I think the independent variable is the temperature, while the dependent variable is the size of the balloon. The factor that is held constant is the amount of air in the balloon. An identical balloon kept at the original temperature. Independent variable in an experiment is the variable that the experiment plans to change while the dependent variable is the variable whose value depends on the independent variable.
Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains.