What's the independent variable? What's the dependent variable? How many bacteria were found at 30 degrees? How many bacteria were found at 15 degrees? How many more bacteria were found at 20 degrees than 10 degrees? How many more bacteria were found at 35 degrees than 0 degrees?

Temperature is the independent variable. The number of bacteria is the dependent variable.

Explanation:

The dependent and independent variables are the two main variables of any experiment or research.

A dependent variable is one whose values depend on another variable. In a function it is usually represented by 'y'. This variable 'y' is a function of the variable 'x', which is the independent variable. An independent variable is one whose value does not depend on that of another variable.

So, the independent variable is the one that changes or is controlled to study its effects on the dependent variable. The dependent is the variable that is investigated and measured.

The independent variable is represented on the x-axis (horizontal line) of a graph, while the dependent variable is represented on the y-axis (vertical line).

In your example, the temperature is the independent variable, because it does not depend on anything and its influence can affect the number of bacteria. And it can be changed or controlled by the scientists. The number of bacteria is the dependent variable, because it depends on the temperature. Also, the number of bacteria is what it is being measured, and can not be changed by the scientists.