Question

Exercise 7: Experimental Variables Determine the variables tested in the each of the following experiments. If applicable, determine and identify any positive or negative controls. Observations 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. A. Independent Variable: B. Dependent Variable: C. Controlled Variables/Constants: D. Experimental Controls/Control Groups:

Answer 1

Answer:

Based on the given information, the different variables used in the experiment are:

Experiment 1:

• A) Independent Variable: Habitat Space (Different sized aquariums)
• B) Dependent Variable: Size of goldfish population (measured in terms of number of surviving fish at the end of the experiment)
• C) Controlled Variables / Constants: Type and amount of food fed to fish, temperature of water, equal cleaning and maintenance of all aquariums.
• D) Experimental Controls / Control Groups: No control group is used.

Experiment 2:

• A) Independent Variable: Type of agar (Nutrient agar, Mannitol-salt agar, MacConkey agar, LB agar)
• B) Dependent Variable: Amount of bacterial growth (measured after one week)
• C) Controlled Variables / Constants: Volume of agar poured in petri dishes, shape and size of petri dishes, storage temperature and air quality.
• D) Experimental Controls / Control Groups:
  • Negative control: Nutrient agar with no E.coli.
  • Positive control: Nutrient agar with E.coli.