Biodiversity is a term that describes the number, variety of any living organism in a geographical area or place. On some parts of the world like Grassland in North America for example the plants need other conditions and characteristics from the ones that are in Germany even though some of them are the same species.
It also means the number of different species in a region.
Biodiversity helps an ecosystem by suggesting to sustain the diversity in a ecosystem because humans affect the use of land and resources that are natural.
Because everything that lives in an ecosystem is a part of the food web (including humans) each organism depends on each other. When one organism dies it could happen that others will die as well because they can reproduce a lot more because they have no predators and then there is not enough food for that species and they will die out. This can continue and can even affect us humans!
This is the same thing that happened to us when we did the speciation lab because there were so many predators so after a time there was almost no prey left and if we would have to live form that food we would have died because it wasn’t enough to survive for a long time.