explain the use of the control in an experiment in biology or chemistry?

Answer 1

Control is a sample that you use to check whether the experiment has worked the way you intended from a "technical" point of view - i.e whether the results you are looking at, are really due to biological/chemical effects and not because of experimental problems.
You need to distinguish between positive control and negative control. A negative control is, generally, a reaction where something has been omitted and you should have no signal. That rules out that, if your results are positive, you are not looking at false positives! For example, if you want to check the effect of a drug on cells (say, the S-phase inhibitor aphidicolin), than you'll leave a sample of cells untreated as comparison.
A positive control is a sample treated in such a way that you can predict the result - normally a strong positive signal. This will tell you that, if you DO NOT see this signal, the whole experiment did not work and you can scrap it. In the previous example, you could use Hydroxyurea, which is known to block S-phase in mammalian cells.

Hope this helped

Answer 2

Control is what is not changed in the experiment. A variable is what you change in the experiment. So if I was trying to grow two plants and added wonder-gro to one of them. Wonder grow would be my variable. But the fact that I did not add Wonder Gro to the other plant, that plant would be my control. In every experiment its always Control vs Variable. Or in simple terms No Change vs A Change. Control is when you do not apply a treatment to your experiment. While variable is the complete opposite, you are adding a treatment.

Answer 3

The main idea of a control is to ensure that the results you record in your main experiment are only as a direct result of the variable you are changing.

Answer 4

Control is a comparison standard for experiments.
Example: to find the effect of deficiency of iron in rose plants, you would grow two rose plants- one in nutrient medium having all nutrients and another in a medium having all nutrients as the first one except iron.That way, the first plant is control and second one can be compared with it to find the consequences of iron deficiency.
Hope it helped.

Answer 5

Try this: http://en.wikipedia.org/wiki/Experimental_control.

It took me under twenty seconds to do that, Next time, try it yourself, then you'll have the satisfaction of doing your own homework.