Difference between Light Reactions and Dark Reactions in Photosynthesis

Main difference

Photosynthesis is the food-making process carried out by organisms that have chlorophyll cells. Mainly, this food-making process is associated with plants that have abundant chlorophyll cells. The photosynthesis process is a kind of inverse process to respiration that takes place in each and every one of the organisms. It is always said that the photosynthesis process requires sunlight for it to take place while, by taking a closer look at the process, it can be divided into two phases; Light reactions and the other are dark reactions.As its name suggests, the light reaction is the initial phase of the photosynthesis process and requires light, while the dark reaction is the later phase of the photosynthesis process and does not require light energy . In reaction to the light,

Comparative chart

Light reactions Dark reactions in photosynthesis
Definition As the name suggests, the reaction to light is the initial phase of the photosynthesis process and requires light. The dark reaction is the last phase of the photosynthesis process and does not require light energy.
Principal function In the reaction to light, the photolysis of water takes place and energy molecules such as NADPH2 and ATP are formed. In the dark reaction, the reduction of carbon takes place using the energy products of the light reactions NADPH2 and ATP.
Day and night Reactions to light can take place during the day as they require light. Dark reactions can take place 24 hours a day.
Reaction site Reactions to light take place in the grana of the chloroplast. The dark reactions take place in the stroma of the chloroplast.
What are reactions to light?

Light reactions are the initial phase of the photosynthesis process, these types of reactions require light to happen. As the light reactions occur in the initial stage, they produce the complementary products that are used in the next phase, which is a phase independent of light (dark reactions). Light reactions take place in the chloroplast grana in the presence of light; it can be sunlight or artificial light. Sunlight is said to be a great source of energy, so such reactions occur best in sunlight. Two main or necessary functions that are performed in this phase are the photolysis of water and the formation of energy molecules such as NADPH2 and ATP. In the process of photolysis of water, the water molecule oxidizes (loses electrons) and splits into two hydrogen atoms or protons and one oxygen atom. After this decomposition of water, under light, the formation of energy molecules such as NADPH2 and ATP takes place. The products obtained from this phase are even used in light-independent reactions, although in the subsequent formation it does not require light energy.

What are dark reactions in photosynthesis?

Dark Reactions is the second phase of the photosynthesis process that follows the reaction to light. As its name suggests, it does not require light energy to be produced. The dark reactions take place in the stroma of the chloroplast; It consists mainly of two types of cyclic reactions: Calvin Cycle or C3 Cycle and Hatch-Slack Cycle or C4. The main function that occurs in this phase is the reduction of carbon dioxide to form carbohydrates. Sugar molecules are synthesized using carbon dioxide molecules. Carbon dioxide binds to carbohydrates using energy molecules like NADPH2 and ATP. This process as complete is called the carbon fixation process. In this phase, the products of the phase of light reactions are taken and the reduction of carbon dioxide occurs without the presence of light.

Light vs. Dark Reactions in Photosynthesis
  • As the name suggests, the reaction to light is the initial phase of the photosynthesis process and requires light, while the dark reaction is the later phase of the photosynthesis process and does not require light energy.
  • In the light reaction, the photolysis of water takes place and energy molecules such as NADPH2 and ATP are formed, while in the dark reaction the reduction of carbon occurs using the energy products of light reactions NADPH2 and ATP.
  • Reactions to light can take place during the day as they require light, on the other hand, dark reactions can take place 24 hours a day.
  • Light reactions take place in the chloroplast grana while dark reactions take place in the chloroplast stroma.

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