Dark Reactions of Photosynthesis

Dark Reactions of Photosynthesis

The dark reactions, also known as the light-independent reactions, are the second stage of the two-part process of photosynthesis, following the light-dependent reactions. While the light-dependent reactions rely on solar energy to create high-energy molecules such as ATP and reduced NADPH, the dark reactions use these energy molecules to convert carbon dioxide into glucose through the process known as the Calvin cycle. The dark reactions occur within chloroplasts, specifically in the stroma, which is the fluid-filled space surrounding the stacked thylakoids called grana.

The primary goal of the dark reactions is to fix atmospheric CO2 using the high-energy compounds produced during the light-dependent reactions. This process involves several key steps, including the activation of Rubisco enzyme with ATP, the formation of a carbocation intermediate, the addition of water or phosphate group to form two triose-phosphates, and the regeneration of RuBP by the use of NADPH and ATP from the light-dependent reactions. The final step in the Calvin cycle is the synthesis of glucose or other sugars from these three-carbon molecules.

In summary, while the light-dependent reactions are powered by sunlight and involve the absorption of photons by pigments like chlorophyll, the dark reactions rely on the high-energy molecules generated during these light processes to create glucose and other organic compounds. Together, both stages work together to sustain life by converting solar energy into chemical energy that can be used by living organisms.