Microbial Discovery Activity Pond Scum – Page 2

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Author

Mark Gallo, Ph.D. Associate Professor of Biology Niagara University, NY 14109 [email protected]

Contributor

George A. Jacob, Ph.D. St. Xavier High School Cincinnati, OH 45224 [email protected]

Intended Audience

K-4 X 5-8 X 9-12 X

Activity Specifications Classroom setting X Requires special equipment X Uses hands-on manipulatives X Requires mathematical skills Can be performed individually X Requires group work Requires more than one (45 min) class period X Appropriate for special needs student X

American Society for Microbiology Education Department 1752 N Street, NW Washington, DC 20036 [email protected]

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Description In this exercise, students discover a diversity of microorganisms living in a small drop of pond water.

Abstract Little else can stimulate a student’s interest in biology like a drop of pond water teaming with invisible life viewed with a microscope. This activity describes two means of observing pond water other than the traditional hanging drop or temporary wet mount slide preparation.

Core Themes Addressed Microorganisms and the Environment

Keywords Aquatic, Environment, Protozoa, Biofilm, Water quality, Classification

Learning Objectives At completion of this activity, learner will be able to: • appreciate (acknowledge) the previously unseen life in pond water. • prepare a biofilm slide. • draw and describe a microorganism.

National Science Education Standards Addressed

Unifying Concepts and Processes – This activity incorporates evidence of microscopic life.

Standard 1: Science as Inquiry – In completion of this activity student performs directed, inquiry based observations of microorganisms.

Standard 3: Life science - In completion of this activity student will have had a chance to view living organisms from an environment and determine the characteristics of the microorganisms.

Standard 5: Science and Technology – Biofilms will be noted as constructs by living organisms, microscopes will be used as a tool to recognize the microbes, students will be asked to determine what defines a living organism.

Standard 6: Science in Personal and Social Perspectives – In this activity learner monitors the quality of fresh water ecosystems by observing indicator microorganisms.

Life Science Concepts: May incorporate responses of unicellular organisms.

Scientific Thinking: Student can make predictions about water quality.

Scientific Tools and Technologies: Microscopes, centrifuges, slide preparation.

Scientific Communication: Sharing observations with classmates and teachers.

Scientific Investigation: Hands-on manipulative experiment created from a known water source.

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Necessary Student Background Student must be familiar with the workings of a microscope.

Teacher Background Information The diversity of life becomes self-evident in the microscopic world and has fascinated individuals since the first glances at it through the microscopes of Antonie van Leeuwenhoek. Students can explore this world of numerous single-celled and multi-cellular organisms. One can explore the questions of what is living/non-living, how are cells organized, what are the size limitations of life, how do microbes move, sense their world, interact with other microbes and the world around them.

Students may want to peruse two outstanding websites to investigate pond water life: • “Water World” at the Microbe Zoo: http://commtechlab.msu.edu/sites/dlc-me/zoo/zwpmain.html • Florida State University’s Molecular Expressions Digital Video Gallery, Streaming Video, and Downloads of protozoa commonly found in ponds: http://micro.magnet.fsu.edu/moviegallery/pondscum.html

Class Time Approximately 45 minutes of class time is required.

Teacher Preparation Time Time must be allotted for specimen gathering and slide preparation: • Biofilm slide preparation should be performed at least 24 hours prior to class. • Pond water, lake water, river water (etc) needs to be collected or brought in by students. • Order Demoslides and slide holders from: Connecticut Valley Biological Supply Company, Inc. 1-800-628-7748 or from Carolina Biological 800.334.5551 • You may also want to order some live cultures of mixed protozoa. These typically last for several weeks or more and are excellent in that they show a robust, diverse population of microbes.

Materials and Equipment

I. Biofilm preparation (supplies for each team)

• 2 - 4 microscope slides • 22 x 40 coverslips (if available - other coverslips will do) • small container such as a deli or fast food container that will hold water to a depth of approximately 3 cm. • microscope • Centrifuge or strong string

II. Demoslide preparation (supplies for each team)

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• 1 demoslide tube with lid • 1 demoslide holder • microscope • centrifuge or a length of string, about 2 feet long

Demoslides: From http://www.demoslide.com “Designed to simplify the preparation of living protozoa for microscopic examination in the classroom. Culture chamber and examination chamber combined into one unit. No more transferring of materials for study. The growth chamber holds 5 ml. of algae or protozoan culture and can be maintained there for up to a week or longer, depending on the type of culture. The unique Microscope Stage Adapter allows for easy positioning of the Demo Slide and the Demo Slide Tube Rack holds 12 tubes either horizontally or vertically. Demo Slides are based on the Cen- Slide® system from DAVSTAR)”

Methods I. Biofilm preparation 1. Place 2 - 4 glass slides on the bottom of a small container. 2. Pour pond water over the slides and rearrange the slides if they moved. Slides should not overlap. The water should be about 3 cm deep. 3. Cover the container if it will be more than 24 hours before you can view the biofilm. 4. Set the container in a spot where it will not be disturbed. 5. After 18 - 24 hours (or longer if necessary), carefully remove a slide and wipe the BOTTOM with a paper towel. 6. Carefully lay one long coverslip over the top of the slide. If you don’t have long coverslips, lay two smaller coverslips side by side. 7. Observe the biofilms using the 4X, 10X and 45X objectives.

