LAB TOPIC 2A

The Process of Scientific Inquiry

Introduction

Scientific inquiry is a particular way of answering questions. It can't be used for all types of questions. The questions that can be answered by science must meet specific guidelines and scientific investigations must be carried out using certain rules. When an investigation is designed properly and meets these guidelines, then the results are acceptable to other scientists and are added to the body of scientific knowledge. If an investigator cannot show that his or her experiment was done according to the guidelines, then the results of that experiment will not be recognized as valid by other scientists.

 

The purpose of such guidelines can be understood by comparing them to sports records. For example, a new record set in a track and field event only counts if the meet was approved by the governing body that sets the guidelines. The site and equipment used are scrutinized to be sure that they are within the regulations and the athlete is tested for use of illicit substances. Only when these required conditions are met is the record certified as valid.

 

In this laboratory you will learn about the basic elements of scientific inquiry and how to apply this process to solving problems.

 

Outline

Exercise 2.1: The Black Box

Exercise 2.2: Defining a Problem

Exercise 2.3: The Elements of an Experiment Exercise 2.4: Designing an Experiment

 

 

EXERCISE 2.1

The Black Box

 

Objective

After completing this exercise, you should be able to

1. Explain the scientific inquiry method, which you apply to various examples in this exercise.

 

You will use the "black box" exercise as a model of how scientific inquiry is carried out. Each lab team has a container with one or more objects sealed inside. Each team also has an empty container of the same type and a plastic bag holding objects that might be inside the sealed container. Your task is to devise a way to find out what is in the box without opening it.  The steps listed below give you some idea of how to proceed. Answer the questions to keep a record of what you did.

 

Procedure

1. Make observations. Investigate the container by any means available to you except opening the container.

What are your observations?

 

 

How did you make your observations? 

 

 

What other methods that are not available to you right now might be used to make observations? 

 

 

Why is making observations an important first step in solving this problem? 

 

 

 

2. Make a guess about the contents of the box.

 

 

What did you base your guess on? 

 

3. For now, you still can't open the sealed container. How can you test whether your guess is correct?

 

 

4. Use the method you described above to check your guess. Record your results below Was your guess correct? How sure are you?

 

 

 

5. If you aren't sure you know yet what is in the box, what should you do next?

 

 

 

6. Short of opening the box, what's the best you can do to find out what's in it?

 

 

 

7. Suppose you tell your instructor what you have concluded is in the box, and he or she says that you are wrong. What are some things that could have led you to make the wrong conclusion?

 

 

 

8. Summarize the methods you used to solve the problem of the black box.

 

 

 

 

 

The steps you used to determine the contents of the black box are similar to the procedure followed in one type of scientific investigation. The investigator poses a question-for example, "What is in the box?" From the question and preliminary observations, the investigator makes an educated guess (known as a hypothesis) about the answer. She then devises an experiment to test the hypothesis, performs the experiment, and draws a conclusion from its results. The hypothesis may be revised, and further experiments may be done if the results are not conclusive. Eventually the investigator reaches a point where she is confident that her conclusions are correct.

In Exercises 2.2 and 2.3 you will learn to recognize the elements of a good scientific investigation. In this and later laboratories you will design your own investigations.

 

EXERCISE 2.2

Defining a Problem

 

Objectives

After completing this exercise, you should be able to

1. Identify questions that can be answered through scientific inquiry and explain          what characterizes a good question.
2. Identify usable hypotheses and explain what characterizes a good scientific    hypothesis.

 

Every scientific investigation begins with the question that the scientist wants to answer. The questions addressed by scientific inquiry are based on observations or on information gained through previous research, or on a combination of both. Just because a question can be answered doesn't mean that it can be answered scientifically. Discuss the following questions with your lab team and decide which of them you think can be answered by scientific inquiry.

 

What is in the black box?

 

Are serial killers evil by nature?

 

What is the cause of AIDS?

 

Why is the grass green?

 

What is the best recipe for chocolate chip cookies?

 

When will the Big Earthquake hit San Francisco?

 

How can the maximum yield be obtained from a peanut field?

 

Does watching television cause children to have shorter attention spans?

 

How did you decide what questions can be answered scientifically?

