STUDENT INVESTIGATION 3.1

Background

In research, it is often desirable to draw conclusions about the scientific results obtained from different populations. A population is a group of individuals related by some factor that sets them apart from another group. The population could be related by the fact that they are all humans (as opposed to, for instance, dogs), or that they are all men, or that they are all humans between the ages of 30 and 40 years old. Researchers carry out studies to determine the average behavior of a given population in the area of interest. Here, we will look at hematocrit values and try to guess what population those values were obtained from.

In the Introduction section to this (Dr. Alfrey's) experiment, we learned that the hematocrit is a determination of the percentage of RBCs per unit of blood volume; that is, a hematocrit value of 47 (which is an average value for men) suggests that 47% of the entire blood volume consists of RBCs. The hematocrit value varies between different populations, and hematocrit values can change according to the state of health of an individual, the oxygen availability, or because of heavy bleeding, when many blood cells can be lost. Review the Introduction section along with Figure 2 before proceeding with this exercise.

Procedure

1. Each student should complete this exercise independently.
2. Observe the test tubes illustrated in Figure 5. Imagine that these represent blood samples of five different subjects. Imagine further that these test tubes have been centrifuged and the components of blood have separated to enable us to make a deter mination of the hematocrit level.
3. Use the scale on the left side of the test tubes and write down the hematocrit values on a separate sheet of paper.
4. When all of the hematocrit values have been determined, answer the questions at the end of this exercise. Review your results with the whole class.

Figure 5. The test tubes contain blood samples collected from five different individuals. Each test tube has been spun in a centrifuge to separate the blood components.

Questions

1. Which blood sample was probably taken from a female?
On what information do you base your decision?
2. Which blood sample was probably taken from an anemic person? On what information did your base your decision?
3. Which blood sample was probably taken from a person who smokes? (Hint: Smoking produces carbon monoxide in the body and it enters the bloodstream. Carbon monoxide has 200 times the affinity (attraction) for hemoglobin than does oxygen and won't readily "let go" of the hemoglobin available to carry oxygen. How would this affect the body's RBC production?)
4. Which blood sample was probably taken from a person who lives at high altitude? On what information did you base your decision?
5. Which blood sample was probably taken from a male astronaut in space? On what information did you base your decision?