1SCIENTIFIC METHOD LEARNING OUTCOMES Upon successful completion of this lab, you will be able to: Describe the steps of the scientific method Formulate research questions, hypotheses, and predictions Design and conduct an experiment Interpret and report results Identify the parts of a scientific paper Describe the purpose and content of a scientific paper PART A. THE SCIENTIFIC METHOD Scientists use the scientific method to study and understand the world around us. The scientific method is a step-by-step procedure, which uses experiments and observations to find an answer to a question or solve a problem. The scientific method generally involves six steps (Table 1). 1. Observation Observation is the first step in the scientific method. This step involves observing a phenomenon, an aspect of an organism, or the discovery of a problem. Observations can also come from examining the literature on a particular topic of interest. 2. Question A question is posed about the observation (or the problem to be solved is stated). The question must be simple and testable. The question is often in the form of How, What, or Why? EXERCISE 1: SCIENTIFIC METHOD 3
Table 1. Steps of the scientific method. Step Biological example Real world example 1 Observation Tree leaves change color in fall The flashlight stopped working 2 Question 3 Hypothesis 4 Prediction 5 Experiment 6 Conclusion What causes tree leaves to change color in fall? Leaves change color in fall due to lower light levels If light level is decreased, then the tree leaves will change color Expose tree leaves to different light levels a) Leaves change color at low light and the hypothesis is accepted. b) Leaves do not changes color at low light and the hypothesis is rejected. A new hypothesis is created and tested. What causes the flashlight to not work? The batteries are the source of the problem If the batteries are dead, then replacing the batteries will make the flashlight work. Replace batteries with new batteries a) The flashlight works and the hypothesis is accepted. b) The flashlight does not work and the hypothesis is rejected. A new hypothesis is created and tested. 3. Hypothesis The hypothesis is a potential explanation to the question (or cause of the problem). It is usually based on information that is already known. A hypothesis can be general or specific. Example General: Pesticides are lethal to termites. Specific: A spray containing 0.1% fipronil is lethal to worker termites. 4. Prediction A prediction is a result that will occur if the hypothesis is correct. Predictions generally take the form of an if/then statement. For example, If the hypothesis is correct, then the results of the experiment will be For each of the observations in Table 2, list a possible question, hypothesis and prediction. 4 EXERCISE 1: SCIENTIFIC METHOD
Table 2. Formulating questions, hypotheses, and predictions. Observation Question Hypothesis Prediction Chicken soup seems to cure a cold. Adding a penny to a vase of flowers seems to make them last longer. Bananas seem to brown faster in the refrigerator. 5. Experiment An experiment is designed and conducted to test the hypothesis. Experiments have three kinds of variables (also called factors or conditions). The independent variable (or treatment) is the factor that is changed or manipulated by the experimenter. The dependent variable is the factor that is observed and/or measured. The experimenter observes the response of the dependent variable to the change in the independent variable. Controlled variables are factors of the experiment that are kept the same for all groups. Controlled variables are kept constant to prevent them from influencing the dependent variable. The experimental variables can also be of two types. A continuous variable is one that is measured quantitatively and uses a logical order of numbers (e.g., temperature, length). A discrete variable is measured qualitatively and uses categories or an unordered set of numbers (e.g., color, shape). In an experiment, the items under study are divided into two groups. The experimental group is the group treated with the independent variable. The control group is the group where the independent variable is standardized. The control is used to compare the results of the experimental (treatment) group. Another important aspect of experimental design is replication. An experiment must be repeated several times to ensure that the results are reliable and not due to chance. Replicating an experiment allows an average result to be obtained from different trials. It is also important to have a large sample size (number of samples). The greater the number of samples the more accurate the results. Table 3 provides examples of factors in a study on fall tree leaf color. EXERCISE 1: SCIENTIFIC METHOD 5
