4) (12pt) You have isolated chloroplasts and are illuminating them with 540 nm l

Question

4) (12pt) You have isolated chloroplasts and are illuminating them with 540 nm light in the presence of a necessary for photosynthesis ("System A"). (a) Is NADPH produced in System A esno l factors (b) Is ATP s/no)? the System A described above, you add excess herbicide DcMU (let's call this "System B"). DCMU blocks electron transport between pheophytin "Ph" in the Z-scheme shown on the back of the cover sheet) and plastoquinone C"OHa" in the Z-scheme). IS NADPH produced in System B? Briefly explain ? Explain. (e) To System B you then add 0.2 nmol of reduced methylene blue (methylene blue is a 2 electron carrier that can transfer electrons to plastocyanin "PC") in the cyt bif complex). Is NADPH produced2 If so,what is the theoretical maximum yield?

Explanation / Answer

4b) In system 2 ATP and NADPH synthesis would be continued. For the method of photosynthesis, Photosystem II absorbs light that are membrane bound. Photosystem II takes infrared and red light at 540nm and hence photosynthesis is maxmum under red light.

c) DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a herbicide that block the photosynthesis.

DCMU is an inhibitor which is very specific and perceptive of photosynthesis. It blocks the PSII binding site to the plastoquinone, not permiting the flow of electron from where it is produced, in PS II, to plastoquinone. This disrupts the electron transport chain in photosynthesis and hence, decreases the plant's ability to convert light energy into chemical energy (ATP and NADPH).

DCMU interfere electron transport from PSII only, but has no effect on PS I or different reactions in photosynthesis, like light absorption or carbon fixation in the Calvin cycle. And hence the production of ATP and NADPH is compromised in system 2.

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