The planet Earth itself is considered to be a closed system because there is a limit to the amount of matter that is exchanged. However, there are open systems that are ON Earth.
It should have 10 electrons
Organic elements, depends on the context of the question but I suspect that is the answer. The organic elements are H,O,C,N,P,S
I believe the answer is gills
Fish's use gills to breathe, so tadpoles should use gills too
hope this helps
(got the info from a documentary i watched a couple years ago)
