What is Dark reaction ?

The term "dark reaction" refers to the process of carbon fixation in photosynthesis, specifically the part of the process that occurs in the absence of light. During photosynthesis, plants convert light energy into chemical energy in the form of glucose. This process occurs in two stages: the light-dependent reactions and the dark reactions.

The light-dependent reactions take place in the thylakoid membrane of the chloroplasts and involve the absorption of light by pigments, primarily chlorophyll. This light energy is used to generate ATP and NADPH, which are used in the dark reactions to reduce CO2 to form glucose.

The dark reactions, also known as the Calvin cycle or the carbon-fixation cycle, occur in the stroma of the chloroplasts. During this process, CO2 is fixed by the enzyme ribulose bisphosphate carboxylase (RuBisCO) to form an unstable intermediate, which is then converted into a stable compound, such as glucose. The Calvin cycle is a cyclic process, meaning that the same set of reactions is repeated multiple times in order to produce a large amount of glucose.

The dark reactions require the energy from the light-dependent reactions in the form of ATP and NADPH, as well as the enzyme RuBisCO. The Calvin cycle has three main stages: carbon fixation, reduction, and regeneration. During carbon fixation, CO2 is incorporated into an organic molecule. In the reduction stage, the newly formed organic molecule is converted into a carbohydrate, such as glucose. In the regeneration stage, the enzyme RuBisCO is regenerated so that it can be used again in the carbon fixation stage.

One of the unique features of the Calvin cycle is its ability to use CO2 from the air, which allows plants to grow in environments where water is scarce. This process also plays a critical role in maintaining the Earth's carbon balance by removing CO2 from the atmosphere and storing it in the form of organic compounds.

In summary, the dark reaction, also known as the Calvin cycle or carbon-fixation cycle, is the process of converting CO2 into glucose using the energy from light-dependent reactions, which occur in the absence of light. This process is essential for the survival of plants and plays a crucial role in maintaining the Earth's carbon balance.