Nitrogen gas is more abundant in our atmosphere than oxygen! However, nitrogen needs to be converted into different forms to be used by many organisms. Bacteria are highly involved in this! Describe the role of (A) bacteria fixing nitrogen as they live symbiotically with some plant species, (B) nitrifying bacteria, and (C) denitrifying bacteria in the nitrogen cycle.

Crinoids, also known as sea lilies, appear to be sea plants but are not plants at all. crinoids are an echinoderm species which uses anchoring structures called holdfasts to attach themselves to the sea floor. crinoids were most abundant in pennsylvania during the mississippian period, which ranged from 375 to 320 million years ago. fossils of the crinoids shows that during most of this time pennsylvania was that provided favorable conditions for crinoid growth. a) glacial terrain b) a dry and sandy plain c) mostly mountain ranges d) covered by warm, shallow seas