Chemical and Physical Changes in Digestion

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Food that enters the digestive system undergoes chemical and physical changes as it makes its way down.

Can you swallow an entire hamburger at one time? Probablynot. It is far too big to fit into your mouth and down your esaphagus. Luckily for you, you have many structures that help to break the food down from a large thing into many smaller parts. This is called the digestive system. The first part of the digestive system is your mouth. Here your teeth work to break the large bites of food into smaller, more manageable pieces. This physical change is the beginning of mechanical digestion. Anything that involves movement is mechanical. While in the mouth chemical digestion also begins. The saliva it produces helps to soften the food and make it easier to swallow. Your mouth also makes an enzyme that breaks down starch. This sort of breaking down is a chemical change. Mechanical digestion continues as you swallow and the chewed-up food gets pushed down the esophagus into the stomach. Here, as in the mouth, both mechanical and chemical digestion take place. The muscles of the stomach

churn and grind the food, while other enzymes and acids produced by the stomach chemically break it down. Between these two events, the large food particles are broken into much smaller ones with a simpler chemical makeup. From the stomach, mechanical digestion pushes what is left of the food into the small intestine. It is here that most of the chemical digestion and chemical changes take place. Many enzymes are released into the small intestine that break down sugars, fats, and proteins that were stored within the food you ate. These nutrients get absorbed through the wall of the small intestine into the blood stream so they can be transported around the body. After the nutrients have been taken out of what’s left of the food in the small intestine, what is left gets pushed into the large intestine. Here, water is reabsorbed and the waste is compacted. This is another physical change. It continues down the large intestine until, finally, it is time to remove it from the body.

Discovery Education Science © Discovery Communications, LLC

Chemical and Physical Changes in Digestion

Comprehension Questions 1. What is the difference between mechanical and chemical digestion? 2. Where does most of the chemical digestion take place? What causes it to happen?