Can zoos help to protect endangered species?

All species are endangered. For example the polar bear. Humans don’t know what problems will be a lot of specie4s are endangered to extinguish.
A lot of people think that zoos are a way for protect the animals or endangered species. Other people think that zoos exposer endangered species to be seen by people.
In my opinion zoos are only form to maltreat the animals. They take these species and put it in small cages feeling it bad. These animals are not used to live in these conditions.
I think that to salve these problem zoos wouldn’t take endangered species. And the rest of people would have find solutions or find the factors which do that species becoming in endangered species and don’t do it.
If each person brings a little granite sand, the problem will be solved.