Dependent variable Diversity of algal species Independent variable Oil spill d

# Dependent variable diversity of algal species

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Dependent variable: Diversity of algal species Independent variable: Oil spill d. Light absorption by a pigment is measured for red, blue, green, and yellow light. Dependent variable: Light absorption Independent variable: Different colored lights e. Batches of seeds are soaked in salt solutions of different concentrations, and germination is counted for each batch. Dependent variable: Batches of seeds Independent variable: Different concentrations STEP 4: IDENTIFYING THE CONSTANT or CONTROLLED VARIABLES A third type of variable is the constant or controlled variable. Constant 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, he must try to eliminate the possibility that other variables are influencing the outcome. This is accomplished by keeping the other variables at constant levels. For example, if the scientist has chosen the amount of fertilizer as the independent variable, he wants to be sure that there are no differences in the type of fertilizer used. He would use the same formulation and same brand of fertilizer throughout the experiment. READING CHECK: What other variables would have to be standardized in this experiment? The other variables that would have to be standardized in this experiment are light, soil,
amount of fertilizer, water, and plant type. READING CHECK: Define constant variable(s). A constant variable is a factor that is 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. STEP 5: WRITING THE HYPOTHESIS 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 a statement explaining that a causal relationship exists between an underlying factor (variable) and an observable phenomenon As the investigator devises an experiment, he should also make predictions about the effect of the independent variable on the dependent variable in each situation. 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. The predictions should state specifically how the dependent variable will change in relation to the independent variable and must be stated as an If ... Then statement. The general format for an If ... Then statement is “if the independent variable is changed in this way, then the dependent variable will change this way.” For example, if the amount of fertilizer applied to a field is doubled, then the number of peanuts produced will double. Or, if the temperature of the reactants in a chemical reaction increases, then the rate of the reaction will increase.

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• Fall '16
• investigator, Experimental Group, Scientific control

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