cell respiration - (Dec/06/2006 )

1. On my book, it says 'The reactions of anaerobic respiration occurs within the general cytoplasm.' But my teacher told us that the respiration occurs in the mitochondria. So i want to know which one is right.
2. The thin, moist walls of the alveoli are composed of a single layer of cells. What does it mean by 'single layer of cells' here?
BTW, what's the function of 'medulla' in respiration?
Thanks for help.

1. Ocurrs in cytoplasm. In aerobic respiration piruvate is transported to mitochondria and converted to acetyl-coA by oxydative decarboxilation. In anaerobic respiration piruvate can't be transported to mitochondria, but is transformed to lactate in cytoplasm.
2. 'single layer of cells' means an epithelium, alveolar epithelium.