Abiologist wants to test some lake water for the presence of nitrates. he has a sensor that detects even the tiniest amount of nitrates by turning an internal light from green to red. a) what will be his positive control? (specific). b) what will be his negative control? (specific). c) why does he need o include these controls?

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