Photosynthesis is the process by which plants, algae, and some bacteria use sunlight energy to convert carbon dioxide and water into glucose (a sugar) and oxygen. This process can be divided into two stages:
1. Light-Dependent Reactions (Light Reactions):
* Location: Thylakoid membrane of chloroplasts.
* Inputs: Sunlight, water, and the pigment chlorophyll.
* Outputs: ATP (energy currency), NADPH (electron carrier), and oxygen.
* Process:
* Light absorption: Chlorophyll absorbs sunlight energy.
* Electron transport chain: The absorbed light energy is used to excite electrons in chlorophyll, which are then passed along an electron transport chain.
* Photolysis: Water molecules are split, releasing oxygen as a byproduct.
* ATP and NADPH production: Energy released during electron transport is used to create ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).
2. Light-Independent Reactions (Calvin Cycle):
* Location: Stroma of chloroplasts.
* Inputs: CO2, ATP, and NADPH.
* Outputs: Glucose (sugar) and other organic molecules.
* Process:
* Carbon fixation: CO2 from the atmosphere is incorporated into an organic molecule (RuBP).
* Reduction: The carbon-containing molecule is reduced using energy from ATP and electrons from NADPH.
* Regeneration: RuBP is regenerated to continue the cycle.
Summary:
* Light-dependent reactions: Capture light energy and convert it into chemical energy (ATP and NADPH) while releasing oxygen.
* Light-independent reactions: Use the energy from ATP and NADPH to convert CO2 into glucose and other organic molecules.
In essence: The light-dependent reactions act like a "battery charger", producing energy-rich molecules that power the light-independent reactions, which then act as the "factory" that builds the sugar molecules.
Note: The light-independent reactions are often called the Calvin Cycle, named after Melvin Calvin who won the Nobel Prize for his work in elucidating this process.
