Apossible explanation for a set of observations or answer to a scientific question is called

An hypothesis is a possible explanation for a set of observations or answer to a scientific question. A supposition or proposed explanation made on the   
basis of limited evidence as a starting point for further  
 investigation. 
 And practically, an hypothesis is used as the basis for further experiments, where the hypothesis is rigorously tested under varying conditions. The hypothesis that is tested and modified under different conditions may become a general 
 theory
 .The hypothesis that has the least number of variables sufficient to explain the phenomenon is preferred.

They are both used to view parts of the cell