A scientific question is usually phrased more formally as a hypothesis, which is simply a statement of the scientist's educated guess at the answer to the question.

 

A hypothesis is usable only if the question can be answered "no." If it can be answered "no," then the hypothesis can be proven false. The nature of science is such that we can prove a hypothesis false by presenting evidence from an investigation that does not support the hypothesis. But we cannot prove a hypothesis true. We can only support the hypothesis with evidence from this particular investigation. For example, you used hypotheses to investigate the contents of your sealed box. A reasonable hypothesis might have been, "The sealed box contains a penny and a thumbtack." This hypothesis could be proven false by doing an experiment: putting a penny and a thumbtack in a similar box and comparing the rattle it makes to the rattle of the sealed box. If the objects in the experimental box do not sound like the ones in the sealed box, then the hypothesis is proven false by the results of the experiment, and you would move on to a new hypothesis. However, if the two boxes do sound alike, then this does not prove that the sealed box actually contains a penny and a thumbtack. Rather, this investigation has supplied a piece of evidence in support of the hypothesis.

 

You could test almost any hypothesis you made by putting objects in the empty box. What one hypothesis could not be proven false by experimentation? 

 

 

 

You may now open the sealed container. Was your final conclusion about     its contents correct.?        

           

 

If your conclusion has now been disproven, explain how you reached an erroneous conclusion. (You may have found that your conclusion was wrong in spite of accurate observations and careful experimentation. Conclusions reflect the best evidence available at the time.)

 

 

 

Can you think of any areas of scientific inquiry where a new technology or technique might challenge or disprove hypotheses that are already supported by experimental evidence? 

 

 

The scientific method applies only to hypotheses that can be proven false through experimentation (or through observation and comparison, a different means of hypothesis testing). It is essential to understand this in order to understand what is and is not possible to learn through science. Consider, for example, this hypothesis: More people behave immorally when there is a full moon than at any other time of the month. The phase of the moon is certainly a well-defined and measurable factor, but morality is not scientifically measurable. Thus there is no experiment that can be performed to test the hypothesis. Propose a testable hypothesis for human behavior during a full moon. 

 

 

 

 

Which of the following would be useful as scientific hypotheses? Give the reason for each answer.

 

Plants absorb water through their leaves as well as through their roots. 

 

Mice require calcium for developing strong bones. 

 

Dogs are happy when you feed them steak. 

 

An active volcano can be prevented from erupting by throwing a virgin into it during each full moon. 

 

The higher the intelligence of an animal, the more easily it can be domesticated. 

 

The earth was created by an all-powerful being. 

 

HIV (human immunodeficiency virus) can be transmitted by cat fleas. 

 

EXERCISE 2.3

The Elements of an Experiment

 

Objectives

After completing this exercise, you should be able to

1. Define and give examples of dependent, independent, and standardized variables.
2. Identify the variables in an experiment.

3,  Explain what control treatments are and why they are used.

4.  Explain what replication is and why it is important.

 

Once a question or hypothesis has been formed, the scientist turns his attention to answering the question (that is, testing the hypothesis) through experimentation. A crucial step in designing an experiment is identifying the variables involved. Variables are things that may be expected to change during the course of the experiment. The investigator deliberately changes the independent variable. He measures the dependent variable to learn the effect of changing the independent variable. To eliminate the effect of anything else that might influence the dependent variable, the investigator tries to keep standardized or extraneous variables constant.

 

Dependent Variables

The dependent variable is what the investigator measures (or counts or records). It is what the investigator thinks will vary during the experiment. For example, she may want to study peanut growth. One possible dependent variable is the height of the peanut plants. Name some other aspects of peanut growth that can be measured. 

 

 

 

All of these aspects of peanut growth can be measured and can be used as dependent variables in an experiment. There are different dependent variables possible for any experiment. The investigator can choose the one she thinks is most important, or she can choose to measure more than one dependent variable.

 

Independent Variables

The independent variable is what the investigator deliberately varies during the experiment. It is chosen because the investigator thinks it will affect the dependent variable. Name some factors that might affect the number of peanuts produced by peanut plants. 

