Why are water samples diluted before counting the bacteria in a laboratory setting?

• A. To eliminate all bacteria from the sample.
• B. To increase the growth rate of bacteria in the sample.
• C. To change the pH of the water sample.
• D. To reduce the concentration of bacteria to a countable level.

Answer: (D)

Verified step by step guidance

1. Understand the purpose of dilution: In microbiology, diluting a sample is a common practice to reduce the concentration of bacteria to a manageable level for counting.
2. Recognize the problem with high concentrations: When bacteria are too concentrated, it becomes difficult to distinguish individual colonies, making accurate counting impossible.
3. Learn about serial dilution: This is a stepwise dilution of a substance in solution, often used to achieve a desired concentration that is easier to work with.
4. Consider the practical aspect: By diluting the sample, you ensure that the bacteria are spread out enough to form distinct colonies on a petri dish, which can then be counted accurately.
5. Conclude with the correct reason: The primary reason for diluting water samples in a lab setting is to reduce the concentration of bacteria to a countable level, not to eliminate bacteria, increase growth rate, or change pH.