Why is it important that cell membranes are semipermeable membranes?

This is a biological reaction due to a stimulus. i need this quickly !

Aremote community desperately needs more electrical energy. it is located in an area with the following characteristics: average wind speed of 15 – 20 km/hr some medium-sized rivers with slow-moving currents few coal deposits some oil exploration being conducted within 400 miles based on the above information, which energy source would be the most economical and safest for the community to pursue? a. fossil fuel b. hydroelectric c. nuclear d. wind

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