What I need to know about the Scientific
Method and Experimental Design
Scientific Method
What is the scientific method and why do we use it when conducting lab experiments?
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Bias
1. What is bias?
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2. Explain how bias can affect the outcome of an experiment.
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3. Identity the factors that may cause bias in the following scenario about Supersweet:
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A new artificial sweetener, Supersweet, is used in some foods and drinks to reduce calories.
Mrs. Breen once read an article from a local newspaper that stated, Supersweet is known to
cause severe headaches. She has used it twice in her morning coffee and got a severe
headache. So, now she tells everyone that Supersweet causes headaches in everyone.
4. How to improve your experiment and prevent bias:
Keep an _____________ mind.
Always include a _______________ for comparison.
Change only ______________ variable at a time.
Keep all set-ups the ____________ except for the tested variable.
Do ___________________trials.
Record ___________ data
Problems & Hypotheses
Read the following problems and develop testable hypotheses.
1. Two different types of paper towels claim to absorb more water. Towel A has a unique
pattern that it claims will absorb more water. Towel B uses the standard dots and claims it
will soak up more liquid than any other paper towel on the market.
Problem: Which paper towel will absorb more water?
Hypothesis:
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2. At the state fair, two types of candles were being judged for their burning time. One
candle was made of bees wax and the other made of paraffin.
Problem: Which type of wax candle will burn longer?
Hypothesis:
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3. What problem was being investigated to gather this data?
Hours of Sunlight
2
4
8
10
Oxygen Produced
(ppm=parts per million)
40 ppm
80 ppm
120 ppm
160 ppm
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4. What problem was being investigated to gather this data?
Amount of Rainfall
(cm)
1
1.5
2
2.5
Plant Height (cm)
3
7
12
15
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Variables/Control Groups/Constants
Scenario A: 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. Identify the independent variable in this experiment. _________________________
2. Identify the dependent variable. __________________________
3. What is the control group in this experiment? __________________________
4. What is the experimental group? __________________________
5. What factors are held constant? __________________________
Scenario B: How Penicillin Was Discovered
In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria (this is also known as a
staff infection) 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.
1. Identify the independent variable in this experiment. _________________________
2. Identify the dependent variable. __________________________
3. What is the control group in this experiment? __________________________
4. What is the experimental group? __________________________
5. What factors are held constant? __________________________
Scenario C: Ten seeds were planted in each of 5 pots found around the house. Each pot
contained 500g of “Pete’s Potting Soil.” The pots were given the following amounts of distilled
water each day for 40 days: Pot 1, 50 ml; Pot 2, 100 ml; Pot 3, 150 ml; Pot 4, 200 ml; and
Pot 5, 250 ml. Pot 3 received the recommended amount of water. The height of each plant
was measured at the end of the experiment.
Identify the following in this experiment:
Hypothesis
Independent Variable
Dependent Variable
Control Group
Constants
Scenario D: Look at the graph and identify the dependent and independent variable.
The independent variable is _______________________________.
The dependent variable is ________________________________.l
Safety
1. Two students are conducting a lab experiment that requires heating up a test tube.
Student A places a stopper on the test tube while its contents are being heated up.
Once the substance in the test tube is heated up, Student B removes it by grabbing the
top and placing it in the test tube rack. Both student A and B are performing unsafe
practices in the lab.
What should Student A and B do to make their experiment safer?
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2. Mrs. Blizzard asks her students to prepare for a laboratory experiment by first putting
on their safety equipment which consists of a pair of ________________ and an
_____________. ____________ must always be worn during all lab experiments to
prevent injuries to the eyes.
Data
1. Is it qualitative or quantitative?
2. There are two types of data that are collected when conducting a lab experiment. The
first is ___________________ and this is represented by recording the height, weight,
volume, years, etc. in numbers. The other type of data is reflected in a data table by
recording factors like height using the words small, medium, and/or large. This type of
data that is recorded using only words is called _____________________.
3. Make a data table to describe the characteristics of three different animals.