If the new drug doesnt work we can rule out a problem with our equipment by

If the new drug doesnt work we can rule out a problem

This preview shows page 4 - 7 out of 10 pages.

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. The “negative-control” sets what we sometimes call the “baseline”. Suppose we are testing a new drug to kill bacteria (an antibiotic) and to do this we are going to count the number of bacteria that are still alive in a test tube after we add the drug. We could set up an experiment with three tubes. One tube could contain the drug we want to test. The second tube would contain our positive control (a different drug which we know will kill the bacteria) The last tube is our negative control – it contains a drug which we know has no effect
Image of page 4
on the bacteria. This tells us how many bacteria would be alive if we didn’t kill any of them. If the new drug is working, there should be fewer cells left alive in the first tube compared to the last tube and ideally then number of cells still alive (if any) should be the same in the first and second tube. So “controls” are important to scientists because it helps us validate the performance of our experimental set- up and tells us what effects we can reasonably expect to observe. CHECK FOR UNDERSTANDING Tell whether the control group is positive or negative control. a. An investigator studies the amount of alcohol produced by two groups of yeasts when one group is incubated in the presence of sugar, and one group in the absence of sugar. Positive or Negative Control: Negative b. The effect of artificial light on photosynthesis is measured by collecting oxygen produced by a group of plants exposed to an artificial light, and a group of plants exposed to natural sunlight. Positive or Negative Control: Positive STEP 7: DETERMINING REPLICATION Another essential aspect of experimental design is replication. Replicating the experiment means that the scientist repeats the experiment numerous times using exactly the same conditions to see if the results are consistent. Being able to replicate a result increases our confidence in it. However, we shouldn't expect to get exactly the same answer each time, because a certain amount of variation is normal in biological systems. Replicating the experiment lets us see how much variation there is and obtain an average result from different trials. Part II: For each of the statements identify the variables, control group, and experimental group. In the control group determine whether your control group is positive or negative control. In the experimental group, make sure to identify the constants. 1. Eating breakfast increases performance in school. Independent Variable: Eating breakfast Dependent Variable: Performance in school Control Group; type of control: Students who don’t eat breakfast, negative Experimental Group w/ Constants: Students who eat breakfast 2. Salt in soil affects plant growth. Independent Variable: Salt in soil Dependent Variable: Plant growth Control Group; type of control: Positive
Image of page 5
Experimental Group w/ Constants: Amount of salt, amount of soil, type of salt, type of plant, type of soil Part III: Write a hypothesis for each of the following problem statements. Identify the dependent and independent variable for each. **Remember a hypothesis is an IF (cause or IV)...THEN (effect or DV)
Image of page 6
Image of page 7

You've reached the end of your free preview.

Want to read all 10 pages?

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

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors