Your body turns food into usable energy through a series of chemical reactions called cellular respiration. Food molecules, especially glucose from carbohydrates, store energy in their chemical bonds. Cells break glucose apart in small steps so the energy can be captured safely instead of released all at once.
The main usable energy molecule made by this process is ATP, which powers muscle movement, nerve signals, growth, and repair.
Cellular respiration begins with glycolysis in the cytoplasm, where glucose is split into smaller molecules. The process continues inside mitochondria, where the Krebs cycle releases carbon dioxide and loads energy onto carrier molecules. The electron transport chain uses oxygen to help convert that stored energy into a large amount of ATP.
In simple form, the overall process is glucose plus oxygen produces carbon dioxide, water, and ATP.
Key Facts
- Overall cellular respiration equation: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP
- ATP stores usable cell energy in its phosphate bonds: ATP -> ADP + P + energy
- Glycolysis happens in the cytoplasm and splits one glucose into two pyruvate molecules.
- The Krebs cycle happens in the mitochondrial matrix and releases CO2 while making energy carriers.
- The electron transport chain happens on the inner mitochondrial membrane and makes most of the ATP.
- Oxygen is the final electron acceptor in aerobic respiration and helps form water.
Vocabulary
- ATP
- ATP is the main energy-carrying molecule cells use to power life processes.
- Glucose
- Glucose is a simple sugar that cells break down to release stored chemical energy.
- Mitochondrion
- A mitochondrion is an organelle where most ATP is made during aerobic cellular respiration.
- Glycolysis
- Glycolysis is the first stage of cellular respiration, where glucose is split into two pyruvate molecules.
- Electron Transport Chain
- The electron transport chain is a series of proteins that uses electrons and oxygen to drive ATP production.
Common Mistakes to Avoid
- Saying mitochondria create energy from nothing is wrong because they convert chemical energy in food into ATP, which cells can use.
- Forgetting oxygen as an input is wrong because oxygen is needed at the end of the electron transport chain for aerobic respiration to continue.
- Thinking glycolysis happens inside the mitochondrion is wrong because glycolysis occurs in the cytoplasm before pyruvate enters the mitochondrion.
- Treating ATP as the same thing as glucose is wrong because glucose is a fuel molecule, while ATP is the immediate energy currency used by cells.
Practice Questions
- 1 Write the balanced overall equation for cellular respiration using glucose and oxygen as reactants.
- 2 If one glucose molecule can produce about 30 ATP in a cell, about how many ATP molecules could 5 glucose molecules produce?
- 3 A muscle cell has plenty of glucose but very little oxygen. Explain why it would make much less ATP than a muscle cell with both glucose and oxygen.