One of the fundamental questions about biological cells often asked is what is cellular respiration. To know what is cellular respiration, we have to know how cells operate and what do they do. Cells are the basic building blocks of any biological entity. From the bacteria that have unusual behaviors as a one cell organism to the trees, human beings, all the animals and fish, sea-weed, everything has cells that build up the whole construction. Like bricks in a building, the cells are what make these biological entities what they are. We humans have cells too. Interestingly though, most of our cells have some common properties and that's why, we can easily define them. The main reason of this definition is to differentiate between what physics says about basic building blocks to what biology says. Both are correct but here is the thing, biology deal with living beings where as physics has pretty much nothing to do with life. So the definition of building block for physics and biology is not the same.

A cell in biology means the smallest unit that performs the basic biological functions. One of these functions is respiration, breathing, in and out. But the term breathing can be applied to only larger beings, not to cells. In cellular terms, respiration is what keeps them alive. Cellular respiration means the way cells get energy from the nutrients in them. The way cells do this is by taking in oxygen inside them and then ‘burning' the food in a metabolic process. This process involves breaking the food i.e. the glucose into smaller molecules. After the breaking down of food in cytoplasm, mitochondria or the energy house of cells uses oxygen in a reaction where water, carbon dioxide and energy is the product. The energy stays in chemical energy form but now in molecules and can be used readily by the cell in order to perform its purpose.