Section 7 - The Scientific Method & Experimental Design! of! 1 5

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1 Section 7 - The Scientific Method & Experimental Design of 1 5 Read the information below. You will be asked to identify parts of an experiment and errors in experimental design on your first test. Understanding this process thoroughly will be crucial to your success in this year s science fair. What is science? Science is a body of knowledge based on the study of nature. The nature, or essential characteristic of science is scientific inquiry - the development of explanations. Scientific inquiry is both a creative process and a process rooted in unbiased observations and experimentation. In order for a particular area of study to be classified as science, it must adhere to the following: 1. Science relies on evidence. Science combines what is already known with consistent evidence gathered through observations and experiments. A. When enough evidence from many related investigations supports an idea, scientists consider that idea a theory - an explanation of a natural phenomenon supported by many observations and experiments over time. Theories are generally accepted as true, until substantial evidence proves otherwise. Example: long ago, it was believed that the Earth was flat, until substantial evidence proved that the Earth is, in fact, spherical in shape. B. Some areas of study are based on observation, but may not be supported by scientific experimentation. These areas of study are known as pseudosciences. Pseudosciences often try to imitate science, but may be driven by cultural or commercial goals. Pseudosciences are unlikely to change over time, though data may indicate that their practices are not scientifically accurate. Examples of pseudosciences include astrology, horoscopes, psychic readings, and palmistry. These do not provide science-based explanations about the natural world. 2. Science expands scientific knowledge. A. Most scientific fields are guided by research, which constantly reevaluates what is known. This reevaluation often leads to new knowledge that is further evaluated by scientists worldwide. This constant evaluation, critique, and questioning expands the body of scientific knowledge. B. With pseudosciences, little research is done. If research is completed, it is often to justify existing knowledge rather than to extend the knowledge base. Research conflicting with a particular area of pseudo science is often dismissed. 3. Science challenges accepted theories. Scientists welcome debate on one another s ideas. They regularly attend conferences to discuss new developments and findings. Disagreements often occur. This leads to additional investigations to substantiate claims. 4. Science questions results. Observations that are not consistent with current scientific understanding are of interest to scientists. These inconsistencies often lead to further investigations. In pseudoscience, data that is inconsistent with current beliefs is often ignored.

2 Section 7 - The Scientific Method & Experimental Design of Science tests claims. Scientists use standard experimentation procedures to conduct their research. They make claims based on large amounts of observations from unbiased investigations and carefully controlled experimentation. Conclusions are based upon evidence. Pseudosciences, in contrast, often make claims that cannot be tested. These are often mixtures of fact and opinion. 6. Science undergoes peer review. Before the results of an experiment are made public, the information is reviewed by a scientist s peers - experts in the same field of study. Peer review is a process by which procedures and results of an experiment are evaluated by other scientists in the same field or who are conducting similar research. 7. Science uses the metric system. To make communication easier, scientists have chosen to use the metric system when collecting data and performing experiments. The Scientific Method The scientific method is a process used by all scientists to conduct experiments effectively. The number of steps in the scientific method is debatable, but the same general process is followed each time. Listed below are the steps to the scientific method: 1. Observation - A scientist observes something in the natural environment and questions why it happens. When a scientist makes observations, he or she will often write down notes, questions, or diagrams about the topic of interest. 2. Research - The scientist researches information about the phenomenon observed. Sometimes, the phenomenon has already been studied and a clear answer is available. Other times, an answer is not provided. In either case, the scientist may choose to design an experiment to gain additional knowledge. - The process of combining what you already know with what you have learned is called inferring; the conclusions themselves are called inferences. 3. Hypothesis - The scientist will create a hypothesis based upon what is known and what is being questioned. This hypothesis is a testable explanation of the situation. It is based upon research and it predicts what will happen in the given experiment. The hypothesis is often written as an if-then statement. - Serendipity is the occurrence of unexpected but fortunate results. 4. Experiment - The scientist will conduct an experiment and record data based what he or she observes. Every successful experiment must contain the following parts: A. A control group - the group in an experiment that is used for comparison. This group will not receive the factor or condition being tested. They exist under normal conditions to compare experimental results and note changes made (if any). B. One or more experimental groups - the group(s) being exposed to the factor being tested.

