Lesson Plan

Microorganisms in the Utah Desert

Lumpy, multi-colored black, yellow, green and orange biological soil crust
Grade Level:
Middle School: Sixth Grade through Eighth Grade
Subject:
Science
Lesson Duration:
90 Minutes
State Standards:
Standard 6.4.1 Analyze data to provide evidence for the effects of resource availability on organisms and populations.
Standard 6.4.4 Construct an argument supported by evidence that the stability of populations is affected by changes to an ecosystem
Thinking Skills:
Analyzing: Break down a concept or idea into parts and show the relationships among the parts.

Essential Question

What can we learn about microorganisms in the high desert ecosystem through gathering and analyzing data about them?

Objective

On this field trip, students collect and examine data to understand how availability of resources affects populations of microorganisms in the desert. Students observe desert potholes and learn about strategies organisms use to survive in these diminishing ecosystems. Students also examine desert lichens to see how the orientation of rocks affects a lichen’s ability to thrive.

Background

Utah State Science Core Curriculum Topic: 

Standard 6.4.1 Analyze data to provide evidence for the effects of resource availability on organisms and populations in an ecosystem. Ask questions to predict how changes in resource availability affects organisms in those ecosystems. 

Standard 6.4.4 Construct an argument supported by evidence that the stability of populations is affected by changes to an ecosystem. Emphasize how changes to living and nonliving components in an ecosystem affect populations in that ecosystem. 

Microorganisms are everywhere and play many important roles in the high desert ecosystem. Some microorganisms are plants or animals, but some belong to the other three kingdoms of living things. 1) Monera comprises bacteria, including cyanobacteria. Monerans are small, simple, single cells, and sometimes form chains or mats. 2) Protista includes protozoans and algae of various types. These are large, complex, single cells, sometimes forming chains or colonies. 3) Fungi are molds and mushrooms. These have a multicellular filamentous form with specialized complex cells. 4) Plantae are plants, including mosses, ferns, woody plants, and non-woody plants. They photosynthesize. 5) Animalia includes everything from sponges and worms to mammals. Viruses aren’t included in the kingdoms because they are on the borderline between living and non-living things. They are noncellular parasites that cannot live or reproduce outside a living organism.  

On this field trip, we use the term microorganisms to refer to organisms that are so small you need microscope to see their details. Students can often see these organisms swimming around in the water or growing on the rocks.  

Lichens are organisms that consist of different species of fungi, algae, and cyanobacteria in a symbiotic relationship. Every lichen contains a partner that photosynthesizes (either algae or cyanobacteria or both) and fungi partners. A single lichen can contain up to 20 different species of organisms, and 20 percent of fungus species can be "lichenized". The algae's/cyanobacteria's role in the relationship is to provide the fungi with the sugars it needs to survive; the fungi cover the algae and protects it from the sun and exposure. Lichens are not individual species, but communities of organisms, more similar to an ecosystem than individuals. Scientists classify lichens based on their morphology, the shape that forms the structure of the lichen. Scientists have identified 20,000 types of lichens worldwide, but even so, similar lichens growing near to each other might have different species of fungi and algae that make up their community.  

Lichens cover approximately 7 percent of the Earth's surface and are found in most environments from the tundra to the tropics. Some lichens are extremely hardy and can shut down photosynthesis when conditions are not ideal. Lichens have been sent into space and were still able to re-start photosynthesis when brought back to the Earth's surface.  

Lichens are also important to the greater ecosystems in which they are members. They are often the first organisms to colonize disturbed areas and can help weather rocks to create new soil. Lichens are excellent indicators of air quality; because they do not have roots or stems, they accumulate many of their nutrients from the air, which makes them very sensitive to pollutants. Dry lichens have the ability to absorb more than their own weight of water. They can carry on food production at any temperature above 32ºF. Temporary water, such as dew, can be taken almost directly into the algal cells of the lichen; the water does not need to go through roots and stems as it does in vascular plants. 

Desert potholes provide homes to a fascinating array of small organisms and microorganisms. Pothole dwellers have unique adaptations, enabling them to survive in this feast or famine environment. Most of these organisms have shortened life cycles, reducing the time they are dependent on water, and thus allowing them to live in shallow, short-lived pools. The life cycles of clam shrimp and fairy shrimp are 5-10 days. The life cycle of a tadpole shrimp is 12-14 days. Tadpole shrimp, as a result, require deeper potholes in order to survive.  

