This is Steve. Today, with the help of Steve, we will gain an understanding of how cellular respiration works. He is feeling hungry and decides to have a sandwich for lunch. Let's see what happens!
When Steve starts to chew, he breaks the sandwich into smaller pieces. With the help of the enzyme amylase, the carbohydrates of the sandwich are also broken down so they can be absorbed faster. The sandwich does down his esophagus into his stomach.
The partially broken down sandwich enters the stomach and is further broken down into molecules of energy. It is passed onto the small intestine. Steven is breathing while chewing because breaking down food uses oxygen, and carbon dioxide is the waste product. It is expelled every time Steve breathes out.
Steve is feeling tired after that big meal and decides to sit down for a while. During this time, the sandwich is being digested and nutrients are being extracted in the small intestine by the villi. While Steve is resting, his body is breathing out carbon dioxide and storing energy to use for later.
After Steve wakes up from his nap, he decides that he needs to use the toilet. He urinates and does a number 2. At this stage, the sandwich has passed through his digestive system and water (in his feces and urine) is excreted from his body.
Steve is using up his energy from his sandwich to walk on the treadmill. He is sweating profusely. His sweat is also a product of cellular respiration. After this, he goes home and has dinner, and the whole cycle starts again.