What is Cellular Respiration?
Cellular respiration is the process cells use to convert glucose and oxygen into usable energy (ATP), carbon dioxide and water. It unfolds in four connected stages inside the cytoplasm and mitochondria.
Cellular respiration is the set of metabolic reactions — glycolysis, pyruvate oxidation, the Krebs cycle and oxidative phosphorylation — that break down glucose to produce roughly 30-32 ATP per molecule.
- 1↓GlycolysisIn the cytoplasm, glucose splits into 2 pyruvate, yielding 2 net ATP and 2 NADH.
- 2↓Pyruvate OxidationIn the mitochondrial matrix, each pyruvate becomes acetyl-CoA, releasing CO2 and 1 NADH per pyruvate.
- 3↓Krebs CycleAcetyl-CoA is fully oxidized, producing 6 NADH, 2 FADH2, 2 ATP and CO2 per glucose.
- 4Oxidative PhosphorylationNADH and FADH2 feed electrons into the electron transport chain, driving ATP synthase to make ~26-28 ATP and forming water.
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Step-by-step worked examples
A cell fully oxidizes 3 glucose molecules aerobically. Estimate the total ATP produced (~31 ATP per glucose).
ATP ≈ 31 × number of glucose molecules ATP ≈ 31 × 3 = 93 ATP
Without oxygen, the same cell can only run glycolysis (2 net ATP per glucose). How much ATP from 3 glucose molecules anaerobically?
ATP = 2 × 3 = 6 ATP This is about 15× less than full aerobic respiration.
Glycolysis yields 2 net ATP and 2 NADH per glucose. If oxidative phosphorylation converts each NADH to ~2.5 ATP, how much extra ATP do those 2 NADH contribute?
Extra ATP = 2 NADH × 2.5 ATP/NADH Extra ATP = 5 ATP
Flashcards
Quick quiz
Q1.Which stage of cellular respiration does NOT require oxygen?
Q2.Where does the electron transport chain take place?
Q3.What is the overall approximate ATP yield of aerobic respiration per glucose?
Q4.What is the final electron acceptor in the electron transport chain?
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Common mistakes
Cellular respiration only happens in animal cells. — Correct: It occurs in nearly all eukaryotic cells (plant, animal, fungal) that use mitochondria for aerobic metabolism.
Photosynthesis and respiration are the same process reversed with no difference in location. — Correct: Respiration occurs in mitochondria; photosynthesis in chloroplasts — they're linked but distinct pathways.
All four stages happen in the mitochondrial matrix. — Correct: Glycolysis occurs in the cytoplasm; only the Krebs cycle and oxidative phosphorylation occur in mitochondria.
Cellular respiration produces glucose. — Correct: It consumes glucose and produces ATP, CO2 and water — the reverse of photosynthesis.
FAQ
What is cellular respiration?
The process cells use to convert glucose and oxygen into ATP, carbon dioxide and water.
What are the stages of cellular respiration?
Glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation.
How much ATP does cellular respiration produce?
Aerobic respiration of one glucose molecule yields roughly 30-32 ATP.
What is the difference between aerobic and anaerobic respiration?
Aerobic respiration uses oxygen and yields ~30-32 ATP; anaerobic respiration (fermentation) skips oxygen and yields only 2 ATP via glycolysis.