Biodiversity means a natural diversity of species. For instance, a forest has trees that shade undergrowth plants, which in turn protect the soil from animals that eat the trees. There are insects that eat dead trees and fallen leaves, converting them into mulch and natural fertilizer, and birds that eat the insects and nest in the trees. Its a whole community of literally hundreds of species that depend on one another in one way or another. Lumber companies cut down the trees and then plant a 'monoculture' of one type of fast-growing tree, so this ancient forest becomes no more than a tree farm with one species.
Every -natural habitat- is naturally biodiverse--the rainforest, the jungle, the ocean, the prairie.
Multiculturalism means that a country is tolerant of many cultures. The US is an 'immigrant nation' in that nearly all the people who live here came from somewhere else only a few generations ago. Everyone brought part of his culture with him, so our culture is a combination of all of these, they all enrich our culture. Canada, Argentina, and Australia are also 'immigrant nations'. Here in California where I live there are neighborhoods or whole cities where Spanish or Hindi or Urdu or Vietnamise are the 'standard' language. But we are all tolerant of one another (by and large) and we have a wonderful selection of ethnic restaurants. 8^)