3 Section 7 - The Scientific Method & Experimental Design of 3 5 C. An independent variable - the single factor or condition that is being tested in the experiment. It is expected to affect the outcome of the experiment. (Hint: this is often identified in the if portion of a hypothesis.) D. The dependent variable - the factor that is being measured in the experiment. It is expected to change in response to the applied independent variable. E. Constants - factors that remain fixed during an experiment, to eliminate interference. 5. Data Analysis - The scientist will study the data collected in the experiment and compare the results to the expected outcome. A. Quantitative data is represented using numbers. B. Qualitative data is detected by the senses (ex: smells, color changes). 6. Conclusions - Based on the data collected, the scientist will draw conclusions about whether or not the data supports the initial hypothesis. A. If the hypothesis is supported, the results may be reported for peer review. B. If the hypothesis is rejected, the scientist may adjust features of the experiment to conduct further tests. 7. Peer review - A scientist s peers will evaluate the experiment and results to be certain that no errors were made and the the results are, in fact, valid and reliable. 8. Additional testing - Scientists will then replicate the experiment to determine if similar results are consistently obtained. Example: A scientist wants to test whether or not his fertilizer is the best option for his tomato plants. Based on his past tomato crops, he predicts that the fertilizer he is using is the best option for growing tall plants. He decides to test 4 different groups of tomato plants, each containing 50 plants. He plants one group into soil without fertilizer. He plants another group into soil with the fertilizer he is currently using. He plants the last two groups with two different fertilizers from competitive brands whose recommended dosage is the same. With each of the fertilizer groups, he applies the same amount of fertilizer. He makes sure each set of tomato plants is found in the same soil, receives the same amount of sunlight, and receives same amount of water each day. He records each plant s height on a weekly basis for eight consecutive weeks. Parts of his experiment include: Independent variable - different brands of fertilizer Dependent variable - plant height Control group - the plants that receive no fertilizer (normal condition) Experimental groups - the three groups receiving different fertilizer brands Constants - sunlight, water, soil content, type of tomato plant used, number of plants tested Hypothesis - The tomato plants receiving the scientist s chosen fertilizer will grow tallest in eight weeks.

4 Section 7 - The Scientific Method & Experimental Design of 4 5 Common Problems with Experimental Design There are several errors that are common in experimental design. These errors include: 1. The experiment has more than one independent variable. The independent variable is named as such because it is the one factor that is being changed in the experiment. If more than one factor changes, we cannot be certain which factor has the greater impact (if any). For example, if the scientist in the experiment above had changed both the type of fertilizer and the amount of water provided to each group of plants, he would not be able to prove whether or not water or fertilizer affected plant height. In any experiment, we may change one factor (the independent variable) and all other factors must remain constant. 2. The experiment has no control group. A control group is necessary to provide comparison for the experimental groups. If the scientist in the example above had not set aside one group of tomato plants to receive no fertilizer, he would not be able to prove whether or not any of the fertilizer types actually had a substantial impact on plant growth. 3. The experiment has too few test subjects (small sample size) or is not replicated. The more data available to support a hypothesis, the more reliable the results are. Had the scientist above only tested 5 tomato plants in each group, his results would not be as meaningful, because they would provide him with less data. In some experiments, it is more beneficial to test small groups and simply repeat the test multiple times. In others, one large test may be completed, but there are several test subjects involved (large sample). Answer the following questions on a separate sheet of paper. Remember to use the following formatting: - If typed, use size 12 Times New Roman font and single spacing. - If handwritten, print your responses neatly. - Leave one line of blank space between each response. - Use the following heading in the top left corner of your response sheet: Student Name Pre-AP Biology Summer Assignment, Section # Date of completion (not the due date) Section 7, Part I Review Questions: In each of the questions below, identify the following: hypothesis, independent variable, dependent variable, control group, experimental group(s), constants. You may list these on separate lines, but use complete sentences with each problem. 1. A study was done to test if smoking affects the number of holes that a person gets in his or her lungs. The scientists ask one group of people to smoke one cigarette per day. They ask another group to smoke two cigarettes per day. They keep another group of people from smoking any cigarettes. They ask all participants to follow a regulated diet and exercise program. They then measure the number of holes in their lungs after one year.

5 Section 7 - The Scientific Method & Experimental Design of A baker decides to conduct an experiment. He makes four different cakes. He adds no flour to the first cake. He adds two cups of flour to the second cake (the normal amount), three cups of flour to the third cake, and four cups of flour to the fourth cake. He then measures how high each cake rises. All cakes follow the same recipe otherwise, and are baked using the same materials, the same oven, and the same temperature for the same length of time. 3. A student wants to determine if drinking Diet Coke helps her stay up late. She decides to have the same dinner three nights in a row, and stays home to conduct her experiment all three nights. She doesn t drink Diet Coke one night. The next night, she drinks one Diet Coke at 8 pm. The next night she drinks two Diet Cokes, beginning at 8 pm. Each night, she records the time she begins to feel sleepy. Section 7, Part II Review Questions: For each of the following experiments, identify the problem with the experiment, and propose a change that would make the experiment more valid or reliable. 1. Jerome wanted to see if feeding his hamsters less food would help them lose weight. He weighed his 100 hamsters and then started to feed them 20% less food and put an exercise wheel in their cages. At the end of four weeks, his hamsters weighed on average 20g less than they had at the beginning of the experiment. Jerome concluded that the reduction in food helped his hamsters lose weight. 2. Marcus wanted to see if he could get his plants to grow better if he watered them more often. He decided to water half of his 250 beans and half of his 250 tomatoes once a week and to water the other halves three times a week. He found that the plants he watered three times a week grew taller and produces more beans and tomatoes. He concluded that watering his garden helps it grow more. 3. Francine wanted to test the idea that your cholesterol can be lowered with diet and exercise. She started eating well and exercising every day for two months. At the end, she tested her cholesterol and found that it was 160. She decided diet and exercise lowered her cholesterol. 4. Devon wanted to see if drinking energy drinks helped students to study for tests. He had 3 students take quizzes without drinking red bull, and the average student got 75% correct the next day. He had 3 students drink two red bulls before studying for their weekly quizzes and the average student got 80% correct the next day. He concluded that drinking energy drinks helps you do well on quizzes.