Make Your Own Pond Water

Activity Plan Make Your Own Pond Water Summary of Lab: In this lesson students will be introduced to the hidden microorganisms found within pond water and write an observational report describing their observations. Objectives: 1. Identify microscopic pond organisms, including those that could be parasites 2. Make structural and behavioral observations about identified organisms 4. Write a report summarizing observations Grade Level: Grades 6-8 (could be scaled up for 9-10) Background Information: • • • • • • • Pond water is a good model for students to learn about ecosystems and the presence of microorganisms. There are a large variety of organisms which may be present including: bacteria, protozoa, algae, rotifers, gastrotrichs, worms, bryozoa, hydra, tardigrades, and arthropods. Students should understand that not all organisms in water can cause disease in humans. There is a whole microscopic world located in the water they could potentially be swimming in or even drinking. As the other lessons in the module have discussed, water is a common route of disease transmission for parasites. Two parasites: Cryptosporidium and Giardia, are the most common causes of water-related illness in people. Both of these parasites may be carried by animals that drink out of ponds or whose feces may wash into the pond. Parasites are not the only problems in pond water. Water may also contain disease causing bacteria and viruses. When people swim in untreated water such as ponds, they greatly increase their exposure to potential parasites and other infectious agents that may cause disease. An introduction to microbes (bacteria, protists, viruses, and fungi) is found at http://peer.tamu.edu/curriculum_modules/Properties/Module_1/lesson.htm. A short tutorial on protozoa is found at http://peer.tamu.edu/curriculum_modules/Properties/module_1/lesson_protozoa1.htm A short tutorial on food poisoning is found at http://peer.tamu.edu/curriculum_modules/organsystems/module_2/hazards2.htm Time Required: 1-2 class periods Materials Needed: • • • • • Microscope Microscope slide Cover slip Eye dropper/ pipette Water sample and container Recommended Procedures: • • • • • • The day before you are ready to complete this lesson you can have the students collect a water sample from any water source with vegetation (pond, creek, ditch, lake). Begin by surveying the students in the class. Ask how many of them go swimming in lakes, creeks, rivers, ponds, the ocean, or any other untreated water source. Ask the students if they have ever gotten sick on know anyone else that has from the swimming (such as ear infections, swimmer’s itch, or diarrhea)? Remind the students about the zoonotic parasites lesson and how not only parasites, but viruses and bacteria can be found in water that may cause diseases in people. Once you have got the students thinking about what all may be found in water have them investigate their own samples of water. Divide the class into small groups of 3-4 students if there are not enough microscopes for all of the students to have their own. Have the students gently mix their water sample in case the organisms have settled to the bottom of the container, then prepare a wet-mount slide. This is done by placing one drop of the water on the slide and gently placing a cover slip over the drop of water. • • • • • Beginning with the lowest power objective, have the students scan over the entire sample. As they locate different things increase the magnification to get a more detailed look. For help with microscope techniques go to Microscope Techniques As the students increase their magnification they will begin to see smaller and smaller organisms. Allow the students to use an online site to identify the organisms they were seeing. Have the students record their observations about what they see. Have them make drawings and make sure the descriptions include size, shape, color, amount, and movement of all the different organisms they locate. After the students have finished looking at their samples and making observations have them complete a one page report on what they found. In the report they should describe what they saw, what they learned about pond water from this activity and answer the following questions: How did you determine which organisms were living and which were non-living? Movement is key to identifying what is living versus nonliving. Also the color green is indicative of plant material or algae which are living. What was the most numerous type of organism you saw? This will vary depending on where the sample came from Could you identify the organisms that create their own energy through photosynthesis and which ate other organisms? How? The color green usually is a give away that an organism is able to complete photosynthesis. Any other organism which doesn’t complete photosynthesis must get nutrients somehow. For small unicellular protozoa they gain nutrients through phagocytosis. For larger organisms such as roundworms they ingest food through their mouth. Some students may be lucky enough to see an amoeba engulfing food through phagocytosis if they are patient. What would happen if the water was heated or cooled? Why might you want to cool the water? Increasing temperature increases movement in the organisms while a decrease in temperature decreases the overall activity. Any extreme in either direction can be deadly. Cooling the water may be beneficial to slowing down fast moving organisms and getting a closer look. For a good demonstration of this concept go to Goldfish Demo How might this water sample look different during drought conditions? Here you might have to help the students but you want them to think about the concept of population density. During droughts when water levels drop this increases the concentration of microorganisms in the water. Assessment: The teacher will assess the students understanding through the written report. Vocabulary: Words belonging to word families: Word ecosystem phagocytosis (phage = eat or consume; cytosis = cell) Family of Related Words ecology, economy, Meaning common to the family exchange/interaction among diverse elements phage (bacteriophage), eat or consume coprophagic, Meaning of This word a complete community of living organisms and the nonliving materials of their surroundings “eating” or consumption of small particles by a cell Other Words: • • • • • • Parasite: An organism which lives within or upon a different host species and my cause harm to the host Microorganism: organisms which can not be seen with the naked eye Bacteria: prokaryotic unicellular microorganisms Protozoa: group of unicellular eukaryotic organisms Algae: primitive photosynthetic eukaryotic organisms Rotifers: microscopic multicellular fresh water organisms that contain a complete digestive tract • • • • • • • Gastrotrichs: phylum of microscopic marine animals which have bilateral symmetry and a complete digestive tract Worms: common name for phylum nematode which consists of roundworms Playhelmintes: phylum of flat worms which lace a body cavity Bryozoa: tiny colonial animals similar to coral that are commonly called moss animals Hydra: freshwater members of the phylum cnidaria which is characterized by radial symmetry Tardigrades: microscopic segmented water dwelling animals with 8 legs commonly called water bears Arthropods: phylum of animals characterized by jointed exoskeletons, includes insects and crustaceans