2 Pond water and the scientific

Transcription

1 LABORATORY 2 Pond water and the scientific method Today we will reinforce our understanding of the scientific method while observing living organism in different environments. In this lab we will: identify prokaryotic and eukaryotic cells make wet mounts compare samples by identifying protists and cyanobacteria practice hypothesis testing use environmental indicators to determine water quality There are 4 different samples of pond water on your table. Each person at your table should make a wet mount of one of the different pond samples and determine where your sample came from. Be sure to view each of the 4 samples by looking at the wet mount slides made by other students in your group. Use the photos located on the last page of your lab manual to determine which organisms are found in which type of conditions and use the reference microscopes on the counter to compare with the organisms you see in your sample. Compare the samples amoung your group members and use the attached format for the scientific method to describe the details of your scientific method. Good luck! Here is refresher for the preparation of wet mount slides: 1. Be sure to stir the pond water sample to insure uniform distribution of the organisms present in the water. 2. Take a clean microscope slide and place two to three drops of the stirred sample in the center of the slide. 3. Take a clean coverslip and place it at the edge of the water drop at a 45 0 angle to permit water and material to spread evenly beneath the tilted coverslip. 4. Slowly lower the coverslip until there is a film of water with organism and NO air bubbles under the coverslip 5. View the slide using the techniques learned in laboratory 1 6. When using the reference microscope be sure to notice the magnification 2-1

2 ***NO TOXIC SAMPLES ARE BEING USED IN THIS LAB*** Using the scientific method to determine water quality Take a moment to review the steps of the scientific method from exercise 1. We will use the same method to determine the locations and possible contamination of pond water samples. Observation: We know that the relative abundance of certain organisms indicate water quality. The quality of surface water(streams, lakes, rivers, estuaries, and seas) influences not only the health of aquatic ecosystems, but also whether that water can safely be used for human activities such as drinking, agriculture, or recreation. The amounts of selected substances in surface water indicates the impact of human settlements and land use on the environment. Indicator organisms are organisms that are present in unnaturally high concentration due to a change in a key aspect of an ecosystem. Their absence in an ecosystem, where they would normally be present, may also indicate an environmental change. Photosynthetic protists such as algae and prokaryotic cells such cyanobacteria are the simplest form of organisms that can be used as indicator organisms. Cyanobacteria (also called blue -green algae) are aquatic single-cell organisms which have some Table Health of aquatic ecosystems and indicator organisms Category Natural unpolluted lake Toxic waste contamination No Algae Indicator Explanation High species diversity The algal community often is diverse with several groups present. A balanced ratio of diatoms and green algae is commonly observed Although some algae species are very resistant to toxic waste products, most are not and thus very few algae will be present in the contaminated ecosystem Sewage discharge Nitrogen rich pollution (fertilizer) Cyanobacteria Euglena 2-2 Organic pollution (sewage discharge) in a lake or stream causes blooms of cyanobacteria that form thick algal mats Nitrogen rich contamination increases the ratio of euglenophytes (Euglena) above normal levels. Very little diversity is observed in this type of aquatic ecosystem.

3 properties that are characteristic of bacteria (no nucleus) and some that are characteristic of algae. In addition, eukaryotic protists and multicellular plants and animals (those with a nucleus) can also be found in pond water. The relative abundance of these organisms are indicators of conditions such as slow streamflows due to over consumption of water and high levels of nutrients and sediments being added to an aquatic ecosystem. Under some conditions cyanobacteria increase in the environment. This high count of cyanobacteria can potentially render the water unsuitable for human use because some species produce chemicals that can be toxic to humans and livestock. Use the information found in Table 2-1 to complete Table 2-2. After doing this you will be ready to observe and analyze your samples. Table Practice using observational information Organisms Pond Location Category of ecosystem present Chemical Plant retention pond Cattle pasture Lake in uninhabited forest Pond near large tomato farm Question: Can we tell where these samples were taken from based on the relative abundance of certain organisms? Hypothesis: (See page 1-7 from exercise 1) H o : There is no difference between. H a : There is a difference between. Prediction: The differences in relative abundance of organisms found in pond water can help you determine the location and contamination of your samples. Experiment: Based on the information given in Table 2-1 match the indicator organisms with those in your sample to determine the most probable location where your sample was obtained. Use the pictures on the last page of this exercise to help you identify the indicator organisms. Discuss the procedure you will use to test your hypotheses with the other students at your table. 2-3

4 Write your procedure as you do it (remember, someone else must be able to redo your experiment using these directions.) Be sure to include in your procedure the use of the reference microscopes on the side counter where known samples are labeled. Since each student must make their own conclusions, everyone at the table must look at all the samples prepared at your table as well as looking at the samples on the reference microscopes. Use space below to write your procedure. Experimental methods Data and Analysis: Complete the table below only after you have viewed all four samples at your table and verified your ability to identify each indicator organisms using the reference microscopes. Pond Water Data Table Sample Number Species indicated Most likely location Conclusion: Reject/Accept null hypothesis Decision: Should we incorporate the use of biologial indicators in water quality monitoring? Yes No 2-4

5 Pond Water Organisms Volvox Spirogyra Oscillatoria Euglena Diatoms Nostoc 2-5

6 Diverse pond water - labeled Diverse pond water - labeled 2-6