How does summation operate in a post-synaptic cell? a). it adds up all of the previous action potentials and releases one of that value. b). post-synaptic cells do not fire. c). input from many cells is required for it to fire. d). sodium ions are moved from one cell to the next in an additive way.

What is point source pollution of an aquatic ecosystem? a) pollution of freshwater sources b) pollution from many sources that combine into one c) pollution that occurs over a wide area; water that runs off from fields, parking lots, and other land surfaces d) pollution that can easily be identified with a single discharge source, such as an open pipe which drains into a body of water