Cellular respiration produces ATP (energy) plus byproducts carbon dioxide and water. Depending on the organism and conditions, there can be additional byproducts or variations (such as lactate in anaerobic muscle or ethanol and CO2 in yeast), but the core outputs are ATP, CO2, and H2O. Key outputs
- ATP: the usable energy currency for cellular processes.
- Carbon dioxide (CO2): waste product exhaled or expelled, often used by plants in photosynthesis.
- Water (H2O): formed from hydrogen and oxygen during the reactions; can be excreted or used in other physiological processes.
Overview by stage
- Glycolysis (cytosol): glucose is split to form 2 pyruvate, yielding a net 2 ATP and 2 NADH.
- Pyruvate oxidation (mitochondrial matrix): each pyruvate is converted to acetyl-CoA, producing NADH and releasing CO2.
- Citric acid cycle (mitochondrial matrix): acetyl-CoA is oxidized to CO2, yielding NADH, FADH2, and a small amount of ATP (or GTP).
- Oxidative phosphorylation (electron transport chain and chemiosmosis): NADH and FADH2 donate electrons, ATP synthase produces the bulk of ATP; oxygen acts as the terminal electron acceptor, generating water.
Notes on variations
- Aerobic respiration (with oxygen): yields about 30–38 ATP per glucose, depending on cell type and shuttle systems.
- Anaerobic respiration or fermentation (no oxygen): plants, yeast, and some bacteria can regenerate NAD+ to continue glycolysis, producing lactate or ethanol and CO2, with little or no additional ATP beyond glycolysis (2 net ATP per glucose).
If you’d like, I can tailor this to a specific organism or clarify differences between aerobic and anaerobic pathways.
