In which of the following situations is it most relevant to determine the number of bacterial cells present in a sample?

• A. Classifying bacteria based on their Gram stain reaction
• B. Identifying the shape and arrangement of bacterial cells under a microscope
• C. Studying the genetic sequence of a single bacterial species
• D. Assessing the safety of drinking water by detecting potential contamination

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the context of each option by considering what information is needed for each microbiological task. For example, classifying bacteria by Gram stain focuses on cell wall properties, not cell quantity.
2. Step 2: Recognize that identifying shape and arrangement under a microscope is a qualitative observation, which does not require counting the number of cells but rather observing their morphology.
3. Step 3: Note that studying the genetic sequence of a single bacterial species involves molecular techniques that focus on DNA analysis, not on quantifying cell numbers.
4. Step 4: Consider that assessing the safety of drinking water involves detecting contamination levels, which directly depends on quantifying the number of bacterial cells present to evaluate potential health risks.
5. Step 5: Conclude that determining the number of bacterial cells is most relevant in situations where contamination levels impact safety, such as in drinking water testing, because it helps assess whether bacterial counts exceed safe limits.