Photosynthesis
ஒளிச்சேர்க்கை
Photosynthesis is not just 'making food'; it is the fundamental energy transduction process of the biosphere. If the light-dependent reactions fail, the entire carbon fixation cycle collapses. Do not mistake this for a simple chemical reaction; it is a complex physico-chemical necessity for life.
The idea
Photosynthesis is a physico-chemical process where green plants utilize light energy to synthesize organic compounds. It involves the conversion of light energy into chemical energy, stored in the bonds of carbohydrates. This process is the primary source of all food on Earth and the sole biological mechanism for atmospheric oxygen release. It occurs primarily in the chloroplasts of mesophyll cells.
Why it matters
It exists to convert solar energy into stable chemical energy (glucose) that sustains life on Earth and provides the oxygen necessary for aerobic respiration.
NEET lens
NEET focuses on the definition and the dual nature of the process: physico-chemical. Expect questions linking the light reaction to oxygen evolution and the dark reaction to carbohydrate synthesis. Memorize the equation and the site of occurrence. Do not confuse the source of oxygen with the source of glucose.
Clinical significance
Oxygenic photosynthesis is the reason aerobic respiration exists in humans. Without the continuous release of O2 by photoautotrophs, the electron transport chain in human mitochondria would cease, leading to immediate cellular death. Ecosystem collapse is the direct clinical consequence of photosynthetic failure.
Introduction
Photosynthesis is the process by which autotrophs (plants, algae, cyanobacteria) convert light energy into chemical energy (glucose) using CO₂ and H₂O, releasing O₂ as a byproduct.
Core concept
Overall equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Two stages: Light reactions (thylakoid membranes) — absorb light, produce ATP + NADPH + O₂. Dark reactions/Calvin cycle (stroma) — use ATP + NADPH to fix CO₂ into glucose. O₂ comes from water splitting (photolysis), not from CO₂. Chloroplast is the site — thylakoids (light reactions) and stroma (dark reactions).
Go deeper
Van Niel's hypothesis (1930s): O₂ in photosynthesis comes from water, not CO₂. He studied purple sulphur bacteria that used H₂S instead of H₂O → released S, not O₂. Generalized equation: CO₂ + 2H₂A → [CH₂O] + 2A + H₂O. Later confirmed by isotope tracing (¹⁸O in water → ¹⁸O₂).
From Class 10
Plants make their own food from sunlight and CO₂. This process is photosynthesis — the foundation of almost all life on Earth.