Question

Bacteria which can also live in the absence of oxygen are
(a) Obligate aerobes
(b) facultative aerobes
(c) Obligate anaerobes
(d) Facultative anaerobes

Answer 1

Hint: Bacteria are microscopic simple prokaryotic organisms whose cells lack a well-defined nucleus. Bacteria can be divided into various groups based on their degree of oxygen required for the process of cellular respiration.

Complete answer:
Bacteria are broadly divided into aerobic or anaerobic based on their requirement of oxygen for respiration or not. Each of them can be further classified into obligate and facultative.
Facultative anaerobes are the ones which respire aerobically in the normal conditions but can switch over to the mode of anaerobic respiration in the absence of oxygen or if it becomes deficient. E.g halophiles like Halobacterium salinarum.

Additional Information: -Obligate aerobes are the bacteria that can respire only aerobically i.e in the presence of oxygen. Under anaerobic conditions, they get killed.E.g. Bacillus subtilis.
-Facultative aerobes are the bacteria that normally respire anaerobically but under certain conditions where oxygen is present in the environment, then they can survive by respiring aerobically. E.g. Most of the photosynthetic bacteria like Rhodopseudomonas are facultative aerobes.
-Obligate anaerobes belongs to the category of bacteria that can only respire anaerobically and the presence of oxygen in the atmosphere proves harmful to them.E.g Clostridium botulinum.
-Halophiles are found in saline environments like in the great salt lake of the US. They buildup sufficient quantities of solute concentration in their cells in order to maintain osmotic balance with their surroundings.
So, the correct answer is ‘Facultative anaerobes.’

Note: -Bacteria can also be divided into Gram-positive and Gram-negative bacteria based on staining techniques.
-Gram-negative bacteria do not retain the crystal violet dye due to a thin layer of peptidoglycan in their cell wall. E.g. Salmonella, Escherichia.
-Gram-positive bacteria retain crystal violet dye and thus stain dark violet or purple. This is due to the thick layer of peptidoglycan in their cell wall.E.g. Staphylococcus, Streptococcus.