Willis' Science



Experimental Design

A blueprint of the procedure that enables the researcher to test his/her hypothesis by reaching valid conclusions about relationships between independent and dependent variables. It refers to the conceptual framework within which the experiment is conducted.

Components of an Experiment

Controlled variables: items in the experiment that are the same throughout experiment. Such things may be the length of tubing, the amount of sunlight, the amount of water added to plants, etc.

Experimental Independent Variable: the item that is changed throughout your experiment. The measurements of this are placed on the x axis for graphing purposes.

Experimental Dependent Variable: the item that you are measuring in your experiment. The measurements of this are placed on the y axis for graphing purposes. The dependent variable changes in response to the independent variable.

A control: A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable. This increases the reliability of the results, often through a comparison between control measurements and the other measurements.

Hypothesis: An educated guess about the results of the experiment. Sometimes stated in an “if…, then…” format.

Experimental Design Practice

Directions: Read the following experiments and fill in the blanks that follow. For 3 and 4 answers, there is not a control group listed in the example.

1) A study was created to test the effects of jazz on people’s sleep patterns. The hypothesis of the experiment was that if people listened to jazz music as they fall asleep, they will sleep for longer periods of time. For the experiment, 2 groups of people were created. One group was placed in a quiet room where they went to sleep and they were timed on how long they slept. The other group was placed in a room where jazz music played softly as they began to sleep and played throughout the night. As each group awoke, their sleep times were monitored.

Experimental Dependent Variable: ______________________ Control Group: ____________________________

Experimental Independent Variable: _____________________ Experimental Group: _______________________

Create an alternate hypothesis for this experiment: _______________________________________________________

2) A study was created to test the effects of fear in children. The hypothesis of the experimenters was that if babies were exposed to fuzzy pandas and at the same time a loud cymbal was struck close behind them, then that child would be afraid of all fuzzy things. Another group of children would be exposed to pandas without any loud noises. The study was carried out as planned and as a result, hundreds of young children developed fear of all cute furry pandas.

Experimental Dependent Variable: ______________________ Control Group: ____________________________

Experimental Independent Variable: _____________________ Experimental Group: _______________________

Create an alternate hypothesis for this experiment: ____________________________________________________

3) Shortly after Ms. Willis’ cat, Coco Cakes, was born, Ms. Willis realized Coco wasn’t eating enough. She went to the pet store and bought many different kinds of food and fed Coco different types every day. Each day she noted the type of food and how much Coco ate out of her dish. Eventually Coco ate a lot of the Friskies brand food and Ms. Willis bought that for her from then on.

Experimental Dependent Variable: ______________________

Experimental Independent Variable: _____________________ Experimental Group: _______________________

Create a hypothesis for this experiment: _______________________________________________________

4) At a preschool, the staff has had problems with the children behaving badly every day. They begin to test to see how the children react if the staff gives them large amounts of candy when they are good and no candy when they are bad. The staff hopes that the incentive for the children will improve their behavior.

Experimental Dependent Variable: ______________________

Experimental Independent Variable: _____________________ Experimental Group: _______________________

Create a hypothesis for this experiment: _______________________________________________________

Practical Situations: Read the situation below and design an experiment.

A) Jennifer M. has been hired by the city of Manhattan Beach to investigate the recent shark attacks off the coast. She has a budget of $40,000, a 25 foot boat, and three graduate student assistants to help her. A helicopter has also been donated by a local television station, should she need one.

* * *

1. List 2 hypotheses Jennifer and her crew may have come up with for the recent shark attacks.

a. If_____________________________________, then ______________________________________

b. If_____________________________________, then ______________________________________

2. Pick one of the two hypotheses and determine the following:

a. Control Group: time of year when elephant seals are not present or another area with no elephant seals

b. Experimental Group: times/areas when/where elephant seals vary

c. Experimental Dependent Variable:________________________________

d. Experimental Independent Variable:______________________________

3. What type of data do you think Jennifer will collect (What will be the results of the experiment)?

4. What conclusions will Jennifer be able to make from the results of the experiment?

B: Marlyn wants to know the effect of different colors of light on the growth of plants. She believes that plants can survive best in white light. She buys 5 ferns of the same species, which are all approximately the same age and height. She places one in white light, one in blue light, one in green light, one in red light and one in the closet. All of the ferns are planted in Miracle-Grow and given 20 mL of water once a day for 2 weeks. After the two weeks, Suzie observes the plants and makes measurements.

Hypothesis: If plant growth is affected by color of light, then white light will produce the most plant growth.

Experimental Independent Variable: Experimental Dependent Variable:

Control Group: Experimental Group:

What could be the controlled variables?

What types of measurements can Marlyn make on the plants to determine how they did in different types of light?

Scientific Method in Action: Real Case Studies!

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, and 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 and 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 and how would you test it?

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 nutrient broth. Fleming then added the nutrient broth in which the mold had grown to a culture of bacteria. He observed that the bacteria died which was later used to develop antibiotics used to treat a variety of diseases.

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 lead to the development of what major medical advancement?

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