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APPENDIX H-2 Example of A Traditional Laboratory Exercise LAB #2: THE EFFECT OF pH ON THE GROWTH OF DUCKWEED NAME INTRODUCTION PER Duckweed is a common aquatic plant that can be grown in the lab in a simple nutrient culture medium. The growth of these plants occurs by mitosis and can be quantified by counting the number of new buds found on the plant after a period of time. The growth of a population of plants establishing itself in a new area typically follows an S-shaped curve. This curve consists of three phases: 1. A period of slow growth, the lag phase, followed by; 2. Exponential growth and finally; 3. An equilibrium phase where the population levels off. Time 225
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226 PROFESSIONAL DEVELOPMENT OF SCIENCE TEACHERS Biotic and abiotic factors influence the growth of individuals and populations. The pH of an aquatic environment is an abiotic factor which dramatically influ- ences its inhabitants and their growth. In this experiment, you will determine the optimal pH for the growth of duckweed, along with the effects of sub-optimal pH values on the growth of duckweed. MATERIALS 50 ml graduated cylinder 6 containers of culture media each with a specific pH (4, 5, 6, 7, 8, 9) 6 petri dishes duckweed marking pens inoculation loops PROCEDURE 1. Take 6 sterile petri dishes and label each with your initials and one pH value starting with 4 for the first dish, continuing until the last dish is labeled 9. Label on the bottom or side of the dish. 2. To the petri dishes add 25 ml of the culture media (decholorinated tap water plus liquid fertilizer) at the given pH. 3. With an inoculating loop transfer 15 duckweed plant lobes to each of the petri dishes. Record the total number of lobes per petri dish. Each lobe is actually a plant, although you often consider a three-lobed structure a plant. For statistical tests, it is IMPERATIVE that each group start with as close to 15 lobes as possible. 4. Place your 6 labeled petri dishes on the counter under the lights and allow them to remain undisturbed for one week or more, depending upon the success of the experiment. 5. Observe the plants in the petri dishes each day and record the number of pH DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAT 6 DAY 7 DAY 8 DAY 9 4 5 6 ~7 8 9
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A TRADITIONAL LABORATORY EXERCISE DAY 10 DAY 1 1 DAY 12 DAY 1 3 DAY 14 227 lobes in each dish. Count weekends as one day. Do this up until 14 class days and record data below: 6. With all the growth data for each pH as one population, do an ANOVA F test on your data to see if each group is similar. Your Null Hypothesis here would be that all the populations of duckweed grew at the same rate despite the pH. F test value = Degrees of freedom for numerator = Degrees of freedom for denominator Critical F value on the ANOVA chart Do you reject of fail to reject your Null Hypothesis? Explain in complete sentences: 7. Collect class data on the following charts so you can compare growth per pH for all of the 8 groups, using the statistical ANOVA F test.