Enzymes
You can easily taste how your enzymes work breaking down your food into smaller pieces. Do this experiment right after lunch, when you'll have a lot of enzymes in your saliva. Get a slice of plain bread (a starch) and chew it slowly. Keep chewing for a long time, but don't swallow the bread. What happens to it? (Once you think you know, you can swallow it or spit it out.)
After a while, the bread should begin to taste sweet. The digestive enzymes in your spit will gradually digest the starch in the bread and turn it into smaller sugar (glucose) molecules, that will be easier for your cells to get through the cell membranes to turn into energy. That's why starchy things like bread and noodles and rice and potatoes, and sweet things like chocolate bars, are both carbohydrates - they're both made mainly of carbon and hydrogen atoms, and if you break apart a starch molecule, it turns into sugar molecules.
If you've ever vomited up food, you know what the enzymes in your stomach do - that's the difference between food you chewed up and food that your stomach enzymes have partly digested.
Main page about enzymes
To find out more about cells, check out these books from Amazon.com or from your library:
