Question

Explain the importance of biodiversity.

Answer 1

This is a great site for what you are looking for :D
http://library.thinkquest.org/08aug/00473/whatisit.html

Answer 2

The are a number of reasons biodiversity is important, the one that always springs to mind for me is the matter of redundancy. That is, the more diverse organisms you have the more likely there will be another species to replace the role of another if one dies out. This means the ecosystem will have greater resilience to disturbance.