Exercise 1: Data Interpretation

Dissolved oxygen is oxygen that is trapped in a fluid, such as water. Since many living organism requires oxygen to survive, it is a necessary component of water systems such as streams, lakes and rivers in order to support aquatic life. The dissolved oxygen is measured in units of ppm (parts per million).

The data in Table 4 came from an experiment to identify the amount of oxygen required to support the maximum number of fish.

Post-Lab Questions

1. What patterns do you observe based on the data in Table 4?

2. What would have been the hypothesis of the scientists performing this experiment?

3. What were the independent and dependent variables?

4. What were the control(s) in this experiment?

Exercise 2: 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:

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:

Exercise 3: Testable Observations

Determine which of the following observations (1-6) are testable. For those that are testable answer the following questions:

Determine if the observation is testable (quantitative) or not testable (qualitative) and explain why.

If the observation is testable:

• Write a hypothesis
• What would be your experimental approach – how will you collect your data?
• What are the dependent and independent variables?
• What are your controls – both positive and negative?

Observations

1. A plant grows three inches faster per day when placed on a window sill than it does when placed on a on a coffee table in the middle of the living room.

2. The teller at the bank with brown hair and brown eyes is taller than the other tellers.

3. When Sally eats healthy foods, her blood pressure is 10 points lower than when she eats fatty foods.

4. The Italian restaurant across the street closes at 9 pm but the one two blocks away closes at 10 pm.

5. For the past two days, the clouds have come out at 3 pm and it has started raining at 3:15 pm.

6. George did not sleep at all the night following the start of daylight savings.