Problem 28 - Objective Biology for NEET

Question

Which element is related to the splitting of water in light reaction of photosynthesis? (a) \(\mathrm{Mn}\) (b) Mo (c) \(\overrightarrow{\mathrm{Fe}}\) (d) \(\mathrm{B}\)

Step-by-Step Solution

Answer

The element related to the splitting of water in light reaction of photosynthesis is (a) Mn.

Step 1: Elimination of unlikely elements

Based on knowledge from botany, photosynthesis splits water into hydrogen and oxygen in a process called photolysis. This process is primarily facilitated by an enzyme complex that has manganese ions (Mn). B, Mo, and Fe do not play a direct role in the splitting of water during photosynthesis. So we can safely eliminate options (b), (c), and (d).

Step 2: Final Confirmation

The element that is directly related to the splitting of water in the light reaction of photosynthesis is manganese (Mn). This element is part of the oxygen-evolving complex in photosystem II, a group of four Mn ions that catalyze the photolysis of water.

Key Concepts

Light Reaction

The light reaction is the first stage of photosynthesis, occurring in the chloroplasts. It takes place in the thylakoid membranes and requires light energy. This energy is captured from sunlight by chlorophyll pigments and used to split water molecules, producing energy-rich molecules like ATP and NADPH.

These molecules store the energy that will be later used in the Calvin cycle to synthesize glucose. The oxygen that results from water splitting is released as a byproduct.

• The light reaction consists of photosystems I and II.
• It transforms solar energy into chemical energy.
• It involves the splitting of water molecules (photolysis).

Photolysis

Photolysis refers to the splitting of water molecules into oxygen, protons, and electrons due to light energy. This process is vital in the light reaction of photosynthesis and takes place within Photosystem II.

Photolysis provides essential components for the rest of photosynthesis:

• Electrons that travel through the electron transport chain, creating chemical energy.
• Protons that contribute to a proton gradient used to generate ATP.
• Oxygen, which is released as a byproduct into the atmosphere.

By supplying these elements, photolysis helps sustain the entire photosynthetic process.

Oxygen-Evolving Complex

This complex plays a critical role in the photolysis process. Also known as the water-splitting complex, it is part of Photosystem II.

Its primary role is to split water molecules (H₂O) to release molecular oxygen (O₂).

• Four manganese ions and a calcium ion are involved in the complex's operation.
• The complex harnesses electrons from water and transfers them to the chlorophyll molecule.
• By releasing oxygen as a byproduct, it supports life by replenishing Earth's oxygen supply.

Manganese in Photosynthesis

Manganese is essential for the proper functioning of the oxygen-evolving complex in photosynthesis. It is key due to its ability to participate in redox (reduction-oxidation) reactions that are necessary for splitting water molecules.

Here’s what manganese does:

• It forms a cluster with other manganese ions in the oxygen-evolving complex.
• Acts as a catalyst in the conversion of water molecules into oxygen, protons, and electrons.
• Enables the release of oxygen by cycling through different oxidation states and facilitating electron flow.

Without manganese, the photolysis of water couldn't occur, illustrating its vital role in maintaining photosynthetic efficiency.