To determine if the type of agar affects bacterial growth, a scientist cultures e. coli on four different types of agar. five petri dishes are set up to collect results: one with nutrient agar and e. colione with mannitol-salt agar and e. colione with macconkey agar and e. colione with lb agar and e. colione with nutrient agar but no e. coliall of the petri dishes received the same volume of agar, and were the same shape and size. during the experiment, the temperature at which the petri dishes were stored, and at the air quality remained the same. after one week the amount of bacterial growth was measured. a. independent variable: b. dependent variable: c. controlled variables/constants: d. experimental controls/control groups