Problem 32 - Objective Biology for NEET

Question

The element involved in splitting of water is (a) \(\mathrm{Mn}\) (b) \(\mathrm{Ca}\) (c) \(\mathrm{Cl}\) (d) All of these

Step-by-Step Solution

Answer

The correct answer is (a) Mn (Manganese).

Step 1: Understanding the involvement of elements in photosynthesis

In photosynthesis, water is split into oxygen, hydrogen ions, and electrons. This process is called photolysis of water. It happens during the light dependent reactions of photosynthesis.

Step 2: Identifying the correct element

Different elements are involved in this process. However, manganese (Mn) is the most significant one as it forms the core of the oxygen-evolving complex in the photosystem where the photolysis of water occurs.

Key Concepts

Photosynthesis

Photosynthesis is a fascinating process that allows plants, algae, and some bacteria to convert light energy into chemical energy. This process is essential for life on Earth as it provides oxygen and organic compounds used by many organisms.
Photosynthesis occurs in two main stages: the light-dependent reactions and the Calvin cycle (also known as light-independent reactions). In the light-dependent reactions, sunlight is captured by chlorophyll and used to generate energy-rich molecules, such as ATP and NADPH.
These molecules then power the Calvin cycle, where carbon dioxide is converted into glucose.

• Photosynthesis is vital for producing oxygen.
• It converts light energy into a form usable by living organisms.
• It takes place mainly in the chloroplasts of plant cells.

It's incredible to think that all the air we breathe and the food we eat start with this amazing process.

Light-Dependent Reactions

The light-dependent reactions are the first stage of photosynthesis and occur in the thylakoid membranes of the chloroplasts. Their main purpose is to capture light energy and transform it into chemical energy in the form of ATP and NADPH.
During this process, chlorophyll absorbs light, which excites electrons and starts a chain of reactions.

Photolysis of Water

One of the key events in light-dependent reactions is the splitting of water molecules, known as photolysis. This step is essential because it provides the electrons needed to replace those lost by chlorophyll.

• Photolysis produces oxygen as a byproduct released into the atmosphere.
• Hydrogen ions (protons) are used later in the process to form NADPH.
• The energy released is utilized to pump protons, creating a gradient that helps form ATP.

This stage is like the powerhouse of photosynthesis because it generates the energy molecules that drive the entire process.

Oxygen-Evolving Complex

The oxygen-evolving complex (OEC) is a vital part of the photosystem II in the chloroplasts, playing a crucial role in the photolysis of water. It is the machinery that splits water molecules and releases oxygen, a critical step in photosynthesis.
The OEC is composed of several inorganic cofactors, including manganese ion ( Mn^{2+}) clusters, which are essential for its function.

The Role of Manganese

Manganese ions are particularly important because they help stabilize the complex and facilitate the splitting of water molecules into oxygen, protons, and electrons.

• Each water-splitting cycle releases four electrons.
• Manganese works alongside calcium and chloride ions in the OEC.
• This process replenishes the electrons lost by chlorophyll during light reactions.

Without the oxygen-evolving complex, plants would not be able to produce oxygen, eliminating a vital component of our atmosphere.