Chapter 10 Bio 1801 Vocab

Photosynthesis Vocab

Calvin Cycle

In photosynthesis, the set of reactions that uses NADPH and ATP formed in the light-capturing reactions to drive the fixation of CO2, reduction of the fixed carbon to produce sugar, and regeneration of the substrate used to fix CO2.

NADP+ (Nicotinamide Adenine Di-nucleotide Phosphate) / NADPH

Oxidized and reduced forms, respectively, of nicotinamide adenine dinucleotide phosphate. A nonprotein electron carrier that is reduced during the light-dependent reactions in photosynthesis and extensively used in biosynthetic reactions. 

Thylakoids

A membrane-bound network of flattened sac-like structures inside a plant chloroplast that functions in converting light energy to chemical energy. Stacks of thylakoid discs make up grana.

Lumen 

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

Stroma

The fluid matrix of a chloroplast, enclosed inside a double membrane envelope in which the thylakoids are embedded. Site of the Calvin cycle reactions.

Wavelength 

The distance between two successive crests or troughs in any regular wave, such as a light wave, sound wave, or wave in water.

Electromagnetic Spectrum

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).

Visible Light

The range of wavelengths of electromagnetic radiation that humans can see, from about 400 to 710 nanometers.

Photons

A discrete packet of light energy; a particle of light.

Chlorophylls

Any of several closely related green pigments, found in chloroplasts, that absorb light during photosynthesis.

Carotenoids

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. Includes carotenes and xanthophylls. 

Action Spectrum

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, such as O2 production, versus wavelength.

Absorption Spectrum

The amount of light of different wavelengths absorbed by a pigment. Usually depicted as a graph of light absorbed versus wavelength.

Fluorescence

The spontaneous emission of light from an excited electron in a pigment falling back to its normal (ground) state.

Photosystems

One of two types of units, consisting of a central reaction center surrounded by antenna pigments, that is responsible for the light-capturing reactions of photosynthesis.

Antenna Pigments

Part of a photosystem; chlorophyll molecules and accessory pigments organized and modified by proteins to capture light and direct energy to a central reaction center during photosynthesis.

Reaction Center

Centrally located component of a photosystem containing proteins and a pair of specialized chlorophyll molecules. It is surrounded by antenna pigments that transmit resonance energy to excite the reaction center pigments.

Resonance Energy Transfer

Process of transferring energy from an excited donor pigment to an adjacent acceptor pigment, where another electron is excited in response.

Photosystem II

Photosystem that contains antenna pigments and a reaction center with a pair of P680 chlorophyll molecules. Absorbed light energy is used to reduce electron carriers in an electron transport chain that produces a proton-motive force for the synthesis of ATP. Oxygen is a by-product when water is split to obtain electrons.

Photosystem I

Photosystem that contains antenna pigments and a reaction center with a pair of P700 chlorophyll molecules. Absorbed light energy is used to reduce NADP+ to NADPH in noncyclic electron flow or ATP in cyclic electron flow.

Light-Harvesting Complex

A mobile accessory structure consisting of pigments that absorb light and transmit resonance energy to antenna pigments in photosystems.

Pheophytin

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

Plastoquinone (PQ)

A nonprotein electron carrier in the chloroplast electron transport chain. Receives excited electrons from photosystem II (noncyclic) or photosystem I (cyclic) and passes them through an electron transport chain. Also transports protons from the stroma to the thylakoid lumen, generating a proton-motive force.

Photophosphorylation 

Production of ATP molecules by ATP synthase using the proton-motive force generated either (1) during photosynthesis, as light-excited electrons flow through an electron transport chain, or (2) in some bacteria or archaea, as rhodopsin-like molecules use absorbed light energy to pump protons across that plasma membranes to create a chemiosmotic gradient.

Oxygenic

(“oxygen-producing”) Referring to any process or reaction that produces oxygen. Photosynthesis in plants, algae, and cyanobacteria, which involves photosystem II, is oxygenic because it uses water as an electron source and produces O2 as a byproduct.

