That's right.....we talked about making the food, now we focus on breaking that food down to release the energy that was stored.
Cellular respiration is the process by which food molecules are broken down (i.e. their bonds are snapped) to release energy.
All cells need energy; therefore all cells have to process food to release that energy. We tend to assume that this process happens solely in the mitochondria, but that isn't the case. Otherwise organisms that lack mitochondria wouldn't be able to process food and release energy. The first step happens in the cytoplasm without the presence of oxygen. The first step (glycolysis) happening outside the mitochondria doesn't make a lot of ATP, but it does allow bacteria to process their food.
The next 2 steps (citric acid cycle and the electron transport chain) happen in the presence of oxygen within the double membrane of the mitochondria.
In comparison with photosynthesis, the input of cellular respiration is the output of photosynthesis. What this means is instead of taking in carbon dioxide and water, cellular respiration minimally needs a carbon compound (namely sugars and lipids) to start the process of releasing energy.
The first time sugar is split in the cytoplasm no oxygen is required. The lack of oxygen is known as anaerobic respiration.
Aerobic respiration occurs when an organism further breaks down the split sugar within a mitochondria.
Aerobic respiration only releases 2 ATP while aerobic respiration can release 36-38 ATP per the same glucose molecule.
Here is a picture to review the structure of the mitochondria! Enjoy!
May the ATP with you!