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Microbial Discovery Activity Pond Scum – Page 2 MMMiiicccrrrooobbbiiiaaalll DDDiiissscccooovvveeerrryyy AAAccctttiiivvviiitttyyy PPPooonnnddd SSScccuuummm::: IIInnnvvveeessstttiiigggaaatttiiinnnggg MMMiiicccrrroooooogggrraaannniiisssmmmsss 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] IIInnntttrrroooddduuuccctttiiiooonnn 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. ASM Microbial Discovery Activity Pond Scum – Page 2 TTTeeeaaaccchhheeerrr HHHaaannndddooouuuttt Pond Scum: Investigating Microorganisms 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) ASM Microbial Discovery Activity Pond Scum – Page 3 • 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. ASM Microbial Discovery Activity Pond Scum – Page 4 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. ASM Microbial Discovery Activity Pond Scum – Page 5 SSSuuuppppppllleeemmmeeennntttaaarrryyy IIInnnfffooorrrmmmaaatttiiiooonnn 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
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