SKILL: CHOOSING UNITS OF LENGTH
Internal Measurement
It wouldn’t be useful if someone told you the length of
your tongue in meters, or the length of a tooth in
centimeters. To be meaningful, these measurements
must be given in appropriate units.
Example
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measuring length.
Your esophagus is about the length of your forearm.
Choose the appropriate units to measure its length.
Would meters, centimeters, or millimeters be most
appropriate?
(1) Look at your arm from your wrist to your elbow.
It is about the same as a rolling pin. You don’t
need to measure your forearm to see that a meter
would be too large a unit. One meter is about the
height of a lab table.
(2) Look at the ruler in the picture. Compare your arm
to the centimeters shown and the millimeters.
(3) You can measure your arm with either unit, but if
you wiggle a bit, the count of millimeters is
thrown off.
ANSWER Centimeters are the most appropriate units.
Answer the following questions.
1. If you uncoiled a human intestine, its length would
be about equal to that of 2 cars parked end to
end. What would be appropriate units to use to
measure that?
2. What units would you use to measure the length
of your tongue? The length of a tooth?
3. The large intestine is actually shorter than the
small intestine. The small intestine is about the
length of a small bus, and the large is about as
long as a car’s back seat. Tell the units you would
choose for each. Explain why.
CHALLENGE Your stomach when empty is about
the size of your clenched fist. To measure its volume (the space it takes up), what units would
you use?
The ruler shows 20 centimeters (cm).
There are 10 millimeters (mm) in
each centimeter.
1 cm
Chapter 17: Absorption, Digestion, and Exchange 613