Cellular respiration is a complex process but you can think of it as a change machine. You have a $10 bill but, at the arcade, all the games take change. Cellular respiration allows you (a cell) to break down your $10 (a glucose molecule) into change (ATP). Recall that different steps of cellular respiration make different numbers of ATP. Those steps relate to coins of different denominations (pennies, nickels, dimes, quarters, etc.).

Explanation: Cellular respiration is the process of breaking down sugar to give energy.  It can also be said to be the process of takes in food thereafter  using the food taken in it to create ATP (a chemical which the cell uses for energy).

This process starts when a glucose molecule(from consumed food) is converted into carbon dioxide and how its energy is harvested as ATP.

It involves 4 steps which are:

1. Glycolysis: Here, glucose undergoes a chemical transformation which at the end is converted to molecules of pyruvate.

2. Pyruvate Oxidation: At this step the pyruvate produced from glucose above is converted into a two-carbon molecule to Coenzyme A, known as acetyl CoA. Here carbon dioxide is produced as well.

3. Citric acid cycle: At this step, the acetyl CoA produced above combines with a four-carbon molecule and goes through a cycle of reactions. This reactions produces four carbon starting molecules which are: ATP, NADH, FADH 2 and carbon dioxide.

4. Oxidative phosphorylation: Here, the molecules produced above  NADH, FADH 2 deposit their electrons in the electron transport chain thereby releasing energy. At the end of the electron transport chain, oxygen accepts electrons and takes up protons to form water.

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