Question

An obligate anaerobe is
A. Ulothrix
B. Spirogyra
C. Methane bacteria
D. Onion

Answer 1

Hint: Some organisms are known to be found in a variety of different habitats. They are well suited for a variety of extreme environments and can even cope with the absence of oxygen. These organisms are well suited to the habitats that are normally harmful or unsustainable by another different organism.

Complete step by step answer: The organisms that are able to grow and develop in conditions that are totally devoid of oxygen are known as aerobic organisms. These organisms do not require oxygen for their growth and are able to thrive in extreme environments that do not contain oxygen. They are also known as anaerobe. They react to the presence of oxygen in the environment and it can cause their death.
THe anaerobic organism may range from the single celled bacteria, protozoans or multicellular organisms such as fungi. THe anaerobic organism can be divided into three distinct categories which are obligate anaerobes, aerotolerant organism and facultative anaerobes.
THe aerotolerant organism are organisms which can tolerate the presence of oxygen but they are unable to utilize oxygen for growth. The facultative anaerobes are organisms that can grow in absence of oxygen but in the presence of oxygen, it can use the oxygen for its growth. THe obligate organism are the organism that cannot tolerate the presence of oxygen and oxygen can produce a negative effect on them.
THe obligate anaerobe are the organisms that survive even in the extreme environmental conditions and temperatures and are harmed by the presence of oxygen. They are killed by the normal concentration of oxygen and are highly sensitive to the oxygen level in the atmosphere. They are known to metabolize energy by the process of fermentation. It is a process of anaerobic respiration. THe respiration products produced are different than the normal pathways of respiration and they utilize an electron acceptor other than the oxygen.
Methane bacteria are obligate anaerobic in nature and they are found to survive in extreme anaerobic conditions and produce methane as a byproduct of metabolism.
 Ulothrix belongs to the genus of non-branching filamentous green algae and is photosynthetic in nature. Spirogyra is a filamentous green alga and is commonly known as water silk. Onion is an underground stem vegetable.
Therefore, the correct option is option C.

Note: The obligate anaerobic organism are organisms that are able to survive to grow and reproduce in conditions that do not contain oxygen. They are extremely sensitive to the present of oxygen in the environment which may be harmful to them. Methane bacteria or methanogens are organisms that are able to survive in anaerobic conditions.