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Some Like It Hot

Life in Yellowstone’s Extreme Environments

CONTENT AREA Biological Sciences


BIG IDEA/UNIT Organisms are adapted for their environment; resource availability restricts the organisms that can live in an ecosystem.

ESSENTIAL PRE-EXISTING KNOWLEDGE A basic understanding of how to make and interpret tables and graphs

TIME REQUIRED Four 55-minute class periods

COST Initial cost: approximately $60 Yearly cost: approximately $15

SAFETY Eye protection (indirectly vented chemical splash goggles), vinyl gloves, and non-latex aprons for set-up, hands-on, and take down components of this activity.

Yellowstone National Park is home to large populations of big animals such as bison, elk, and bear, as well as tall plants such as lodge pole pines, quaking aspen, and Engelmann spruce. But Yellowstone is also home to some of the smallest organisms on Earth, called microorganisms or microbes. An individual microorganism is too small to be seen with the naked eye. In fact, it would take over 500 of these very small organisms lined end-to-end to reach across the period at the end of this sentence. Microbes are not only found inside and outside of our body, but because of their diverse evolutionary adaptations, they are found in almost every habitat in the world.

Microorganisms that thrive in physically or geochemically extreme conditions, conditions so extreme that no one would expect to find life flourishing there, are called extremophiles. These creatures are so amazing and so strange they seem to have come from another world. Extremophiles can survive in these harsh conditions because their cells are very different from ours. Imagine living in water with a pH of 13, similar to materials used to clean your oven; these microbes are called alkaliphiles or alkaline-loving (Yellowstone National Park 2010). Let’s move to the other end of the pH scale. Microbes that thrive in an environment with a low pH such as 2, similar to lemon juice, are called acidophiles or acid-loving. Imagine living in water at near-boiling temperatures—ouch! Extremophiles that thrive in high temperatures are called thermophiles or heat-loving. At high temperatures the proteins in our cells would denature and fall apart, but proteins found in thermophiles stay intact. Now comes the real fun! Extremophiles that live in environments with a high temperature and high pH are called thermoalkaliphiles. Extremophiles that live in environments with high temperatures and low pH are called thermoacidophiles. What is interesting is that Yellowstone National Park has all of these EXTREMOphilic organisms.

Individually they are invisible because of their microscopic size, but populations of microbes can grow to astronomical numbers and clump together to form large, easily visible “mats” of various colors, depending on the pigmentation of the particular microbial species dominating the mat. They are able to form mats because some microbes produce a slimy, gluelike material that keeps the cells together. The vivid colors are the result of millions of microbes using sunlight energy during photosynthesis to produce its own life-sustaining energy. As mats grow, the photosynthetic microbes underneath become shaded and are no longer able to grow (Yellowstone National Park 2020). They are replaced by other microbes capable of surviving in the dimmer light or through a process called chemosynthesis.

Scientists who study extreme environments are drawn to Yellowstone because it contains more active geothermal features than any other place on the planet. To Yellowstone’s thermophiles, these geothermal features are home-sweet-home. The type of thermophile found in each geothermal feature depends on the temperature, pH, and chemistry (iron, sulfide, etc.) of the water.

When tourists visit Yellowstone’s eight geyser basins, how can they tell these amazing thermophiles apart from one another? Along with water temperature and chemistry, it just so happens that all these beautiful colors are important clues. The colors in the geothermal waters are a wonderful diagnostic tool for determining the species of thermophile. For example, visitors flock to the Midway Geyser Basin to observe the breathtaking view of the Grand Prismatic Hot Spring (see Figure 1). This football-field-size hot spring displays a distinct array of color bands which is the result of millions of thermophiles that form mats of color—color that is heat dependent.

extended thermometer key
Figure 1
|	FIGURE 1: The Grand Prismatic Hot Spring is the largest, most photographed hot spring in Yellowstone National Park. The distinct bands of color provide evidence that different species of thermophiles (heat-loving microorganisms) call Grand Prismatic home.

The Grand Prismatic Hot Spring is the largest, most photographed hot spring in Yellowstone National Park. The distinct bands of color provide evidence that different species of thermophiles (heat-loving microorganisms) call Grand Prismatic home.