 

 

 

 

In many cases, the investigator does not manipulate the independent variable directly He collects data and uses the data to evaluate the hypothesis, rather than doing a direct experiment. For example, the hypothesis that more crimes are committed during a full moon can be tested scientifically. The number of crimes committed is the dependent variable and can be measured from police reports. The phase of the moon is the independent variable. The investigator cannot deliberately change the phase of the moon, but can collect data during any phase he chooses.

 

Although many hypotheses about biological phenomena cannot be tested by direct manipulation of the independent variable, they can be evaluated scientifically by collecting data that could prove the hypothesis false. This is an important method in the study of evolution, where the investigator is attempting to test hypotheses about events of the past.

 

The investigator can measure as many dependent variables as she thinks are important indicators of peanut growth. By contrast, she must choose only one independent variable to investigate in an experiment. For example, if the scientist wants to investigate the effect that the amount of fertilizer has on peanut growth, she will use different amounts of fertilizer on different plants; the independent variable is the amount of fertilizer. Why is the scientist limited to one independent variable per experiment? 

 

 

 

 

 

 

Time is frequently used as the independent variable. The investigator hypothesizes that the dependent variable will change over the course of time. For example, she may want to study the diversity of soil bacteria found during different months of the year, However, the units of time used may be anywhere from seconds to years, depending upon the system being studied.

 

What was the independent variable in your black box investigation? 

 

What was (or were) the dependent variable(s)? 

 

 

Identify the dependent and independent variables in the following examples (circle the dependent variable and underline the independent variable):

 

Height of bean plants is recorded daily for 2 weeks. 

 

Guinea pigs are kept at different temperatures for 6 weeks. Percent weight gain is recorded. 

 

The diversity of algal species is calculated for a coastal area before and after an oil spill.

 

Light absorption by a pigment is measured for red, blue, green, and yellow light. 

 

Batches of seeds are soaked in salt solutions of different concentrations, and germination is counted for each batch. 

 

An investigator hypothesizes that the adult weight of a dog is higher when it has fewer littermates.

 

Standardized Variables

A third type of variable is the standardized or extraneous variable. Standardized variables are factors that are kept equal in all treatments, so that any changes in the dependent variable can be attributed to the changes the investigator made in the independent variable. 

 

Since the investigator's purpose is to study the effect of one particular independent variable, she must try to eliminate the possibility that other variables are influencing the outcome. This is accomplished by keeping the other variables at constant levels, in other words, by standardizing these variables, For example, if the scientist has chosen the amount of fertilizer as the independent variable, she wants to be sure that there are no differences in the type of fertilizer used. She would use the same formulation and same brand of fertilizer throughout the experiment. What other variables would have to be standardized in this experi-ment? 

 

Predictions

A hypothesis is a formal, testable statement. The investigator devises an experiment or collects data that could prove the hypothesis false. He should also think through the possible outcomes of the experiment and make predictions about the effect of the independent variable on the dependent variable in each situation. This thought process will help him interpret his results. It is useful to think of a prediction as an if/then statement: If the hypothesis is supported, then the results will be ....

 

For example, a scientist has made the following hypothesis: Increasing the amount of fertilizer applied will increase the number of peanuts produced. He has designed an experiment in which different amounts of fertilizer are added to plots of land and the number of peanuts yielded per plot is measured.

 

What results would be predicted if the hypothesis is supported? (State how the dependent variable will change in relation to the independent variable.) 

 

 

 

What results would be predicted if the hypothesis is proven false? 

 

 

 

Levels of Treatment

Once the investigator has decided what the independent variable for an experiment should be, he must also determine how to change or vary the independent variable. The values set for the independent variable are called the levels of treatment, For example, an experiment measuring the effect of fertilizer on peanut yield has five treatments. In each treatment, peanuts are grown on a 100 m² plot of ground, and a different amount of fertilizer is applied to each plot. The levels of treatment in this experiment are set as 200 g, 400 g,

600 g, 800 g, and 1000 g fertilizer/100 m².

