Question

What is the first step in cellular respiration?

Answer 1

Hint: Cellular respiration is a process that involves respiration through which cells extract energy from stored food molecules by using oxygen to conduct its cellular metabolic activities.

Complete answer
Cellular respiration completes in four steps. these steps are enlisted below:
Glycolysis: It is the very first step of cellular respiration that is concerned with breaking down of the stored food (that is glucose). This is the reason for it being called glycolysis. It involves formation of two pyruvate molecules ($C_{3}H_{4}O_{3}$) and ATP (the ultimate energy currency of the body) such that NAD (the electron carrying coenzyme) is converted into $NADH^+$.

Pyruvate oxidation: This is the second step of cellular respiration that involves oxidation of the pyruvate molecules released from glycolysis. This reaction takes place at mitochondrial compartments. It converts the three carbon molecules pyruvate into two carbon molecules by using NADH. It releases Carbon dioxide as an end product along with coenzyme acetyl CoA.
Citric acid cycle: It is the third step that is concerned with production of a four Carbon molecule by using acetyl CoA. This step releases ATPs, Carbon dioxide and $NADH^+$ gets converted into $FADH^+$.
Oxidative phosphorylation: It is the last step of cellular respiration that involves extraction of electrons from all the coenzymes formed throughout the process that is, $NADH^+$, $FADH^+$, etc. They all get converted into their original state that is $NAD^+$. This creates a gradient of protons outside the mitochondrial cell which is sooner balanced by an enzyme called ATP synthase. This leads to formation of ATP that eventually breaks down to release chemical energy for carrying out metabolic processes.

Note:
Respiration is a process that is preceded by breathing as it maintains oxygen supply for the cells. In case of absence of oxygen, this respiration takes place anaerobically, that is without oxygen. However, energy supply from such a process is comparatively lower and slower.