1. Light-Dependent Reactions:
* Capture Light: Plants contain a green pigment called chlorophyll, which absorbs sunlight, primarily in the red and blue wavelengths.
* Water Splitting: The absorbed light energy is used to split water molecules (H₂O) into hydrogen ions (H+), electrons (e-), and oxygen gas (O₂). The oxygen is released into the atmosphere.
* Electron Transport: The energized electrons are passed along a chain of molecules, releasing energy along the way.
* ATP Production: This energy is used to create ATP (adenosine triphosphate), the cell's primary energy currency.
* NADPH Formation: The electrons are also used to create NADPH (nicotinamide adenine dinucleotide phosphate), a high-energy electron carrier.
2. Light-Independent Reactions (Calvin Cycle):
* Carbon Dioxide Fixation: The plant takes in carbon dioxide (CO₂) from the atmosphere and uses the energy stored in ATP and NADPH to convert it into a simple sugar called glucose.
* Sugar Production: This process involves a series of complex chemical reactions, ultimately creating glucose (C₆H₁₂O₆) and regenerating the molecules needed to continue the cycle.
Overall Equation for Photosynthesis:
6CO₂ (carbon dioxide) + 6H₂O (water) + light energy → C₆H₁₂O₆ (glucose) + 6O₂ (oxygen)
Where it Happens:
* Chloroplasts: Photosynthesis takes place within specialized organelles called chloroplasts, which contain chlorophyll and other necessary components.
* Thylakoids: Within the chloroplast, light-dependent reactions occur in structures called thylakoids.
* Stroma: The Calvin cycle (light-independent reactions) takes place in the stroma, the fluid-filled region surrounding the thylakoids.
Significance:
Photosynthesis is essential for life on Earth because:
* Food Source: It provides the primary food source for all life forms, either directly (plants) or indirectly (animals that consume plants).
* Oxygen Production: Photosynthesis releases oxygen as a byproduct, which is crucial for the respiration of most organisms.
* Climate Regulation: Plants absorb carbon dioxide, a greenhouse gas, helping to regulate Earth's climate.
Factors Affecting Photosynthesis:
* Light Intensity: Higher light intensity generally leads to increased photosynthesis, up to a certain point.
* Carbon Dioxide Concentration: Increased CO₂ availability enhances photosynthesis.
* Temperature: Photosynthesis has an optimal temperature range, and rates decrease at extreme temperatures.
* Water Availability: Water is essential for the process, and lack of water can significantly reduce photosynthesis.