 

The investigator's judgment in setting levels of treatment is usually based on prior knowledge of the system. For example, if the purpose of the experiment is to investigate the effect of temperature on weight gain in guinea pigs, the scientist should have enough knowledge of guinea pigs to use appropriate temperatures. Subjecting the animals to extremely high or low temperatures can kill them and no useful data would be obtained. Likewise, the scientist attempting to determine how much fertilizer to apply to peanut fields needs to know something about the amounts typically used so he could vary the treatments around those levels.

 

Control Treatments

It is also necessary to include control treatments in an experiment. A control treatment is a treatment in which the independent variable is either eliminated or is set at a standard value. The results of the control treatment are compared to the results of the experimental treatments. in the fertilizer example, the investigator must be sure that the peanuts don't grow just as well with no fertilizer at all. The control would be a treatment in which no fertilizer is applied. An experiment on the effect of temperature on guinea pigs, however, cannot have a "no temperature" treatment. Instead, the scientist will use a standard temperature as the control and will compare weight gain at other temperatures to weight gain at the standard temperature.

 

For each of the following examples, tell what an appropriate control treatment would be.

1. An investigator studies the amount of alcohol produced by yeast when it is incubated with different types of sugars. Control treatment: 

 

 

2. The effect of light intensity on photosynthesis is measured by collecting oxygen produced by a plant. Control treatment: 

 

 

3. The effect of NutraSweet sweetener on tumor development in laboratory rats is investigated. Control treatment:

 

 

4. Subjects are given squares of paper to taste that have been soaked in a bitter-tasting chemical. The investigator records whether each person can taste the chemical. Control treatment: 

 

 

5. A solution is made up to simulate stomach acid at pH 2. Maalox antacid is added to the solution in small amounts, and the pH is measured after each addition. Control treatment: 

 

 

 

Replication

Another essential aspect of experimental design is replication. Replicating the experiment means that the scientist repeats the experiment numerous times using exactly the same conditions to see if the results are consistent. Being able to replicate a result increases our confidence in it. However, we shouldn't expect to get exactly the same answer each time, because a certain amount of variation is normal in biological systems. Replicating the experiment lets us see how much variation there is and obtain an average result from different trials.

 

A concept related to replication is sample size. It is risky to draw conclusions based upon too few samples. For instance, suppose a scientist is testing the effects of fertilizer on peanut production. He plants four peanut plants and applies a different amount of fertilizer to each plant. Two of the plants die. Can he conclude that the amounts of fertilizer used on those plants were lethal? What other factors might have affected the results? 

 

 

 

When you are designing experiments later in this lab course, consider sample size as an aspect of replication. Since there are no hard and fast rules to follow, seek advice from your instructor regarding the number of samples and the amount of replication that is appropriate for the type of experiment you are doing. Since the time you have to do experiments in lab is limited, inadequate replication may be a weakness of your investigations. Be sure to discuss this when you interpret your results.

 

Methods

After formulating a hypothesis and selecting the independent and dependent variables, the investigator must find a method to measure the dependent variable; otherwise, there is no experiment. Methods are learned by reading articles published by other scientists and by talking to other scientists who are knowledgeable in the field. For example, a scientist who is testing the effect of fertilizer on peanuts would read about peanut growth and various factors that affect it. She would learn the accepted methods for evaluating peanut yield. She would also read about different types of fertilizers and their composition, their uses on different soil types, and methods of application. The scientist might also get in touch with other scientists who study peanuts and fertilizers and learn about their work. Scientists often do this by attending conferences where other scientists present results of investigations they have completed.

 

In this course, methods are described in the lab manual or may be learned from your instructor.

 

Summary

 

Figure 2.1 summarizes the process of scientific investigation. The process begins and ends with the knowledge base, or what is already known. When a scientist chooses a new question to work on, he first searches the existing knowledge base to find out what information has already been published. Familiarity with the results of previous experiments as well as with the topic in general is essential for formulating a good hypothesis. After working through the rest of the process, the scientist contributes his own conclusions to the knowledge base by presentations at professional meetings and publication in scientific journals. Because each new experiment is built upon past results, the foundation of knowledge grows increasingly solid.

