Question:

Read the following statements. (i) Z scheme of light reaction takes place in presence of PS I only. (ii) Only PS I is functional in cyclic photophosphorylation. (iii) Cyclic photo phosphorylation results into synthesis of ATP and $NADPH_2$. (iv) Stroma lamellae lack PS II as well as NADP. Which of these statements are correct?

Updated On: Jul 28, 2022
  • (ii) and (iv)
  • (i) and (ii)
  • (ii) and (iii)
  • (iii) and (iv)
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The Correct Option is A

Solution and Explanation

$Z$ scheme involves both $PSI$ and $PSII$ to transfer electron excited by light starting from $PSII$ uphill to the acceptor, down to the electron transport chain to $PSI$, which further comprise of excitation of electrons, transfer to another acceptor and finally down hill to $NADP^{+}$ causing reduction of it to $NADOH+H^{+}$. Stroma lamella contains $PSI$ only
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Concepts Used:

Electron Transport System

The electron transport chain or system is the sequence of electron carriers, enzymes, and cytochrome that passes electrons from one to another through the redox reaction. It is electron transport-linked phosphorylation.

It contains flavin nucleotides (FAD), nicotinamide adenine dinucleotide (NAD), coenzyme Q, and cytochromes localized in F1 particles of mitochondria. It occurs in the inner mitochondrial membrane along with cristae.

In this process five (5) complexes are involved namely, I- NADH-UQ reductase, II- Succinate-UQ reductase, III- UQH2 -cytochrome C reductase, IV- Cytochrome C oxidase, and V is connected with F0−F1 particles.

In this process, NAD and FAD are minimized.

Steps:

  • Redox at complex I: Four (4) protons are pumped from the matrix to intermembrane space.
  • Redox at complex II: Coenzyme Q collects the electrons from complex I and II, and goes to complex III.
  • Redox of complex III: Four (4) protons are again pumped from matrix to intermembrane space and cytochrome C transports electrons to the complex IV.
  • Redox of complex IV: Two (2) protons are pumped from the matrix to intermembrane space and the formation of water occurs in the matrix.
  • ATP synthase action: It pumps protons from intermembrane space to matrix and generates ATP. It is associated with oxidative phosphorylation.