This document discusses biodiversity and the classification of species. It explores where life can be found on Earth and estimates there are over 1.7 million classified species but up to 15 million total species. The document examines three main ways species can be classified - biologically based on ability to breed, morphologically based on physical features, and phylogenetically based on evolutionary history. It provides examples of interspecies interactions like food chains, symbiotic relationships, and ecosystems reliance on biodiversity.