Cellular respiration is the process by which plants and animals use oxygen to convert glucose (sugar) into ATP (adenosine triphosphate), which is the energy currency of the cell. ATP is then used to power all of the cell's activities, including growth, reproduction, and movement.
The overall equation for cellular respiration is:
$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy$$
In this equation, glucose (C6H12O6) reacts with oxygen (O2) to produce carbon dioxide (CO2), water (H2O), and energy in the form of ATP.
Cellular respiration takes place in the mitochondria of cells. Mitochondria are small organelles that are often referred to as the "powerhouses" of the cell because they produce ATP.
The process of cellular respiration can be divided into three main stages:
1. Glycolysis. This is the first stage of cellular respiration, and it takes place in the cytoplasm of the cell. During glycolysis, glucose is broken down into two molecules of pyruvate, which are then converted into acetyl-CoA.
2. The citric acid cycle (Krebs cycle). This is the second stage of cellular respiration, and it takes place in the mitochondria. During the citric acid cycle, acetyl-CoA is broken down further, and the energy released from this process is used to produce ATP, NADH, and FADH2.
3. Oxidative phosphorylation. This is the third and final stage of cellular respiration, and it takes place in the inner membrane of the mitochondria. During oxidative phosphorylation, electrons are transferred from NADH and FADH2 to oxygen, and the energy released from this process is used to pump protons across the inner mitochondrial membrane. This creates a proton gradient, which is used to drive the synthesis of ATP.