Allelopathy Lab (Best Version).doc.docx



Allelopathy/Experimental Design LabBackgroundFrom childhood most of us have known that animals are territorial and that they aggressively defend resources needed for survival. Vivid memories of carnivores attacking territorial challengers have been embedded into our minds from numerous nature shows and classroom discussions.What many of us do not realize is that plants can be just as aggressive in defending their resources. Many plant species are capable of poisoning the soil and air around them. They do this by exuding toxic chemicals called allelotoxins from their leaves and roots; this toxic effect by a compound on plant growth is known as phytotoxicity (“phyto” is a prefix that means having to do with plants or botony). Allelotoxins prevent the germination of seeds and the encroachment of vegetative growth from other plants. By keeping competitors at bay, the defending plant can reserve precious resources such as soil nutrients, water, and sunlight for itself. Those plants that have evolved the strongest defenses will be the most likely to survive and pass these good genes on to the next generation of plants.For instance, have you ever noticed the ground under a pine tree? Generally, if you go out to examine a pine forest, you will discover that no plants are growing beneath the trees. This paucity of growth is due to more than just a lack of sunlight. This happens because fallen pine needles contain acid, which leaches down into the soil as they decompose, thus, lowering the pH beyond the range of tolerance for most plant species. The acidic soil, which does not affect the pine trees, essentially eliminates other contenders for precious water and mineral resources beneath the forest floor.In all ecosystems, species, both plant and animal, are competing for limited resources. Numerous strategies are applied in the ongoing struggle for survival. Most of us are familiar with camouflage, mimicry, ambush predation, and thorns, spines, and needles. As stated above, plants, because they cannot move from place to place, have evolved a heavy reliance on allelotoxins – poisonous chemicals. Some of these allelotoxins are transferred to other plants through volatilization which is when allelochemicals are exuded into the air, and, in turn, are absorbed through the leaves of competing plants killing them. Other protective strategies by plants include the release of defensive chemicals into the soil through their roots, which assures that intruding roots from other species cannot grow, and are thus rendered incapable of monopolizing valuable water and mineral supplies. Other defenders poison the soil around them as their leaves drop to the ground and transfer allelochemicals onto the topsoil and thus prevent the germination of seeds from their own species or other petition, which can be defined as one organism having a negative or restrictive effect on another, may be intraspecific, occurring between individuals of the same species, or interspecific, occurring among different species. In addition, it should be noted that there are two general ways an organism can limit the resources available to another organism: exploitation competition or interference competition.339090183769000Allelopathy is a type of chemical interference competition utilized by plants. The word allelopathy is derived from two basic root words: allelon (of or from each other) and pathos (to suffer). Allelopathy involves a chemical inhibition of one species by another. Molecules produced by one plant, mostly secondary metabolites, are released into the environment and then influence the growth and development of neighboring plants. For example, in the Mojave Desert of the Southwestern United States, where water is a limiting factor for growth, creosote shrubs exude allelochemicals from both their leaves and roots that prevent other desert plants from encroaching upon their immediate territory. When viewed from a distance, the creosote bushes are spaced out, like pegs in a cribbage board, for as far as one can see with a life-sustaining three to five meters between them. The process of roots & shoots emerging from a seed is called germination.Pre Lab—questions must be completely answered before you may participate in lab.How are allelotoxins related to phytotoxicity?Producing allelotoxins are energetically expensive. Producing this costly chemical must be an advantage to the plant. Describe why a plant might produce this chemical. Do a little research and find another example of a plant that produces allelotoxins (besides the ones in the introduction) and describe it here.How are allelotoxins “sent” to other plants since plants can’t move?What is the difference between intraspecific and interspecific competition?Do plants compete for resources? Explain.What is allelopathy?Why is allelopathy important to the long-term stability of an ecosystem?How might knowledge about allelopathic chemicals be used to create natural herbicides and help to promote sustainable agriculture?Why might knowledge of allelopathic effects be important to farmers who are concerned about crop to crop and weed to crop interactions?Many ecosystems are dependent on low intensity ground fires as opposed to catastrophic wildfires which can destroy important soil decomposers such as fungus and