In anoxygenic photosynthesis, what is the primary role of bacteriochlorophyll within the reaction center and antenna complexes?

Difficulty: Easy

Correct Answer: use light energy to energize an electron

Explanation:


Introduction / Context:
Bacteriochlorophyll is the photopigment in many anoxygenic phototrophs. Understanding its fundamental photophysical role helps differentiate pigment function from downstream redox chemistry.



Given Data / Assumptions:

  • Organisms: green and purple bacteria.
  • Pigment: bacteriochlorophyll in reaction centers and light-harvesting complexes.
  • Process: conversion of light energy into excited electronic states.


Concept / Approach:
Upon absorbing photons, bacteriochlorophyll elevates an electron to an excited state. This energized electron is transferred through the reaction center, initiating cyclic or noncyclic electron flow. Direct reduction of NADP or ferredoxin is typically mediated by specific dehydrogenases or electron carriers downstream.



Step-by-Step Solution:

Identify the primary photochemical event: photon absorption by bacteriochlorophyll.Result: creation of an excited electron capable of charge separation.Therefore, the correct role is energizing an electron using light.


Verification / Alternative check:
Flash photolysis and spectroscopy show rapid charge separation following excitation of the special pair in reaction centers.



Why Other Options Are Wrong:
Reduce ferredoxin/NADP directly: These are downstream redox steps involving carriers and enzymes. Transfer to sulfide intermediate: Sulfide oxidation involves separate enzymes; bacteriochlorophyll initiates, but does not specifically perform this transfer.



Common Pitfalls:
Confusing the initial photochemical excitation with later electron-transport steps and terminal reductant formation.



Final Answer:
use light energy to energize an electron

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