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Light reactions, Photo Systems Video Lecture - NEET

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1. What are light reactions in plants?
Ans. Light reactions in plants are the initial steps of photosynthesis, where light energy is converted into chemical energy. These reactions occur in the thylakoid membranes of the chloroplasts and involve the absorption of light by chlorophyll and other pigments.
2. What are the two photosystems involved in light reactions?
Ans. The two photosystems involved in light reactions are Photosystem I (PSI) and Photosystem II (PSII). PSII functions first and absorbs light energy to excite electrons, which are then passed through an electron transport chain. PSI then receives these electrons and further energizes them before they are used in the production of ATP and NADPH.
3. How do light reactions contribute to the production of ATP and NADPH?
Ans. Light reactions contribute to the production of ATP and NADPH through a process called photophosphorylation. During this process, light energy is used to generate a proton gradient across the thylakoid membrane. This gradient is then harnessed by ATP synthase to produce ATP. Similarly, NADP+ molecules are reduced to form NADPH by accepting high-energy electrons from the electron transport chain.
4. What is the role of water in light reactions?
Ans. Water plays a crucial role in light reactions as it serves as an electron donor. In PSII, water molecules are split through a process called photolysis, releasing electrons, protons, and oxygen. The released electrons replace those lost by chlorophyll molecules, while the protons contribute to the proton gradient used in ATP synthesis. The oxygen produced is released as a byproduct.
5. How does light intensity affect light reactions?
Ans. Light intensity directly affects the rate of light reactions. Higher light intensity means more photons are available for absorption by chlorophyll, leading to an increased rate of electron excitation and subsequent ATP and NADPH production. However, beyond a certain threshold, light intensity can damage the photosynthetic machinery, reducing the efficiency of light reactions.
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