Call Us: US - +1 845 478 5244 | UK - +44 20 7193 7850 | AUS - +61 2 8005 4826

affects bacterial growth

Experimental Variables

Determine the variables tested in the each of the following experiments. If applicable, determine and identify any positive or negative controls.


1.    A study is being done to test the effects of habitat space on the size of fish populations. Different sized aquariums are set up with six goldfish in each one. Over a period of six months, the fish are fed the same type and amount of food. The aquariums are equally maintained and cleaned throughout the experiment. The temperature of the water is kept constant. At the end of the experiment the number of surviving fish is surveyed.

A.    Independent Variable:

B.    Dependent Variable:

C.   Controlled Variables/Constants:

D.   Experimental Controls/Control Groups:

2.    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. coli

§  One with mannitol-salt agar and E. coli

§  One with MacConkey agar and E. coli

§  One with LB agar and E. coli

§  One with nutrient agar but NO E. coli

All 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.