 

 

 

 

 

Figure 2.1.  Summary of scientific inquiry

 

Scientific knowledge is thus an accumulation of evidence in support of hypotheses; it is not to be regarded as absolute truth. Hypotheses are accepted only on a trial basis. When you read about current scientific studies in the newspaper, keep in mind that the purpose of the media is to report news. In science, "news" is often preliminary results that are therefore quite tentative in nature. It is not unusual to hear that the results of one study contradict another. Some results will hold up under future scrutiny and some will not. However, this does not mean that scien-tific knowledge is flimsy and unreliable. All scientific knowledge falls somewhere along a continuum from tentative to certain, depending on the evidence that has been amassed. For example, it takes an average of 12 years to get a new drug approved by the FDA as researchers progress through laboratory evaluation of possible compounds, animal studies, and an escalating series of trials in humans. Even so, there are cases of drugs being recalled when new information is discovered. In a way, every medicine you take is still being tested -- on you. We don't object to this because we feel confident that the knowledge base is firm, that the science is "done" to an acceptable degree. 

 

It is now your turn to design and carry out an experiment.  

Continue on to LAB TOPIC 2B. 

LAB TOPIC 2B  

 

 

Scientific Inquiry Experiment

 

Georgia Lind, Ph. D. and Craig Hinkley, Ph.D.

 

 

 

OBJECTIVES:

 

1. Describe the steps used in the scientific method.
2. Define the terms:  hypothesis and theory.
3. Distinguish between dependent, independent and extraneous variables.
4. Utilizing the scientific method, design and conduct a scientific experiment to address a biological problem. 
5. Explain the concept of a control, and include an appropriate control in the experiment.
6. Present and interpret the results of the experiment.

 

 

* Before coming to lab, read the appropriate section of your text and this exercise.

 

 

 

 

 

1. INTRODUCTION AND BACKGROUND

 

 If you have a question to which you want an answer, there are many techniques you could use to try to find that answer.  You could look it up at the library.  You could ask a classmate, or someone else you might know that is an expert in the area.  You could Google it!!!

When scientists want answers to their questions, they sometimes cannot use any of these techniques.  Often this is because their questions are about subjects where the answers aren’t yet known. For example, when James Watson, Francis Crick, and Rosalind Franklin found a material (DNA) that made strange scatterings of X-rays while using a technique called X-ray crystallography, they wanted to know the answer to the question, what is the structure of this DNA that causes it to make these strange patterns?  As you probably know, when they first started working on the problem, the answer to that question was unknown. Because they used an important technique called the scientific method, they were able to answer the question, and later Watson and Crick received a Nobel Prize for their work.

 

2. SCIENTIFIC METHOD

 

The scientific method is one anyone can use to solve a problem. At its best, it is an unbiased step-by-step method followed to test answers to questions in a manner that can be duplicated and verified.  First, the student or scientist looks carefully at something that they don’t understand, and often make notes about it.  This is called observation, and the notes are called observations.  Watson, Crick and Franklin looked carefully at the scattered X- rays, and described the patterns they observed.  The second step involves using the observations, experience and any other appropriate information. From this, the student or scientist can guess what the observations might mean. This educated guess is called a hypothesis.  The hypothesis is a statement (not in the form of a question) that describes what you think is happening. Watson and Crick’s educated guess (published in 1953) was that the DNA had a double-helix structure. Experiments are then designed and completed to produce evidence, called data or results. Results are additional observations that can be used to decide if the hypothesis is supported or not. The last part of the scientific method is to look carefully at the results, and decide what they mean.  These two steps are called analysis and conclusions. Unlike in mathematics where you can prove if something is correct, in science, a hypothesis can only be supported or not supported.  Data that is in agreement with the hypothesis is said to support the hypothesis. In writing the analysis and conclusions, the experimenter presents the evidence from the data that they believe allows them to decide if the hypothesis is supported or contradicted by the results that have been collected.  Watson and Crick’s data supported the double helix hypothesis.

When extensive experimentation consistently supports a hypothesis, it is accepted as a theory.  Because all of science is based on research and evidence, all conclusions, even theories, are accepted only as long as they continue to be supported by all new evidence that accumulates. In addition, the conclusions based on experiments are always open to modification.

