The answer is; Sodium (Na+) and Potassium (K+) Ions
These cations are pumped out of the cell by Na+-K+ transmembrane protein pumps leaving the inside of the cell electronegative in relation to the extracellular matrix. This membrane potential is significant especially for neurons. Depolarization of the membrane enables transmissions of an impulse along the neurons.
When the body becomes dehydrated, a chemical signal is sent that causes nephrons in the kidneys to absorb more water and excrete more salts. This is an example of a <em>D Feedback loop</em>.
The correct answer is fitness. The Theory of Evolution defines fitness as a result of the adaptations an organism has which increase its chance of survival.
