Explanation:
A similar question was asked online, here is the answer it gave:
'“Negative control” is a treatment that by definition is expected not to have any effect (neither positive effect, nor negative effect). “Positive control” is treatment with a well-known chemical that is known to produce the expected effect with the assay that you are studying. Application of an antagonist is not a negative control in your case. “Negative control” is condition that should be treated with the same solutions or buffers as your “treatment” condition, with the only difference that instead of the chemical that you investigate you should add just the solvent that was used to dissolve you chemical in the respective final concentration that you have in the “experimental treatment” condition. For example if your chemical is dissolved in DMSO – than the correct negative control will be to add to the medium/buffer just DMSO in the same final concentration that you reach with your “treatment” condition. One of the reasons of using such negative control is to verify that the solvent is having no effect in your assay. Note that among all treatment conditions (“negative control”, “positive control”, “experimental treatment you are investigating”) the volumes and the composition of the treatments that you are doing should be uniform: always treat with the same volume of medium or buffer, always containing the same concentration of the used solvent (e.g., DMSO). The only difference should be the presence or absence of the defined compound-treatments (agonist, antagonist, the chemical for the experimental investigation etc.).'
My best advice is to use the textbook you have, or use examples of a negative control when testing organic compounds because you have to find something that you can assign, like a worm in a box of dirt, the worm could have enough food to survive, so that is your negative control, but when it comes to finding the best, that would have to rely on something within the parameters of being self sufficient like a plant getting its energy from photosynthesis, etc.
Atanasov, Atanas. (2013). Re: Positive control and negative control. Retrieved from: https://www.researchgate.net/post/Positive_control_and_negative_control/515968f2d039b1fe50000025/citation/download.
During electrophoresis, the fragment that travelled the furthest will be the smallest one. So if it's coming from top to bottom, then the band closest to the bottom will be the smallest one.
