Digestion & Enzymes
Describe the organs of the human digestive system and how food is physically and chemically digested, including the role of enzymes as biological catalysts
What a learner can do afterwards
- Traces the journey of food from mouth to large intestine, naming each organ and its role
- Explains what enzymes do and names where they are produced (salivary glands, stomach, small intestine)
- Distinguishes physical digestion (chewing, churning) from chemical digestion
The lesson
You already know the main stops food makes on its way through your body. Now look closer at how food actually gets broken down. Digestion happens in two ways: physical digestion, which breaks food into smaller pieces, and chemical digestion, which breaks food's molecules apart using enzymes.
Enzymes are proteins that speed up chemical reactions. In digestion, enzymes break big food molecules into small ones your body can absorb. Salivary glands make an enzyme that starts breaking down starch. The stomach makes an enzyme that breaks down protein. The small intestine makes and receives enzymes that finish the job on starches, proteins, and fats.
When you chew a piece of bread, your teeth physically tear it into smaller bits. At the same time, an enzyme in your saliva called amylase starts breaking the starch in the bread into sugar molecules. Physical and chemical digestion happen at the same time, in the same bite.
Ask yourself: is the food's size changing, or is its molecules changing? Chewing and churning change size and shape, so they are physical. Enzymes changing food into new smaller molecules is chemical.
Physical digestion breaks food into smaller pieces; chemical digestion, powered by enzymes made along the way, breaks it down into molecules your body can absorb.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.