In the early studies of chemistry, scientists used properties and changed to identify compounds. this is still done today. if you were given the following observation about salt water, how would you classify it? "when electricity flows through a flask of salt water, bubbles form in the water. these bubbles, when collected, will burn."

as an inflammable substance

Explanation:

Because when it reacts with electricity and water start to produce bubbles, and these bubbles burn, that mean is a substance flammable.

Now a days it is needed to have more test to identify a substance and to classify not just by the physical properties, also by the chemical properties and even  more, by the chemical behavior in front of other substances.

answer: they produce more slow than unicellular organisms.