NEW DELHI: Describing the biodiversity of India as a "unique treasure " for the entire humankind, Prime Minister Narendra Modi on Sunday urged people to preserve and conserve it.Addressing his monthly ' Mann ki Baat' radio address, the Prime Minister referred to Tamil poetess Avvaiyar to drive home his point."What we know is just a handful of sand. What we do not know is like a universe in itself," he said quoting her.Similar is the case with the biodiversity of this country, the Prime Minister pointed out."The more you know, the more you realise the magnitude of what you do not know. Our biodiversity too is a unique treasure for the entire human kind. We have to preserve it, conserve it and explore further," he said.