Table 3. Factor Examples of experimental factors to study the cause of changing tree leaf color. Example Experimental group Control group Independent variable Dependent variable Controlled variable(s) Leaves exposed to fall light levels Leaves exposed to summer light levels Light level Leaf color Water, fertilizer, temperature, soil, etc. For each of the questions in Table 4, list an example of an independent, dependent, and controlled variable of an experiment. Table 4. Experimental variables. Question Independent Variable Dependent Variable Controlled Variable What sugar concentration do ants prefer? Which bait catches the most fish? Does talking to plants help them grow? Data Presentation Data generated from an experiment must be presented visually to understand the results, see trends or patterns, and explain the data to others. Presenting data (singular: datum) usually takes the form of tables and graphs. Data sheets are used to record the raw data (original) before it is formatted or summarized into tables and graphs. Tables A table is made up of rows and columns of data. Tables are used to collect raw data during an experiment or for summarizing and presenting final data (e.g., averages) in a report. The basic structure of a table is shown in Table 5. 6 EXERCISE 1: SCIENTIFIC METHOD
2 1 Table 5. Plant height over a 5-week period. Plant Height (cm) 3b 3a Week Plant 1 Plant 2 Plant 3 1 3 2 4 2 5 4 5 4 3 8 7 9 4 11 10 12 5 13 13 14 A table generally consists of 4 components (Table 5): 1. Name and Number Tables must be named and numbered consecutively (e.g., Table 1, Table 2) and should appear in a report in the order they are referred to in the text. The table number has a period at the end and comes before the table title. 2. Title The title (caption) provides a brief description of the contents of the table. It should include the key variables in the table. A table s title always goes above the table and follows the table number. 3. Column Headings Headings identify the data in each column with units of measurement (SI units) noted in parentheses (3a). The independent variable is usually placed in the first column and the dependent variables are placed in succeeding columns. In some cases it may be necessary to create a heading that spans across several columns to describe groups of data in those columns (3b). 4. Body The raw or final data is placed in the body of the table. No units should occur in the body. Lines are used to divide rows and columns to more easily present the information. EXERCISE 1: SCIENTIFIC METHOD 7
Create a table with the following data. At one bird feeder, the amount of seed consumed was 10 percent of seed type A, 15 percent of seed type B, and 50 percent of seed type C. At a second bird feeder, 30 percent of seed type A, 20 percent of seed type B, and 40 percent of seed type C was consumed. At a third bird feeder, 50 percent of seed type A, 5 percent of seed type B, and 45 percent of seed type C was consumed. Be sure to include all of the parts shown in Table 5. Graphs Line graphs show the relationship between variables in an experiment. They are best suited when the independent variable is continuous. Figure 1 is an example of a line graph using the data from Table 5. If the graph contains more than one data series, each series must be identified with a legend (see Figure 2). 8 EXERCISE 1: SCIENTIFIC METHOD
Figures generally consist of 5 components (Figure 1): 1. Name and Number Figures must be named and numbered consecutively (e.g., Figure 1, Figure 2) and should appear in a report in the order they are referred to in the text. The figure number has a period at the end and comes before the figure title. 2. Title The title (caption) provides a brief description of the contents of the figure. It should include the key variables in the graph. The title always goes below the figure and follows the figure number. 3. Y-axis Label A y-axis (vertical) label generally identifies the dependent variable with any units in parentheses. The y-axis should also have an appropriate scale and divisions (e.g., if using percentage, the axis should not exceed 100%). 4. X-axis Label The x-axis (horizontal) label generally identifies the independent variable with any units in parentheses. The x-axis should also have an appropriate scale and divisions (e.g., if using months, the axis should not exceed 12). 5. Body The data is plotted as distinct points (scatter plot), points connected by a line (line graph), or as a set of bars (bar graph). If the graph contains more than one data series, each series must be identified with a legend (see Figure 2). EXERCISE 1: SCIENTIFIC METHOD 9
