Photosynthesis (Clean)

Photosynthesis is the biological process by which green plants, algae, and certain bacteria convert light energy into chemical energy stored in glucose. The process takes place primarily in the chloroplasts of plant cells, specifically within structures called thylakoids that contain the pigment chlorophyll. The overall chemical equation for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. This reaction occurs in two main stages. The light-dependent reactions take place in the thylakoid membranes and produce ATP and NADPH, while releasing oxygen as a byproduct. The light-independent reactions, known as the Calvin cycle, occur in the stroma and use the ATP and NADPH to fix carbon dioxide into glucose. Chlorophyll absorbs light most efficiently in the blue (around 430-450 nm) and red (around 640-680 nm) wavelengths of the visible spectrum, which is why most plants appear green — they reflect the green wavelengths that chlorophyll does not absorb. Plants also contain accessory pigments such as carotenoids and anthocyanins that capture additional wavelengths. Photosynthesis is responsible for producing the oxygen in Earth's atmosphere. Cyanobacteria were among the first organisms to perform oxygenic photosynthesis, beginning approximately 2.4 billion years ago during what is known as the Great Oxidation Event. Today, terrestrial plants and oceanic phytoplankton together produce the vast majority of atmospheric oxygen through photosynthesis.