READING CHECK Define hypothesis A hypothesis is a statement explaining that a

# Reading check define hypothesis a hypothesis is a

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READING CHECK: Define hypothesis. A hypothesis is a statement explaining that a casual relationship exists between an underlying factor (variable) and an observable phenomenon. READING CHECK: What is the general format for a hypothesis? The general format for a hypothesis is to be straight to the point and to not form it into a question. STEP 6: IDENTIFYING THE EXPERIMENTAL & CONTROL GROUP In order to make sure that only one factor is being changed in an experiment, the independent variables are then divided into two groups. One group, called the control group, is exposed to all of the circumstances of the experiment but does not get whatever is being tested or changed in the experiment. At the same time, the experimental group gets all of the circumstances of the experiment PLUS the one variable being tested by the experiment. In the fertilizer example, the investigator must be sure that the peanuts don't grow just as well with no fertilizer at all. The control would
be a treatment in which no fertilizer is applied. The experimental group is the peanuts that are given different amounts of fertilizer. An experiment on the effect of temperature on guinea pigs, however, cannot have a "no temperature" treatment. Instead, the scientist will use a standard temperature as the control and will compare weight gain at other temperatures to weight gain at the standard temperature. READING CHECK: Define experimental group. An experimental group gets all of the circumstances of the experiment plus the one variable being tested by the experiment. READING CHECK: Define control group. A control group is exposed to all of the circumstances of the experiment but doesn't get whatever is being tested or changed in the experiment. CHECK FOR UNDERSTANDING Tell what an appropriate control and experimental group would be for each of the following examples. a. An investigator studies the amount of alcohol produced by yeast when it is incubated with different types of sugar. Control Group: How much alcohol is produced with no sugar Experimental Group: The yeast that is incubated with different types of sugar b. The effect of light intensity on photosynthesis is measured by collecting oxygen produced by a plant. Control Group: The measure of the light intensity Experimental Group: The amount of photosynthesis measured by the oxygen produced by a plant STEP 6B: IDENTIFYING POSITIVE VS. NEGATIVE CONTROLS A negative control is a control group in an experiment that uses a treatment that isn’t expected to produce results. A positive control is a control group in an experiment that uses a treatment that is known to produce results. For scientists, positive controls are very helpful because it allows us to be sure that our experimental set-up is working properly. For example, suppose we want to test how well a new drug works and we have designed a laboratory test to do this. We test the drug and it works, but has it worked as well as well as it should? The only way to be sure is to compare it to another drug (the positive control) which we know works well. The positive control drug is also useful because it tells us our experimental equipment is working properly. If the new drug doesn’t work, we can rule out a problem with our equipment by showing that the positive control drug works.

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

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