Dissolved Oxygen  0 2 4 6 8 10 12 14 16 18 # of fish observed 0 1 3 10 12 13 15 10 12 13  . Develop a hypothesis relating to the amount of dissolved oxygen measured in the water sample and the...

Dissolved Oxygen  0 2 4 6 8 10 12 14 16 18

# of fish observed 0 1 3 10 12 13 15 10 12 13

 

. Develop a hypothesis relating to the amount of dissolved oxygen measured in the water sample and the number of fish observed in the body of water.

3. What would your experimental approach be to test this hypothesis?

4. What are the independent and dependent variables?

5. What would be your control?

6. What type of graph would be appropriate for this data set? Why?

7. Graph the data from the table above.

8. Interpret the data from the graph made in Question 7.

 

 

Expert Answers
sciftw eNotes educator| Certified Educator

There are a bunch of possible hypotheses that you could come up with relating to the amount of dissolved oxygen in a body of water and the number of fish observed in that body of water. A hypothesis is an idea that you can test, and what is great about a hypothesis is that it can be an idea that you want to prove correct or incorrect. Not "proving" a hypothesis can be just as valuable as proving a hypothesis. With that in mind, the following statements could all work as a hypothesis for the observation regarding fish and oxygen: 

  • There is no correlation between the dissolved oxygen and the number of fish.  
  • There is a positive correlation, wherein the oxygen level increases as well as the number of fish.  
  • There is a positive correlation, wherein the oxygen level decreases as well as the number of fish.  
  • As the oxygen level increases, the number of fish will not change.  

Some of those statements are not supported by the data, but remember, a hypothesis is written before an experiment is done. I am not sure if the oxygen and fish information is the initial observation or the experimental data.  

In order to test any of these hypotheses, we need to design an experiment. A good experiment will have a control setup, an experimental setup, controls, and one independent variable. The experiment should also be repeatable. For this experiment, you will need a body of water with some fish in it and a way to manipulate the amount of oxygen in the water. You will also need another body of water in which the oxygen level is held constant.  

The independent variable is the variable that the experimenter changes on purpose. I tell my students that "I" change the independent variable. "Independent" starts with the letter "i," and that is the variable that I change on purpose. Because I changed the oxygen level, the number of fish observed changed. It would seem that the fish depend on the oxygen amount. That would make the number of fish observed the dependent variable.

The control setup is the body of water that does not have changing oxygen levels. In addition to an entire control setup, the experimental setup with the changing oxygen should be "controlled." This means that the only thing we want changing is the oxygen level. Everything else should be held constant. The amount of water, the pH, and the salinity should not change. Water temperature and amount of sunlight also need to be held constant between both the control group and the experimental group.  

Graph type is up to you. Bar, column, and line graphs would all work to show the data. It is important to pick the graph that most clearly displays the data. For that reason, I almost always recommend that my students use line graphs. They very clearly show negative and positive correlations. I would put the oxygen levels on the x-axis and the number of fish observed on the y-axis.  

Based on the data, you could conclude with a fair amount of confidence that there is a correlation between oxygen amounts and fish health. You could not conclude that more oxygen is always better. There appears to be an optimal amount of oxygen because after 12 ppm, the number of fish begins to drop off.

aimeefarnum eNotes educator| Certified Educator

Hypothesis:  If you increase the amount of dissolved oxygen in the water, then more fish will be observed because fish need oxygen for cellular respiration.

Independent Variable:  Amount of dissolved oxygen

Dependent Variable:  Number of fish observed

Control variables:  same temperature, body of water, amount of light, same amount of fish food

Control experiment:  Water from the body of water without altering the oxygen.

Experiment:  Create a series of aquariums with different levels of dissolved oxygen (0ppm, 2ppm, 4ppm, 6ppm, 8ppm, 10ppm) including one take designed to have the exact same conditions as the pond the minnows come from.  Place 100 minnows in each tank.  Take data daily on number of fish in each tank.  Proceed for a week. Remove dead fish from the tank.


Data analysis:  Dissolved oxygen is necessary for fish to perform cellular respiration.  In this experiment it was determined that these fish thrive in water sources that are between 6-14 ppm with the most fish found in 12 ppm at 15 fish.  The least amount of fish were found in water sources with 0 ppm which is otherwise known as anoxic conditions.