Chapter 2. Population Ecology

Learning Objectives

Pre-Lab—Spectrometer
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General Purpose

Conceptual

  • Be able to relate changes in light absorption to changes in solution concentration.

Procedural

  • Be able to use a standard curve to convert absorbance readings to concentration values.

General Background Information

Conducting experiments in biology requires the use of certain specialized equipment and techniques. To perform these techniques and use this equipment accurately and efficiently it is important to understand how the equipment works and to become practiced in the techniques. One of these techniques is spectrometry. The spectrometric techniques you are going to use during this exercise will be used during many of the other laboratory exercises this semester, and you may use them in other courses in the future. These techniques are also used in a wide variety of fields from industry to health care.

Spectrometry

Spectrometers are one of the most widely used laboratory instruments. Before continuing on, please read Appendix A, which describes the basic operation and use of a spectrometer in more detail. Spectrometers are instruments designed to detect the amount of radiant energy absorbed or scattered by the molecules or particles in a solution. When light passes through a medium (e.g., solution) containing an absorbing (or scattering) substance, the decrease in the intensity of the light that is transmitted (or the increase in the intensity of the light absorbed) by the substance is directly proportional to the concentration of absorbing (or scattering) species. In other words, as the concentration of a substance in solution increases, the amount of light absorbed by the solution increases. Furthermore, because the amount of light absorbed is proportional to the concentration of a compound, spectrometry is useful in determining concentrations.

Using wavelengths in the near infrared allows any absorbance by light gathering pigments or proteins of the cell to be avoided. The result is that the absorbance of our “compound” of interest, the unicellular algae Chlamydomonas, is a function of the number of cells in solution. In lab, we will quickly and easily determine the absorbance of this alga and convert it to its population size or concentration, using a standard curve.

Pre-Lab Quiz

Proceed to the Pre-Lab Quiz