Without biodiversity, the earth would be a completely different and nonfunctional place. Learn from this video about the utmost importance of of need for biodiversity.
Learn all about elephant seals, animals that reached near extinction about 100 years ago because of human need for their blubber.
Evolution has created millions of species, all unique. This has resulted in the tremendous biodiversity we see on Earth.
What qualifies as the largest organism depends on how you define it, but it's a tree or a fungus.