Question

In Z-scheme of electron transport, water splitting complex supplies electrons to
A. $Photosystem - I$
B. Plastoquinone
C. Pheophytin
D. $Photosystem - II$

Answer 1

During the non-cyclic flow of electrons, the two photosystems are connected in the series as $PS - II$ and $PS - I$. The Z-scheme or non-cyclic flow of electrons begins with the absorption of a photon by $PS - II$followed by$PS - I$I. When $PS - II$ absorbs the photon, it excites and transfer the electrons to Pheophytin which in turn passes the electron to $PS - I$.

Complete answer:
Step 1: The splitting of water is catalysed by the oxygen evolving complex (OEC), a protein complex present on the luminal surface of the thylakoid membrane. OEC oxidizes water and passes on the 4 electrons one at a time to the $p680$ ($PS - II$).
Step 2: After receiving the electron, $p680$ excites to $p680*$. This excited reaction centre then passes on the electrons to Pheophytin, a chlorophyll in which the Magnesium ion in the centre has been replaced by two hydrogen atoms. Pheophytin transfers the electrons to the $PlastoquinoneQA$and $QB$. $Plastoquinone$ pass the electrons to the $Cytochrome b6 f$complex which in turn passes these electrons to the Plastocyanin, a blue-coloured Copper containing protein.
Step 3: $PS - I$ receives the electrons from Plastocyanin and after absorption of a photon get excited from $p700$ to $p700*$. The excited $PS - I$ then passes these electrons to the primary electron acceptor A0 which then passes the electrons to A1 which is a phylloquinone also called $Vitamin K1$.
Step 4: A1 then pass the electrons to a series of Iron-sulfur proteins (${F_X} {F_A} and {F_B}$) which finally transfers the electrons to soluble Ferredoxin followed by FNR (Flavoprotein- Ferredoxin-NADP reductase) which reduces the $NAD{P^ + }$to $NADPH$.

Hence, the correct answer is option (D).

Note: The $PS - I$ was discovered by Louis Duysens and the $PS - II$ was discovered by Pierre Joliot. These two photosystems contain many pigments which help to trap light energy and convert them to chemical energy.