Final answer:
The composition of dmem must be isotonic to the cells' extracellular fluid to ensure proper cellular function and maintenance of osmotic pressure, which is particularly important for physiological stability and health.
Step-by-step explanation:
The question you've asked touches on the concept of isotonic environments and the importance of the composition of the extracellular fluid with regard to the osmotic balance in living organisms. In this case, dmem seems to refer to the Dulbecco's Modified Eagle Medium, which is a type of culture medium used in biology for growing cells. For the cells to function properly without undergoing lysis or crenation, the dmem must be isotonic compared to the cells' extracellular fluid.
Mammalian systems, and by extension the cells grown in dmem, need to maintain osmotic pressure and electrolyte balance for cellular health. This balance is so crucial that changes in plasma membrane composition can occur in response to different environmental conditions, as described comparing cells from the Mediterranean coast and the Mojave Desert, which might develop different mechanisms to cope with different osmotic pressures.
Therefore, to maintain cellular integrity and function, the composition of dmem should be adjusted to match the osmolarity of the extracellular fluid of the species being studied.