Assignment 2: Chapter 3 Questions

1. How big are bacteria?

Bacteria are between 1 and 10 micrometers in size.

2. How does the size of bacteria compare to the size of viruses?

Viruses are between 10 and 100 nanometers in size. This means that bacteria are roughly 300 times larger than viruses.

3. What is the difference between a simple stain and a differential stain? Which type is gram staining?

A simple stain is the use of a single dye to reveal basic cell shapes and arrangements. A differential stain in the use of two or more stains to distinguish between different types of cells or organisms or to differentiate between different parts of an organism.

4. Why do Gram-positive bacteria retain the purple stain?

The Gram-positive bacteria retain their purple stain because of the thick cells walls, which is due to large amounts of peptidoglycan.

5. What are the differences between gram positive and gram negative bacteria that cause them to stain differently?

The thickness of the cell walls is a large difference between the Gram positive and Gram negative bacteria.

6. What is the difference between Gram-variable and Gram-nonreactive cells?

Gram-variable cells are a mix of purple and pink cells which could be from the broken cells from an old sample (dyes both negative and positive). Gram-nonreactive do not stain because they do not have a cell wall.

7. What can you determine about a cell using the Ziehl-Neelsen Acid Fast Stain?

The Ziehl-Neelsen Acid Fast Stain is used on organisms that are not decolorized by acids in alcohol. A positive result is red, and negative is blue.

8. Compare and contrast negative staining with endospore staining.

Negative staining is the dyeing of the background around the organism, leaving the organism itself clear so that it stands out from the background. Endospore staining is where you are trying to visualize the spores on a bacteria. Both of these samples are difficult to stain and they both need heat in order to accept the stain.