Why are they called the quot;light reactionsquot; and the quot;dark reactionsquot;?
Light reactions need light to produce organic energy molecules (ATP and NADPH). They are initiated by colored pigments, mainly green colored chlorophylls. Dark reactions make use of these organic energy molecules (ATP and NADPH). This reaction cycle is also called Calvin Benison Cycle, and it occurs in the stroma. ATP provides the energy, while NADPH provides the electrons required to fix the CO2(carbon dioxide) into carbohydrates.
There are 2 stages in photosynthesis: the light reaction (also called the light-dependent reaction) and the dark reaction (also called the light-independent reaction). The metabolic steps of the Calvin cycle are sometimes referred to as light-independent reactions, because none of the steps requires light directly. What I mean by directly is that the Calvin cycle only makes sugar through the help of ATP and NADPH from the light reactions.
Because the light reactions require light and the dark reactions don't. The light reactions are the ones that use energy from light to split water and make ATP. The Dark reactions are also referred to as the calvin cycle. It uses the ATP produced in the light reactions to fix carbon dioxide into larger sugar molecules.
These terms are somewhat outdated. During light reactions sunlight and water are used to produce energy, this is called photosynthesis. The dark reaction which is known as carbon fixation, takes place during the photoperiod as well as the dark period.
