Why do eukaryotic cells and many prokaryotic cells need oxygen?
Hint: Eukaryotic cells have a nucleus enclosed within a nuclear envelope. A prokaryotic cell, however, lacks a nuclear membrane-enclosed nucleus. Both these cells utilise oxygen for surviving.
Complete Answer: The organelles inside the cells, often called the “energy factories” of a cell, are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule, through cellular respiration. Cellular respiration is the way the cells produce energy from the molecules of food consumed. The general scheme for aerobic respiration in eukaryotic cells consists of three complex steps: glycolysis, citric acid cycle and the electron transport chain reactions. This type of respiration mostly takes place in specialized organelles in eukaryotic cells called mitochondria. The first step with anaerobic respiration in prokaryotic cells is also glycolysis, which yields two molecules of ATP from one glucose. It also produces pyruvate, which is then turned towards fermentation or toward lactic acid (used by animal cells under some circumstances). This type of cellular respiration mostly takes place in the cytoplasm. Some prokaryotes need oxygen, some are poisoned by it, and some can take it or discard it depending on availability. Prokaryotes that need oxygen in order to metabolize are termed obligate aerobes. Prokaryotic cells which are facultative anaerobic make ATP by aerobic respiration if oxygen is present, but can also survive without oxygen. Examples of facultative anaerobic bacteria are the Staphylococci species, Escherichia coli, Corynebacterium sp., and Listeria sp..
Note: Most eukaryotic cells use aerobic respiration, which relies on oxygen and is most efficient for energy production. However, some eukaryotic cells turn to anaerobic respiration when oxygen is unavailable. Scientists recently discovered three surprising eukaryotes that live in a part of the ocean without oxygen and therefore always use anaerobic respiration.