Question

1. bacteria are grown in a petri dish. one side of the dish is sprayed with an antibiotic. after a week, the number of bacteria colonies are counted on each side.

Explanation:

Identify the independent variable

Using the Independent Variable knowledge point

• The independent variable is the factor deliberately changed or manipulated by the experimenter.
• In this setup, the presence or absence of the antibiotic (sprayed on one side of the petri dish but not the other) is the manipulated factor.
• Therefore, the independent variable is the application of the antibiotic.

Identify the dependent variable

Using the Dependent Variable knowledge point

• The dependent variable is the factor being measured or observed in response to the independent variable.
• In this setup, the experimenter counts the number of bacteria colonies on each side after one week.
• Therefore, the dependent variable is the number of bacteria colonies.

Identify the controlled variables

Using the Controlled Variables knowledge point

• Controlled variables are factors kept constant to ensure a fair test.
• These include the type of bacteria, the agar medium in the petri dish, the temperature, and the incubation time (one week).

Answer:

Based on the experimental setup described:

• Independent Variable: The presence or absence of the antibiotic (whether a side of the dish is sprayed with the antibiotic).
• Dependent Variable: The number of bacteria colonies counted on each side.
• Controlled Variables: The type of bacteria, the growth medium (agar), the incubation temperature, and the duration of the experiment (one week).