NEET Biology-04 Plant Physiology

Why does oxygen released during photosynthesis come from water—and not from carbon dioxide? Follow the story of how scientists pieced photosynthesis together, from Priestley’s mint plant “restoring” air in a bell jar to Ingenhousz proving that light and the green parts of a plant matter, Sachs linking photosynthesis to starch storage, Engelmann mapping the first action spectrum with Cladophora and bacteria, and Ruben and Kamen using oxygen-18 to settle the oxygen-source debate for good. You’ll also learn the overall equation (6 CO₂ + 12 H₂O → C₆H₁₂O₆ + 6 O₂ + 6 H₂O) and why it summarizes many reactions, not one step. Then zoom into the leaf and chloroplast: mesophyll cells, grana, stroma, thylakoid membranes, and exactly where the photochemical and biosynthetic phases happen—plus why “light independent” never means “dark only.” You’ll trace electrons through the Z scheme carrier by carrier, compare cyclic vs non-cyclic photophosphorylation, and understand chemiosmosis and ATP synthase. From Calvin’s C₃ cycle costs to photorespiration losses and the C₄ solution (Kranz anatomy, PEP carboxylase, and a brief CAM mention), you’ll be able to reason through limiting factors, classic exam traps, and real-world scenarios like heat stress and CO₂ enrichment.