nitrogen fixing bacteria. How do allelochemicals help to reduce the possibility of catastrophic wildfires occurring in forest and other ecosystems?PROCEDUREAs a researcher interested in studying how allelochemicals affect germination of seed, what data points could you collect from germinating seed/seedlings?Circle everything in your list from #1 that would be quantitative data.How might we expect a seed germinated with an allelochemical to differ from a seed germinated without the allelochemical?Team IdeasWhole Class ideasCircle the idea from the chart that we will test in our experiment.The thing that you circled is a prediction. You may be surprised to hear that predictions are not the same as hypotheses. A prediction tends to be pretty specific about data: “If I change X in some way, then Y will change in some way.” But a hypothesis is a tentative explanation. It’s an idea--that may or may not be true--that explains the prediction. For example: Let’s suppose that I am investigating the effect of light on leaf surface area. I predict that plants grown in the dark will have less leaf surface area than plants grown in the light (“If a plant is grown in the dark, then it will have less leaf surface area.”). I hypothesize that light is necessary for building chlorophyll, the molecule responsible for making plants appear green.Generate a hypothesis for the prediction we’ve identified.Team HypothesisWhole Class Hypothesis5. Statistical “hypotheses”, on the other hand, are statements about whether or not a pattern or trend or difference is present in your data. Statistical tests are used to distinguish between the null hypothesis and one or more “alternative hypotheses”.The “Null Hypothesis” (also called “H0”) states that there is no pattern or trend in the data (e.g. there is no difference between groups, no relationship between two variables). An “Alternative Hypothesis” (also called “HA”, or “H1, H2, etc. if more than one alternative exists) states that there is a distinct pattern or trend in the data (e.g. there is a difference between groups, or a relationship between two variables). For example, in an observational study about which sex sings more frequently in chickadees, your statistical hypotheses might be: Null hypothesis (H0): “There is no significant difference in the number of songs that are performed by male and female chickadees.”Alternative hypothesis (HA): “There is a significant difference between males and females in the number of songs they perform.”Develop a null hypothesis and an alternative hypothesis based on the hypothesis you have generated.H0HAYour team will have access to the materials:10 seedPlastic petri dishesPaper towelsWaterRulersAluminum foilMintTitle: If your own experiment, generally written as: “The effect of ____ on ____” If published study, list title, first three authors, date published, and journal/publication source title.Question: Generally written as: “What is the effect of ‘A’ on ‘B’?” Explanatory Hypothesis: This is the proposed, testable explanation for the phenomenon being investigated that the experiment is exploring.Prediction: A prediction in science is a prophecy, a specific and measurable event that is likely to happen in the future as the result of an experiment if the hypothesis is valid. Basically it is what you think is going to happen in the experiment based on what you know.Independent Variable (IV): One variable, or experimental condition, to manipulate. This variable is considered the most important variable by which to test the investigator’s hypothesis. Dependent Variable (DV): The variable that is being measured in the experiment. You may decide to measure more than one variable to determine the effect of the independent variable. Include units.Level of Treatment: The value set for the independent variable. This might be a single value or a range of values. Include units.Control Group(s): Group in which the independent variable is held at an established level or is omitted. This group serves as a benchmark that allows the scientist to decide whether the predicted effect is really due to the independent variable. It is sometimes necessary to have a negative control group & a positive control group. The?negative control?group is a group in which no response is expected. A positive control group is one where a known response is expected.Experimental Group(s): Group where the independent variable is applied. If there is a range of levels of treatment there could be several experimental groups.Constants/Controlled Variables—Variables that are kept the same during the experiment so that you can determine whether the independent variable had an effect. You should always have several of these. Should be specific—“each group will receive 1ml of distilled water each day at 9am”.Replicates/Sample Size—number of individuals in each group. Needs to be large enough to account for individual differences.Replication—number of times experiment is conducted. Scientific investigations are not valid if the conclusions drawn from them are based on one experimentWhen your team has completed the organizer, let Ms. Minzenmayer know. She will randomly sample a team member’s experimental design. If it is approved, you should begin to set up your experiment. ................
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