II. Demoslide preparation 1. Pour well mixed pond water into a demoslide tube and cap tightly. 2. Centrifuge, if possible, at a slow speed for 10 minutes. 3. If a centrifuge is not available then set tube upright for a period of time and some microbes will settle into the bottom. Be careful to not trap a bubble in the bottom. If one exists you may be able to dislodge by lightly squeezing or squirting liquid into the tube. Another simple technique when working in the field involves the use of a string. A piece of string is tied tightly around the tube, right below the cap. The tube is then whirled for a minute to concentrate the pond water microbes in the bottom of the tube. CAUTION: This may be difficult and somewhat dangerous to do with younger students. Even high school students may not be careful enough and they could send a tube flying across the room. Therefore, they must be closely supervised. Also, care must be taken to ensure that the string will not slip out of the tube.

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4. Affix the tube to the slide holder and place it on the microscope stage. 5. Observe the tube using the 4X, 10X and 45X objectives.

Microorganisms Microorganisms are present in this activity, the type varies based on the sample. It is important to stress to the students to not bring in samples from water sources known to be contaminated with human or animal waste.

Safety Precautions Remind students to wash their hands after handling pond water samples.

Assessment Below are possible assessment techniques. • Have students identify 5 different organisms using an identification guide and ask them to answer the following questions about each organism: o Into what Kingdom is this organism classified? o What do the terms prokaryote and eukaryote mean? o Is this organism prokaryotic or eukaryotic? o If this organism is motile, how does it move? o How does this organism obtain necessary nutrients? o How does this organism reproduce? • Have the students draw a picture of the organism and write a paragraph about the life and times of the organism for a museum exhibit. • Create a poster of the web of life of the different microorganisms noted by the class. • Use a dichotomous key to identify microorganisms. • Ask students to consider the term indicator organism and how microbes can be used to assess environment quality.

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Demoslides

• Demoslides and approximate costs: $84 (2007) for a kit with 30 slides, a demoslide rack, and 4 stage adapters (From Carolina Biological Supply)

Tips/Suggestions: • Demoslides are excellent for inquiry-based experiments. The environment can be altered (temperature, pH, light) and the tubes can be observed without disruption over long periods of time. • Undoubtedly the teacher will be called upon to answer the question “What is this???” many, many times. There are two ways to address this. One is to allow the students to be the “discoverers” of these creatures and let them create appropriate names for the organisms. The class can then use this as a means to form a classification system. Another option is to allow them to compare what they have seen with what is known and described in identification guides. The following are available through bookstores or online vendor sites: How to Know the Freshwater Algae (George W. Prescott) How to Know the Protozoa (Theodore Jahn) Guide to Microlife (Kenneth Rainis) A Guide to Common Freshwater Invertebrates of North America (J. Reese Voshell, Jr.) • Set up your own mini-ponds by following the “Puddles: exercise from the Meet the Microbes” projects published by the National Association of Biology Teachers. The activity can be found at http://www.microbeworld.org/resources/experiment/pgs58-61.pdf (Accessed September 30, 2007).

Suggested Student Answer Key

1. Which source had the most organisms? In most cases this will be the one with the most organic material present. Students are always meek and choose to bring in relatively clean water. They also typically sample from a clear region of their sample.

2. Which source had the most diversity? Again the answer is typically the one with the most organic material.

3. Do all your water samples contain the same organisms? Propose a mechanism for your observations. It is very unusual to find the same organisms in every sample. Point out to theme that just like big organisms some will only be found in certain ecosystems. In fact certain microbes are used as indicator organisms that are useful to assess water quality.

4. Suppose you changed the time that a slide stayed in water. How would you predict that this would affect your observations?

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One may find that there is an initial time period where nothing is associated with the slide after which one will find organisms increase in number.

5. What may happen to the number and diversity of microorganisms throughout the year in an aquatic environment? The number and diversity may decrease during colder months and increase during warmer months.

6. How would you identify producers, consumers, and degraders in the microbial world? Producers which are photosynthetic and are typically green. Consumers would eat other live microorganisms. Decomposers may be found associated with some dead or decaying material. To add to the confusion there are some photosynthetic protozoa that can also act as consumers.

