Variables

Manipulated: The extracellular pH at which E. coli cells are made competent and transformed.

Responding: The transformation frequency
Transformation frequency = Number of transformants per plate/
                                               Number of bacteria plated per plate

Controlled:

• The temperature of each stage
• The growth phase of the E. coli
• The concentrations of competence developing solutions, LB medium, LB agar, and ampicillin in the LB agar
• The population density at each stage
• The pH for a given sample must be constant at all stages
• The strain of E. coli used
• The plasmid with which the E. coli are transformed
• The length of time the cells spend at each stage
• The volumes of solutions added to the cells
• The volume and dilution of E. coli plated
• The depth of the LB agar plates