Problem 59 - Objective Biology for NEET

Question

Which of the following is incorrect about nitrogen fixation in nodulc? (a) It is a high energy process. (b) Leg-haemoglobin acts as oxygen scavenger. (c) \(\mathrm{Mg}\) is requircd as a cofactor for nitrogenase cnzyme. (d) This process uses atmospheric nitrogen but not atmospheric hydrogen directly.

Step-by-Step Solution

Answer

The incorrect statement is (d). This process uses atmospheric nitrogen but not atmospheric hydrogen directly.

Step 1: Understand Nitrogen Fixation

Nitrogen fixation is a high-energy process that converts atmospheric nitrogen (\(N_2\)) into ammonia (\(NH_3\)), which plants can use. It is executed by nitrogen-fixing bacteria in root nodules of leguminous plants.

Step 2: Role of Leg-Haemoglobin

Leg-haemoglobin in the root nodules acts as an oxygen scavenger. It ensures that the nitrogenase enzyme, which is responsible for the fixation process, operates in an oxygen free environment as oxygen can deactivate this enzyme.

Step 3: Role of Magnesium

Magnesium (\(\mathrm{Mg^{2+}}\)) acts as a co-factor for many enzymes and is necessary for nitrogenase enzyme activity. It stabilizes the transition state and assists in the breakdown of ATP to provide energy for the process.

Step 4: Evaluate the Process of Nitrogen Fixation

The nitrogen fixation process uses atmospheric nitrogen directly while it doesn't use atmospheric hydrogen directly. Instead, hydrogen is obtained as a byproduct of other reactions in the plant.

Key Concepts

Leg-Hemoglobin

In the fascinating world of nitrogen fixation, leg-hemoglobin plays a crucial role in the root nodules of leguminous plants. Imagine these nodules as small, specialized environments where bacteria work tirelessly to convert atmospheric nitrogen ( _2 ) into ammonia ( _3 ), a form of nitrogen that plants can readily absorb and utilize. However, this process is sensitive and requires a specific condition: an oxygen-free environment.

Here is where leg-hemoglobin comes into play. This protein binds with oxygen, effectively scavenging it away from the nodules. This ensures that the nitrogenase enzyme, essential for nitrogen fixation, operates optimally and is not deactivated by oxygen presence.
- It is akin to a protective agent, ensuring efficiency in nitrogen conversion. - Without leg-hemoglobin, the entire process could be compromised. - It maintains a delicate balance within the root nodule, enabling bacteria to perform their task without interference.

Nitrogenase Enzyme

The nitrogenase enzyme is the workforce behind the nitrogen fixation process. It has a unique ability to convert inert atmospheric nitrogen ( _2 ) into usable ammonia ( _3 n). Simply put, it acts as a catalyst for the reaction, providing the necessary environment for the chemical transformation to take place.

The nitrogenase enzyme comprises several components that work together:

• A molybdenum-iron protein, which is the actual site of _2 binding and reduction.
• An iron protein that provides electrons and energy for the reaction.

However, the presence of oxygen can stop the enzyme from working effectively. This is why leg-hemoglobin is so important. Moreover, the process is energy-intensive.
This means a substantial amount of energy, typically in the form of ATP, is required to break the strong triple bonds in the _2 molecule. The nitrogenase enzyme meticulously works, even under these challenging conditions, to produce ammonia efficiently.

Magnesium Cofactor

Magnesium ( Mg^{2+} ) is an unsung hero in the nitrogen fixation process. As a cofactor, it is crucial for the enzyme's activity, stabilizing the complex structures involved. Magnesium's role is multifaceted:

• It helps stabilize the transition states of reactions.
• Assists in the hydrolysis of ATP, providing the energy required for nitrogen fixation.

Thanks to magnesium, the nitrogenase enzyme's sensitive structure is protected, enabling it to perform its function. This element is also pivotal in energy transactions within the plant, making sure that the chemical energy needed for fixation is available and usable. By maintaining these crucial interactions, magnesium ensures that the nitrogen-fixing bacteria in the nodules can operate under optimal conditions, facilitating the conversion of atmospheric nitrogen into a form that plants can absorb and thrive on.