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Light Reactions & Photo-Phosphorylation Video Lecture | Biology Class 11 - NEET

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1. What are light reactions in photosynthesis?
Ans. Light reactions are the initial phase of photosynthesis where light energy is converted into chemical energy. These reactions occur in the thylakoid membranes of chloroplasts and involve the absorption of light by pigments such as chlorophyll. The energy is then used to generate ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are essential for the subsequent dark reactions.
2. How does photo-phosphorylation occur in light reactions?
Ans. Photo-phosphorylation is the process of generating ATP using light energy during the light reactions of photosynthesis. It occurs through two different mechanisms: cyclic and non-cyclic photo-phosphorylation. In cyclic photo-phosphorylation, the excited electrons from the reaction center of photosystem I are passed back to the electron transport chain, creating a proton gradient that drives ATP synthesis. In non-cyclic photo-phosphorylation, the excited electrons from photosystem II are used to reduce NADP+ to NADPH, and the resulting proton gradient is utilized by ATP synthase to generate ATP.
3. What is the role of chlorophyll in light reactions?
Ans. Chlorophyll is a pigment found in chloroplasts that plays a crucial role in light reactions. It absorbs light energy from the electromagnetic spectrum, particularly in the red and blue regions, and transfers this energy to the reaction centers of photosystems I and II. The excited electrons from chlorophyll are then passed through an electron transport chain, leading to the generation of ATP and NADPH. Without chlorophyll, plants would not be able to capture and utilize light energy for photosynthesis.
4. How does the electron transport chain function in light reactions?
Ans. The electron transport chain is a series of protein complexes embedded in the thylakoid membrane of chloroplasts. During light reactions, this chain functions by accepting high-energy electrons from the reaction center of photosystem II. These electrons are then passed through a series of redox reactions, releasing energy that is used to pump protons (H+) across the thylakoid membrane and create a proton gradient. This gradient is essential for ATP synthesis and the subsequent reduction of NADP+ to NADPH.
5. What is the significance of light reactions in photosynthesis?
Ans. Light reactions are vital for the process of photosynthesis as they capture and convert light energy into chemical energy. They produce ATP, which is the primary energy currency of cells, and NADPH, a reducing agent necessary for the dark reactions (Calvin cycle) that produce glucose. Without light reactions, plants would not be able to generate the energy and reducing power required for the synthesis of carbohydrates, essential for their growth and survival.
182 videos|365 docs|153 tests
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