Most likely the students are using a crude measurement of time, like a stopwatch. They would get the best results with a scientific apparatus that uses a computer and optical sensors. Even recording their dropped objects with a video camera and analyzing the video would give more consistent results. Results will also vary greatly if different people are taking the time measures instead of one person making all measurements.
Dichotomous Keys are used to find out what type of animal,plant,fungi,prokaryote,eukaryote,or bacteria an organism is. A branching diagram is used to find what domain,kingdom,phylum,class,order,family,genus,species an organism belongs in.
(1) they keep toxic substances out of the cell;
(2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment;
(3) they separate vital but incompatible metabolic processes conducted within organelles.