Question

Which process is most directly driven by light energy?

(A). creation of a pH gradient by pumping protons across the thylakoid membrane.

(B) reduction of NADP+ molecules

(C) transfer of energy from pigment molecule to pigment molecule

(D) ATP synthesis.

Short answer

1. The statement “creation of a pH gradient by pumping protons across the thylakoid membrane.” is false.
2. The statement “reduction of NADP+ molecules” is false.
3. The statement “transfer of energy from pigment molecule to pigment molecule” is true.
4. The statement “ATP synthesis” is false.

Step-by-step solution

Photosynthesis

Photosynthesis is essential for the process observed in autotrophs. This process requires solar energy to produce the desired products (glucose). Light-sensitive and temperature-sensitive reactions are part of photosynthesis.

Explanation of option (A)

Marinating the pH gradient by pumping of hydrogen ions is generally not linked directly with the light reaction. The energy in the form of ATP is developed while moving out of the hydrogen ion from the thylakoid lumen to the stroma.

The splitting of water molecules helps in the generation of protons, electrons, and oxygen molecules inside the thylakoid.

Therefore, the given statement is false.

Explanation of option (B)

NADP+ is reduced to the NADPH at the last stage of the electron transfer in the photosystem. NADP reductase helps in reducing the NADP+ molecule. Ferredoxin complex help in shifting the electrons to ferredoxin-NADP+ oxidoreductase.

The reduction of NADP+ is not directly linked with the light-driven process as this light is not initiating electrons to reduce any molecule.

Therefore, the given statement is false.

Explanation of option (C)

There are two kinds of pigment systems in green plants. One is Photosystem I (PS-I), and the other is photosystem II (PS-II). PS-I is associated with the cyclic flow of electrons, while PS-II is non-cyclic.

If the light energy excites both the pigment systems, when light excites the PS-I, it transfers the electron to the iron-sulfur compound. Light energy also excites PS-II, which transfers an electron to pheophytin at the initial stage, and then it enters the cyclic photosystem (PS-I).

Therefore, the given statement is true.

Explanation of option (D)

ATP is synthesized in between the cyclic photosystem. One ATP is formed between the ferrodoxin and cytochrome b complex, while another is between the cytochrome b and f complex in PS I.

Light generally does not directly help in the synthesis of ATPs. Production of ATP is indirectly linked with solar energy when it is produced in PS-I.

Therefore, the given statement is false.