Glossary

aerobic cellular respiration       (air-OH-bik)
The most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel. Aerobic means containing oxygen; referring to an organism, environment, or cellular process that requires oxygen.

ATP synthase
A protein complex that produces ATP.

autotroph       (AW-toh-TROHF)
An organism that obtains organic food molecules without eating other organisms. Autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones.

C3 plant
A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.

C4 plant
A plant that prefaces the Calvin cycle with reactions that incorporate CO2 into four-carbon compounds, the end-product of which supplies CO2 for the Calvin cycle.

Calvin cycle
The second of two major stages in photosynthesis (following the light reactions), involving atmospheric CO2 fixation and reduction of the fixed carbon into carbohydrate.

chlorophyll
A green pigment located within the chloroplasts of plants; chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy.

chloroplast       (KLOR-oh-plast)
An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

cyclic electron flow
A route of electron flow during the light reactions of photosynthesis that involves only photosystem I and produces ATP but not NADPH or oxygen.

heterotroph       (HET-ur-oh-TROHF)
An organism that obtains organic food molecules by eating other organisms or their by-products.

light reactions
The steps in photosynthesis that occur on the thylakoid membranes of the chloroplast and convert solar energy to the chemical energy of ATP and NADPH, evolving oxygen in the process.

NAD+ (nicotinamide adenine dinucleotide)
A coenzyme present in all cells that helps enzymes transfer electrons during the redox reactions of metabolism.

noncyclic electron flow
A route of electron flow during the light reactions of photosynthesis that involves both photosystems and produces ATP, NADPH, and oxygen; the net electron flow is from water to NADP+.

nondisjunction
An accident of meiosis or mitosis, in which both members of a pair of homologous chromosomes or both sister chromatids fail to move apart properly.

photorespiration
A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide.

photosynthesis
The conversion of light energy to chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain prokaryotes.

photosystem
The light-harvesting unit in photosynthesis, located on the thylakoid membrane of the chloroplast and consisting of the antenna complex, the reaction-center chlorophyll a, and the primary electron acceptor. There are two types of photosystems, I and II; they absorb light best at different wavelengths.

polyploidy       (POL-ee-ploid-ee)
A chromosomal alteration in which the organism possesses more than two complete chromosome sets.

proton-motive force
The potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.

rubisco
Ribulose carboxylase, the enzyme that catalyzes the first step (the addition of CO2 to RuBP, or ribulose bisphosphate) of the Calvin cycle.

stroma
The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

thylakoid       (THY-luh-koid)
A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

visible light
That portion of the electromagnetic spectrum detected as various colors by the human eye, ranging in wavelength from about 400 nm to about 700 nm.