why are controls set up?

Question

Ok we did an experiment on agglutination, whereby rabbits had been immunized with sheep red blood cells. We measured the agglutination titres of immune and non immune sera.

During the experiment we set up control wells, containing 0.2ml dilution buffer and 0.2ml cell suspension. The result was negative. But what is the purpose of the control wells, what does this prove? And how would I write this in my report? Thanku, just really stuck on this bit..xx

Answer 1

I've never done an agglutination assay, but since there are wells, can I assume that it is a photometric or colorimetric assay? If that is the case, the dilution buffer would serve as your blank.

Any substance that you put in the well is going to have an effect on the light that passes through it. By using it as a blank, you can subtract out any effect that the dilution buffer has on your readings (since it is the one constant throughout all of the wells).

The cell suspension would be a negative control, and would show that agglutination is not a function of the cells, but one of the sera. In other words, if that control came back positive, you would know that you had a problem with your cells, either with self-agglutination, or with the assay itself.

Answer 2

A control is designed to show what would happen anyway, and the experiment is designed to vary ONE factor only.

In your experiment your control shows that it's the sheep blood cells that do the trick, not anything that the cells are carried in,