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Make Up Your Mind
  Teaching Guide
Activity 1: Grades 5-8

Atmosphere, whether it is the blanket of air surrounding the Earth or the air trapped within Biosphere II, (which we saw in "The Second Earth") is a closed system. Because the atmosphere systems are closed, the metabolic processes that occur within these systems affect their composition.

Respiration removes Oxygen as it releases Carbon Dioxide. Photosynthesis performs the reverse exchange, removing Carbon Dioxide and releasing Oxygen. It is this delicate balance of processes along with non-organic reactions that accounts for stability within the atmospheres of closed systems.

Image of girl and seedling

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This activity page will offer:

  • Experience with acid/base indicators
  • Opportunity to germinate seedlings
  • Chance to observe the effects of biological processes on closed systems


  • Bromthymol blue*
  • Seeds
  • Cotton
  • Two shallow plastic containers with lids (from deli-section of grocery store)
  • Two container caps (from plastic soda container)
  • Medicine dropper

    *This indicator solution is often sold in pet stores as a testing tool for aquarium acidity levels.

Shifting the Balance
As seeds germinate, they use oxygen to breakdown molecules of sugar. This reaction (respiration) releases the energy needed for the seeds to wake from dormancy. As sugar is metabolized, Carbon Dioxide and water vapor are released. In this activity, you will observe how respiration affects the gas composition of a closed system. As seeds become metabolocally active, the released Carbon Dioxide diffuses into an indicator dye solution. The dye responds with a radical change in color.


  1. Work in groups of two. Clean and dry two shallow plastic containers and airtight lids. Label one container "Bromthymol blue" and the other "Non-
  2. Bromthymol blue."
  3. Place a length of fluffed cotton along the inner margin of each container.
  4. Insert a variety of seeds into the space between the cotton and each containers' wall.
  5. In the center of each container, place a small bottle cap. Position the cap so that its well faces upwards.
  6. Use a medicine dropper to fill each cap with water
  7. Add several drops of bromthymol blue to the water-filled caps.
  8. Use the medicine dropper to dampen the cotton in one of the containers. Keep the cotton within the other container dry.
  9. Seal both containers and place them side-by-side in a location that is out of direct sunlight.
  10. Each day, observe the color of the indicator solution. Also compare the appearance of the seeds.
  11. As the seeds germinate, observe and record any changes in the indicator's appearance.


  1. What was the role of the bromthymol indicator?
  2. Why was water added to the cotton?
  3. Why was the cotton in only one container dampened?
  4. Describe any changes in appearance of the indicator solution.

Critical Analysis
What can you infer from your observations?


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.

An Historic Connection
In the eighteenth century, the English chemist, John 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 with the mouse, the air seemed to be purified. How can you explain these observations in terms of the products of respiration and photosynthesis?


Carbon Dioxide, the Atmosphere, and Song Lyrics
It's time to write the lyrics for a song. Work with a partner. Select a familiar poem or song - or write an original one. Research the effects of increased amounts of carbon dioxide on our atmosphere. Identify the major sources of this gas. Find out what natural processes (both chemical and biological) help to buffer any quick changes in the atmosphere's composition. Communicate this information as lyrics to a song or poem. Share your creation with others in a classroom "Concert for the Earth".


Acid Base Indicators

A non-intimating primer on acid/base indicators.

Seed Germination

This site offers an introduction to germination and seed dormancy.

CO2 Science Magazine
This rich, online resource offers a weekly review of topics that addresses a variety of issues related to Carbon Dioxide and climate change.

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

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