90% of the available energy is lost in some form of heat, transferring light energy into different living organisms
Natural selection and speciation: 'Ecological speciation'. ... Natural selection is generally recognized as a central mechanism of evolutionary change within species. Thus, natural selection plays a major role in generating the array of phenotypic and genetic diversity observed in nature.
This is just an educated guess. As the purple pigment, caused by anthocyanins, are on the bottom side of the plant, their purpose could probably be to direct the light.
Specifically, a purple pigment on the bottom of the plant would absorb certain wavelengths near the purple spectrum, and reflect other wavelengths back toward the portion of the plant with chlorophyll. In this way, light does not simply pass through the leaf, instead it is reflected back in towards the chlorophyll to maximize the amount of light being used for photosynthesis.
Answer:
The exudation(To discharge through pores or incisions, as moisture or other liquid) of drops of water from the leaves of some vascular plants as a result of root pressure.
Note;- Text extracted from Wiktionary
