The Cellular Respiration Process: How We Get Energy from Food

January 13, 2026 •

2 min read

Over 90% of a cell's energy currency, adenosine triphosphate (ATP), is produced by mitochondria through cellular respiration. This multi-stage process is how we get energy from food, enabling everything from muscle contraction to complex thought.

Quick Summary

A multi-stage biological pathway called cellular respiration converts the chemical energy in food into a usable fuel for our bodies. This intricate process involves digestion, glycolysis, the Krebs cycle, and the electron transport chain, all working together to generate ATP.

Key Points

Digestion: Large food molecules like carbohydrates, fats, and proteins are broken down into smaller subunits such as glucose, fatty acids, and amino acids.
Cellular Respiration: The metabolic pathway that converts the chemical energy in nutrients into adenosine triphosphate (ATP), the main energy currency of cells.
ATP: Adenosine triphosphate is the molecule used by cells to power essential functions, including muscle contraction, protein synthesis, and cell division.
Mitochondria: These organelles within cells are often called the "powerhouses" because they produce over 90% of the body's ATP through cellular respiration.
Aerobic vs. Anaerobic Respiration: Aerobic respiration, which uses oxygen, yields significantly more ATP (30-32 molecules) per glucose molecule than anaerobic respiration (2 ATP), which occurs without oxygen.

From Digestion to Cellular Fuel: The Macro Journey

Before our cells can produce energy, the food we eat must be broken down into smaller, usable molecules. This journey begins in our digestive system.

Stage 1: Digestion

Carbohydrates: Complex carbohydrates, such as starches, are broken down into simple sugars, with glucose being the most important fuel molecule.
Fats (Lipids): Fats are broken down into fatty acids and glycerol.
Proteins: Proteins are digested into their building blocks, amino acids.

These smaller nutrient molecules are then absorbed into the bloodstream from the small intestine and transported to the body's cells.

Cellular Respiration: The Energy-Making Factory

Once inside the cell, a process called cellular respiration takes over, converting the chemical energy of these nutrients into ATP (adenosine triphosphate). This process is most efficient when oxygen is present, known as aerobic respiration.

Glycolysis: The First Split

Glycolysis, which means "splitting of sugar," occurs in the cytoplasm of the cell. Glucose is broken down into two pyruvate molecules, yielding a small amount of ATP and NADH.

The Krebs Cycle: Harvesting More Energy Carriers

Pyruvate molecules enter the mitochondria and are converted to acetyl-CoA, which then enters the Krebs cycle (also known as the citric acid cycle). This cycle produces more energy carriers (NADH and FADH2) and carbon dioxide.

The Electron Transport Chain: The Big Payoff

The electron transport chain, located on the inner mitochondrial membrane, is where the majority of ATP is produced. Electron carriers from previous stages deliver electrons, powering the creation of an electrochemical gradient used by ATP synthase to generate ATP. Oxygen is the final electron acceptor, forming water.

Aerobic vs. Anaerobic Respiration


Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen Requirement	Requires oxygen	Does not require oxygen
ATP Yield (per glucose)	Up to 38 ATP (realistically ~30-32)	Only 2 ATP
Speed	Slower and more sustainable	Faster for immediate, high-intensity needs
Byproduct	Carbon dioxide and water	Lactic acid (in humans) or ethanol (in yeast)
Example	Most everyday activities and cardio exercise	Short, explosive bursts of exercise, like sprinting

Conclusion

From digestion to cellular respiration, the process of obtaining energy from food is a complex and efficient biological system. Digestion prepares nutrients, while cellular respiration, primarily within the mitochondria, converts their chemical energy into ATP to power all cellular functions, supporting growth, movement, and thought.

Sources

How Cells Obtain Energy from Food - NCBI: https://www.ncbi.nlm.nih.gov/books/NBK26882/
How does our body convert food into energy? - Quora: https://www.quora.com/How-does-our-body-convert-food-into-energy-What-can-we-do-to-make-this-process-more-efficient-Assuming-a-generally-balanced-diet
How Does The Body Produce Energy? - Metabolics: https://www.metabolics.com/blogs/news/how-does-the-body-produce-energy
Cellular Respiration: Steps, Process, and Stages - Osmosis: https://www.osmosis.org/answers/cellular-respiration

Frequently Asked Questions

The main purpose of cellular respiration is to convert the chemical energy stored in food molecules (carbohydrates, fats, proteins) into ATP, a readily usable energy currency for the body's cells.

Cellular respiration consists of three main stages: glycolysis (splitting glucose), the Krebs cycle (further breakdown), and the electron transport chain (generating the majority of ATP).

Oxygen is crucial for efficient energy production because it acts as the final electron acceptor in the electron transport chain, allowing for a much larger yield of ATP compared to respiration without oxygen.

Fats are broken down into fatty acids, which are then converted into acetyl-CoA and fed into the Krebs cycle and electron transport chain. Fats are a more energy-dense fuel source than carbohydrates.

When oxygen is limited, cells resort to anaerobic respiration. This less efficient process, relying on glycolysis and fermentation, produces only a small amount of ATP and can result in lactic acid buildup.

Excess glucose from food is stored as glycogen in the liver and muscles. When immediate energy is not needed, carbohydrates can also be converted into fat and stored for long-term use.

ATP, or adenosine triphosphate, is a molecule that stores and carries energy in cells. It's called the 'energy currency' because cells use it to pay for various metabolic tasks, much like money fuels our daily activities.