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1bScientificInvestigation

1bScientificInvestigation - Exercise 1B Scientific...

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Biology 6C 11 Exercise 1B Scientific Investigation: Experimental Design Applied Adapted from Investigating Biology, Morgan & Carter, 6 th 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. 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. Fig. 1.2
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12 Exercise 1.B. Scientific Investigation: Experimental Design Applied Record your two questions below: Hypothesis Record a hypothesis for each of your questions: The Experiment In this experiment you will compare the ratios of height to head circumference and arm length in newborns and yourselves. Work in your group to discuss experimental design and complete the questions below. What is the dependent variable in your experiments? What is the independent variable? What are some controlled variables? Body Part Description of Measurement Size (cm) Length/Height From sole of foot to top of head Head circumference Head at largest diameter Upper limb (total arm) From shoulder joint to tip of middle finger Hand length From wrist to tip of middle finger Span Between fingertips of middle finger with arms outstretched Lower limb (total leg) From sole of foot to joint where leg meets hip laterally Crown-rump length In seated position, from top of head to surface of a
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