Question

19) In chloroplasts, one reason why photosystem I is localized with better access to the stroma than photosystem II is to better supply NADPH and ATP for carbon assimilation.

Give another reason why photosystems I and II should be physically separated. Explain your answer. (2 sentences)

Answer 1

Photosystem two absorbs solar energy which leads to the excitation of electrons present in it. Ultimately the electrons are passed onto photosystem 1 and then to NADP+ to form NADPH. Although This can happen directly by passing the electrons from photosystem 2 to photosystem 1 and then to the electron carrier. But in real photosystem 2 passes its electrons to other electron Carriers located in thylakoid membrane.

The most important reason behind this is that passing of electrons from photosystem 2 to electron carrier and then to photosystem 1 leads to the generation of proton gradient across thylakoid membrane. Whenever electrons are passed on from one electron carrier to the other, protons are also formed from thylakoid lumen into the stroma of chloroplast. This leads to the generation of proton gradient and the electrochemical energy stored in this gradient is used for the generation of ATP by ATP synthase enzyme.

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