Whats a control!!??

Question

Okay so I need to put a control on my science fair board. My brother gave me an example of one. Like you have three plants. One gets sunlight, another gets a little bit, and the third one gets none. He said the control is the third one. But how would you write that??

Answer 1

hey gm. label ur plants #1, #2, and #3. just put plant #3.

Answer 2

The third plant in this experiment would be the control only if you are showing the effects of certain amounts of sunlight on plants.   Another example of a control would be a 3 party wieght loss study; Person #1 could go on say, the south beach diet, Person #2 could go on weight watchers, Person #3 (the control) could not go on any diet.  Perhaps this is a bad example because of differences in things like genetics, metabolism, etc, but I'm just getting at the BASIC premise of a control here.

Answer 3

The experimental control for an experiment depends on the variable that is being isolated, and examined by the experiment. Say for example that a pharmaceutical company is testing a new drug. They would give one group of test subjects the new drug, another group they would give a sugar pill (placebo effect), and a third group would receive nothing. The third group is the control for the experiment. The control acts as a baseline measurement to see if changes to the experimental variable had any effect.

In your case, it depends on what you are testing for. If you are testing for how differing amounts of sunlight affect plant growth, then your example plant group not exposed to sunlight would be correct. As long as every other variable stays the same (water, humidity, soil, fertilizer, etc.). Then you can attribute changes in growth to amount of sunlight.

To write this, create a "key" identifying what each test group on your poster is. Group / Plant 1, 2, 3. Clearly state in the key which was the control. Also indicate the control when you explain the design / methods of your experiment. Say some like this...

"Three groups were used to test the relationship between sunlight and plant growth. Each group had 3 germinated  Arabidopsis thaliana seed placed in identical 2 inch x 2 inch containers filled with x-grams of potting soil. Each plant received x-milliliters of tap water daily. All plants were kept indoors; humidity level and temperature were kept constant for the duration of experiment. The experimental groups received light from a Philips Agro-Lite 40 Watt HPS lamp, kept 3 feet from the surface of the soil, directly above the plant container. Group 1 received X-hours of light per day from the time the seed was planted until final measurement was taken at x # weeks. Group 2 received X-hours of light per day from the time the seed was planted until final measurement was taken at x # weeks. Group 3, acting as the experimental control, received no light from the time the seed was planted until final measurement was taken at x # weeks."