The two processes involved in photosynthetic reactions are the light-dependent reactions and the light-independent reactions, also known as the Calvin cycle. Let's dive into the details of each process:
1. Light-dependent reactions:
The light-dependent reactions occur in the thylakoid membrane of the chloroplasts. They require light energy to convert light energy into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These reactions can be divided into several sequential steps:
a. Absorption of light energy: Chlorophyll and other pigments in the chloroplasts absorb photons (light energy) from the sun. This energy is then transferred to electrons in the chlorophyll molecule, exciting them from their ground state to a higher energy level.
b. Splitting of water molecules: The excited electrons from chlorophyll molecules are transferred to an electron transport chain. In this process, water molecules are split, releasing oxygen, hydrogen ions (H+), and electrons. The electrons replace the excited electrons in chlorophyll, and oxygen is released as a byproduct.
c. Generation of ATP: As the electrons move through the electron transport chain, they release energy that is used to pump hydrogen ions across the thylakoid membrane, creating a concentration gradient. This gradient allows ATP synthase, an enzyme, to produce ATP by adding a phosphate group to ADP (adenosine diphosphate).
d. Production of NADPH: Another electron carrier molecule called NADP+ (nicotinamide adenine dinucleotide phosphate) accepts the high-energy electrons from the electron transport chain, along with hydrogen ions, to form NADPH. NADPH is essential for the next stage, the light-independent reactions.
Overall, the light-dependent reactions capture light energy and convert it into chemical energy (ATP and NADPH) while releasing oxygen.
2. Light-independent reactions (Calvin cycle):
The light-independent reactions, also known as the Calvin cycle, take place in the stroma of the chloroplasts. These reactions use the ATP and NADPH generated in the light-dependent reactions to convert carbon dioxide (CO2) into glucose and other organic compounds. The light-independent reactions can be divided into three main steps:
a. Carbon fixation: During this step, the enzyme RuBisCO (ribulose bisphosphate carboxylase/oxygenase) combines carbon dioxide (CO2) with a five-carbon molecule called RuBP (ribulose-1,5-bisphosphate). This results in the formation of a six-carbon molecule that quickly splits into two three-carbon molecules known as 3-phosphoglycerate (3-PGA).
b. Reduction: In the reduction phase, ATP and NADPH generated from the light-dependent reactions provide the energy and electrons required to convert 3-PGA into glyceraldehyde 3-phosphate (G3P). Some of the G3P molecules are used to regenerate RuBP, while others become the building blocks for glucose and other carbohydrates.
c. Regeneration of RuBP: In the last step, some of the G3P molecules are used to regenerate the RuBP molecule, which is crucial for the continuation of the Calvin cycle. This step requires ATP.
The light-independent reactions do not directly require light energy. However, they depend on the energy and reducing power (electrons) stored in ATP and NADPH produced during the light-dependent reactions.
Overall, the light-independent reactions convert carbon dioxide and the products of the light-dependent reactions into glucose and other sugars, which serve as the primary fuel and building blocks for plants and other photosynthetic organisms.
List and explain extensively the two process involved in photosynthetic reaction
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