7. Make a list of six (6) factors that could influence a water environment. Explain how each would impact the biota. Temperature, pH, salinity, turbidity, oxgygen content, regular influx of fresh water, pollution from either animal wastes or runoff from yards and farms, solar exposure, as well as many other factors.

8. Organisms can be used as indicators of water quality. Find an example of a microorganism that can only be found in undisturbed high quality water environments. Find an example of a microorganism that can be found in a eutrophic environment. Find an example of a microorganism that can be found in a polluted environment. Rotifers and diatoms are typically found only in high quality water. Spirogyra and Chlamydomonas can be found in eutrophic water and Spirillum and Microcystis can be found in polluted water. There are many other indicator organisms than the ones listed.

Modifications Simplify student questions when used for middle school, or elementary school students.

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SSStttuuudddeeennnttt HHHaaannndddooouuuttt Pond Scum: Investigating Microorganisms

Introduction Fresh water is teeming with living organisms. This experiment will allow you to be able to see and identify many living organism with the aid of a microscope and keys.

Necessary Student Background To prepare for this activity you must be familiar with the use of a microscope.

Vocabulary

Biofilm- Biofilms form when bacteria attach to surfaces exposed to water, and begin to excrete a slimy, glue-like substance. Protozoan- single celled organism such as an amoeba that can move and feed on organic compounds of nitrogen and carbon. Demoslide- Combination collection/storage/and microscopic observation tubes for Protozoa and other cell cultures. Motile- having the ability to move. Biota- A collective term for the animal and plant life of a region Eukaryote – an organism possessing a nucleus and numerous other membrane-bound organelles. Eutrophic – water source rich in nutrients and organic material that promotes a proliferation of life, with some microorganisms growing in excess, using up the available oxygen.

Safety Considerations

1. As with any experiment, it is important to gather your materials before starting, be familiar with their purpose, and READ THE DIRECTIONS.

2. Glass slides may be slippery and may break. If breakage occurs, please tell your teacher so the broken glass can be properly disposed of is not a danger to others.

3. After your teacher asks you to clean up, it is very important to wash your hands with soap and water.

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Materials Checklist

microscope

demoslide + chamber

biofilm slide + cover slips

water sample

centrifuge or capped tube + string

Procedure I. Biofilm preparation 1. Place 2 - 4 glass slides on the bottom of a small container. (It has been found that coating the slide with a thin layer of glue with a glue stick and allowing it to dry before placing it into the container attracts a lot more organisms to the slide. Try it as a variable in your experiment.) 2. Pour pond water over the slides and rearrange the slides if they moved. Slides should not overlap. The water should be about 3 cm deep. 3. Cover the container if it will be more than 24 hours before you can view the biofilm. 4. Set the container in a spot where it will not be disturbed. 5. After 18 - 24 hours (or longer if necessary), carefully remove a slide and wipe the BOTTOM with a paper towel. 6. Carefully lay one long coverslip over the top of the slide. If you don’t have long coverslips, lay two smaller coverslips side by side. 7. Observe the biofilms using the 4X, 10X and 45X objectives.

III. Pond water slide Pond water is full of life however only a small amount of it is visible to the naked eye. 1. Observe your sample for macroscopic organisms (those that are visible to the naked eye). 2. Take a dropper and remove some water from near the interface of the water and mud.

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3. Place a small drop onto your microscope slide. Gently drop on a cover slip. If excess water is present blot with paper towel prior to placing on stage of the microscope. 4. Look around the slide using low power (4X objective). Observe around the edges of debris present on the slide. 5. If you find interesting creatures try moving the objective lens up to the next higher power and observe the additional detail. If you are unsuccessful finding anything with your first slide try making another. 6. Observe the microbes as you have with the other protocols, this time try to determine how they make a living. In particular try to determine their food source. 7. Use different sources of water. Try to find some from pristine, undisturbed water sources, others from a pond or lake that may receive a heavy load of organic material, termed a eutrophic environment, and perhaps others that have been polluted.

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Student Name: ______Date: ______

I. Draw your observations below and describe what you see. Describe color of objects and motility, if noted.

Biofilm slide

Demoslide

Pond water slide

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II. Please answer the following questions.

1. Which source had the most organisms?

2. Which source had the most diversity?

3. Do all your water samples contain the same organisms? Propose a mechanism for your observations.

4. Suppose you changed the time that a slide stayed in water. How would you predict that this would affect your observations?

5. What may happen to the number and diversity of microorganisms throughout the year in an aquatic environment?

6. How would you identify producers, consumers, and degraders in the microbial world?

7. Make a list of six (6) factors that could influence a water environment. Explain how each would impact the biota.

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