Scientific Method – Introduction to Experimental Design

Background

In this lab, you will discover how biologists design experiments, control variables, gather information,

summarize and present data.

Experiments are important tools in biological research. An experiment is a procedure that is designed to test an idea under controlled conditions. In each experiment, there are two types of variables, which are factors that can change. An independent variable is a method, technique, or condition that could possibly influence a response. Independent variables are manipulated by the experimenter. Variables that change in response to an independent variable are called dependent variables.

Experiments can be conducted in many ways. The first step is to ask a question that you wish to answer by doing an experiment. The next step is usually to develop a hypothesis, which is an opinion (answer to your question) that can be tested.

During an experiment, a researcher collects data (recorded observation). The data are usually organized by placing them in a data table. Making tables and graphs of data are methods of presenting data so that it can be interpreted.

In the following experiment, you will practice all the steps of the scientific method.

Materials

Gelatin capsule containing a sponge animal

Clock with a second hand

Beaker or cup with water

Stirring rod

Procedure

1. Each lab station will receive a capsule containing a sponge animal. {Note don’t hold it too much before the experiment – the heat or sweat of your hand could affect it.} Develop a list of 4 questions that you would like answered about the sponge animal. Use complete sentences when writing the questions in the place below.

2. A possible question you might want to investigate is: Do the different colors of sponge animals need different amounts of time to grow? Using this question, write a hypothesis for you investigation on the lines below.

3. At your teacher’s signal you will drop the capsule into the beaker and begin stirring. Try to maintain the same stirring speed until the capsule dissolves. Record the times below in minutes and seconds.

Start time______Emergence time______

4. Your teacher has put the summary data table on the board. Record the time to emerge under your sponge animal color. (examples of colors are given below)

Color of sponge animal Time to emerge Average time for each color

Red
Green
Blue
Yellow
Purple

5. Copy the information from the board onto your data table above. Calculate the average time for each color. Put your answer in the space provided.

6. Make a bar graph of the data in the space below. Include a brief caption containing an explanation of the graph.

7. Clean up your lab station.

Analysis

1. Make a list of the various factors, or variables that might have influenced the results of your experiment.

2. Interpret your table and graph to answer the following questions.

a. What color sponge animal took the longest to emerge?

b. What color sponge animal took the least amount of time to emerge?

c. Was there a significant difference between the different colors of sponge animals to merge?

3. How could you improve the experiment?

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4. What other variable would you like to experiment with, using sponge animals?

______

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Conclusion:______

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