I followed some of the links to those lesson plans. There seems to be a lot of interest in this kind of thing because it’s so obviously a demonstration that can be put together by grade schoolers, but can provide fascination to even a jaded scientist.

I have one tip and one notion to add. The tip is this: if your goal is to keep your biggest animals alive, you probably shouldn’t just bottle up some pond water, as at least one of your link sites did. That pond water is likely to have a lot of nutrients that sooner or later will lead to an oxygen-consuming algal bloom. The MAKE recipe dilutes pond water with a lot of processed water.

The notion is only for the real scientists out there. If you really want to convince yourself that biospheres work, you might want to do a small experimental design that includes control biospheres without lights. You’d be surprised how long these can last — I had one where animals lived for a month. Of course the lighted ones can last even longer. But the animals that go in these things are tough!