Of the following, which additional investigation can be used to determine when the cells are in an isotonic solution? Decreasing the salinity of the environment a little at a time until the ATP usage reaches a maximum A Decreasing the salinity of the environment a little at a time until ATP usage reaches a minimum B Increasing the salinity of the environment a little at a time until ATP usage reaches a maximum C Increasing the salinity of the environment a little at a time until the ATP usage reaches a minimum

An additional investigation to determine when a cell is placed in an isotonic solution is when the salinity of the environment increases until ATP usage reaches a minimum.

Explanation:

A cell placed in an isotonic solution is a cell that has impermeable solutes of equal degree on both aqueous sides. Thus, the smooth movement of water through osmosis across such cell will be through active transportation, since conventionally, the environment is supposed to remain constant. There will be movement of water across the cell membrane even when in the isotonic environment because of the gradients generated by the ATP within the mitochondria of the cell. Therefore, the ATP will build a suction pressure within the cell to disturb the equilibrium system of the cell. This suction pressure will lead to the influx of water molecules into the cell, and consequently, to the increase in the salinity of the environment. This phenomenon will continue until the system became adjusted, such that the movement of water molecules into the cell will take place passively without the need for the usage of ATP. Therefore, the increase in salinity will continue until ATP usage is minimum.