DIRECTIONS: A sandwich cannot cross a membrane, but its pieces can. Read, then answer.
Mechanical breaking makes pieces smaller; the substance stays
the same. Chemical breaking uses enzymes to take the molecules apart, making a new substance.
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What is happening
Mechanical or chemical?
How do you know?
1.
saliva turning a mouthful of bread faintly sweet as you chew
2.
chewing that mouthful of bread
3.
the stomach churning food into a paste
4.
stomach acid and enzymes taking proteins apart
5.
bile breaking a blob of fat into thousands of droplets
What Chewing Is Actually For
Grade 7 · Building a body · Page 2 of 3
DIRECTIONS: Chewing changes no molecule at all. So what is it for?
Enzymes work only on surface they can reach. Cut one lump into eight and there is twice the
surface.
Explain why swallowing food in large lumps makes digestion slower, even though the stomach acid is exactly as strong either way.
Bile is not an enzyme and breaks nothing down chemically. Say what it does and why it makes the fat enzymes far more effective.
A cow chews, swallows, brings the food back up and chews it again. Using this page, say what that is buying — and why an animal eating grass needs it more than you do.
Still Outside You
Grade 7 · Building a body · Page 3 of 3
DIRECTIONS: Your gut is a tube open at both ends: food inside it is not in your body yet.
Food gets in by crossing the small intestine's wall: twenty feet
long, with folds on folds, and many times the area of your skin.
Explain the claim in the directions: in what sense is a swallowed marble never inside your body?
The small intestine is long AND folded AND fringed — three ways of doing one thing. Name the thing, and say why one of the three would not have been enough.
science-06-human-body sheet 10 says what food is FOR. This sheet says how it gets in. In a sentence each, say what question the two sheets are answering.