MCQ
Which activity is performed by $PS-I$ in light reaction?
- AReduction of $NADPH$
- ✓Reduction of $NADP$ $^{+}$
- COxidation of $NADP$ $^{+}$
- DOxidation of $NAD$
Light reaction begins with the $PS-II$. In photosystem-$II$ the reaction centre chlorophyll-a absorb $680 \;nm .$ wavelength of red light causing electrons to become excited and jump into orbit further from the nucleus. These electrons are picked up by an electron acceptor, which passes them to an electron system consisting of cytochromes.
The movement of electrons in $ETS$ of photosynthesis is down hill in terms of oxidation reduction or redox potential scale. The electrons are not used up as they pass through the electron transport chain, but they passed on the pigments of photosystem $I$. Simultaneously, electrons in the reaction centre of $PS-I$ are also excited, when they receive red light of wavelength $700 \;nm$ and are transferred to another acceptor molecule that has greater redox potential. These electrons than are moved down hill again this time to a molecule of energy rich $NAD P^{+i i}$.
The addition of these electrons reduces the $NAD P ^{+i \text { i }}$ to $NADPH + H ^{+i 6}$
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