Lesson overview

This article describes a four-day 5E lesson where students take on the role of microbiologists to explore Yellowstone’s smallest organisms that thrive in some of the harshest environments on Earth. While this article provides the reader with an overview of the Some Like It Hot lesson, detailed lesson instructions and teaching tips can be found in the Supplemental Materials. Students begin their journey learning about optimal living temperatures of Yellowstone’s more common multicellular organisms. Familiarity with the thermometer introduces students to organisms that not only survive, but thrive in environmental temperatures at the upper range on the thermometer. Students collect temperature and pH readings from beakers simulating Yellowstone’s geothermal aquatic environments from which select thermophilic organisms are found. In collaborative groups, the young microbiologists are tasked with identifying organisms that can thrive in diverse environments as they analyze and interpret data collected from Yellowstone’s geothermal features. Students share their findings with researcher Dr. Rob Burnap and his team of microbiologists. Finally, students focus their attention on Yellowstone’s Grand Prismatic Hot Spring, to learn that changes to an environment’s physical conditions can affect the organisms that live in it.

Engagement phase

To facilitate students’ understanding of these amazing organisms, after a short National Geographic video “The Best of Yellowstone: America’s National Parks” (see Online Resources) and a review of temperature measurements in Fahrenheit and Celsius, students receive a photocopy of a thermometer with a temperature range of –20°F (–29°C) to 100°F (38°C). Students also receive six organism cards that contain the names of five Yellowstone animals seen in the short video (bison, gray wolf, mountain lion, river otter, and ruffed grouse). In small groups, students work to identify where each of the five Yellowstone organism’s optimal temperature could be best represented on the thermometer.

Small-group discussions are followed by whole-class discussions when the teacher places a large drawing or enlarged photocopy of a thermometer on the board. Teams take turns placing their organism cards on the teacher’s large thermometer. There is an excellent chance that 100% agreement is not reached when students’ organism cards are placed on the thermometer. This is an opportunity to discuss optimal temperature versus temperature range. We use the placement of organism cards to provide students with practice in giving and receiving respectful critiques about their explanations, an important pedagogical component of teaching about the nature of science. Students learn that all five of the organisms (six including humans) currently posted on the thermometer are mesophiles, which means that they function best in moderate temperatures (68–104°F; 20–40°C).

The discussion is followed by a second short video that serves as an introduction to Yellowstone’s thermophiles. To be able to secure places on the thermometer for these heat-loving organisms, an extended thermometer is introduced that incorporates temperature readings above 175°F (79°C). Students are introduced to two thermophiles (Oscillatoria and Hydrogenobaculum), and place them on the extended thermometer key (see sidebar). Photos of Yellowstone’s colorful hot springs are displayed to further excite students about the unique microorganisms that live in them. As students watch the video and view the photos, they are tasked with writing questions that are generated.

The Engagement phase concludes with the identification of the essential driving question, “Do changes to the physical components (e.g., water temperature or pH) of an ecosystem affect populations that can thrive? Why or why not?” This question is referenced throughout the remainder of the Some Like It Hot lesson. Students are now positioned to learn that ecosystems consist of different physical components that lead to different organisms thriving in very different environments. Changes to physical components of an ecosystem affect which organisms thrive and which organisms die. See Supplemental Materials for all Engagement Teacher and Student Materials.

Exploration phase

Yellowstone National Park is known for the fact that it sits on top of a volcanic hot spot that creates a variety of unique, must-see geothermal attractions. The molten-heated water from far below Earth’s surface makes its exit through Yellowstone’s 10,000 geothermal features. Although some of these features are located in remote areas of the park, many are found in Yellowstone’s eight geyser basins; there, visitors find an array of stunning colors and nose-plugging smells (see Figure 2). Scientists who study thermophiles often visit Yellowstone, but for reasons other than those of the average visitor.

Figure 2
Figure 2

Canary Spring is located in the Mammoth Hot Spring Terraces on the north end of Yellowstone National Park. In the late 1800s, yellow filamentous bacteria thrived, hence the name Canary Spring. Today, the spring exhibits oranges, browns, and greens with occasional splashes of vibrant pinks and neon greens.

The Exploration phase of Some Like It Hot builds on and extends students’ understanding that changes to the physical components of Yellowstone’s hot springs affects the microorganisms that live in these ecosystems. To introduce students to the Extreme Environments Lab activity, we show a brief video that talks about the temperature and pH safety issues surrounding the diverse environments of Yellowstone’s hot springs. Students explore simulated environmental conditions found in Yellowstone’s hot springs as they measure the temperature and pH of six hot spring water samples (see Figure 3; see directions for hot springs solutions in sidebar).

Figure 3
|	FIGURE 3: Beakers full of colored water to represent Yellowstone’s hot spring water samples.

