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Photosynthetic pigments occur on photosynthetic thylakoids of chloroplasts. A stack of thylakoids is called granum.

1. C4 cycle occurs in C4 plants like sugarcane, maize. C4 cycle provides a more efficient way of CO2 fixation than C3 cycle and hence gives more productivity. The rest are C3 plants.
2. C3 cycle needs 18 ATP molecules for synthesis of one molecule of glucose while C4 cycle needs 30 ATP molecules. Due to high energy requirement C4 cycle is more energy expensive than the C3 cycle.
3. Chlorophyll a has a tetrapyrrole porphyrin ring as head (15 × 15Å) and a long hydrocarbon tail called phytol (20 Å) tail attached to the ring structure.
4. After excitement, e⁻ is passed from PS-II (P680) to primary electron acceptor (Pheophytin). From primary e⁻ acceptor, e⁻ is passed to plastoquinone. Plastoquinone (PQ) in turn transfer its e⁻ to Cyt b6f complex. Therefore plastoquinone facilitates the transfer of electrons from PS-II to Cyt b6f complex.

Correct answer: After excitement, e⁻ is passed from PS-II (P680) to primary electron acceptor (Pheophytin). From primary e⁻ acceptor, e⁻ is passed to plastoquinone. Plastoquinone (PQ) in turn transfer its e⁻ to Cyt b6f complex. Therefore plastoquinone facilitates the transfer of electrons from PS-II to Cyt b6f complex.

Solution

The correct statement describes the normal electron transport chain in photosynthesis: excited electrons leave PS-II, move to pheophytin, then to plastoquinone, and finally to the cytochrome b6f complex. Thus PQ acts as the mobile carrier that links PS-II to Cyt b6f.

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