Photosynthesis Terminologies

Contents

Carotenoids
Chloroplasts

Carotenoids

Yellow and orange pigments that are found in chloroplasts and chromoplasts that participate in light absorption as supplementary pigments and protect the molecules of chlorophyll and other active substances from irreversible photo-destruction.

One can distinguish oxygen-free carotenoids (C40H56-lycopeneα-β-γ-carotenoids) and oxidized carotenoids (C40H56O2C40H56O4-xanthophyllsluteinzeaxa-nthin).

Chloroplasts

Specialized organelles of the vegetal cells in which photosynthesis takes place are delimited to the exterior by two membranes—internal and external with the second being incorporated into the homogeneous environment (stroma). The internal membrane form folds called stromal thylakoids and granal thylakoids, in which all the photochemical reactions of the light phase are carried.

The dark phase of photosynthesis

A complex process that includes the sequence of enzymatic reactions that lead to the formation of photosynthesis products and of the organic acceptor of carbon dioxide.

The light phase of photosynthesis

A phase of photosynthesis during which light absorption and transformation of solar energy into the chemical energy of ATP and NADPH+H+ happens. This process occurs in the active photochemical membranes of the chloroplast and represents a system of photophysicalphoto-chemical and chemical reactions.

Acyclic phosphorylation

A process during which light energy is transformed into the macroergic bonds of ATP and NADPH+H+. It is then followed by water photolysis and oxygen elimination.

Cyclic phosphorylation

A process during which the electron emitted by chlorophyll through a series of transformations returns back to the pigment. The absorbed energy is ﬁxed in the macroergic ATP bonds.

Photosynthetic phosphorylation

A process of converting light energy quanta into ATP.

Photodissociation of the water

The light induced decomposition of water molecules that occurs during the light phase of photosynthesis. As a result of water photodissociation, free oxygen which is eliminated and hydrogen which is used to reduce CO2 in the dark phase are produced.

Photosynthesis (Carbon nutrition)—

A fundamental process during which organic compounds are synthesized by green plants and photosynthesizing microorganisms out of simple inorganic substances (CO2 and H2O) in the presence of light and during which the solar energy is transformed into the energy of chemical bonds of organic substances.

Photosystem I

The assimilation unit which has as reaction center a molecule of chlorophyll “a” capable to absorb light with a wave length of 700 nm (noted as P700)as well as 200 molecules of chlorophyll “a” (sometimes chlorophyll “b”) and 50 molecules of carotene in the composition of the light-harvesting complex.

Photosystem II

The assimilation unit has as reaction center a molecule of chlorophyll “a” (P600) and auxiliary light-sensitive pigments: 200 molecules of chlorophyll “a” 200 molecules of chlorophyll “b” and xanthophylls.

Quantum efﬁciency of photosynthesis

The number of CO2 molecules subjected to photochemical transformation per each absorbed light quantum. It equals roughly 0.25 which means that 4 photons of red light are consumed to reduce a
CO2 molecule.

The Robin Hill reaction

The elimination of oxygen from the water molecule by isolated chloroplasts under the action of light and in the presence of artiﬁcial acceptors of electrons. It explains the essence of the 2 phases in the chemistry of photosynthesis.