Gassy Microbes

Gassy Microbes

Activity Type:

Bubbling Methane; Melting Permafrost

What do permafrost and methane have to do with each other? In this video, Torre Jorgenson, a landscape ecologist at Alaska Biological Research, explains the connection. Watch methane bubble up as Jorgenson stirs up a melted permafrost pond.


Grade Level: 6th – 8th grade
Subject Matter: Life Science
National Standards: NS.5-8.1, NS.5-8.3



Some microbes produce different types of gases as a byproduct of their metabolic processes. The microbes in this Science Friday Video released an odorless and flammable gas called methane. The type of gas or gases released by a microbe depends on the species and their metabolic characteristics.


In this activity, students will conduct an experiment to observe the metabolic process of yeast by using household ingredients. Students will vary conditions in the yeast’s surrounding environment and observe the amount of gas that the yeast releases. Students will use the results to determine which environmental conditions are suitable for yeast growth.


Activity Materials

16 oz. clear plastic soda or water bottles, three for each student
Active dry yeast or baker’s yeast
Sugar packets, three for each student
Plastic spoons, one for each student
Small plastic cups, three for each student
Warm water
Large bowls
Permanent marker
Balloons, three for each student


N.B., If any of your students is allergic to latex, DO NOT let him/her handle the balloons. Have students who are allergic work with partners who are not allergic, and who will work with the balloons.



Microbe: a small organism that can be seen only through a microscope.
Metabolism: a series of chemical interactions that happens in living organisms to provide the energy and nutrients needed to sustain life.
Yeast: a single-celled fungus.
Fungus: a single-celled or multi-cellular organism without chlorophyll. A fungus lives by absorbing nutrients from organic matter.


What To Do


  1. Begin the lesson by having students watch the Science Friday Video, “Bubbling Methane; Melting Permafrost.” Explain to students that permafrost is permanently frozen ground found in cold regions such as Alaska. Ask students what could cause permafrost to melt. How can melting permafrost affect the environment?

  2. Tell students that they are going to conduct an experiment to observe how a microbe interacts with its surrounding environment, and how varying conditions in the environment can affect its ability to thrive.

  3. Hand out three plastic bottles to each student. Have students use the permanent marker to label each of the plastic bottles in the following manner: Bottle A – Sugar, Bottle B – Vinegar, Bottle C – Sugar/Ice

  4. Distribute to each student three sugar packets and three plastic cups with small portions of the following ingredients separated into each cup: yeast, warm water, and vinegar. Ask students to explain what yeast is, and how it is used. Why do they think we are using yeast in an experiment about microbes?

  5. In Bottle A, have students mix one spoonful of yeast, one packet of sugar and three spoonfuls of warm water. Gently swirl the ingredients inside the bottle until the contents have dissolved. Cover the top of the bottle with a balloon. Have students observe the contents inside the bottle. Why is it bubbly or foamy? Does it remind them of any footage from the Science Friday Video?

  6. In Bottle B, have students mix one spoonful of yeast, one packet of sugar, three spoonfuls of warm water and one spoonful of vinegar. Gently swirl the ingredients inside the bottle until the contents have dissolved. Cover the top of the bottle with a balloon. What is happening inside the bottle?

  7. In Bottle C, have students mix one spoonful of yeast, one packet of sugar, and three spoonfuls of warm water. Gently swirl the ingredients inside the bottle until the contents have dissolved. Cover the top of the bottle with a balloon. Place the bottle upright in the middle of a large bowl, and place as much ice as possible around the bottle.

  8. Set the bottles aside for about 15 to 20 minutes. During this time, have students create a chart on a sheet of paper with three columns and two rows. Label the columns “Bottle A”, “Bottle B,” and “Bottle C.” Label the top row as “Predictions” and the bottom row as “Results”.

  9. Have students write their predictions in the appropriate column and row for each bottle. Ask students to write explanations for their predictions on the chart. Based on their initial observations, what do they think will happen to the balloons? Which balloon do they think will inflate the most? After students have finished writing their predictions, have them discuss their predictions and explanations with the entire class.

  10. After 20 minutes, have students observe their bottles. What has happened to the balloons? Why have some balloons inflated more than others? Have students write the results in the bottom row of their chart. Compare and contrast their results with each other, and with the students’ predictions.

What's Happening?

Yeast is a single-celled organism that can only be seen through a microscope. We are able to see the yeast in this experiment because a packet of dry yeast sold in a grocery store holds billions of yeast cells (one gram holds about 25 billion cells). These yeast cells lie in a dormant state until they are activated by the warm water, and begin to break down the sugar for energy. As the yeast cells metabolize the sugar, they release carbon dioxide gas. The build up of carbon dioxide gas in the bottle causes the balloons to inflate.


Similar to any other living organism, yeast need to be in an environment that is suitable for survival. The yeast’s ability to thrive in the bottles, or the artificial “environments” that the students have created, can be measured by how well each balloon inflates. A thriving community of yeast will produce more carbon dioxide gas. If less carbon dioxide is produced, the environment for yeast is less suitable.


The balloon for Bottle B will not inflate, because vinegar is a type of acid. An overly acidic environment can hinder the growth of yeast. Yeast tends to thrive in warm environments. By surrounding Bottle C with ice, we have created an environment that is too cold to sustain yeast growth.


Bottle A should have the most inflated balloon of all three because it contains the optimal conditions for the growth of yeast.


Topics for Science Class Discussion

  • How does the acidic environment created in this experiment compare to the effects of acid rain in our environment?

  • How would we create an experiment to simulate the effects of climate change in our environment? What variable would we have to change?

  • Besides carbon dioxide and methane, what are other types of gases or by-products that may be released by microbes?

  • Explain the process of how yeast helps bread dough to rise.

Extended Activities and Links

  • Have students change some of the variables in this experiment. Try different types of possible food sources for yeast (e.g., artificial sweetener, corn syrup, honey, etc). Which food source causes the yeast to produce the most gas? What are other ways that the experiment can be modified?

  • Have students research the different types of microbes that produce gas, where these microbes are found, and how they can play an important role in creating or combating climate change.

  • Try this hands-on science activity on permafrost from the PBS television series Scientific American Frontiers.

  • Learn more about how carbon is exchanged throughout the Earth by playing this interactive online carbon cycle game.

This lesson plan was created by the New York Hall of Science in collaboration with Science Friday as part of Teachers Talking Science, an online resource for teachers, homeschoolers, and parents to produce free materials based on very popular SciFri Videos to help in the classroom or around the kitchen table.


The New York Hall of Science is a science museum located in the New York City borough of Queens. NYSCI is New York City's only hands-on science and technology center, with more than 400 hands-on exhibits explore biology, chemistry, and physics.