In the laboratory, yeast cells are usually grown at a temperature of 25oC. A scientist wanted to determine if yeast cells would reproduce faster or slower when the temperature was dropped to 15oC. The same number of yeast cells were placed in the same medium with the same amount of nutrients. One sample was kept at 25oC and the other one was kept at 15oC. The number of yeast cells was counted every hour for an eighteen hour period.

This question is incomplete, however, it is asking to identify the following variables:

Independent variable: Temperature

Dependent variable: Number of yeast cells

Constants: same amount of nutrients, same number of yeast cells, same medium

Explanation:

- Independent variable is the variable that the experimenter changes or manipulates in order to bring about a measurable effect. In this experiment, the TEMPERATURE at which the yeast are kept is the independent variable.

- Dependent variable is the variable that responds to the changes made to the independent variable. It is the variable that is measured by the experimenter in the experiment. In this case, The NUMBER OF YEAST CELLS was counted, hence, it is the dependent variable.

- Constants are variables that are kept unchanged or same for all groups by the experimenter in order not to influence the experiment's outcome. In this case, the CONSTANTS are: same amount of nutrients, same number of yeast cells, same medium etc.

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