Experimental Design Worksheet: Part 1 1. If skin cancer is related to ultraviolet light, then people with a high exposure to UV light will have a higher frequency of skin cancer. In an experiment, the independent variable (or manipulated) is the ONE variable that is purposely changed or varied by the researcher. The dependent variable (or responding variable) is the observed effect that is measured due to the independent variable. 2. If leaf color change is related to temperature, then exposing plants to low temperatures will result in changes in leaf color. An independent variable is the presumed cause, whereas the dependent variable is the presumed effect. Try to remember: The (Independent variable) causes a change in the (Dependent Variable) 3. If the speed of plant germination is related to the hardness of the hull of its seed, then softening the seed with water or a weakly acidic solution prior to planting will hasten germination. Example: You are interested in how stress affects heart rate in humans. Your independent variable would be the stress and the dependent variable would be the heart rate. You can directly manipulate stress levels in your human subjects and measure how those stress levels change heart rate. 4. If photosynthesis is related to light energy, then the portions of a leaf shaded from light will test negative for starch, since starch is a product of photosynthesis. Controlled variables are quantities that a scientist keeps constant, and to observe them as carefully as the dependent variables. For example, if we want to measure how much water flow increases when we open a faucet, it is important to make sure that the water pressure (the controlled variable) is held constant; the same type of faucet material; same diameter; same length; same height. Control Group: These groups normally require no manipulation on the part of the research team. A plant left by the window in a photosynthesis experiment is your control setup. Experimental Group: is the group that gets all of the required conditions of the experiment PLUS the one variable being tested by the researcher. The plant in the dark is your experimental group in a photosynthesis investigation. 5. If animal metabolism is related to temperature, then increasing resting room temperature will increase animal metabolism (as measured by carbon dioxide gas production which is one of the waste products of animal metabolism). 6. If root growth is related to gravity, then roots will always turn toward the earth regardless of a seed's orientation. 7. If hatching of brine shrimp is related to salinity (or temperature), then the greater the salt concentration, the higher the hatching rate. Experimental Trials: Trials are the amount of times a certain experiment is repeated before a hypothesis is rejected or confirmed. Trials are also known as the reproducibility of an experiment, and how well the same/different results can be achieved (if the trials are testing the same independent variable or one at a time). 9. If the thickness of annual growth rings in trees is related to annual rainfall, then examining wood samples will reveal correlations in the growth rings to the historical records for rainfall in its environment. Given Sample Hypotheses: What will you do to test this proposal? What will you vary or change? What will you measure? What will be your controlled variable(s)? What is the control group? What is your experimental group? How many trials? Independent variable – Dependent variable – Controlled variable – Control Group – Experimental Group – Trials (Replicated or Testing one other variable) 10. If poking a skunk will always result in the emission of noxious and toxic fumes. Experimental Design Worksheet: Part 2 I. Definitions: Define the following words and concepts related to the scientific method. 1. Hypothesis: 2. Independent Variable: 3. Dependent Variable: 4. Control Group: 5. Experimental Groups: 6. Constants (controlled): 7. Trials: II. Practice: Write a hypothesis (If…, then…) for each of the statements and identify the variables, control group, and experimental group. Hypothesis: Independent Variable: Dependent Variable: Control Group: Experimental Group: 3. Where should they perform the experiment (Hint: Where do sharks like to live?) 4. Pick one of the two hypotheses and determine the following: a. Control Group: b. Experimental Group: c. Dependent Variable: d. Independent Variable: 5. What type of data do you think John will collect (What will be the results of the experiment?)? 6. What conclusions will John be able to make from the results of the experiment? IV. In the statements below, write the hypothesis, variable, control groups and experimental groups. 1. Plants grow best in white light. 2. The deer population decreases in the winter due to the lack of food. 3. Students who study perform better in school. 1. Cigarette smoking increases the risk of lung cancer. V. Read the following situation and answer the following questions. 2. Eating breakfast increases performance in school. 3. Hummingbirds are attracted to the color red. 4. Bats locate food using sound waves. 5. iBook batteries last for 5 hours. III. Situations: Read the situation below and design an experiment. I. John Smith has been hired by the city of Manhattan Beach to investigate the recent shark attacks off the resort’s coast. He has a budget of $40,000, a 25 foot boat, and three graduate student assistants to help him. A helicopter has also been donated by a local television station, should he need one. * * * 1. List 2 hypotheses John and his crew may have come up with for the recent shark attacks. 2. What materials will John need to perform this experiment (How will they spend the $40,000?). Suzie Q wants to know the effect of different colors of light on the growth of plants. She believes that plants can survive best in white light. She buys 5 ferns of the same species, which are all approximately the same age and height. She places one in white light, one in blue light, one in green light, one in red light and one in the closet. All of the ferns are planted in Miracle-Grow and given 20 mL of water once a day for 2 weeks. After the two weeks, Suzie observes the plants and makes measurements. Hypothesis: Independent Variable: Dependent Variable: Control Group: Experimental Group: Constants: What types of measurements can Suzie make on the plants to determine how they did in different types of light?
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