Scientific method

In this exercise, you will be investigating whether head circumference is related to height and if the length of the middle finger is related to forearm length. It is common belief that if you measure the circumference of a person’s head and then multiply by 3 that it will give you their height. Likewise, if you measure the middle finger and multiply by 3, that will give you the person’s forearm length.

THE SCIENTIFIC METHOD

OBJECTIVES

After completing this exercise, the student will be able to:

? Define and differentiate between scientific method, hypothesis, prediction, observation, experiment, controls, conclusion, theory
? Understand the nature of scientific knowledge
? Outline and explain the steps of the scientific method process
? To formulate a hypothesis and develop conclusions based on data from previous experiments

INTRODUCTION
Science can be defined as a systematic approach to acquiring knowledge. We, as humans, have many senses that we rely on to interpret our surroundings and other inhabitants of the world around us. However, sometimes these senses can “fool” us and we must rely on technical equipment and tools to conduct experiments and enhance/expand our existing senses. Science is based upon facts and evidence rather than beliefs or superstitions.

To understand Biology and science, you must first examine how scientific knowledge is obtained. Science is a process that involves several steps. We will now explore these steps:

1. The process begins with making an observation about nature or some research done previously on a topic.

Example: Studies suggest that using Hydro-T plant food will make my tomatoes grow twice as fast and big.

2. The next step is to formulate a question about the observation.

Example: Does a weekly dose of 1 cup of Hydro-T plant food really enhance my yield of tomatoes and stimulate the plant’s growth?

3. Next, a hypothesis is needed. This is just merely an educated guess to answer the question you proposed in #2 above. Or put another way, a tentative explanation of the observed phenomenon. The hypothesis MUST be testable! Before stating your hypothesis, you should gather as much data from as many sources as possible. Also, please note: Hypotheses are NOT always correct, and often times you must formulate alternative hypotheses.

Example: Under normal conditions, supplementing my tomato plants weekly with 1 cup of Hydro-T plant food will make them grow bigger and faster.

4. A prediction is made next based upon your hypothesis. The prediction is a way to put your hypothesis to a test. It is usually phrased in an “If…then….” manner. If the prediction is found out to be true, then you will accept your hypothesis. If it is found to not be true, then you will need a new hypothesis.

Example: If weekly supplements with 1 cup of Hydro-T plant food cause tomato plants to grow twice as big and fast, then tomato plants receiving a weekly dose of 1 cup of Hydro-T plant food will grow twice as fast as tomato plants which do not receive a weekly dose of the plant food when both are exposed to identical conditions.

5. Next, a controlled experiment is designed and conducted in order to test the hypothesis. There are 3 types of variables involved. The independent variable (in our example, the Hydro-T plant food) is the condition or event under study for its effect on the dependent variable (in our example, growth rate and tomato yield). Put another way, the dependent variable is the condition or event that may change due to the independent variable. The controlled variables are conditions/events that COULD affect the outcome of your experiments, but do not because they are kept constant by the scientist. During a controlled experiment, the individuals under study are divided into 2 groups. The experimental group is exposed to the independent variable, while the control group is not. All other variables are kept constant.

Example: Gather a group of young tomato plants that have been grown in a laboratory and are all genetically identical. Randomly select 50 of them and put them into the experimental group, which will receive a weekly dose of 1 cup Hydro-T plant food over the period of 1 month. Also, randomly select 50 of the plants and put them into he control group. The control group will NOT receive the weekly dose of plant food. All other variables (i.e., water, sunlight, soil, etc) will be kept identical for each group. After 1 month, the plants are examined for growth rate and yield.

6. The results are collected and analyzed. Keep in mind that the experiments MUST be reproducible!
Example: The plants from the experimental group grew an average of 20 cm over the month, while the plants in the control group grew an average of 10 cm.
7. A conclusion is made as to accept or reject the hypothesis based upon the results. A conclusion often times leads to the formation of a new hypothesis and additional experiments.

Example: In this case, the hypothesis is accepted since the results showed clearly that a supplement of 1 cup of Hydro-T plant food weekly caused the plants in the experimental group to grow twice as fast as compared to the plants in the control group. Scientists use statistical analysis to determine the significance of differences seen in the control group versus the experimental group. However, we will leave the statistics for another lab ?

OBSERVATION
?
QUESTION
?
HYPOTHESIS
?
PREDICTION
?
CONTROLLED EXPERIMENT
?
ANALYSIS
?
CONCLUSION
YOU WILL NOW CONDUCT AN EXERCISE USING THE SCIENTIFIC METHOD

EXERCISE

In this exercise, you will be investigating whether head circumference is related to height and if the length of the middle finger is related to forearm length. It is common belief that if you measure the circumference of a person’s head and then multiply by 3 that it will give you their height. Likewise, if you measure the middle finger and multiply by 3, that will give you the person’s forearm length.

MATERIALS

? metric ruler
? meter stick
? scissors
? string

PROCEDURE

First you need to formulate a hypothesis for the head circumference. State it here:

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Also, state a hypothesis for the middle finger length: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
For each of the subjects in your group (including yourself), do the following:

1. Measure the circumference of the head (at the widest point) with a piece of string. Then place the piece of string against a metric ruler and record the length in Table 1. Repeat for all people in your group.

2. Using the meter stick, measure (without shoes) the height of all people in your group and record the data in Table 1.

3. Using a metric ruler, measure the length of the middle finger of all people in your group and record it in Table 2.

4. Using the string, measure the length of the forearm of all people within your group. Next, lay the string next to a metric ruler and record the length in Table 2.

Table 1. Group Data on the Circumference of the Head.

Name of Person Being Measured Circumference of Head (cm) Multiply by 3 Possible Height (cm) Actual Height (cm) Difference between possible and actual height (cm)
X 3
X 3
X 3
X 3
X 3

Table 2. Group Data on the Length of the Middle Finger.

Name of Person Being Measured Length of Finger (cm) Multiply by 3 Possible Length of Forearm (cm) Actual Length of Forearm (cm) Difference between Possible and Actual Length (cm)
X 3
X 3
X 3
X 3
X 3

Based upon the data you collected in Table 1, does it support or refute your hypothesis? Explain. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Based upon the data you collected in Table 2, does it support or refute your hypothesis? Explain. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
What are some possible errors that could have occurred? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
What are your conclusions for both sets of experiments? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________