Light Reactions vs. Dark Reactions
Day & Night
Place of Reaction
What are Light Reactions?
Light Reactions are the initial phase of the process of photosynthesis, these type of reactions require light for taking place. As the light reactions happen at the initial stage, they produce the complementary products that are further used in the next phase, which is a light independent phase (dark reactions). The light reactions take place in the grana of the chloroplast amid the presence of the light; it can either be the sunlight or the artificial light. The sunlight is said to be a huge source of energy, so such reactions take place best under sunlight. Two main or the necessary functions done in this phase are the photolysis of water and formation of energy molecules like NADPH2 and ATP. In the process of photolysis of water, the water molecule is oxidized (loses electrons) and gets split into two hydrogen atoms or protons and an oxygen atom. Following this breakdown of water, under the light, the formation of energy molecules like NADPH2 and ATP takes place. The products gained from this phase are even used in the light independent reactions, though at the further formation it doesn’t require light energy.
What are Dark Reactions?
Dark Reactions is the second phase in the process of photosynthesis following the light reaction. As the name suggests, it doesn’t require light energy to take place. The dark reactions take place in the stroma of the chloroplast; it mainly consists of two types of cyclic reactions Calvin Cycle or C3 Cycle and Hatch-Slack or C4 cycle. The main function happens in this phase is the reduction of carbon dioxide to form carbohydrates. The sugar molecules are synthesized using the carbon dioxide molecules. The carbon dioxide is fixed to carbohydrates using the energy molecules like NADPH2 and ATP. This process as complete is called the carbon fixation process. In this phase, the products from the light reactions phase are taken, and the reduction of carbon dioxide takes place without the presence of light. This phase of photosynthesis can even occur in the night time, whereas light reactions take place in the presence of sunlight.