What is the term for a type of organism that grows best in the absence of oxygen?
A Aerobic
B Anaerobic
C Faultative
D Microaerophilic
The correct answer and explanation is:
Correct Answer: B. Anaerobic
Anaerobic organisms are those that grow best in the absence of oxygen. These organisms do not require oxygen for their metabolic processes. In fact, for many obligate anaerobes, the presence of oxygen can be toxic. Anaerobes obtain energy through processes such as fermentation or anaerobic respiration, which do not use oxygen as the final electron acceptor.
There are different types of anaerobic organisms. Obligate anaerobes cannot survive in the presence of oxygen at all. Examples include certain bacteria like Clostridium tetani, which causes tetanus. Facultative anaerobes, on the other hand, can survive with or without oxygen, adjusting their metabolism based on availability. Aerotolerant anaerobes do not use oxygen but can survive in its presence.
Anaerobic environments include deep soil layers, sediments at the bottom of lakes, the intestinal tracts of animals, and areas of decaying organic matter. In such settings, anaerobic bacteria play vital roles. For instance, in the human gut, anaerobes help digest food, synthesize vitamins like vitamin K, and maintain a balanced microbial ecosystem.
The other choices are not correct for this question. Aerobic organisms require oxygen to grow. Facultative organisms can grow with or without oxygen but are not defined by growing best in its absence. Microaerophilic organisms require oxygen but at lower concentrations than what is present in the atmosphere.
Understanding whether an organism is aerobic or anaerobic helps in microbiology, medicine, and environmental science. It informs treatment choices for infections, such as deciding whether a wound is likely to harbor anaerobic bacteria, and guides decisions in food production and waste management. Anaerobic digestion, for example, is a process used to treat wastewater and produce biogas.