5.2 The Light-Dependent Reactions of Photosynthesis

Vocabulary terms covering the mechanisms and components of the light-dependent reactions in photosynthesis as described in the lecture notes.

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 emitted from the sun.

Chlorophyll a

A pigment contained 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 pigment that absorbs blue and red-orange light.

Carotenoids

A type of pigment found in photosynthetic organisms that, along with chlorophylls, helps the organism absorb energy from a wider range of visible-light wavelengths.

Absorption spectrum

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

Photosystem

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

Photon

A quantity or "packet" of light energy absorbed by a pigment molecule.

Photosystem II

The photosystem that first receives a photon, transfers a free electron to the electron transport chain, and facilitates the splitting of water molecules.

Electron transport chain

A series of proteins inside the thylakoid membrane that uses energy from passing electrons to actively move $H^+$ ions from the stroma into the thylakoid space.

Photosystem I

The second photosystem where the electron is accepted by a pigment molecule and re-energized by another photon to drive the formation of NADPH.

ATP synthase

An embedded protein complex that allows $H^+$ ions to pass through the thylakoid membrane, using the energy from the ion stream to attach a third phosphate to ADP.

Chemiosmosis

The movement of hydrogen ions ($H^+$) down their electrochemical gradient through a semi-permeable structure like ATP synthase.

Photophosphorylation

The process of forming ATP from ADP by attaching a third phosphate group using energy generated by the flow of hydrogen ions.

NADPH

An energy-carrier molecule formed when energy from a re-energized electron drives the combination of $NADP^+$ and a hydrogen ion ($H^+$).