Photosynthesis: Calvin Cycle - YouTube

Light and dark reactions in photosynthesis Photosynthesis is divided into two parts: 1

Light-dependent reactions (light reactions) 2

The metabolic steps of the Calvin cycle are sometimes referred to as the dark reactions, or fight-independent reactions, because none of the steps requires light directly.

Thus, it is the Calvin cycle that makes sugar, but it can do so only with the help of the NADPH and ATP produced by the fight reactions.

Photosynthesis (Light Reactions) - YouTube

Nevertheless, the Calvin cycle in most plants occurs during daylight, for only then can the fight reactions regenerate the NADPH and ATP spent in the reduction Of C02 to sugar.

To convert C02 to carbohydrate, the Calvin cycle also requires chemical engery in the form of ATP, which is also generated by the light reactions.

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.







AS FIGURE 10.4 shows, the thylakoids of the chloroplast are the sites of the light reactions, while the Calvin cycle occurs in the stroma.