Which of the following best describes the cyclic electron transport carried out

Question

Which of the following best describes the cyclic electron transport carried out by purple photosynthetic bacteria?

A) Absorption of a photon by P960 leads to electron transport through a cytochrome bc_1 complex, then to a pool of quinones, and finally the reaction center is reduced through its quinonesB.) Absorption of a photon by P960 leads to electron transport through a cytochrome bc_1 complex, to a pool of quinones, then to a cytochrome c_2, and finally the reaction center is reduced through its quinones. C.) Absorption of a photon by P960 leads to electron transport through the reaction center quinones to a pool of quinones, to a cytochrome bc_1 complex, and finally the reaction center is reduced through its cytochrome c_2

Which best describers the relationship between photosynthetic reaction centers and light-harvesting complexes?

A) Light-harvesting complexes are needed by photosynthetic reaction centers only during episodes of dim light B.) Light-harvesting complexes absorb most of the photons, and pass the energy randomly among other such complexes until it reaches a reaction center C.) Each photosynthetic reaction center has one light-harvesting complex that directs the energy of absorbed photons to it.

Explanation / Answer

1. Cyclic electron transport is observed in photosynthesis of purple bacteria. The cyclic transport of electrons occur due to little availability of NADP+ to accept electrons. In thisprocess, the electrons from P960 to through a cytochrome bc1 complex, then to a pool of quinones, and finally the reaction center is reduced through its quinones. The resulting proton gradient generated from cytochrome bc1 complex and quinones drives the synthesis of ATP. Option A is correct.

2. Reaction center is the component of photo system. The light harvesting antenna captures the solar energy and transfers to reaction center, which uses captured light energy to drive transmembrane electron transport. There are two photo systems in chloroplasts. They are PSI and PSII. Each photo system consists of two functional components. The light harvesting antenna captures the solar energy and transfers to reaction center, which uses captured light energy to drive transmembrane electron transport. In PSI light – driven electron transport is used for the synthesis of NADPH. Option C is correct.

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