SCIENTIFIC METHOD WHAT AM I EXECTED TO LEARN? Identify the steps involved in the scientific method Develop a testable hypothesis Explain the reason for a control group Identify the hypothesis of an experiment Identify the treatment group of an experiment Identify the control group of an experiment Identify an independent variable of an experiment Identify a dependent variable of an experiment VOCABULARY scientific method hypothesis testable falsifiable dependent variable independent variable experimental control control group treatment group theory BACKGROUND READING Science is a process to learn how things work. Science is also the body of knowledge that comes from that process. Scientific knowledge can change as new information is introduced. Scientists follow a process often referred to as the scientific method. This consists of making observations, then developing a hypothesis to explain the observations. A hypothesis is a tentative explanation for an observed phenomenon. The next steps are to design and carry out an experiment to test the hypothesis. The information collected is called data. When the data have been collected, they will be interpreted and the scientists will accept or reject the hypothesis based on what the data show. If the hypothesis is not supported by the data, a new hypothesis is developed. Hypotheses must be testable and falsifiable (can be proven to be wrong) to be valid. A person may believe that her lettuce grew poorly because it was too hot out. Perhaps she is correct, but perhaps the lettuce grew poorly for a totally different reason. There is no way to test or disprove her explanation, so it is not a valid scientific hypothesis. However, her friend feels that they can develop a testable hypothesis to help learn about lettuce growth so they can have a better harvest next time. The friend predicts that growing temperature affects lettuce growth. This is a testable and falsifiable hypothesis. One way to evaluate a hypothesis is to state it as a prediction that changing a variable (X), will affect another variable (Y). In the lettuce example, the hypothesis would be that the growing temperature (X) will affect lettuce (Y). Another way to express this hypothesis is to say that the Y variable depends on the X variable. For example: lettuce growth (Y) depends on growing temperature (X) Scientists call the Y variable the dependent variable because their hypothesis predicts it will depend on another variable. They call the X variable the independent variable. Once the hypothesis has been determined, the scientist develops an experiment to test the hypothesis. This is done by altering the independent variable (X) and observing the effects, if any, on the dependent variable (Y). In order to be SCIENTIFIC METHOD 1
confident that it is the independent variable causing any observed change in the dependent variable, the scientists does two very important things. First, she makes sure to change only the independent variable of interest. For example, a researcher would not grow lettuce with different growing temperatures and different amounts of water because then one would not know which of those factors affected the outcome. All variables other than the one being investigated must be the same across the board, i.e. they must be standardized. The second important part of an experiment is to change the dependent variable and compare it to what would have happened if that variable had not been changed. That is, to always include an experimental control. A researcher might grow lettuce in a warm greenhouse and compare it to lettuce grown in a cold greenhouse to be certain that it was the temperature, and not some other factor, that caused any observed differences in growth. The comparison group is known as the control group. The group that was exposed to a different level of the independent variable is known as the treatment group. If a tested hypothesis can be shown true in repeated testing, it may be that the information will be added to the general body of knowledge that is science. Only when a hypothesis has been tested many, many times in many circumstances, by many scientists, so that the evidence supporting it is beyond a reasonable doubt, do scientists apply the term theory. Examples of this include cell theory and evolutionary theory. The use of the term theory in science is much different than the way we use it in casual conversation. SCIENTIFIC METHOD 2
SCIENTIFIC METHOD WORKSHEET 1 - SUBMIT BEFORE STARTING THIS ACTIVITY key posted online on Friday 1. List the steps involved in the scientific method, in order. Name Lab Day 2. A scientist hypothesizes that plants survival depends on the amount of water the plants receive. Complete the sentences below using the terms: Independent Variable, Dependent Variable, Treatment Group, Control group The is the variable that is changed by the investigator. EXAMPLE: amount of water provided to the plants each day The is the variable that is measured, counted or recorded by the investigator. It is the factor that varies in response to conditions manipulated with respect to the independent variable. EXAMPLE: plant survival after two weeks The is the group of subjects for whom the independent variable is manipulated. EXAMPLE: plants given no water The is the one where the independent variable is not manipulated. EXAMPLE: plants given 100 ml of water daily 3. All variables other than the one being investigated must be the same across the board, i.e. they must be standardized. Explain why this is so important. SCIENTIFIC METHOD 3
