The two photosystems in the light reactions of photosynthesis are connected by the Z scheme of the electron transport chain. The two photosystems are called photosystem I and photosystem II.
The light reactions are photosynthetic pathways involved in the capture of solar energy to produce adenosine triphosphate, or ATP, and nicotinamide adenine dinucleotide phosphate, or NADPH.
Green plants and cyanobacteria harness solar energy through light-absorbing mechanisms known as photosystems, which contain the pigment chlorophyll and other auxiliary pigments. When photosystem I and photosystem II are connected by the Z scheme electron transport chain, a non-clyclic electron flow occurs. The transport chain is referred to as the Z scheme because diagrams that depict the connection between the two photosystems are in the form of the letter "Z."