What you need to know in photosynthesis .Distinguish between light reactions and

Question

What you need to know in photosynthesis .Distinguish between light reactions and the Calvin cycle and know the subcellular location of each. Identify the splitting of water to produce O2 at Photosystem II as the start of the photosynthetic electron transport chain and the delivery of electrons to NADP after Photosystem I as the end of the chain. Explain how a H gradient is formed across the thylakoid membrane in chloroplasts and used to generate ATP Explain how a H gradient is and is used to generate ATP in photophosphorylation. Distinguish between noncyclic and cyclic electron transport and explain the purpose of each. Identify how ATP and NADPH are produced in the light reactions and used for CO2 fixation in the Calvin cycle. Distinguish between photophosphorylation and oxidative phosphorylation. .

Explanation / Answer

The light reaction takes place in the thylacoid discs of chloroplast and in this reaction water is oxidized and oxygen is released. The electrons freed up (in this process) from water are transferred to ATP and NADPH. This ATP provides the energy and NADPH supplies the electrons for the conversion of CO2 into sugars in the Calvin Cycle (C3 cycle) that takes place in the stroma of chloroplast of photosynthetic organisms. Photosystem II is located in the thylacoid membrane of chloroplast. In this system, enzymes capture photons of light to energize electrons. These electrons transfer through coenzymes, cofactors and reduce platoquinone and then these energized electrons are replaced by oxidizing water to form hydrogen ion and molecular oxygen. Photosystem II replenish lost electrons with electrons from the splitting of water. These energized electrons are passed from Photosystem II to Photosystem I via electron transport chain and used to reduce NADP+ to NADPH. The chlorophyll obtains its electrons from wter and produce oxygen as by product. The electron transfer chain pumped H+ across the thylacoid membrane. This creates an electrochemical gradient across the thylacoid membrane. This gradient drives the synthesis of ATP from ADP in stroma. The phosophorylation of ADP to ATP using the energy of light is called photophosphorylation. It occurs in the thylacoid membranes. Non-Cyclic Phophosphorylation: Electrons do not come back, Water is the first electron donor, involves both PS I and PS II, last electron acceptor is NADP, and net products are ATP, O2 and NADPH. Cyclic Phophosphorylation: Electrons come back, first electron donor is P700 (PS I), only PS I involve, last electron acceptor is P700 (PS I), only product is ATP.

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