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HUMAN ANATOMY & PHYSIOLOGY 1 (101 - 805)

LABORATORY EXERCISE 5

CELLS AND TISSUES OF THE BODY: INTRODUCTION TO HISTOLOGY

PART 1 PREPARATION OF HUMAN CHEEK CELLS

Page 4     To see answers for Figure 1 click here: Figure 1. - p.4

1. Which feature of the cheek cells stains most prominently with methylene blue? the nucleus
2. Which structures in your cheek cells are above the limit of resolution of the light microscope?
All visible structures i.e. nucleus: nucleolus, cytoplasm; cell boundary; large cytoplasmic organelles such as mitochondria (but not possible to identify details of mitochondria with the light microscope), bacteria (on surface of cells).

Note: The Limit of Resolution is the smallest size (or distance between 2 points) that can be distinguished. Above this limit the 2 points can be distinguished.Below this limit the 2 points  cannot be distinguished and appear as one.

Click to enlarge image
3. Which structures in your cheek cells are below the limit of resolution of the light microscope?
Any structures which cannot be seen. These include many small cytoplasmic organelles (e.g. ribosomes, cell membrane, lysosomes). For this reason the term "cell boundary" is used rather than the label "cell membrane" since the cell membrane is within the cell boundary but cannot be resolved.
4.    Estimate the size of a cheek epithelial cell:

Internet sources give cheek cell sizes of 50 -80 micrometers.

In one of our lab cheek smears the cell size is about 80 micrometers (see explanation on right). Click to enlarge image.

This is a high power view of a student's cheek smear.

From the microscope lab the HP field diameter is 400 micrometers.

Here we see that about 5 cells could fit across the diameter.

Therefore each cell is about 400/5 = 80 micrometers.

Extra Questions

"Why was the wicking procedure used?"

Wicking draws stain through a tissue on a slide instead of dropping the stain directly on the tissue. Wicking is used to produce the optimum amount of staining; in our case a good result consisted of lightly blue stained cells on a white background.

 Why was methylene blue used? 

Human cells have little colour and so resolution and contrast would be low without the use of stains. Methylene blue stains the cell and its organelles differentially so that the cell is more clearly seen and some organelles stand out more than others, e.g. the nucleus.