Experimental Design

Chapter 1

1 Define the Problem

What is it you want to find out?

Sometimes called the Purpose or

Question

What are some problems scientists work

on today?

2 Research

Gather as much information as possible

before experimenting

Sometimes called collecting information

3 Form a Hypothesis

Predict the outcome of your

experimentation

Sometimes called an educated guess

Many times hypotheses are stated in the

“If…… then…..” format

4 Experiment

Develop a procedure to test the

hypothesis.

Change only one variable at a time and all

other things as constants.

Independent variable – the thing you

change.

Sometimes called test the hypothesis

5 Analyze the Data

Record the results of your experiment

using charts, graphs, and taking notes

Sometimes called analysis or conclusions

6 Conclusion

Compare the hypothesis to the

experiment’s conclusion and publish your

results for others to see

Sometimes called communicate the

results

Paul Revere Hates Eggs And Cheese

The Strange Case of BeriBeri

In 1887 a strange nerve disease attacked the people in the Dutch East Indies. The disease was beriberi. Symptoms of the disease included weakness and loss of appetite, victims often died of heart failure. Scientists thought the disease might be caused by bacteria. They injected chickens with bacteria from the blood of patients with beriberi. The injected chickens became sick. However, so did a group of chickens that were not injected with bacteria.

One of the scientists, Dr. Eijkman, noticed something. Before the experiment, all the chickens had eaten whole-grain rice, but during the experiment, the chickens were fed polished rice. Dr. Eijkman researched this interesting case. he found that polished rice lacked thiamine, a vitamin necessary for good health.

1. State the Problem

2. What was the hypothesis?

3. How was the hypothesis tested?

4. Should the hypothesis be supported or rejected based on the experiment?

5. What should be the new hypothesis?

How Penicillin Was Discovered

In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria growing in culture dishes. He noticed that a mold called Penicillium was also growing in some of the dishes. A clear area existed around the mold because all the bacteria that had grown in this area had died. In the culture dishes without the mold, no clear areas were present.

Fleming hypothesized that the mold must be producing a chemical that killed the bacteria. He decided to isolate this substance and test it to see if it would kill bacteria. Fleming transferred the mold to a nutrient broth solution. This solution contained all the materials the mold needed to grow. After the mold grew, he removed it from the nutruient broth. Fleming then added the nutrient broth in which the mold had grown to a culture of bacteria. He observed that the bacteria died.

6. Identify the problem.

7. What was Fleming's hypothesis?

8. How was the hypothesis tested?

9. Should the hypothesis be supported or rejected based on the experiment?

10. This experiment led to the development of what major medical advancement?

When Experiments are Testing for

something they have …..

Independent variable (I.V.)- the factor (or

variable) that gets changed on purpose in

an experiment while all others remain

constant.

I.V. – I changed it myself

Dependent Variable

The factors (or variables) that get changed

as a result of the independent variable in

an experiment

The thing you measure

It depends or changes because of the I.V.

Constants

The factors in an experiment that remain

the same. They are not changed.

Control

The group that has no variable acting

upon it so that it can be compared with the

results of the experiment

In drug tests, this group is given sugar pills

(placebos) instead of the medicine. They

are told it is medicine.

Types of Data

Quantitative – has numbers, obtained by

counting, measuring.

Qualitative – descriptions that do not use

numbers, including colors, tastes, smells,

sound or textures

Qualitative or Quantitative

The floor is shiny.

There are 19 students in the class.

The walls are white.

The board is 1 meter high and 2 meters

wide.