing: The process of taking air into the lungs and pushing it out again.
bundle sheath cell: Tightly packed cells that form a sheath around the veins of a leaf.
C3 plant: Plant that uses three-carbon PGA as the first intermediate for carbon fixation.
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.
Calvin cycle: Cyclic series of reactions in the chloroplast stroma in photosynthesis; fixes carbon dioxide and produces carbohydrate.
CAM pathway (crassulacean acid metabolism): A special carbon fixation pathway for plants living in very dry (xeric) conditions.
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.
Carbohydrate: Compound containing carbon, hydrogen, and oxygen, in the approximate ratio of C:2H:O, e.g., sugars, starch, and cellulose.
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.
carotenoids: A group of yellow to orange plant pigments synthesized from isoprene subunits; include carotenes and xanthophylls.
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.
Chemiosmosis: The diffusion of ions across a membrane (specifically, the generation of ATP by the movement of hydrogen ions across a membrane).
chemoautotroph: Organism that obtains energy from inorganic compounds and synthesizes organic compounds from inorganic raw materials; includes some bacteria.
chemoheterotroph: Organism that uses organic compounds as a source of energy and carbon; includes animals, fungi, and many bacteria.
chemotroph: Organism that uses organic compounds or inorganic substances, such as iron, nitrate, ammonia, or sulfur, as sources of energy.
chlorophyll: A group of light-trapping green pigments found in most photosynthetic organisms.
chlorophyll-binding proteins: About 15 different proteins associated with chlorophyll molecules in the thylakoid membrane.
chloroplasts: Membranous organelles that are the sites of photosynthesis in eukaryotes; occur in some plant and algal cells.
Citrate: A six-carbon organic acid.
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.
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.
cyanobacteria: Prokaryotic photosynthetic microorganisms that possess chlorophyll and produce oxygen during photosynthesis. Formerly known as blue-green algae.
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.
Deamination: The removal of an amino group (-NH2) from an amino acid or other organic compound.
Decarboxylation: A reaction in which a molecule of CO2 is removed from a carboxyl group of an organic acid.
Dehydrogenation: A form of oxidation in which hydrogen atoms are removed from a molecule.
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.
Ethyl alcohol: A two-carbon alcohol.
Facultative anaerobe: An organism capable of carrying out aerobic respiration but able to switch to fermentation when oxygen is unavailable; e.g., yeast.
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.
fluorescence: The emission of light of a longer wavelength (lower energy) than the light originally absorbed.
Glucose: A hexose aldehyde sugar that is central to many metabolic processes.
glyceraldehyde-3-phosphate (G3P): Phosphorylated 3-carbon compound that is an important intermediate in glycolysis and in the Calvin cycle.
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.
granum: A stack of thylakoids within a chloroplast.
ground state: The lowest energy state of an atom.
Heat: The total amount of kinetic energy in a sample of a substance.
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.
Lactate (lactic acid) fermentation: Fermentation in which NADH produced during glycolysis transfers hydrogen atoms to private, reducing it to the waste product lactate.
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.
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.
mesophyll: Photosynthetic tissue in the interior of a leaf; sometimes differentiated into palisade mesophyll and spongy mesophyll.
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.
Nitrogen cycle: The worldwide circulation of nitrogen from the abiotic environment into living things and back into the abiotic environment.
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.
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.
nucleoside triphosphate: Molecule consisting of a nitrogenous base, a pentose sugar, and three phosphate groups.
Oxaloacetate: Four-carbon compound; important intermediate in the citric acid cycle and in the C4 and CAM pathways of carbon fixation in photosynthesis.
Oxidation: The loss of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule.
Oxidative phosphorylation: The production of ATP using energy derived from the transfer of electrons in the electron transport system of mitochondria; occurs by chemiosmosis.
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.
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.
PEP carboxylase: An enzyme that catalyzes the reaction by which CO2 reacts with PEP to form oxaloacetate.
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.
phosphoglycerate (PGA): Phosphorylated three-carbon compound that is an important metabolic intermediate.
Phosphorylation: The addition of a phosphate group to an organic molecule in order to produce an organic phosphate.
photoautotroph: An organism that obtains energy from light and synthesizes organic compounds from inorganic raw materials; includes plants, algae, and some bacteria.
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.
photolysis: The photochemical splitting of water in the light-dependent reactions of photosynthesis, catalyzed by a specific enzyme.
photophosphorylation: The production of ATP in photosynthesis.
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.
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.
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.
phototroph: An organism that obtains energy for growth from sunlight.
pigment: A substance that selectively absorbs light of different wavelengths.
Pyruvate: The three-carbon end product of glycolysis.
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.
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).
Reduction: The gain of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule.
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.
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.
Rubisco: The common name of ribulose bisphosphate carboxylase, the enzyme that catalyzes the reaction of carbon dioxide with ribulose bisphosphate in the Calvin cycle.
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.
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.
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.
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.
thylakoid lumen: A fluid-filled interior space enclosed by the thylakoid membrane.
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.
Yeast: A unicellular fungus (ascomycete) that reproduces asexually by budding or fission and sexually by ascospores.