Cellular Respiration Equation
The cellular respiration equation shows how glucose and oxygen produce ATP energy, carbon dioxide, and water.
The Equation
Cellular respiration is the process by which living cells break down glucose to produce usable energy in the form of ATP (adenosine triphosphate). It is the reverse of photosynthesis and occurs in nearly all living organisms — from bacteria to humans. This process happens continuously in the mitochondria of cells.
Variables
| Symbol | Meaning |
|---|---|
| C6H12O6 | Glucose — a simple sugar and the primary fuel molecule (1 molecule) |
| 6O2 | Oxygen — 6 molecules of molecular oxygen used as the electron acceptor |
| 6CO2 | Carbon dioxide — 6 molecules produced as waste (exhaled by animals) |
| 6H2O | Water — 6 molecules produced as a byproduct |
| ATP | Adenosine triphosphate — the energy currency of cells (approximately 36-38 ATP per glucose molecule) |
Example 1
How much ATP is produced from 3 molecules of glucose through aerobic respiration?
Each glucose molecule produces approximately 36-38 ATP
3 molecules × 36 ATP = 108 ATP (minimum)
3 molecules × 38 ATP = 114 ATP (maximum)
Approximately 108-114 ATP molecules
Example 2
How many oxygen molecules are consumed when 5 glucose molecules undergo complete respiration?
From the equation: 1 glucose requires 6 O2
5 glucose × 6 O2
30 molecules of O2 consumed
The Three Stages
Cellular respiration occurs in three main stages, each producing ATP:
- Glycolysis (cytoplasm): Glucose is split into 2 pyruvate molecules. Produces 2 ATP and 2 NADH. Does not require oxygen.
- Krebs Cycle (mitochondrial matrix): Pyruvate is further broken down. Produces 2 ATP, 6 NADH, and 2 FADH2 per glucose.
- Electron Transport Chain (inner mitochondrial membrane): NADH and FADH2 are used to generate the majority of ATP — approximately 32-34 ATP. Requires oxygen.
Aerobic vs Anaerobic
The equation above describes aerobic respiration, which requires oxygen. When oxygen is unavailable, cells use anaerobic respiration (fermentation), which produces only 2 ATP per glucose. In humans, anaerobic respiration produces lactic acid (causing muscle soreness). In yeast, it produces ethanol and carbon dioxide (used in bread making and brewing).
Why It Matters
- Understanding metabolism and energy production in all living things
- Medical science — disorders of mitochondria affect energy production
- Exercise physiology — aerobic vs anaerobic thresholds
- Ecology — the carbon cycle depends on respiration and photosynthesis
- Food science — caloric content relates to how much glucose a food provides