Blog Assignment 2: Chapter 3 Practice Questions

Staining Practice Questions

1. How big are bacteria?
Bacteria is between 1-25 micrometers.

2. How does the size of bacteria compare to the size of viruses?
Viruses are smaller than bacteria.

3. What is the difference between a simple stain and a differential stain? Which type is gram staining?
Simple stains use one dye and show basic cell shapes and arrangements while differential stains use two or more dyes and can show various properties of cell like its type including the different parts in variety of color.

4. Why do Gram-positive bacteria retain the purple stain?
Gram-positive bacteria has thick cell wall containing a thick layer of peptidoglycan that traps in more of the purple dye and prevents it from flowing out.

5. What are the differences between gram positive and gram negative bacteria that cause them to stain differently?
The differences of Gram-positive and Gram-negative bacteria:
a) The thickness of the cell walls of the two bacteria differs from each other. Gram-positive bacteria have thicker wall and thick layer of peptidoglycan comprising 60-90% of the cell wall. Gram-negative bacteria have thinner cell wall and only 10-20% of it contains peptidoglycan.
b) The presence of an outer cell membrane for Gram-negative bacteria which dissolves when the purple stain is washed with alcohol or a decolorizing agent during gram staining procedure. This is another difference between the two bacteria.
c) The presence of periplasmic space for Gram-negative bacteria where cell metabolism and transport functions occurs is another difference. Periplasmic spaces on Gram-positive are rarely observed.

6. What is the difference between Gram-variable and Gram-nonreactive cells?
Gram-variable cells are really positive but the ones that have broken cell walls are stained negative. Therefore the stained results show mixed colors. Whereas Gram-nonreactive cells have no cell wall resulting to poorly stained-cell or not stained at all.

7. What can you determine about a cell using the Ziehl-Neelsen Acid Fast Stain?
The stain using the Ziehl-Neelsen Acid Fast Stain produces vivid red color in acid-fast organism and those that are not can be stained blue.

8. Compare and contrast negative staining with endospore staining.
Both staining procedures show resistance to stain. So to be able to take the stain, these substances should be heated. The difference between them is that negative staining is used for capsules while endospore staining is for spores.