 

Experimental Design

 To investigate hypotheses, you often must design experiments.  Experiments may be conducted in the laboratory, in the field, or both, but importantly, they must be conducted as much as possible under conditions where objective, reliable, measurable, repeatable observations can be made.  The procedures you follow while conducting an experiment are called the experimental design.  Various factors, called variables, are considered in designing an experiment.  For example, suppose you are studying seed sprouting.  How large will your sample size be (how many seeds will you use)?  What will you measure? How often?  Perhaps the appearance of stems, or roots, or their length or weight will be measured.  As we learned in exercise 2A, what you measure is called the dependent variable. 

 What will you choose to vary that might influence the dependent variable?  Perhaps the sunlight, water, or chemicals in contact with the seeds will be different.  Again as we learned above, what is varied which may alter the dependent variable is called the independent variable. In each study, one cannot draw conclusions if there is more than one independent variable. Extraneous variables can also influence the results of the experiment.  They include objects or events that may differ between individuals, or over time, which are unrelated to testing your prediction. It is important to identify and minimize or keep universal (make sure they happen to all parts of the study) these extraneous variables. Sometimes these are known as standardized variables.

 In an experiment, individuals under study are divided into two groups.  The experimental group is subjected to the independent variable, and the control group is identical to the experimental group in all ways, except for the (independent) variable being studied.

 Frequently, the results of an experiment suggest that the original hypothesis was not correct, and a modification of the hypothesis may be needed.  Whenever possible, an experiment should be repeated to validate the results.  This minimizes the possibility of obtaining results solely by chance.  

 

          An Overview of the Scientific Method

 

Observation

 

 

Hypothesis

 

Experiments

Data and Results

 

Analysis and Conclusions

 

 

 

            III.  LABORATORY EXERCISE

 

ALLELOPATHY:

EFFECTS OF VOLATILES FROM CRUSHED PLANT MATERIALS ON SEED GERMINATION AND GROWTH.

 

 

 For this exercise you will design an experiment using the scientific method of inquiry, using available materials as provided by your instructor.  You and your group will formulate a hypothesis, design and conduct an experiment.  After discussion with your group members, and considering the materials available, an experimental strategy will be submitted to your instructor.  Experiments should not begin until your group's design has been evaluated, discussed and approved by your instructor.  

 

 

Introduction

A major concept in the study of biology is that of evolution.  Part of evolution is the idea that organisms compete.  Plants compete for space, light, and nutrients, both with their own species, and also with others, in order to survive and reproduce. One way plants compete is by producing chemicals that protect them. The chemicals can protect them from predators, or from other plants.  A famous plant of the early West was the Loco Weed  (usually Oxytropis  lumberti) which poisons the horses, cattle and sheep that eat it.  

The area of research that focuses on chemical effects of plants upon each other is called alleleopathy.  Alleleopathy is defined as “any direct or indirect harmful or beneficial effect of one plant . . .  on another through production of chemical compounds that escape into the environment” (Rice, 1984). You are going to study the alleleopathy of a very famous plant, garlic (Allium sativum).   Long famous as a folk remedy (to ward off vampires), more recently (reviewed by Blumenthal and Gardner et al,  in 2000) it has also been investigated for possible medicinal effects. As anyone who cooks with it will tell you, when crushed its cloves release a strong characteristic smell. The smell is produced by a volatile, a chemical that evaporates into the air.  When it diffuses to your nose, you smell the garlic.    

What might be the purpose of this volatile?  Is it harmful, or helpful to the garlic, or to other plants?  Does it affect all plants in the same way?  Is it present in pills or dry garlic powder, as well as in crushed cloves?  If it has an effect, how much garlic does it take?  How long does the effect last?  Do the effects of garlic last, after the garlic is removed?   Do other plants that produce smells (say broccoli, oranges, onions) have the same effects?     

These and other questions that you might be interested in answering will be the focus of your laboratory assignment today. Using the materials available in the laboratory, your assignment is to develop a hypothesis, design, and carry out an experiment that will answer a question about the effects of garlic volatiles.  Your instructor will explain the requirements for the report that you will prepare. The following information and worksheet will assist you in this endeavor.

 

General Protocol

Materials 

Experimental seeds

Garlic and non-allium (control) plant materials (carrot root (Daucus carota), broccoli stem

(Brassica oleracea), celery stem (Apiurn graveolens), or romaine lettuce leaves (Lactuca sativa).

