Q1.
What did you observe?
Answer
You see polygon-shaped structures spread out on the slide, as shown in Fig. 2.4. These are cheek cells — they form the inner lining of your mouth.
In each cell you can make out three things:
- a thin outer boundary — the cell membrane;
- a round, deeply stained body near the middle — the nucleus;
- the space between the two, filled with cytoplasm.
Why the stain is needed: a cheek cell is almost colourless, so against a bright background its outline is nearly invisible. Adding a drop of methylene blue increases the contrast — the nucleus takes up the most stain and shows up darkest, so the parts of the cell separate out clearly under the microscope. The drop of glycerin added afterwards stops the cells from drying while you look at them.
Check it yourself: unlike the onion peel, cheek cells often lie scattered or overlapping rather than in neat rows. That is because you scraped them loose from a lining — in the mouth itself they lie side by side like tiles.