Question

Which of the following require oxygen for aerobic respiration but can also grow under anaerobic conditions?

• A. Strict anaerobic bacteria
• B. Micro-aerophilic bacteria
• C. Facultative anaerobic bacteria
• D. Aerobic bacteria

Hint:

Remember: "Facultative" means they have the "facility" or choice to switch.
"Obligate" means they are "obliged" or forced to stick to one condition.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question tests the classification of microorganisms based on their oxygen requirements for growth and energy metabolism. Bacteria are grouped based on how they utilize or tolerate atmospheric oxygen ($O_2$).

Step 2: Detailed Explanation:

• Understanding Microbial Respiration:
Microorganisms obtain energy through various metabolic pathways. Aerobic respiration requires oxygen as the final electron acceptor, while anaerobic respiration or fermentation occurs in its absence.

• Facultative Anaerobes:
These are the most versatile organisms. They prefer to use oxygen for aerobic respiration because it yields significantly more energy (ATP). However, if oxygen is unavailable, they possess the enzymatic machinery to switch to fermentation or anaerobic respiration to survive and grow. Common examples include Escherichia coli and many yeasts.

• Analyzing Other Categories:
- Strict Anaerobes (A): They cannot tolerate oxygen and may die in its presence because they lack protective enzymes like superoxide dismutase.
- Micro-aerophiles (B): They require oxygen but at concentrations much lower than atmospheric levels ($2-10\%$).
- Aerobic bacteria (D): Also known as obligate aerobes, they absolutely require oxygen for survival and cannot grow at all under anaerobic conditions.
Final Answer:
The ability to perform aerobic respiration while retaining the capacity to grow without oxygen defines a facultative anaerobe.