Before the advent of genetics animals and plants were classified in the most simple and exploitable way, that is to say by use, for example the plants was classified in nutritive plants, phytotherapeutics (it even divided into subclasses) Toxic insect repellent ...
Earlier the people were not aware about the genetics and classification of plants and animals. So, they used to classify plants and animals by their use. The plants were used for many purposes such as eating, medicine, cosmetics. Either the plants were usable or non usable. Plants like neem, tulsi, ginger, turmeric were used as medicine. Animals were used for obtained dairy products like milk and butter, for eating, for exacting colors out of them.
There are so many examples for that in different areas, like TPT1 experiment carried out in our lab recently.Here's one link: http://www.alfa-chemistry.com/tpt1-cas-167218-46-4-item-290583.htm
In order to conduct a research you should have an dependent variable, independent variable and the control variable. so in order to study phototropism, then you should need sun light and the growth of the plant and you must have a control that why you need a dark room.
