Terminology

Antenna Pigment Molecules - A series of molecules through which captured energy (in the form of an excited electron) from a photon of light may wander before arriving at a reaction center. Most chlorophylls act as antenna molecules (Figure 17.11).
Bacteriochlorophyll b - A type of chlorophyll found in photosynthetic bacteria.
Carotene - A precursor of vitamin A and an accessory photosynthetic pigment in plants (Figure 17.7).
Calvin Cycle - The series of reactions in the dark cycle of photosynthesis in which carbon dioxide is fixed by adding one molecule at a time to an acceptor molecule and passing the molecule through a series of reactions (Figure 17.20).
Choloroplast - Plant and algae organelle where photosynthesis occurs (Figure 17.4c).
Chromophores - Photosynthetic pigments that absorb specific wavelengths of light for photosynthesis (Figure 17.8).
Cyclic Electron Flow - An alternative pathway of electron flow (compared to noncyclic electron flow), which utilizes the components of photosystem I, plus plastocyanin and the cytochrome bf complex (Figure 17.17).
Dark Reactions of Photosynthesis - The second step of photosynthesis in which NADPH and ATP produced by the light reactions is used in reductive synthesis of carbohydrate from CO 2 and water (Figure 17.3).
Einstein - A unit for a mole of photons.
Electron Transfer - A process where an electron, excited by light in photosynthesis, is passed to a nearby molecule with a slightly lower excited state (Figure 17.11).
Granum (grana) - A chloroplast structure consisting of a stack of thylakoids (Figure 17.4c).
Hill Reactions - Reactions pioneered by Robert Hill that showed when isolated chloroplasts were illuminated in the presence of electron acceptors, such as Fe3+, the acceptor could be reduced.
Inner Chloroplast Membrane - A structure analogous to the mitochondrial inner membrane which is quite selectively permeable to molecules (Figure 17.4c).
Light Reactions of Photosynthesis - The first step of photosynthesis in which energy from light is used to drive photochemical oxidation of H 2O. This produces NADPH, releases O 2, and ADP is phosphorylated to ATP (Figure 17.3).
Light-harvesting Complexes - Part of the photosynthetic apparatus. Each is a multisubunit protein complex containing multiple antenna pigment molecules and a pair of chlorophyll molecules that act as the reaction center, trapping energy quanta excited by the absorption of light.
Noncyclic Electron Flow - In a two-system transfer of electron energy, the process where electrons displaced from photosystem I by excitation are replaced by photosystem II, which receives them from water.
Noncyclic Photophosphorylation - The generation of ATP by noncyclic electron flow.
Outer Chloroplast Membrane - A structure analogous to the mitochondrial outer membrane which is quite freely permeable to most molecules (Figure 17.4c).
Photophosphorylation - A term for the process whereby ATP is synthesized as a result of energy captured from light.
Photorespiration - A pathway favored when the oxygenase activity of ribulose-1,5-bisphosphate carboxylase is active. In it, phosphoglycolate is dephosphorylated and passed into the peroxisomes where it is oxidized to hydrogen peroxide and glyoxylate (Figure 17.24).
Photosynthesis - A process whereby energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water (usually) (Figure 17.1).
Photosystem I - A photosystem in plants that absorbs light up to a wavelength of about 700 nm. A product of electron transfer through this photosystem is reduction of NADP+ to form NADPH (Figure 17.12).
Photosystem II - A photosystem in plants that absorbs light only up to a wavelength of about 680 nm. It is the photosystem associated with the initial excitation of electrons, the splitting of water to form O 2, and the pumping of protons from the stroma into the thylakoid (Figure 17.12).
Photosystems - Well-defined structural units of chloroplasts dedicated to the task of absorbing light photons and recovering some of their energy in a chemical form.
Phycocyanin - An accessory photosynthetic pigment in plants that is covalently attached to a protein via a sulfhydryl group (Figure 17.7).
Planck's Law - A basic equation in physics that relates the energy per photon to the frequency of light - E = hv, where h is Planck's constant, 6.626 x 10-34 J s.
Quantum - A single unit of light energy.
Quantum Efficiency (of photosynthesis) - The ratio of oxygen molecules released to photons absorbed.
Reaction Center - Part of the photosyntetic apparatus where the excited electron from light stimulation is transferred to a primary electron acceptor. The chlorophyll here is in a somewhat different environment than other chlorophylls, so that its excited state energy level is a bit lower, allowing it to trap the quanta of energy absorbed by any other pigment molecules (Figure 17.11).
Red Drop - A phenomenon observed where the quantum efficiency for a compound dropped as the wavelength of monochromatic light used was raised above 680 nm.
Reduction - A process involving the gain of electrons by a molecule.
Resonance Transfer (Exciton Transfer) - A process where energy from light in photosynthesis is passed from one molecule to another (Figure 17.11).
Rhodopseudomonas viridis - A purple sulfur bacterium that conducts photosynthesis.
Stroma - A chloroplast structure analogous to the mitochondrial matrix. It consists of the space between the grana and the inner mitochondrial membrane. The place where the dark reactions of photosynthesis occur (Figure 17.4c).
Thylakoid Lumen - The space inside the inner part of a thylakoid membrane (Figure 17.4c).
Thylakoids - Flat, sac-like membrane structures in the stroma of the chloroplast stacked like coins to form a granum. All of the light reactions of photosynthesis occur within the membranes of these structures (Figure 17.4c).
Z - An intermediate through which electrons from the splitting of water are passed to the oxidized photosystem II reaction center. It is likely a tyrosine residue on one of the polypeptide chains of photosystem II.