In some single-celled protozoans living in fresh water, such as the paramecium, contractile vacuoles are organelles used to pump excess water out of the cell. Explain why a paramecium would require contractile vacuoles while a similar protozoan living in salt water would not.

D. peatlands,grassland,swamps

Na+ loss through sweet plus the dilution has lowered na+ concentration outside of neurons, altering the na+ equilibrium potential. sodium exists more outside the cells than inside. when na+ is lost by sweat plus the dilution( because they drink a lot of water) changes the concentration outside the cell, forcing the water to enter the cell and attempt to balance the concentration inside/outside.the problem is that the abundance of water will cause the cells to swell. most cells can adapt, however, the brain cells can't that's why the runner has confusion and can't control the muscles.  if not treated and this occurs in less than 48 hours, it can be immediately fatal .