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Observation and Classification Lab Class Set – PLEASE RETURN!

Purpose: To classify various cells according to their observed characteristics, and compare that to their classification into biological categories(kingdoms or domains). Materials: microscope, slide & cover slip, methylene blue stain, toothpick, 4 virtual slides of unknown cells on teacher’s web site, “Categories of Life” table and Appendix A. Predict: You will observe 5 specimens representing different categories of organisms. Before you begin observing answer the two questions below. 1. How might you expect these specimens to be different? 2. How might they be similar? Procedure: Work in groups of two. One member will prepare a sample of cheek epithelial cells.

1. Place a small drop of water on a clean slide. See figure 1. 2. Using the end of the toothpick, gently scrape the inside of your cheek. 3. Transfer your cheek cells to the slide by swirling the toothpick in the drop of water then

add a small drop of methylene blue to the specimen on the slide. 4. Cover the drop with a cover slip and view under the microscope using the low power

(40X), and adjust using the course focus knob. Find a single cell that is flat, not folded over, by moving the slide around on the stage while looking for the best example cell.

5. Keeping the specimen in the center of the field, move the objective lens to medium power (100X), focus and then move the high power objective into place (400X).

6. Record characteristics of the specimen in Table 1, such as color, shape, relative size, etc., on the student response sheet, including any intracellular structures that you can identify (see figure 2). Put any other notable observation under the column headed “Other.”

7. Draw the specimen observed in the field of view circles provided with specimen name. • For each specimen that you draw do not fill in the entire circle with cells. Just draw a

maximum of three cells for each circle. • The three cells (per circle) must be clear drawings. Take your time and draw what you see.

Cartoons WILL NOT receive full credit. • All drawings must be the size that you see them in the Field of View. Do not draw them

larger or smaller than they appear! All drawings should include the following information: A. The magnification used while drawing the cell (e.g., 400X). You will see more detail at higher power. B. Label the major cellular structures such as nucleus, cell membrane, etc. 8. Repeat step 7 using any four cell specimens of your choice from my web site. Record the specimen # in Table 1, and on the field o’view circle. 9. Compare the characteristics of the various cells and classify them into their appropriate Domains and Kingdoms. Put your answer on Table 1 of your response sheet. Refer to the information on the “Categories of Life” table and Appendix A.

Figure 1. Wet mount slide preparation

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Questions:

1. Which of the cells would you classify together because of similarities? Why? 2. Which of the cells would you classify separately because of their differences? Why? 3. How can you tell if the sizes of the cells are different?

Hypothesize: Using your observations, generate hypotheses regarding the biological category to which each of the five cells belongs. Several may belong to the same kingdom, while some kingdoms may not be represented. Record your proposed kingdoms in Table 1. Be ready to defend your hypotheses based on your observations.

Figure 2. Typical Eukaryotic Cell

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Appendix  A  The  Domains  and  Kingdoms  of  Life  

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