5.2 The Light-Dependent Reactions of Photosynthesis

Vocabulary concepts covering the mechanics, pigments, and structures involved in the light-dependent reactions of photosynthesis.

Wavelength

The distance between two consecutive, similar points in a series of waves, such as from crest to crest or trough to trough.

Electromagnetic spectrum

The range of all possible wavelengths of radiation.

Chlorophyll a

A pigment found in all photosynthetic organisms that absorbs wavelengths from either end of the visible spectrum (blue and red) but reflects green.

Chlorophyll b

A type of photosynthetic pigment that absorbs blue and red-orange light.

Absorption spectrum

The specific pattern of wavelengths a pigment absorbs from visible light, used to identify different pigment types.

Photosystem

A grouping of pigment molecules and proteins located in the membranes of thylakoids where the light-dependent reactions start.

Photon

A quantity or "packet" of light energy.

Photosystem II

The first photosystem in the light-dependent reaction sequence, named for its order of discovery, which transfers free electrons to the electron transport chain.

Electron transport chain

A series of proteins inside the thylakoid membrane that uses energy from electrons to actively move hydrogen ions ($H^+$) against their concentration gradient.

Photosystem I

The photosystem where a pigment molecule accepts an electron after it passes through the electron transport chain to be re-energized by another photon.

ATP synthase

An embedded protein complex that harvests potential energy from the electrochemical gradient to generate ATP from ADP.

Chemiosmosis

The flow of hydrogen ions ($H^+$) through ATP synthase from an area of high to low concentration.

Photophosphorylation

The process of ATP synthase attaching a third phosphate to ADP to form ATP using the energy generated by the hydrogen ion ($H^+$) stream.

NADPH

An energy-carrier molecule formed from $NADP^+$ and a hydrogen ion ($H^+$) using energy from an electron re-energized in photosystem I.