1. Why is it important to use fresh bacterial cells when performing a Gram stain?

• A. Fresh cells contain more DNA, which is necessary for the Gram stain to work.
• B. Using fresh cells prevents contamination from environmental microbes.
• C. Gram stain reagents only react with newly synthesized proteins in fresh cells.
• D. Older cells may have damaged cell walls, leading to inaccurate Gram reaction results.

Answer: (D)

Verified step by step guidance

1. Understand the principle behind the Gram stain: it differentiates bacteria based on the structure of their cell walls, specifically the thickness of the peptidoglycan layer.
2. Recognize that fresh bacterial cells have intact and well-preserved cell walls, which are essential for the crystal violet-iodine complex to be retained during the staining process.
3. Consider that older bacterial cells may undergo cell wall degradation or damage, which can cause the crystal violet-iodine complex to leak out, resulting in an inaccurate Gram reaction (e.g., Gram-positive cells appearing Gram-negative).
4. Note that the Gram stain does not depend on DNA content or newly synthesized proteins, but rather on the physical and chemical integrity of the cell wall.
5. Conclude that using fresh bacterial cells ensures reliable and accurate Gram stain results by maintaining the structural integrity necessary for proper staining.