Beakers full of colored water to represent Yellowstone’s hot spring water samples.

Directions for Hot Spring Solutions

1. To obtain a pH of 3 (used for two of the six hot spring solutions)

Mix ¾ tablespoon of vinegar with 700 ml of water, stir. Both Hot Spring-A and Hot Spring-D have the same pH but contain a different temperature and a different color.

Pour 300 ml of this solution into a beaker and label the beaker as Hot Spring-A. Add yellow food coloring to create a strong yellow color. Hot Spring-A represents the Hydrogenobaculum thermophile and should be placed on a hot plate at a temperature between 131–162°F (55–72° C).

Pour the 300 ml of the original solution into a second beaker and label this beaker as Hot Spring-D. To create a dark purple or black solution, add both blue and red food coloring but add more blue than red coloring. Hot Spring-D represents the Zygogonium thermophile and should be placed on a hot plate at a temperature between 90–131°F (32–55° C).

2. To obtain a pH of 6

Mix ½ teaspoon of vinegar with 500 ml of water, stir.  Pour 300 ml of this solution into a beaker and label the beaker as Hot Spring-E. Create a red solution by adding red food coloring to the solution. This solution represents the Thermus thermophile and should be placed on a hot plate at a temperature between 104–174°F (40-79°C).

3. To obtain a pH of 7

Distilled water should have a pH at or close to 7. Pour 300 ml of the distilled water into a beaker and label the beaker as Hot Spring-C.  Add green food coloring to the solution to establish a true green color. This solution represents the Synechococcus thermophile and should be placed on a hot plate at a temperature between 125–165°F (52–74°C).

4. To obtain a pH of 8

Mix 1 teaspoon of baking soda (sodium hydrogen carbonate) to 500 ml of water, stir until the baking soda has dissolved. Pour 300 ml of this solution into a beaker and label the beaker as Hot Spring-F. Add yellow food coloring to establish a strong yellow color, then add a drop or two of red food color to obtain an orange color. This solution represents the Oscillatoria thermophile and should be placed on a hot plate at a temperature between 97–113°F (36-45° C).

5. To obtain a pH of 9

Mix 2 teaspoons of baking soda (sodium hydrogen carbonate) to 500 ml of water and stir until the baking soda has dissolved. Pour 300 ml of this solution into a beaker and label the beaker as Hot Spring-B. To create a true green solution, add green food coloring to the water. This solution represents the Chloroflexus thermophile and should be placed on a hot plate at a temperature between 95–185°F (35–85°C).

Students also record the color of each water sample that represents the mat colors unique to each thermophile. They identify which thermophile could thrive in each hot spring and provide evidence to support their claim. To mirror the collaborative nature of science and the nature of scientists, each student group receives incomplete data as they attempt to draw conclusions to determine which microbes could thrive in each of the six environmentally diverse “hot springs.” As student research groups collaborate and share data, a more complete data set provides groups with additional scientific evidence to support their claims. (Note: Because students work with warm-hot water and with water solutions that have pH ranges between 3–9, students must wear safety goggles and laboratory aprons. Additionally, a review of the corrosive nature of pH extreme solutions will go a long way to instilling professional laboratory behavior). See Supplemental Materials for all Exploration Teacher and Student Materials.

Explanation phase

During the Explanation phase, students are invited to work with Dr. Rob Burnap and his research team of microbiologists from Oklahoma State University. In this fictitious scenario, the team of scientists received a grant from the National Science Foundation to study photosynthetic mechanisms in thermophiles, in particular, cyanobacteria (see Teacher Explanation Handout in Supplemental Materials). The team knows that thermophiles are found in Yellowstone National Park and are interested in identifying the exact location of some of these unique microorganisms. The Burnap team has requested assistance in identifying the hot springs and geyser basins of 10 species of microorganisms. Students use multiple data sources to gather evidence of potential locations based on each hot spring’s temperature and pH (see Student Explanation Handout in Supplemental Materials). Data sources include thermophile data cards and descriptive data from Yellowstone’s Hot Springs. Throughout this phase of the lesson, students practice data mining, analyzing data, drawing conclusions based on scientific evidence, and defending their claims. Science is a human endeavor and is embedded by the social and cultural differences of the seekers of that scientific knowledge. Thus, students learn that while scientists may have the same information, how that information is interpreted may result in different conclusions drawn. See Supplemental Materials for all Explanation Teacher and Student Materials.

