Photosynthesis: The Light Reactions Basics
Photosynthesis consists of two main parts: the Light Reactions and the Calvin Cycle. The Light Reactions occur only when sunlight is present and take place in the thylakoid membranes of plant cells.
During these reactions, plants use sunlight and water as reactants. They produce two essential energy carriers: ATP (energy currency) and NADPH (electron carrier). These molecules will later power sugar production in the Calvin Cycle.
The process begins when Photosystem II (PSII) absorbs light energy. The chlorophyll molecule (specifically Chlorophyll 680) at the center of PSII gets so excited by this energy that an electron pops off and moves to an electron acceptor. This creates an electron deficiency that needs to be filled.
💡 Think of chlorophyll like a solar panel that gets so charged up by sunlight that it releases electrons - these electrons then flow through the plant cell like electricity through wires!
To replace these lost electrons, plants perform water splitting - breaking water molecules apart. This process provides new electrons to PSII while releasing oxygen into the atmosphere as a byproduct. The hydrogen ions from water will be used later in the process.