A pothole’s size determines its diversity and species make-up. Microorganisms, such as single-celled algae and protozoans, inhabit shallower pools. Slightly deeper pools might have tiny worm-like larvae of midges wriggling around their bottoms. The deepest and largest pools might contain a variety of tiny crustaceans and insects: fairy shrimp, clam shrimp, tadpole shrimp, water striders, back swimmers, water boatmen, and whirligig beetles.  

A pothole is a unique habitat that is very easily disturbed. Pothole organisms are sensitive to sudden water chemistry changes (brought on by sunscreen, for example), temperature changes, sediment input, being squashed, and being splashed out onto dry land.  

Salinity is the saltiness or dissolved salt content of a body of water. Our potholes tend to stay around 1.0 or less ppt. To compare: salinity of the ocean is 35 parts per thousand; The Great Salt Lake ranges 50 to 270 parts per thousand; the upper limits of freshwater organisms are 100ppt. A solution’s pH is the measure of its hydrogen-ion concentration. The higher the pH reading, the more alkaline and oxygen rich the fluid is. Lower pH readings indicate more acidic and oxygen deprived fluids. PH ranges from 0 to 14, with 7.0 being neutral. The normal range for pH in surface water systems is 6.5 to 8.5. Potholes fluctuate throughout the day, generally in the 5-7 range.

Preparation

PRE-TRIP ACTIVITY

Mystery Photographs 

Essential Question: What is a microorganism? 

Materials: Microorganism powerpoint with pictures and videos; cards with descriptions of each image in the powerpoint (one per student) 

Procedure: 

1) Tell students that we will engage in a short discussion. Introduce the idea that discussions are used to explore ideas where no “right answer” exists. Write the question on the board: What organism is the most successful organism on earth? Have students discuss with the person sitting next to them. As part of their discussion, students should clarify what it means to be “successful” (i.e. how or why is that organism successful). For example, is the organism the most numerous, oldest, cutest, most influential, or most dangerous. If categories are confusing, compare to the various Oscars at academy awards. Give students several minutes to discuss, and then have pairs share their nominations. Record “categories” and nominations on the board.  

2) Write the term “microorganism” on the board. Discuss students’ prior knowledge of microorganisms, including what types of tools scientists might use to study them. Confirm students understand the basic definition of a microorganism: An individual organism so small you need a microscope to see the details of it. Some people think microorganisms are the most successful of all organisms. 

3) Show students a PowerPoint of a variety of microorganisms. Give each student one or two cards with names and descriptions of microorganisms. Tell students how to pronounce tricky names like “spirogyra” as you pass them out. At each slide, students should read their descriptions. If they decide theirs matches the image, they should raise their hand. Call on these students to name of the microorganism. Discuss the organisms throughout the activity, pointing out interesting and relevant information. 

4) Tell students some scientists think microorganisms might be important nominations for these categories, including some microorganisms we will see on the field trip: 

  • Most successful at survival: Tardigrades are among the most resilient animals known, with individual species able to survive extreme conditions—such as exposure to extreme temperatures, extreme pressures (both high and low), air deprivation, radiation, dehydration, and starvation. 

  • Most successful at multiplying: Bacteria can double their population size in minutes. 

  • Oldest: Cyanobacteria have been around since way before dinosaurs and are the oldest known fossils (stromatolites)- (at 3.8 billion years- no need to state this but good to know) or certain Lichen species have been found in the arctic for 8,000 years. 

  • Most helpful organisms: Phytoplankton provide 50% of the earth’s oxygen today. 

  • Most numerous: Plankton make up 1 in 3 cells in the ocean. They include all microscopic sea life. Microbes living in your body outnumber human cells by 10 to 1. Most of them don’t hurt us. Some even help us, like our guts microbes that help digest our food. 

5) Preview the field trip, telling students they will search for some of these microorganisms, using hand lenses and microscopes, and complete some scientific investigations. Review the items students need to bring to school on the day of their field trip.

 

Procedure

STATION #1
Life in a Pothole 

Essential Question: How do the characteristics of a pothole effect the amount and diversity of life inside the pothole? What steps do scientists use to answer questions? 

Materials: dip nets(3); tray; hand lenses; microscopes and slides; Pothole Organisms identification sheets; data book; data collection sheets, pencils; litmus paper, temp gun, salinity monitor, measuring tape, yardstick. clipboard; calculator; eye droppers(7); dixie cups; trash bag. 

