Aerobic respiration equation: glucose + oxygen โ carbon dioxide + water
The aerobic respiration equation is glucose + oxygen โ carbon dioxide + water. Aerobic means using oxygen. Glucose, a sugar, reacts with oxygen inside your cells. The reaction releases energy for the cell and leaves carbon dioxide and water as waste. In symbols the balanced form is CโHโโOโ + 6Oโ โ 6COโ + 6HโO.
Reading the word equation
The two substances on the left are the reactants, the things that go into the reaction. Digestion turns food into small molecules such as glucose, and your blood carries them to your cells. Oxygen enters your blood in the lungs.
The two on the right are the products. Your blood carries carbon dioxide back to the lungs, and you breathe it out.
The reaction gives out energy, so it is exothermic. That energy keeps you warm, lets your muscles move and lets your cells build larger molecules. AQA calls the sum of all the reactions in a cell its metabolism, and respiration powers it.
The symbol equation and a quick atom check
Swap each name for its formula. Glucose is CโHโโOโ, oxygen is Oโ, carbon dioxide is COโ and water is HโO. Then add the numbers in front that make both sides match:
CโHโโOโ + 6Oโ โ 6COโ + 6HโO
- Carbon: the 6 in glucose becomes six COโ molecules, 6 atoms each side.
- Hydrogen: 12 in glucose, and six HโO molecules hold 12.
- Oxygen: 6 in glucose plus 12 in six Oโ makes 18. On the right, 12 in the COโ and 6 in the water also make 18.
AQA lists the four formulae for you to recognise but does not join them into this balanced line. No other GCSE board prints it either. It is the usual balanced form, and the atom counts above show that it works.
Inside the cell
Mitochondria are tiny parts inside animal and plant cells. OCR Gateway (J247) says they contain the enzymes for respiration. Enzymes are proteins that control the reactions in living things. OCR Twenty First Century (J257) adds that respiration uses the cytoplasm as well as the mitochondria. Both appear on the plant cell diagram.
J257 describes the steps in plain terms. The cell first breaks glucose down. The pieces then combine with oxygen, making water and carbon dioxide.
When you exercise
Your muscles need more energy when you run. AQA says your heart rate, breathing rate and the volume of each breath all go up. That sends more blood carrying oxygen to the muscles.
If the oxygen cannot keep up, muscle cells switch to respiring without it. That path is on the anaerobic respiration equation page, and all three versions sit side by side on the respiration equation page.
Edexcel sets a core practical on the rate of respiration in living organisms. J257 suggests a yeast experiment where you collect the carbon dioxide given off.
Common mistakes
- Putting a 6 in front of glucose. Only one glucose molecule reacts, so glucose has no number in front.
- Copying the photosynthesis equation by mistake. In respiration, glucose and oxygen go in, and carbon dioxide and water come out.
- Saying aerobic respiration makes energy. Energy cannot be made. The reaction transfers energy that was stored in glucose.
- Writing 6O for six oxygen molecules. Oxygen gas is Oโ, so six molecules are 6Oโ.
Build the aerobic equation, and the two anaerobic ones, from word tiles in Respiration Equations. Back to the biology hub.
Questions people ask
How does aerobic respiration differ from the anaerobic kind?
Aerobic respiration uses oxygen and breaks glucose down completely. Anaerobic respiration happens without oxygen, breaks glucose down only partly and transfers much less energy.
Do plants carry out aerobic respiration?
Yes. OCR J257 says respiration happens in the cytoplasm and mitochondria of plant cells, just as in animal cells. It goes on day and night, whether or not the plant is photosynthesising.
Is aerobic respiration the reverse of photosynthesis?
The word equations are mirror images. Compare it with the photosynthesis equation: the reactants of one are the products of the other.