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Unformatted text preview: Exercise 1B Scientific Investigation: Experimental Design Applied
th Adapted from Investigating Biology, Morgan & Carter, 6 ed. The shape of an organism depends in part on the relative growth rates of different body parts
during development. The terms allometry and allometric growth are used when describing the
changing relative rates of growth. Specifically, allometry is the phenomenon whereby parts of an
organism grow at different rates, or the disproportionate growth of a part in relation to the entire
organism. This can be observed in humans as seen in Figure 1.2, an illustration of differential
growth rates. Notice in this figure, in which the newborn and adult are scaled to the same height,
that the head is larger in proportion to the body length in a newborn than in an adult.
Allometric growth contrasts with isometric growth when two parts grow at the same rate. This
takes place when proportions between body parts remain constant as the organism grows. You
can imagine this type of growth by taking a photo of the baby in Figure 1.2 and simply enlarging it
as it grows to an adult. For example, if the arms and legs of a human grow isometrically, then their
lengths will be the same relative to the body in a newborn as in an adult. Fig. 1.2
In the following exercise you will collect data to compare ratios of height to selected body parts for
newborns with the same ratios in students (yourselves). This should provide information to
determine if selected body parts grow allometrically or isometrically in humans. In the process you
will practice designing experiments, collecting data, and processing that data. The data for
newborns are given in Table 1.1. These data are taken from Hall
(2007), a handbook of
physical measurements for health professionals.
For this exercise, the two body parts we will be measuring are head circumference and arm
length. Take a few minutes to discuss specific questions that you can ask about growth rates
(allometric, isometric) of head circumference and arm length in relation to height in humans....
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