Summer Research Program for Science Teachers

Columbia University



Maria Perez

The Professional Performing Arts School, Manhattan

August 2003





Experimental Design & the Scientific Method

Every Breath You Take



Topic: Introduction to the Scientific Method.  Later in the year this activity can be related to photosynthesis and cellular respiration.


Content Level: Living Environment/Biology/ Life Sciences


Time: 2 class periods


Materials:  goggles, 3 beakers for each group, graduated cylinder water, droppers, Bromothymol Blue (BTB), plastic straws, Elodea plants, 2 plastic test tubes with caps for each group


Background: Indicators are substances that show the presence of certain chemicals by changing color.  Bromothymol blue (BTB) is an indicator that turns green or yellow in the presence of a weak acid.  Carbon dioxide reacts with water, forming a weak acid, so bromothymol blue can indicate the presence of carbon dioxide in water. The focus of this lab activity is for students to predict and analyze why the water changes color in the presence of substance, Bromothymol Blue, and what BTB indicates instead of being told.  Students can be referred to this lab later on in the year when they study photosynthesis and cellular respiration. 




1.)    Students will explore the Scientific Method and Experimental Design.


2.)    Students will interpret the actions of an indicator; conclude that bromothymol blue turns yellow in the presence of a weak acid.


3.)    Students will understand acids and bases and the uses of indicators.


4.)    Later in the year, students can relate the interdependce of the processes of cellular respiration and photosynthesis to living organisms.


5.)    Furthermore, students can revisit this lab and be able to explain how the processes of cellular respiration and photosynthesis are dependent upon each other (the oxygen/carbon dioxide cycle.) 



Skills:  observing, inferring, collecting data, recording, analyzing, interpreting data, measuring, and experimenting.


Demo/Motivation: Sing my Emory University Alma-Mater song:

End of song:

Emory, Emory, Here’s to My Emory

For the Blue and Gold

Use a large flask with water and bromothymol blue for the last part of the song and allow students to see the change in color of water from blue to yellow/gold.


Ask students why they think the water changed colors from blue to gold?




Part I.


1.)    Students should be divided into groups of 3-4 and should receive the materials listed above.


2.)    Students will be asked to record all of the appropriate information on a worksheet (see appendix.)


3.)    Students should fill one beaker with about 200ml. of water using a graduated cylinder.  Then they should use a dropper to add enough BTB to turn the water blue.


4.)    Have students use a plastic straw to blow into the water.  They should record their observations on the worksheet and try to explain why the water changed color.


5.)    Discuss each group’s thoughts about this short activity.  Once students understand the idea of indicators, specifically bromothymol blue, and why the water changed color, lead the students in designing an experiment to test the presence of carbon dioxide in an elodea plant.


Part II.


6.)    Have students discuss the pre-experimental design questions on the worksheet.


7.)    Students should then design their experiment with the elodea plant. Make sure students understand the concept of a control in this experimen (just BTB and water/ no elodea plant.).


8.)    The next day students will make observations, record data, and analyze their results.


9.)    Student will make conclusions and present their findings to the rest of the class.


National Science Education Standards:


Science Teaching Standards: Standard A, B, & D


Science Content Standards, Grades 9-12: Standard A, E, & G 






APPENDIX: Worksheet for Lesson Plan







Every Breathe You Take Activity


1.)    Decide who will take on what role in your group and circle your role:


v     Materials Collector: This student will make sure the group has all of the appropriate materials, make sure the materials are returned to the front of the room as they were received at the end of the class period, and clean your table (with the help of your other group members.)


v      Experimenter: Although every student will have a chance to participate in Part II. of this experiment, this person will do Part I. with the help of the other group members.


v     Recorder: Even though every student is required to record data, this person must turn in their recorded information for a grade as a reflection of the groups’ work.  


v     Presenter: This student will present the groups’ findings to the rest of the class.


2.)    Make sure you have all of the appropriate materials for your group (you can check off each material):

q       Worksheets for each group member

q       Googles

q       3- beakers

q       graduated cylinder

q       water

q       dropper

q       BTB

q       Plastic straw

q       2- plastic test tubes with caps

q       elodea plant


3.)    Fill one beaker with 100 ml. of water using the graduated cylinder to measure out 100 ml.


4.)    Use a dropper to add enough BTB to turn the water blue.


5.)    The experimenter should use a plastic straw to blow into the water.  Record your observations down below:


What did you observe when a straw was used to blow into the water?




Discuss with your group why you think this happened? State your reason or reasons in complete sentences:






Pre-Experimental Design Questions: What makes a scientific investigation scientific


1.)    In your group, name and define at least 5 essential components/parts to a simple scientific experiment.











2.)    What makes an investigation “scientific”?






3.)    Why do scientists use a control in an experiment?






4.)    You will be designing your own experiment to test the presence of carbon dioxide in an elodea plant in different conditions.  Why do you think we are using an elodea plant?











5.)    What will be your control for this experiment?






6.) Design your experiment: Where will you place your two test tubes and how will you measure the presence of carbon dioxide?















7.) Write down all of your observations, record your data and analyze your results on the back of this page.


8.) Your group will make conclusions and your presenter will present your findings to the rest of the class.  Your recorder should also turn in your data/answers for a grade.


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