I think it's A. Tell me if I'm wrong.
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It has a lot of advantages as well as disadvantages; but they prevent or suppress the entry of pathogens; colonies produced by some organisms of normal flora have a harmful effect on the pathogens; endotoxins liberated by normal flora may help the defense mechanism of the body. (Make me the brainless please)
Answer:
The correct answer is - mitochondria.
Explanation:
The reaction the generates the energy by the oxidation and reduction reaction that takes place in the cell is cellular respiration which converts biochemical reaction from the nutrients to ATP which is the currency of the energy in living beings.
The cellular respiration has three-stage glycolysis ( takes place in the cytoplasm), Oxidative decarboxylation and TCA cycle. Oxidative decarboxylation and TCA cycle take place in the mitochondria which involves oxidation of pyruvate and reduction of NAD+ in this process.
Thus, the correct answer is - Mitochondria.