Yogendra Prasad Saksena [email protected] Assistant Professor Department of Botany Plant Physiology and Biochemistry Photosynthesis The process of food (Organic compound) synthesis by green plant under sunlight is called photosynthesis. This is a biological mechanism by which solar energy enter into biological system through a chain of biological reaction This is only a process by which physical energy can be convert into biochemical energy . This is a unique process adopted by plant which make them different from animal and other heterotrophic individual . This process convert CO2 into carbohydrate and release the O2 as by product which further required for respiration to provide ATP for cell. The Brief history of Photosynthesis Jan Baptist van Helmont rejected the ancient idea that plants take most of their biomass from the soil. Joseph Priestley did a series of experiment, one of the famous experiment of mouse and candle. He first observed that a mouse and a candle behave very similarly when covered, in that they both “spend” the air. However, when a plant is placed with either the candle or mouse, the plant “revives” the air for both. Thomas Engelmann found that Spirogyra algae produce oxygen mostly in the blue and red parts of the spectrum. This was a huge finding . It tells that the key photosynthetic pigment should accept blue and red rays, and thus reflect green rays. Blue-green chlorophyll best fits this description. Photosynthetic Unit The whole process of photosynthesis take place in a chloroplast which have different photosynthetic unit . Thylakoid membrane Stroma These photosynthetic unit having many important protein , pigment and enzyme for process Thylakoid membrane The thylakoid membranes of a chloroplast is an internal system of interconnected membranes, that carry out the light reactions of photosynthesis. They are arranged into stacked and unstacked regions called grana and stroma thylakoids, respectively, that are differentially enriched in photosystem I and II complexes. Stroma Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana (stacks of thylakoid), and the sub- organelles or daughter cells, where photosynthesis is commenced before the chemical changes are completed in the stroma. Photosynthesis occurs in two stages. Photosynthetic unit Thank you.