Create a line graph using the following data. Be sure to include all of the parts identified in Figure 1. Amount of Rainfall (cm) Month Site 1 Site 2 Site 3 1 6 4 3 2 12 10 15 3 65 68 69 4 112 12 15 5 127 135 141 10 EXERCISE 1: SCIENTIFIC METHOD
Plant Height (cm) Bar graphs can be used to compare data and identify trends. They are best suited when the independent variable is discrete. Figure 3 is an example of a bar graph. The independent variable (amount of fertilizer) is plotted on the x-axis and the dependent variable (plant height) is plotted on the y-axis. Notice that a bar graph follows the same structure as a line graph (Figure 1). Histograms are similar to bar graphs except that each bar represents a range of independent variable values rather than a single value. 25 20 15 10 5 0 0 50 100 Fertilizer (%) Create a bar graph using the data table you created on birdseed types. Be sure to include all of the necessary components in Figure 1. EXERCISE 1: SCIENTIFIC METHOD 11
6. Conclusion The final step in the scientific method is to interpret and discuss the results. The results of the experiment are used to determine whether the hypothesis is accepted (the results match the prediction) or rejected (the results do not match the prediction). If the hypothesis is rejected, a new hypothesis or a new experiment can be designed and tested. If the conclusion is that the hypothesis is accepted then the scientist must determine how it fits in with the existing knowledge on the topic and it must be accepted by other scientists. If a hypothesis remains accepted after many experiments and scientists then it can be called a theory. Theories in biology include the cell theory and the theory of evolution. Your hypothesis is that moths prefer white flowers. You conducted an experiment and collected the following data. Trial Number of Visits White Flower Yellow Flower 1 15 2 2 10 0 3 8 5 4 10 3 5 3 3 Summarize the results of the experiment in a table or graph. Based on these results, is this hypothesis supported or rejected? Explain. 12 EXERCISE 1: SCIENTIFIC METHOD
OBSERVATION: Making an observation from the world around us triggers the scientific method. The following is an observation that could have triggered our hypothetical experiment. BACKGROUND INFORMATION: This section is devoted to reading up on topics related to the observation in order to learn more about it. For our example, we could read to investigate the function of the heart and circulatory system, why heart rate increases with exercise, why being aerobically fit reduces heart rate, and what type of exercise is necessary in order to become aerobically fit. QUESTION: Next, ask a question that is related to the observation. Pose a question concerning the observation that is suggested by your Background Information. HYPOTHESIS: The next step is to formulate a hypothesis. The difference between the question and the hypothesis is that the hypothesis is testable. The hypothesis makes a specific prediction regarding the outcome of a carefully designed experiment; your educated guess. Thus, the hypothesis must be written so that an experiment can be designed to test it. Then the actual results can be compared to the prediction made by the hypothesis. Rephrase your question into a testable hypothesis. When this information is complete, the scientist has an idea of what type of experiment to conduct. Therefore, the next step is to design an experiment that will test the hypothesis. Scientific experiments are based on the comparison of a control group with an experimental group. The control group and the experimental group are identical except for the one factor being tested by the experiment. This factor is called the independent variable. INDEPENDENT VARIABLE: The independent variable (also called the manipulated variable) is the one factor in the experiment that separates the control group from the experimental group. What is the independent variable for this experiment? EXERCISE 1: SCIENTIFIC METHOD 13