Elaboration phase

During the Elaboration phase Living Colors activity, students learn that while each species of thermophile has its own unique optimal temperature and pH range, multiple species can thrive in the same hydrothermal feature—in this case, Yellowstone’s Grand Prismatic Hot Spring. Students view a photo of the stunningly beautiful Grand Prismatic Hot Spring, which is used to frame two Think-Pair-Share writing prompts. Using a template, students draw their own picture of Grand Prismatic using water temperature indicators to guide their color bands (see Figure 4). The activity concludes with students writing a statement that supports or refutes whether Dr. Burnap and his team of cyanobacteria researchers should come to the Grand Prismatic to conduct their research. See Supplemental Materials for all Elaboration Teacher and Student Materials.

Figure 4
Grand Prismatic student drawing

Grand Prismatic student drawing

Evaluation phase

The lesson Some Like It Hot provides multiple forms of assessments to monitor students’ knowledge and understanding of how the physical components of an ecosystem determine the organisms that can thrive. In the Evaluation phase, students are provided with a storyline and tasked with extrapolating information learned from each of the Some Like It Hot activities to compare and critique two competing statements. In a written response, students are challenged to either support or refute each statement based on their analysis and interpretation of prior data to provide evidence that changes to the physical components of an ecosystem may or may not affect its organisms. See Supplemental Materials for all Evaluation Teacher and Student Materials.

Storyline and student writing prompt

With over 3,000 earthquakes each year, Yellowstone National Park is one of the most seismically active areas in the United States. During an earthquake, energy is released along fractures in the crust, causing the ground to shake. Although most of Yellowstone’s earthquakes register under 3.0 on the moment magnitude scale (Mw), on February 20, 2021, Yellowstone experienced an earthquake that registered 6.7 Mw. This seismic event caused a new fracture (or “pipe”) between Norris Geyser Basin and Grand Prismatic Hot Spring. Norris Geyser Basin has some of the hottest water in Yellowstone, which is now traveling into the Grand Prismatic. Since the earthquake, geologists from the Yellowstone Volcano Observatory have been monitoring this area and have determined that the Grand Prismatic Hot Spring is experiencing changes to its physical environment. Although the pH of the water has changed very little, the overall water temperature has increased over 15°F. Scientists have two lines of thought about the outcome of the thermophiles who call the Grand Prismatic “home”:

  1. Thermophiles can survive in warm-hot waters and because the pH of the water changed only slightly, the thermophiles that live in the waters of Grand Prismatic will continue to thrive in the hotter water.
  2. Thermophiles can survive in warm-hot waters, but while the pH of the water stayed relatively the same, the increase in water temperature may cause some populations of thermophiles to die.

Students use the scientific evidence collected and scientific reasoning skills they have developed throughout this lesson to compare and critique the two statements. Then students are tasked to make a written argument to support or refute each statement.


This lesson positions students to be actively engaged in learning about heat-loving microorganisms and how changes to the physical components of an ecosystem affects populations. Students’ science content knowledge and skills are strengthened through the introduction of the optimal temperature ranges of larger, more common Yellowstone organisms, and then to Yellowstone’s smallest organisms—thermophiles. Students take on the role of researcher to learn the science concepts and scientific practices common to microbiologists who study organisms, such as the cyanobacteria who live in extreme environments. The research taking place in Yellowstone National Park provides a venue for teachers to present current real-world applications of how an ecosystem’s available resources determine which organisms can thrive. Finally, students learn that scientists share data, and that even when scientists have the same information, interpretations of those data may differ.


We express our sincere appreciation to Dr. Rob Burnap for serving as our cyanobacteria content expert in reviewing for content correctness and for allowing us to use him and his team of researchers in the storyline of this manuscript. This work was funded in part by the National Science Foundation DUE-IUSE-1725714 Transitioning Students to Teacher Researchers and MCB-1716408 Assembly and Function of the Photosystem II (PSII) Complex.

Julie Angle ( is an associate professor in Science Education at Oklahoma State University in Stillwater, Oklahoma. Nichole Jones is a former science teacher at Cushing Middle School in Cushing, Oklahoma and current instructional developer at Oklahoma State University.


Yellowstone National Park. 2010. Recording change at Mammoth Hot Springs microbial diversity from harsh environments. Yellowstone Science 18 (3).

Yellowstone National Park. 2020. Yellowstone resources and issues handbook 2020. Yellowstone National Park, WY: U.S. Department of the Interior, National Park Service, Yellowstone National Park.

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