The Question is from neet-botany , and it was created by the author Mr. NARESH KUMAR K

Question

A bacterium which is capable of utilizing the most abundantly available gas in the atmosphere for one of its metabolic pathways, but cannot utilize the second most abundantly available for its another metabolic pathway is

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Microbial Metabolism & Atmospheric Gases
	**Related Topics**: Nitrogen Fixation, Aerobic Respiration, Anaerobic Respiration
	**Prerequisites**: Composition of Earth's Atmosphere,  Metabolic pathways of bacteria
## SOLUTION PATHWAY
**Given Information**:
	The bacterium uses the most abundant atmospheric gas.
	It cannot use the second most abundant gas.
**Method & Steps**:
	1. Identify the most and second most abundant gases:
		Reasoning: The Earth's atmosphere is composed primarily of Nitrogen ($N_2$ ~ 78%) and Oxygen ($O_2$ ~ 21%).
	2. Relate gas utilization to metabolic pathways:
		Working: Nitrogen fixation is the process of converting atmospheric nitrogen ($N_2$) into ammonia ($NH_3$), which can be utilized by organisms. Aerobic respiration uses oxygen ($O_2$) as the final electron acceptor.
		Key Point:  Obligate anaerobes cannot survive in the presence of oxygen.
	3. Identify the bacteria:
		Result: Obligate anaerobic nitrogen-fixing bacteria can utilize nitrogen ($N_2$) for nitrogen fixation, but cannot utilize oxygen ($O_2$) because they are poisoned by it. 
		Verification: This aligns with the given conditions that the bacteria uses the most abundant gas ($N_2$) but not the second most abundant ($O_2$).
## OPTION ANALYSIS
[A] :x: Aerobic nitrogen-fixing bacteria: These bacteria can utilize both nitrogen ($N_2$) and oxygen ($O_2$).
[B] ✓: Obligate anaerobic nitrogen-fixing bacteria: These bacteria can utilize nitrogen ($N_2$) but not oxygen ($O_2$).
[C] :x: Facultative anaerobic nitrogen-fixing bacteria: These bacteria can utilize both nitrogen ($N_2$) and oxygen ($O_2$), although they can switch to anaerobic pathways if oxygen is absent.
[D] :x: Aerobic denitrifying bacteria: These bacteria use oxygen ($O_2$) for respiration and convert nitrates ($NO_3^−$) to nitrogen gas ($N_2$), so they are not fixing nitrogen from the atmosphere. 
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing nitrogen fixation with denitrification:  Nitrogen fixation converts $N_2$ to $NH_3$, while denitrification converts $NO_3^−$ to $N_2$.
		2. Misunderstanding anaerobic vs. aerobic: Aerobic means requiring oxygen, while anaerobic means living without oxygen (obligate anaerobes are harmed by oxygen).
	**Quick Tips**:
		1. Remember the major components of the atmosphere: Nitrogen ($N_2$) > Oxygen ($O_2$) > Argon (Ar) > Carbon dioxide ($CO_2$).
		2. Associate 'obligate anaerobe' with sensitivity to oxygen.

Mr. NARESH KUMAR K · Answer

Aerobic nitrogen-fixing bacteria

Mr. NARESH KUMAR K · Answer

The correct Option is "Obligate anaerobic nitrogen-fixing bacteria"

Mr. NARESH KUMAR K · Answer

Facultative anaerobic nitrogen-fixing bacteria

Mr. NARESH KUMAR K · Answer

Aerobic denitrifying bacteria

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