Procedure:  

1) Have students lay down on their bellies and examine the potholes. Remind students about the importance of not touching the water. Point out organisms swimming in the water and encourage students to share their wonderings about the creatures they observe. (5 min) 

2) Gather students away from the pothole. Use photographs to discuss the creatures students observed. Share fun facts about each like which creatures are the predators. Ask what might make life difficult in a pothole, include extreme temperatures, changes in water chemistry, and lack of resources as water evaporates. Discuss strategies organisms use to survive such as short life cycles and fun facts like the brine shrimp eggs scientists glued on the outside of a rocket, or the tadpole shrimp eggs found on a shelf.  

3) Tell students that scientists often use data to help make sense of what is happening in an ecosystem. Show students the pothole data sheets from the past and explain. PH is the level of acidity in the water. Salinity is the level of salt in water, compare to the ocean 35 parts per thousand, and the Great Salt Lake ranges from 50-270 ppt. Both can affect pothole life. Tell students they are going to be adding today’s data to the sheet. Give each student a data collection tool and explain their “mission”. Give them time to collect their data and enter it on the data collection sheet. (3-5 min) 

4) Gather students and compare today’s data to that of previous groups and previous years. Have them pick one aspect of their data they think will influence the number of species and individuals and discuss results found on past days with similar data. In addition, examine at the trends seen over the past several days. Ask students to predict if the number of organisms they will observe is more or less than the previous group. Discuss the reasoning behind their predictions. (3-5 min) 

5) Show students how to use eye droppers to catch pothole organisms and place them under the microscopes. Help students while they observe and catch pothole organisms. Once organisms are seen by the group, they should be placed in a tray for additional observation with hand lenses. Try to catch a smaller organism and mount it on a slide under the microscope. When students no longer seem to be interested in the smaller organisms, hand out dip nets or spoons. Have students record each of the organisms they collect on the organism identification sheets. (30-40 min) 

6) With 5-7 minutes left for the station. Gather the students, tally the number kinds of organisms seen as well as the numbers of creatures seen. Return all living organisms to the pothole. Enter the results on this year’s data sheets. Have students compare the results on their insect observation sheets to those of previous groups. Encourage students to find patterns in the data. Use phrase “why do you think that is?” to encourage students to construct explanations about how changes in pothole might influence the numbers of organisms. Does predation play a role? Does the abundance or lack of resources (i/e water) play a role? Discuss how further changes to this fragile ecosystem might further change the populations.  
 

Hybrid two pothole version – 

If students get frustrated about not finding anything in their first pothole, consider taking them to a second or third pothole. Explain that the group will go to another pothole that is different and comparing the two. Guide them to make specific observations about the first pothole before leaving. While walking to the other pothole, point out dried up potholes and explain that a few weeks ago, there were more potholes that held water.  

When you reach the second pothole, ask students about similarities and differences they observe between these potholes. For example, depth, water clarity, and size. Explain that every pothole has a different number of creatures, and some have many types and some have only one type. If students notice this pothole only has one species (i/e fairy shrimp, but lots of them), ask students if they can tell if they are all the same age or different ages. Explain that fairy shrimp lay eggs that hatch with different triggers. Ask students what might happen if we introduced a tadpole shrimp into this pothole. Discuss how organisms get from one pothole to another. Ask students if they think resources or predators (or something else) played a bigger role in the dynamics of these potholes. 

STATION #2 

Lichens Up Close 

Essential Question: What environmental factors influence lichen growth? What steps do scientists use to answer questions? 

Materials: hand lenses; name tags (algae; fungus; water and minerals; sunlight; oxygen; carbon dioxide; photosynthesis); pictures of lichens (e.g. Sharnoff, 1997, 58-71; Corbridge and Weber 1998); inside a lichen picture; lichen model; microscopes(2); copies of and Data Collection Sheet; cardboard plot frames(5); pencils; clipboards; compass(1); white board; temp guns(3). 

