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The Scientific Method and Testable Hypotheses

Exercise 1:

Dissolved oxygen is oxygen that is trapped in fluid, such as water. Since virtually every 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- or parts per million. Examine the data in Table 2 showing the amount of dissolved oxygen present and the number of fish observed in the body of water the sample was taken from; finally, answer the questions below.

(see attached file for tables)
1. Based on the information in Table 2, what patterns do you observe?
Based on the information given in the table, at first, it appears that as the amount of dissolved oxygen went up the number of fish went up as well. But at the end of the table when the level of oxygen is the highest, the number of fish decreases.
2. 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.
The amount of dissolved oxygen present in a body of water has no effect on the number of fish found in that water.
3. What would your experimental approach be to test this hypothesis?
4. What are the independent and dependant 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.

Exercise 2:
Determine which of the following observations are testable. For those that are testable:
Write a hypothesis and null hypothesis
What would be your experimental approach?
What are the dependant and independent variables?
What is your control?
How will you collect data?
How will you present your data (charts, graphs, types)?
How will you analyze your data?

1. When a plant is placed on a window sill, it grows faster than when it is placed 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. I caught four fish at seven o' clock in the morning but didn't catch any at noon.

4. The salaries at Smith and Company are based on the number of sales and Billy makes 3,000 dollars more than Joe.

5. When Sally eats healthy foods and exercises regularly, her blood pressure is lower than when she does not exercise and eats fatty foods.

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

7. Bob bought a new blue shirt with a golf club on the back for twenty dollars.

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

9. George did not sleep at all last night because he was up finishing his paper.

10. Ice cream melts faster on a warm summer day than on a cold winter day.

11. How can you apply scientific method to an everyday problem? Give one example.

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My response is attached as a pdf document.

Exercise 1:
Dissolved oxygen is oxygen that is trapped in fluid, such as water. Since virtually every 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- or parts per million. Examine the data in Table 2 showing the amount of dissolved oxygen present and the number of fish observed in the body of water the sample was taken from; finally, answer the questions below.

Table 2: Water quality vs. fish population
Dissolved Oxygen (ppm) 0 2 4 6 8 10 12 14 16 18
Number of Fish Observed 0 1 3 10 12 13 15 10 12 13
1. Based on the information in Table 2, what patterns do you observe? The number of fish observed in the body of water initially increases with an increase in dissolved oxygen and decreases at a relatively high concentration of oxygen.
2. 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.
A hypothesis is an educated guess to explain an observed phenomenon. A good hypothesis is testable and falsifiable. Testing a hypothesis should result in a clear answer that either supports it or proves it wrong.
Possible hypotheses:
1. When too much or too little oxygen is present in the body of water, the number of fish in the water decreases. The following links describe toxicity to fish resulting from high levels of dissolved oxygen:
http://www.sciencemag.org/content/163/3867/576.1
http://www.unuftp.is/static/fellows/document/yovita07prf.pdf
2. Note: One can argue that the decrease in the number of fish at the higher levels of oxygen is just by chance unless further tests are done. Based on that argument, one can formulate a simpler hypothesis while disregarding the minor drop in the number of fish at the higher end of the oxygen scale: The number of fish in the body of water increases with increasing amount of dissolved oxygen in the water.
3. ...

Solution Summary

The following posting helps answer problems regarding two experiment-related exercises. One problem involves an oxygen trapping experiment and the other helps to determine whether certain observations are testable.

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