LABORATORY REVIEW
CELL RESPIRATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Light energy excites electrons in the thylakoid membrane electron transport chain.
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The electrons lost from the reaction centre are replaced by electrons derived from water.
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Photons are passed along to a reaction centre chlorophyll.
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Chlorophyll donates a pair of protons to NADP+, which is converted to NADPH.
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Detailed explanation-1: -Light energy excites electrons in the electron transport chain in a photosynthetic unit.
Detailed explanation-2: -The two electrons lost from photosystem II are replaced by the splitting of water molecules. Water splitting also releases hydrogen ions into the lumen.
Detailed explanation-3: -In photosystem II, the electron lost from the reaction center is replaced with an electron that comes from water. When two water molecules are split, four electrons and four protons are released. It requires a lot of energy to break the bonds in a water molecule-much more energy than a single photon of light contains.
Detailed explanation-4: -During the light reactions of photosynthesis, photosystem II reaction centre P680 absorbs light to boost its electrons and attains oxidized state. To reduce the oxidized chlorophyll molecules or to regain the lost electrons, the source of electrons is water in green plants and cyanobacteria.