Final answer:
Glycolysis, the first stage of cellular respiration, does not require oxygen and can proceed anaerobically, leading to anaerobic respiration or fermentation when oxygen is not available.
Step-by-step explanation:
Unlike aerobic respiration, glycolysis does not require any oxygen.
Summary of Glycolysis and its Relation to Oxygen
The first stage of cellular respiration, known as glycolysis, takes place in the cytosol of the cytoplasm and does not require oxygen to proceed. In contrast, the later stages of cellular respiration, such as the Krebs cycle and the electron transport chain, do occur in the mitochondria and require oxygen to produce ATP efficiently. When oxygen is not available, cells can still produce ATP through anaerobic pathways, namely fermentation, which involves regenerating NAD+ from NADH to allow glycolysis to continue. The two main types of fermentation are alcoholic fermentation and lactic acid fermentation. For example, during vigorous exercise when oxygen is scarce, human muscle cells engage in lactic acid fermentation, leading to the temporary build-up of lactate.