A Microbial Ecologist Is Interested in Whether the Microbial Community

question 9

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.
​

-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 contribution to the χ² statistic from the "pre-rainfall : Salmonella" category?

• A) 1.01
• B) 2.02
• C) 3.03
• D) 4.04

---

Definitions:

Total Profit

The net income a business earns after subtracting all costs, expenses, and taxes from the total revenue.

Per Unit Profit

The profit earned from selling one unit of a product, calculated by subtracting the cost per unit from the selling price per unit.

MR = MC Rule

A principle in economics where the optimal level of output is reached when marginal revenue equals marginal cost.

Price Taker

An individual or company that must accept prevailing prices in the market of its products or services, lacking the market power to influence prices on its own.