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SKILL: USING GRIDS TO ESTIMATE
Chloroplast Math
MATH TUTORIAL
CLASSZONE.COM
Click on Math Tutorial for
more help with perimeter
and area.
You can’t count the number of chloroplasts in a leaf very easily,
but you can estimate the number. For example, if you know the
number of chloroplasts in a small area, you can estimate the
number of chloroplasts in a whole leaf.
Example
Suppose you are studying how lilacs make food from sunlight. You
read that there are 50 million chloroplasts for every square centimeter of a leaf. You want to know the number in a whole leaf.
(1) Cover the leaf with centimeter grid paper.
(2) Count the number of whole
squares covering
the leaf.
7
1 cm
(3) Match pairs or sets of
partly covered squares, that
add up to a whole square.
7 5 12
1 cm
(4) Add on any remaining 0.5 (half), 0.025 (quarter), or 0.75
(three-quarters) of a square.
12 .5 12.5
(5) Finally, multiply the number of squares by the number of
chloroplasts in one square.
ANSWER 50,000,000 12.5 625,000,000.
Give estimates for the following amounts.
1. Trace the beech leaf shown on this
page onto a sheet of centimeter
grid paper. What is the leaf’s
approximate area in cm2?
2. About how many chloroplasts are
in this beech leaf?
3. A eucalyptus leaf is long and thin. Suppose a healthy leaf is
1.5 centimeters wide and 6 centimeters long. Estimate its area.
Hint: Make a sketch.
4. What is the approximate number of chloroplasts in the
eucalyptus leaf described above?
CHALLENGE Collect two leaves. Trace the leaves on
centimeter grid paper. Label each tracing with its name,
estimated area, and its approximate number of chloroplasts.
Chapter 3: Plants 115