DEPENDENT VARIABLE: The dependent variable (also called the responding variable) is the factor that changes as a result of changes in the independent variable. It can easily be recognized because it is the variable being measured as part of the experiment. What is being measured in this experiment? Be very specific. EXPERIMENTAL GROUP: What criteria are necessary for a person to belong to the experimental group? CONTROL GROUP: Who belongs to the control group? CONSTANT CONDITIONS: In a scientific experiment, it is vital to hold all conditions other than the independent variable constant. That way any differences noted are due to the independent variable, not some other cause. Describe the constant conditions for this experiment. PROCEDURE AND MATERIALS: Write a detailed procedure to test your hypothesis. Include the complete list of materials and precise directions to the steps of your experiment. Someone besides you should be able to read this section and have all the information needed to run the experiment. In your lab report, the procedure and material list should be written in paragraph form. Now that you have a well planned experiment, you are ready to conduct the experiment, collect data in tables, draw a graph, interpret your results, and present your conclusion regarding whether or not the hypothesis is supported by the data. QUANTITATIVE RESULTS TABLES: Quantitative refers to numerical data. It is presented in table form. Below is a table that provides possible results for the above experiment so you can continue the exercise by analyzing it. Notice a table has a descriptive title and all numerical values are labeled with units. 14 EXERCISE 1: SCIENTIFIC METHOD
QUALITATIVE RESULTS OBSERVATIONS: Describe in words what you saw happening in the experiment. What are the differences found between the two groups? Use Table 1 to complete this section. DATA PRESENTATION GRAPHS: The data presented in the table is usually easier to interpret from a graph. The two most common types of graphs in lab reports are bar graphs and line graphs. Line graphs show continuous data, and trends can be visualized. Bar graphs compare discontinuous events, showing differences between groups rather than showing trends. Bar graphs are useful when one variable is nonnumerical. Your lab instructor will let you know which type of graph you should draw. The data from this current cardiovascular experiment is best presented with a bar graph. In setting up a graph, the independent variable always goes on the x-axis (horizontal axis) and the dependent variable goes on the y-axis (vertical axis). Draw a bar graph to represent the data in Table 1. Be sure to include a descriptive title and label the x-axis and y-axis correctly (use units where necessary). Figure 1: Average Change in Heart Rate for Aerobically Fit and Non-fit Subjects EXERCISE 1: SCIENTIFIC METHOD 15
ANALYSIS AND INTERPRETATION: Interpret your graph by describing what it tells about the relationship between the IV and DV. The results obtained should also be related back to the introduction s background information. CONCLUSION: Based on all of the evidence and data collected, what conclusion can be made regarding the hypothesis? Did the data support or fail to support your hypothesis? POTENTIAL ERRORS: It is important to alert other scientist to potential problems that may have influenced your results or areas of the experiment that are particularly tricky. List three potential errors from this cardiovascular exercise. RECOMMENDATIONS FOR FUTURE EXPERIMENTS: Make recommendations for additional/different experiments that will further study the question. A good approach is to take one of your constant conditions and make it the IV. This section is not for suggestions to improve the experiment you just completed. ORGANIZATION OF A WRITTEN LAB REPORT: A lab report is divided into four sections. Each section should be labeled and contain the following information: Introduction: Observation Background Information Question Hypothesis Methods Independent Variable Dependent Variable Constant Conditions Experimental Group Control Group Procedure and Materials Results Table Observations Graph 16 EXERCISE 1: SCIENTIFIC METHOD
Discussion Analysis and Interpretation Conclusions Potential Errors Future Recommendations REVIEW 1. Define scientific method. 2. Define experimental group. 3. Define dependent variable. 4. You notice that plant stems bend toward a window. a) Formulate a question related to this observation. b) Formulate a hypothesis for this question. c) Formulate a prediction for this hypothesis. EXERCISE 1: SCIENTIFIC METHOD 17
5. You want to study the effect of sugar on the growth of bacteria. You make up solutions of 0, 25, 50, 75 and 100% sugar concentration. You pour the media into Petri dishes and inoculate each dish with a culture of bacteria. After 24 h, you measure bacterial growth by estimating the percent coverage of bacteria in each dish. a) What is the independent variable? b) What is the dependent variable? c) What are the controlled variables? 6. Describe 3 limitations of the scientific method. 7. Describe the purpose and importance of a scientific paper. 18 EXERCISE 1: SCIENTIFIC METHOD