Part 1 - Exploring Indicators

1. What happened when your exhaled breath bubbled through the solution?
   (The solution changed from blue to yellow).
2. What component of your exhaled breath caused this change?
   (Carbon dioxide)
3. How was this carbon dioxide produced?
   (In order to meet energy needs, cells combine oxygen with sugar and release this waste gas.)

CRITICAL THINKING
Why did you place a snip in the side of the straw?
(It lessened that chance that if you accidentally drink the liquid if you sucked in on the straw. Liquid rising in the straw would exit through the snipped hole.

Part 2

Questions

1. What was the role of the bromthymol indicator?
   (It was used to indicate increasing carbon dioxide levels within the chamber)
2. Why was water added to the cotton?
   (Water was needed to germinate the seeds.)
3. Why was the cotton in only one container dampened?
   (The activity was setup as a controlled experiment. The seeds only germinated in the dampened cotton container.)
4. Describe any changes in appearance of the indicator solution.
   (In the container in which the seeds germinated, the indicator turned from blue to yellow. In the other container, it remained blue.)
5. Critical Analysis What can you infer from your observations?
   (Germinating seeds release sufficient amounts of carbon dioxide to produce a color change in bromthymol blue indicator solution.)
   

EXTENSIONS

Greening of Inquiry
Now that you are familiar with the action of bromthymol blue, it's your turn to create a strategy for inquiry that would explore the effects of photosynthesis within a closed air system. With access to the same materials and small green plants, design a controlled experiment that shows how photosynthesis affects the composition of the air trapped within a sealed container.
(Create two parallel setups, each containing a green plant and bromthymol blue that has already turned yellow. Place one setup in light. Keep the other in darkness. As photosynthesis proceeds, it should turn the solution in the lit container back to blue)

An Historic Connection
In eighteenth century, the English chemistJohn Priestly, explored the metabolic needs of living things. In doing so, he uncovered the intimate relationship between plants and animals. When a healthy mouse was placed in a sealed chamber, the animal showed signs of distress caused by breathing "spoiled air". However, when a green plant was placed into the sealed container, the air seemed to be purified. How can you explain these observations in terms of the products of respiration and photosynthesis?
(By itself, the mouse consumed the chamber's limited oxygen supply to meet its respiration needs. The plant, however, used the waste carbon dioxide in photosynthesis. The product of this process was oxygen gas. Therefore, the plant maintained a renewed supply of oxygen to meet the animal's respiratory needs.)

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).

Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools, Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA
Gary Pinkall, Middle School Science Teacher, Great Bend Public Schools, Great Bend, KS