Procedure:  

1) Have students point to something growing on the rocks. Discuss what they notice, what things look like, and if the lichens remind students of anything. Distinguish between lichens and mosses by discussing characteristics of both. Moss is a dormant plant. Pour water on the moss and observe it turning green. When wet, moss wakes up and starts photosynthesizing. Pour water on lichen and have students observe what happens. In addition, discuss a lichen ghost and desert varnish. Remind students that both moss and lichens are fragile, so they should be careful not to pick at them or remove them from the rock. Discuss lichens growth rates. Measure a lichen that is approximately 11mm in diameter and discuss how that lichen is as old as the students. (2-3 min) 

2) Tell the students they are going to build a human model of lichen to learn how the organism gets the resources it needs to survive. Lichens are made up of two organisms that have a mutualistic relationship. Ask if any student likes to cook? Have that student stand up and hold the algae nametag. Algae makes the lichen’s food. It is the only organism of the two that can photosynthesize. Discuss the parts of photosynthesis and hand out corresponding name tags. Have the students with the oxygen, carbon dioxide and sunlight nametags stand around the algae. Ask if anyone likes to build things? Have that student stand up and hold the fungus name tag. Fungus attaches to rock, bringing in much of the water and minerals necessary for making food. The fungus also acts as a sunscreen protecting the algae from uv light. Discuss the use of water and minerals. Have a student hold this nametag and stand next to fungus. (As an alternative, you can place the nametags on the ground in front of you.) (5 min) 

3) Pretend to take a picture of them and show students the inside the lichen picture as their selfie. Use the 3d lichen model to point out the different parts. For an amusing review, tell students you have a really bad joke, which goes: “Allen Algae and Frieda Fungus took a lichen to each other. Allen did the cooking, and Frieda built the house. But, you know what I hear? Their marriage is on the rocks.” Groan along with the kids. Discuss the resources show in the model and which might be the most difficult to obtain in the desert. (1-2 min) 

4) Prior to the station, find loose pieces of lichen and place them under the microscopes for investigation. Tell students they will make observations of lichens. Encourage students to examine examples of lichen with their hand lens and the microscope. Have them focus on lichens they notice, what they look like, and what they remind them of. Encourage them to look for patterns about where the lichens are growing. In addition, ask students to find one favorite. Give boundaries. After no more than 5 minutes, gather the students. Have each student bring the group to their favorite lichen and describe why it fascinates them. Discuss patterns they notice in the number of lichens they find in specific areas. Make observations yourself about lichen density in certain areas. (5-10 min) 

5) Show students pictures of lichens around the world to discuss the following information:  

  • How many types of lichens are in the world? (Answer: over 15,000)  

  • Lichens are important as air pollution indicators, because they are sensitive to pollution.  

  • Lichens are a food source for some animals. 

  • Navajo people use lichens for plant dye for some rugs. 

  • Lichens can help archaeologists date items. Remind students of growth rates. (5 min) 

6) Save about 35-40 minutes for the rest of this station. Remind students they noticed lichens growing more in some areas than others. Have students discuss their observations and ponder why they think this might be the case. Tell students they are going to collect some data to further examine patterns about where the lichen populations are thriving. They will then analyze this data to make a scientific claim about where lichen grow. Explain that a claim is how scientists design experiments to answer questions. Often, the first step is to gather data and look for patterns. As an example, select a student wearing a lot of the same-colored clothing. Tell the students that you are going to make a claim: This student is wearing a lot of “x” colored clothing because “x” is their favorite color. Ask the students how they might experiment or find more evidence to back up this claim. (i/e observe them on multiple days). (5 min) 

7) Have the students find a partner and give each pair an investigation sheet. Tell the students they will gather information from 6 different plots. Collect the first set of data as a group to demonstrate how to collect temperature, number of colors, and amount of lichen growing. Demonstrate how to select a plot randomly by having one partner close their eyes, turn around twice, and place the plot at their feet. Hand out materials, give the students boundaries, and have them collect data from 2 more plots with lots of lichen and 3 plots with very little lichen. If they notice anything else unique about a plot, have them make a note on their data sheets. (20 min) 

8) When finished gathering data, have the students examine their data and notice patterns in lichen populations. Then have students imagine they have thousands of data sets; it would be much harder to see a pattern. Tell the students scientists analyze data using things like graphs to make the patterns easier to see. Plot the students’ data sets together on the whiteboard and discuss patterns they observe. Using this evidence, have the students make a scientific claim about lichen populations. Tell them that when they make their claim, it should have a cause and effect. For example, “When the rock is (hotter/colder), lichen populations are (bigger/smaller).”  