Anoxygenic 

(“no oxygen-producing”) Referring to any process or reaction that does not produce oxygen. Photosynthesis in purple sulfur bacteria is anoxygenic because it does not use water as an electron donor, so no O2 is produced.

Ferredoxin

In photosynthetic organisms, an iron- and sulfur- containing protein that is reduced by electrons from photosystem I. Can transfer electrons to the enzyme NADP+ reductase, which catalyzes formation of NADPH.

Z-Scheme

Model for changes in the potential energy of electrons as they pass from photosystem II to photosystem I and ultimately to NADP+ during the light-capturing reactions of photosynthesis.

Plastocyanin (PC)

A small protein that shuttles electrons originating from photosystem II to the reaction center of photosystem I during photosynthesis.

Noncyclic Electron Flow

Path of electron flow in which electrons originate from oxidizing water in photosystem II and then pass through an electron transport chain to photosystem I, where they ultimately reduce NADP+ during the light-dependent reactions of photosynthesis.

Cyclic Electron Flow

Path of electrons in which excited electrons of photosystem I are transferred back to the plastoquinone (PQ), the start of the electron transport chain normally associated with photosystem II. Instead of reducing NADP+ to make NADPH, the electron energy is used to make ATP via photophosphorylation.

Stoma

Generally, a pore or opening. In plants, a microscopic pore on the surface of a leaf or stem through which gas exchange occurs; typically surrounded by specialized cells that open the pore.

Carbon Fixation

The process of converting gaseous carbon dioxide into an organic molecule; often associated with photosynthesis.

Ribulose Bisphosphate (RuBP)

A five-carbon compound that combines with CO2 in the first step of the Calvin cycle during photosynthesis or with O2 in the first step of photosynthesis.

Rubisco

The enzyme that catalyzes the addition of a molecule of CO2 (Calvin Cycle) or O2 (photorespiration) to ribulose bisphosphate.

Photorespiration

A series of light-driven chemical reactions that “undoes” photosynthesis by consuming O2 and releasing CO2. Usually occurs when there are high O2 and low CO2 concentrations inside plant cells, which occurs in land plants when stomata must be kept closed to prevent dehydration.

C4 Pathway

A variant type of photosynthesis in which atmospheric CO2 is first fixed by PEP carboxylase into four-carbon molecules, rather than the three-carbon molecules of the classic C3 pathway. Used to concentrate CO2 to reduce photorespiration in the Calvin cycle while stomata are closed to prevent water loss.

C3 Pathway

The most common form of photosynthesis in which atmospheric CO2 is fixed by rubisco to form 3-phosphoglycerate, a three-carbon molecule. Used in the first phase of the Calvin cycle.

PEP Carboxylase

An enzyme that catalyzes addition of CO2 to phosphoenolpyruvate, a three-carbon compound, forming a four-carbon organic acid.

Mesophyll Cells

A type of cell, found near the surfaces of plant leaves, that is specialized for the lightcapturing reactions of photosynthesis.

Bundle-Sheath Cells 

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

Crassulacean Acid Metabolism (CAM)

A variant type of photosynthesis that is related to the C4 pathway in which CO2 is fixed and stored in four-carbon organic acids. To reduce water and CO2 loss by photorespiration, CO2 is fixed at night when stomata are open and then released to feed the Calvin cycle during the day when stomata are closed.

Glyceraldehyde-3-Phosphate (G3P)

The phosphorylated three-carbon carbohydrate formed from the fixation and reduction of CO2 in the Calvin cycle.

Gluconeogenesis 

Synthesis of glucose, often from non-carbohydrate sources (proteins and fatty acids). In plants, used to produce glucose from products of the Calvin cycle. In animals, occurs in the liver in response to low insulin levels and high glucagon levels.

Sucrose

A disaccharide formed from glucose and fructose. One of the two main products of photosynthesis.

Starch

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 carbohydrate in plants.