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ACTIVITIES Work in groups of 4. 1. A researcher wants to find out if spraying fruits and vegetables with pesticides affects the vitamin C content of those foods. Write the hypothesis and state is as a prediction. Design an experiment and describe it here: What is the independent variable? What is the dependent variable? What is the treatment group? What is the control group? 2. A researcher want to know if eating a late-night snack bad for people. Write the hypothesis and state is as a prediction. Design an experiment and describe it here: What is the independent variable? What is the dependent variable? What is the treatment group? What is the control group? What are some variables that the researcher should standardize so they do not influence the results of this experiment? What are some advantages of conducting the experiment on a specific subset of the general population? (i.e. just males) What are some disadvantages of conducting the experiment on a specific subset of the general population? (i.e. just males) SCIENTIFIC METHOD 5
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SCIENTIFIC METHOD WORKSHEET 2 - SUBMIT AT THE END OF LAB key posted online on Friday Name Lab Day 1. A(n) is a prediction or statement that can be tested. (a) conclusion (b) observation (c) control (d) hypothesis 2. A sample that is treated exactly like the other experimental groups except that the treatment is not applied to it is a(n). (a) observation (b) variable (c) control (d) hypothesis In a controlled experiment, a scientist is studying how long it takes parachutes of different colors to fall to the ground. 3. What is the independent variable? (a) the color of the parachute (b) the height from which the parachute is dropped (c) the size of the object carried by the parachute (d) the time it takes for the parachute to drop 4. An experiment for a new asthma medication was set up into two groups. Group A was given the new drug for asthma, while group B was given a sugar pill. The sugar pill serves as a. (a) control (b) constant (c) experimental variable (d) dependent variable 5. The factor you measure and record as data in an experiment is known as the: (a) control (b) independent variable (c) constant (d) dependent variable 6. You suggest that the presence of water could speed up the growth of bread mold. This is a (a) conclusion (b) experiment (c) hypothesis (d) analysis 7. An Indian legend describes the origin of Devil's Tower in Wyoming as the result of a giant bear scratching claw marks in the rock as it pursued Indian braves. The hypothesis that the devil really made Devil's Tower could be tested scientifically. (a) True (b) False 8. To learn if a new drug called Thindown is effective in promoting weight loss, scientists will supplement the food of male rats twice daily with 20 mg of Thindown. An appropriate control for this experiment is: (a) female rats also fed Thindown (b) male rats not fed Thindown (c) rats given 20 minutes of exercise twice daily (d) male rats fed Thindown once daily SCIENTIFIC METHOD 7
Ms. Johnson tests to see the effects of fertilizer on the growth of her fern plants. One group of plants gets water and fertilizer, and the other group of plants gets water only. 9. Which is the treatment group? (a) The plants that receive water and fertilizer (b) The plants that receive only water (c) The fertilizer (d) The water 10. Which is the control group? (a) The plants that receive water and fertilizer (b) The plants that receive only water (c) The fertilizer (d) The water 11. Identify and name one standardized variable for this experiment: A student decides to set up an experiment to see if detergent affects the growth of seeds. He sets up 100 seed pots. 50 of the seed pots will receive a small amount of detergent in the soil and will be placed in the sun. The other 50 seed pots will not receive detergent and will be placed in the shade. All 100 seed pots will receive the same amount of water, the same number of seeds, and the same type of seeds. He grows the seeds for two months and charts the growth. 12. What is wrong with his experiment? (a) More than one variable is being tested. (b) The student should have a larger number of pots. (c) There is no way of measuring the outcome. (d) There is no independent variable. In a controlled experiment, a student is studying how long it takes cats of different colors to catch a mouse. One calico cat is tested and compared to a black cat. 13. What is wrong with her experiment? (a) More than one variable is being tested. (b) There is no way of measuring the outcome. (c) The student should test a larger number of cats. (d) There is no dependent variable. 16. Explain your answer. SCIENTIFIC METHOD 8