Procedure
Part A - Human Cheek Epithelium

A view of three human cheek epithelial cells and many tiny bacteria under a compound light microscope observed at 40X magnification. The cells are stained with methylene blue with arrows pointing to parts of you observe. The alphabetically labeled parts to which the arrows points are: A. inside of one of the cells, B. the darkly stained structure at the center of one of the cells, C. Small structures in the body of one of the cells, D. dark structure inside the nucleus, E. outermost lining of one of the cell, F. many tiny structures outside of the epithelial cells.

• View the image of a human cheek epithelial cell in Figure 3.1.
• In lab this is what you would see under the microscope after staining the cells taken from inside your own mouth.
• The cells on this slide have been stained with methylene blue to make them easier to see.
• These cells are being viewed with the high power objective (40X) lens.
• The 3 large cheek cells are covered in many tiny bacterial cells.
• Recall in lab 2 we saw bacterial cells with a total magnification of 1000x. These have a total magnification of 400x. That is why the bacteria appear as only tiny specks on the outside of the larger cheek cells.
• Use Figure 3.1 to answer questions in Part A of the Lab Report

Part B - Comparison of Human & Frog Blood

• Watch the video to see the differences between human and frog blood cells.

Click here to watch Human & Frog Blood VideoFigure 3.2 shows a comparison of differences in human and frog blood. Identify the cells on the tip of the arrow marked with letters in frog and the human blood smears respectively. The cells marked in frog blood cells are A-oval red nucleated cells, B-round fully stained cells. In the human blood smear, the cells marked are, C-red, round anucleated cell, D- bigger, stained, multilobed nucleated cells.

• Use Figure 3.2 to answer questions in Part B in Lab 3 Lab Report.

Part C - Elodea & Plasmolysis

• Watch the videos to understand the process of plasmolysis.
• This is a plant cell so notice the rigid cell wall and many chloroplasts.

Click here to watch Plasmolysis videoFigure 3.3 shows a magnified Elodea cells before and after the addition of salt water. In the before image, labeled 0 minutes. A is pointing to the structure immediately surrounding the cell. B is pointing to the rigid outer structure surrounding the cell. C is pointing to one of the small green spheres inside the cell. In the after image, labeled 5 minutes. D is pointing to the structure immediately surrounding the cell. This structure has pulled away from the outer structure. E is pointing to the rigid outer structure surrounding the cell. This structure has not changed shape. F is pointing to one of the small green spheres inside the cell. The many green spheres now seem to be clumped together.

• Use Figure 3.3 to answer questions in Part C in Lab 3 Lab Report

Part D - The Cell Cycle & Mitosis

Click on each button below to watch the videos to understand the Cycle Cycle & phases of mitosis.

First Cell Cycle VideoSecond Cell Cycle VideoThird Cell Cycle Video

• After watching these 3 videos you should have a good visual idea of how to distinguish the cells in different parts of the cell cycle. If you do not watch the videos you will struggle with this part of the lab.
• Use Figure 3.4 to answer questions 20-24 in Part D in Lab 3 Lab Report.

Onion (Allium) root tip cells showing the nucleus and chromosomes in different phases of the cell cycle. Using this Fig 3.4, identify the cells tagged as A-E with arrows and answer questions 20-24 in Part D in Lab 3 Lab Report. The tagged cells appear as: A- chromosomes at opposite poles with cell plate visible between daughter cells, B- the sister chromatids separate and now on opposite poles of the cell, C- the cells have an intact nuclear membrane and there are no visible condensed chromosomes. Most of the cells in the image look like this, D-the nuclear envelope is disappearing and chromosomes seem to appear as they begin to condense, E-the fully condensed chromosomes in these cells are align at the center of the cell.  Using Fig 3.5, identify and distinguish the 40 dividing onion root tip cells in different stages of the cell cycle. The cells upon observation appear as: 31 of them with an intact nuclear membrane with chromatids inside, 6 cells with visible chromosomes and lack a nuclear envelope, 1 cell with sister chromatids aligned at the equator, 1 cell with sister chromatids separated and moving towards the opposite pole, and 1 cell with chromosomes in opposite poles with developing cell plate between them.

• Now that you are sure you can distinguish cells in different stages of the cell cycle see how many cells in this image are in each stage of the cell cycle.
• Use Figure 3.5 to answer questions 25 - 29 in Part D in Lab 3 Lab Report.
• NOTE - you may not see every phase. If you do not see a cell in a certain phase record the number as "0".
• NOTE- There are 40 cells in this image. Make sure you identify the phase that each of these cells is in!

• Now combine YOUR data (the answers to questions 20-24) with data collected from other lab groups and listed in Table 3.1.
• You will need to add your data (Location 1) with the data from those listed for Locations 2-4 to get the total number of cells in each phase of the cell cycle/mitosis.
• Answer questions 30 - 34 in Part D in Lab 3 Lab Report.

The table compiles your observations (Location 1) of the cell cycle phases (answers to questions 25-29) with different groups (Location 2-4). Using the numbers obtained by other groups, calculate the total and answer questions 30-34 in Part D in Lab Report. Add your data for how many cells were in interphase to the data from Location 2 = 24, Location 3 = 20 and Location 4 = 16 to obtain the total number of cells in interphase. Add your data for how many cells were in prophase to the data from Location 2 = 16, Location 3 = 15 and Location 4 = 10 to obtain the total number of cells in prophase. Add your data for how many cells were in metaphase to the data from Location 2 = 8, Location 3 = 9 and Location 4 = 10 to obtain the total number of cells in metaphase. Add your data for how many cells were in anaphase to the data from Location 2 = 1, Location 3 = 1 and Location 4 = 3 to obtain the total number of cells in anaphase. Add your data for how many cells were telophase to the data from Location 2 = 2, Location 3 = 1 and Location 4 = 3 to obtain the total number of cells in telophase.

• Use the TOTALS obtained in the above table to answer questions 35 - 39 in Part D in your Lab 3 Lab Report.
• NOTE- If you look up the answer online you may get it incorrect. We are basing the answers to these questions on the data in Table 3.1 only!
• NOTE - Interphase is NOT a phase of mitosis. It is the phase between mitotic divisions.

Non-majors College Biology Lab Manual © 2021 by Marie McGovern Ph.D. is licensed under CC BY-NC 4.0