A Microbial Ecologist Is Interested in Whether the Microbial Community

question 32

Multiple Choice

A microbial ecologist is interested in whether the microbial community of a pond changes when it rains. She knows that rainfall will increase the number of bacteria, but she is interested in the pattern of diversity. She collects a water sample from a pond two days before a rainfall and two days after and plates her samples on agar (a method to measure bacteria) and counts the number of colonies she observes for each of three bacteria: E. Coli, Salmonella, and Giardia. In the pre-rain sample she observes 21, 57, and 32 colonies respectively. In the post-rain sample she observes 59, 83, and 88 colonies respectively.
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-To determine whether there appears to be a statistically significant relationship between rainfall and bacterial diversity she would conduct a χ² analysis. When performing this analysis, which of the values below is closest to the number of degrees of freedom she would use?

• A) 1
• B) 2
• C) 3
• D) 4

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