Other materials could be tested.)

Seed Germination setup (9 cm Petri dish with two pieces of Whatman filter paper)

Distilled water (3 ml per setup)

Masking tape

Tinfoil or 35 x 10 Falcon tissue culture dishes

Garlic press

Triple beam balance.     

 

General Procedure

(This should be modified depending upon your particular investigation) 

Crush the plant material with a garlic hand press (both garlic and controls). Weigh 1.0 g samples on a triple beam balance and transfer the material samples to a tinfoil boat. Place the crushed plant material in a petri dish that contains 2 pieces of Whatman #1 filter paper and 25 lettuce seeds. Add 3 ml of water, seal the dishes with masking tape, and incubate for three to seven days under classroom conditions. Controls are set up as described above but lack garlic. Note that test seeds are in contact with only the volatiles from crushed plant material. 

 

Recording Results:  

Total seedling length or other information should be recorded. A length of zero is recorded for seeds that do not germinate. 

 

 

WORKSHEET

Fill out the following description of your experimental design and discuss it with your instructor before proceeding.

1. Write the question your group will address and investigate:

 

                                                                                                                       

 

 

2. What is your Hypothesis:

 

 

                                                                                                                      

            2a.  What results do you predict?

 

 

 

            2b.  What result(s) would cause you to accept your hypothesis?

 

                                                                                                                      

 

 

            2c.  What result(s) would cause you to reject your hypothesis?

 

                                                                                                                      

 

3. How large or small a sample size will you be using (n =?  How many seeds?)?

 

 

 

 

 

4. What treatment(s) will you use? Will there be different levels of treatment?  (Explain what you will use (what materials) and how it will be used (how many plates?  What amount of material?)

 

 

 

 

 

 

 

 

 

 

 

 

 

5. Dependent variable (what will you measure?):

 

6. Independent variable?:

 

 

 

 

 

7. Will a control be required?  Why/why not?  Describe your control(s):

 

 

 

 

 

 

 

 

 

 

 

8. Extraneous, standardized, stabilized, or controlled variables:  [Write the variable, and how you will control it (minimize or eliminate its influence).]

 

Variable                                                           Describe how it will be “controlled”

 

a.

 

 

b.

 

 

c.

 

 

d.

 

 

e.  

 

 

 

 

 

 

9. Experimental Design:  detail the steps and procedures of your experiment here, including what data will be collected, when and how.

 

 

1.

 

 

2.

 

 

3.

 

 

4.

 

 

5.

 

 

 

6.

 

 

10. Should your study be replicated?  Why or why not?  If yes, how will that be done?

 

 

 

 

 

 

 

11. Do you have a prediction of the outcome?

 

 

 

 

 

 

Recording Data for Analysis and Interpretation

 

 The following data sheets may be useful for recording your data.  Your instructor will specify how the results should be presented.  After the experiment is complete, you and your group will analyze and interpret the data to determine whether to accept or reject your hypothesis.  Please remember that even data that do not come out as you expected are valid!  Perhaps the hypothesis wasn't the "right” guess, or perhaps there was a flaw in the experimental design?  Careful (re)evaluation of the experiment may demonstrate this to be the case.  

 

            BIBLIOGRAPHY

 

Blumenthal, M. (Editor) (2000).  Herbal Medicine Expanded Commission E Monographs (pp. 130148).  Newton, MA:  Integrative Medicine Communications. 

 

Gardner, C. D., Chatterjeer, L. and Carlson, J. (2000).  The effect of garlic on serum cholesterol levels.  In W.R. Bidlack, S. T. Omaye, M. S. Meskin and D. K. W. Topham (Editors), Phytochemicals as Bioactive Agents. (pp.  199-212).  Lancaster, PA:  Technomic Publishing Company.

 

Gates, Frank C.  (August, 1925)  The Loco Weed and its Effect on Live Stock.  Manhattan, KA:  Agricultural Experiment Station, Kansas State Agricultural College, Department of Botany, Circular 115.  

 

Rice, E.L. (1984).  Allelopathy.  2^nd. Edition.  Orlando, FL:  Academic Press, Inc.  

 

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