Photons and photosynthesis — identify the statement that is not true Which of the following statements about a photon and its role in photosynthesis is incorrect?

Difficulty: Easy

Correct Answer: It donates an electron directly to reduce carbon dioxide to glucose

Explanation:


Introduction / Context:
Understanding what a photon is and how light energy is converted into chemical energy in photosynthesis is foundational for plant physiology and bioenergetics. This question asks you to separate correct physical and biological descriptions from an incorrect one.



Given Data / Assumptions:

  • A photon is the quantum of electromagnetic radiation.
  • Photosynthetic pigments absorb photons and enter excited states.
  • Photosynthetic electron transport ultimately powers carbon fixation in the Calvin cycle.


Concept / Approach:

Photon energy is inversely related to wavelength. In photosynthesis, photons are absorbed by pigments in antenna complexes and reaction centers. Absorption does not mean that a photon donates an electron; rather, the energy of the photon excites an electron within a pigment molecule, which then participates in electron transfer chains that lead to the generation of ATP and NADPH. These energy carriers are later used to reduce carbon dioxide to carbohydrate in enzyme-catalyzed reactions.


Step-by-Step Solution:

Recall that E = h * c / lambda, so shorter wavelength gives greater energy.Recognize that photosystems absorb photons via pigments like chlorophyll and carotenoids.Understand that excitation energy moves electrons within pigments and along transport chains.Identify the false statement claiming that photons donate electrons directly to reduce carbon dioxide.


Verification / Alternative check:

Biochemistry texts describe carbon fixation as enzyme-driven reductions using NADPH as the electron donor, not the photon itself. This confirms the incorrectness of the electron donation claim.


Why Other Options Are Wrong:

Options A, B, and E correctly state physical facts about photons and excitation. Option C is acceptable phrasing for pigment capture in the photosynthetic unit. Only option D misrepresents the role of photons.


Common Pitfalls:

Confusing the energy of light with electrons as particles donated by light. The photon supplies energy, while electrons come from molecules such as water in oxygenic photosynthesis.


Final Answer:

It donates an electron directly to reduce carbon dioxide to glucose

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