9) Discuss the cause-and-effect relationship of their claim by discussing what caused the effect. Remind students of your discussion about resources lichens need to survive. (air, water, minerals) Use the whiteboard and their graph to help the students create a “cause and effect” flow chart. Discuss how some areas of rock have more resources than others. If they struggle, ask if water might evaporate faster in one area than another. Ask when they sweat more - in the sun or the shade, when it’s hotter or cooler? An example claim might be: When the rock is hotter, water evaporates faster, leaving less water for lichens to use to grow. (5-7 min) 

10) Tell students the next step a scientist would take is to test their claim to provide more evidence. Ask the students what experiments they would design to test how temperature effects lichen populations. What results do they predict for these experiments and why?

Essential Question: How does the diversity and abundance of microorganisms in a pond compare to that in a pothole? 

Materials: microscopes; microscope slides; eyedroppers; water collected from a pond; clear cups of pondwater for each station; paper cups to set out the above items at each station; water and absorbent cloths for cleaning slides; prepared slides (for focusing microscopes); pond life field guides; extension cords and power bar as needed; dry erase markers 

Procedure:  

1) Briefly review the field trip. Review the microorganisms found in potholes and list these on the board. Review the resources available in a pothole and other factors (like predators) that affect the abundance of microorganisms found in a pothole. (2-3 min) 

2) Describe the pond and resources available for pond microorganisms. Make sure students understand the pond is a larger habitat and water is available all year. Invite students to make predictions about how many and what microorganisms live in the pond water. (2-3 min) 

3) Demonstrate and write on the board (in abbreviated form) the steps students will use in gathering data for this investigation:  

a. Hold up the cup to look for moving microorganisms. Catch microorganisms using the dropper. Use an eyedropper to put one small drop of pond water on a microscope slide. Demonstrate and stress this drop should be smaller than a dime.  

b. Look at a slide through the microscope. Tell students the little black line in the view is a pointer line and is supposed to be there. Discuss how to tell if they are seeing a microorganism or dust. Most small sand or silt grains have rounded edges, although some have broken edges like glass breaks. Students should look for movement, cells, hairs, or things like the photos they’ve seen of microorganisms. This is also the time to explain how to focus the microscope and how to handle it without damaging it. Remind students to show other group members anything they suspect of being a microorganism. 

c. Each group will make a list of different organisms seen. The list can include the organism’s name, if known, and/or a written description or a school appropriate made-up name. Each group should have notes good enough to determine if another group’s sighting is the same or different than their sightings.  

d. Show students how to clean slides. (5 min) 

4) Assign groups to microscope stations (one group per available microscope). Circulate among the groups at the microscopes. (20-30 min) 

5) After the investigations are completed, bring students back together and compare the lists of microorganisms of the pothole and pond organisms. Discuss how resource availability and/or predator abundance could affect populations of microorganisms. (5-10 min) 

Additional Resources

Ahmadjian, V. (1989). Lichens are more important than you think. BioScience 45: 164. 

BEETLES Most Successful Organism Discussion http://beetlesproject.org/resources/for-field-instructors/most-successful-organism/ 

Belnap, J., & Gardner, J.S. (1993). Soil microstructure in soils of the Colorado Plateau. Great Basin Naturalist 53: 40-46. 

Brady, Irene. (1998). The redrock canyon explorer. Talent, OR: Nature Works. 

Chan, M.A., Moser, K., Davis, J.M. et al. (2005) Desert Potholes: Ephemeral Aquatic Microsystems. Aquat Geochem 11, 279–302. https://doi.org/10.1007/s10498-004-6274-8 

Corbridge, J. & Weber, W. (1998). A rocky mountain lichen primer. Niwot, CO: University Press of Colorado. 

Graham, T. B. (1999-2000). Life in the fast pool. Plateau Journal (Winter): 29-45. 

Johnston, R. (1997). Introduction to microbiotic crusts. U.S. Department of Agriculture, Natural Resources Conservation Service, Soil Quality Institute, Grazing Lands Technology Institute (July). 

Kuhn, D. (1988). The hidden life of the pond. New York, NY: Crown Publishers.  

Nardo, D. (1991). Germs: Mysterious microorganisms. The Encyclopedia of Discovery and Invention. San Diego, CA: Lucent Books. 

Reid, G. (1967). Pond life: A golden guide. New York, NY: Western Publishing, Golden Press. 

Ricciuti, E. R. (Ed. Vincent Marteka). (1994). Microorganisms: The unseen world. Woodbridge, CT: Blackbirch Press.  

Sharnoff, S. D. (1997). Lichens: More than meets the eye. National Geographic (February): 58-71. 

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Last updated: July 26, 2022