Photosynthesis, the process by which plants and other organisms convert light energy into chemical energy, occurs in two main stages:
1. Light-Dependent Reactions:
* Location: Thylakoid membranes of chloroplasts
* Inputs: Light energy, water (H₂O)
* Outputs:
* ATP (adenosine triphosphate) - energy currency of the cell
* NADPH (nicotinamide adenine dinucleotide phosphate) - an electron carrier
* Oxygen (O₂) - released as a byproduct
What happens:
* Light energy excites electrons in chlorophyll, which then move through an electron transport chain.
* This movement generates a proton gradient across the thylakoid membrane, which drives ATP production.
* Water molecules are split, releasing electrons, protons, and oxygen.
* NADP+ is reduced to NADPH using the excited electrons.
2. Light-Independent Reactions (Calvin Cycle):
* Location: Stroma of chloroplasts
* Inputs: CO₂ (carbon dioxide), ATP, NADPH
* Outputs: Glucose (C₆H₁₂O₆) - a sugar molecule used for energy and growth
What happens:
* Carbon dioxide is fixed into an organic molecule, RuBP (ribulose bisphosphate).
* ATP and NADPH are used to convert this molecule into glucose through a series of reactions.
* RuBP is regenerated to continue the cycle.
Overall: Photosynthesis captures light energy to convert carbon dioxide and water into glucose and oxygen. This glucose provides the energy and building blocks for plants and ultimately all life on Earth.
