Transcript
Oat Seed Lab: Rationales for Doing This Lab
TEACHING RATIONALE I like my students to do a simple controlled experiment involving multiple individuals of one species. Ideally, I would like the study to give results that may be different between the experimental group and the control group, yet with fairly close averages and some overlap in their extremes, so that they can determine (using graphic and statistical tests) if their differences are significant, or not. [I don’t tell my students this; I just want them to expect a reasonable difference, based on the background info and a reasonable hypothesis (explanation for the assumed interaction of substance and organisms)]. Note that a hypothesis here is NOT a prediction of the expected results; rather it suggests a reasonable explanation for their likely interaction. Based on the hypothesis, then, we can set up a simple test and predict what the specific results of the test will likely be. More suggestions for containers: you can use old fruit fly vials. Another teacher has used K-‐cups and wheat seeds (see details below on page 3). Convenient holders for the vials could be 1” pvc couplings (about 50¢ each), gluing enough of these (one end down) to a strip of stiff plastic for each student at a table or row. Be sure a vial would fit loosely in the coupling and be easily grasped and removed before purchasing and gluing. They should be attached to the strip by applying a bit of glue (hot glue or 527 Bonding Cement, etc.) to the edge of one end of the coupling, then place that end in the desired position on the plastic strip. INTRODUCTION TO THE CLASS: On the first or second day of school, you may want to have your students set up the Oat Seed lab ASAP-‐-‐to get it under way and the seeds growing-‐-‐while you introduce elements of the Nature of Science with a number of NOS lessons. However, you should give your students a reasonable introduction to setting up the investigation. To do that, say something like the Background information for the particular study to be done: the Plant Food Study, or the Salt Water Study.
Plant Food Study
Background: Announce the following to your class: "With the time approaching when we will need to consider growing food plants in an orbiting space station, in a lunar base, or in a journey to Mars, it would be important to know just how much fertilizer is absolutely necessary for maximum growth in those environments. Payload size for launching support materials is very precious, so we don't want to send up any more than necessary. Baseline data can be gathered from ground-‐based studies on various food plants and various fertilizers." Then you could ask “How can we do that in the simplest way?” When students suggest growing the seeds in a fertilizer, ask “How would we know whether the fertilizer helps them grow better than they would in just plain water, or not? Hopefully, students will suggest growing more of the same kind of seeds in just plain water without the fertilizer. Or, if they say “Use a control,” say “Describe what that ‘control’ would look like?” and they should suggest the set of seeds in tap water. With that, describe briefly what “we are going to do” and proceed with directions for setting up the vials, “planting” the seeds and adding the liquid (plant food solution or water). I would NOT take time at this point to go into focusing on the Problem, forming a Hypothesis, or Predicting the outcome. That would be done later as students begin to process their data and prepare their reports.
If you like, you can display the following formal information. Or do this later, as students begin to prepare their formal report: Problem: How does a fertilizer affect the germination and growth of oat seeds? Hypothesis: Plant foods (fertilizers) provide nutrients needed by plants for growth. Test: Grow oat seeds in a solution of plant food (liquid fertilizer), and compare their growth with the growth of additional oat seeds (control) growing at the same time in plain tap water. Measure and record their shoot lengths each day of visible growth. Prediction: Since a seed is essentially a plant in a very early stage of life, it is reasonable to expect that anything that provides nutrients for plant growth should also help a seed to germinate and grow better than it would otherwise. Therefore, shoot lengths of oat seeds growing in plant food should be longer each day than for seeds growing in tap water, and this difference should be greater each day.
Alternative: Salt Water Study
Since the ‘modeling” materials and details provided refer to plant food, fertilizer or VF-‐11, I would try to do that study (using whatever liquid “plant food” you can find). However, if you can’t get the plant food, consider doing the Salt Water Study, and having students make the adjustments in their reports. Below is a Background statement (with formal parts following) for such a study. Be sure that you prepare a 0.1% solution of NaCl in tap water (not iodized salt). 1% solution will prevent all growth, so measure carefully! For a 0.1% solution of NacCl, measure 1.0 g NaCl into one liter of tap water (= 0.1 g per 100 ml tap water). Place portions of this solution into clean, clearly labeled containers (bottles or beakers), enough so there is one supply bottle per team of 4 (or other grouping of students). Background: Announce the following to your class: “There is no question that our planet is warming. We are seeing long-‐term glaciers on large land-‐masses melting into the oceans, and this is expanding every year. Sea levels are already starting to rise, and many seacoasts and low islands will be increasingly inundated with seawater. Where croplands lie close to the sea, this means that they are in danger of dying out as the salty seawater comes closer.” “One of the solutions for dealing with this could be the development of salt-‐resistant plants. To begin these studies, we need to know what levels of salt our desired plants can take. Then by selective breeding or genetic engineering, we will use only those plants that grow best in a marginally salty environment, and use their seeds to plant for the next generation of seeds. By repeating this, we should, over time, have selected crops that can be grown to harvest in saltier water than they do now.” If you like, you can display the following formal information. Or do this later, as students begin to prepare their formal report: Problem: How does salt affect plant growth? Hypothesis: Since freshwater plants are currently growing in optimal conditions, it is likely that more salt in their water would probably reduce their growth rate, perhaps by osmotically drawing water out of the plant cells, essentially drying them out.
Test: To test this hypothesis, we will first try growing oat seeds in a very low concentration of salt (0.1% NaCl) in tap water (not “soft water”), measuring and recording their heights daily. We will run a control group of oat seeds in an identical environment, but watering them with plain tap water. As the water is evaporates and is used up by the seeds, we will replace the missing water with more tap water (to both vials), every two or three days. (Why wouldn’t we add more salt water to the saltwater vial?) As the young seedlings grow, we will measure their lengths each day, and compare their growth patterns. Prediction: The seedlings growing in salt water will, on average, not be as tall as the control seedlings. That difference in tallness will increase each day of the study, due to the slower growth rate of the seedlings in salt water. OTHER VARIATIONS & SUGGESTIONS: Wheat seeds in K-‐cups “I use untreated wheat seeds that are very inexpensive and most large grocery stores carry them in their "natural" section of the store. The seeds grow very quickly and it is a commodity crop as well so the kids see the impact on monetary side of agriculture for the pollutants that they are using. The kids have used them with "greenhouse gas" experiments, acid rain (vinegar dilutions), groundwater pollution (water the pots from below), gray water applications to soil, salt tolerance (perfect for our climate) and macronutrients - nitrogen, phosphorus and potassium. They track germination, measure the size of plant and when we are done they will measure the length of the root. I have also had them sketch parts as well. The kids keep an on-going log of qualitative information along with the chart of quantitative. When complete, they graph information as well as write a formal report. I recycle K-cups (for Keurig-type coffee makers) to use as planters. We strip off the tops and put the coffee in the compost pile along with the small internal filter. The cup has a hole in it from the coffee-making process. The cups easily hold 10 seedlings and can be used multiple times.” Pam Stewart, DeWitt, NY
