The breakdown processes must act on food taken in from outside.
Stage 1 in the enzymatic breakdown of food molecules is therefore digestion, which occurs either in our intestine outside cells, or in a specialized organelle within cells, the lysosome.
Stage 2 starts in the cytosol and ends in the major energy-converting organelle, the mitochondrion.
Stage 3 is entirely confined to the mitochondrion.
Hope this helps!
