How do cells maintain homeostasis with their environment?

Cells maintain homeostasis with their environment primarily through the cell membrane's selective permeability. The cell membrane acts as a barrier that regulates the movement of substances into and out of the cell, allowing essential nutrients to enter while keeping harmful substances out. This selective permeability is crucial for maintaining the internal balance of ions, nutrients, and waste products, enabling the cell to react appropriately to changes in the external environment.

For example, the cell can selectively transport water, ions, and other molecules through various mechanisms, such as passive diffusion, facilitated diffusion, and active transport. This regulation is vital for processes like nutrient uptake, waste elimination, and electrical charge maintenance, which are essential for the overall functioning of the cell and, by extension, the organism.

The other options relate to important cellular processes but do not directly address the mechanisms of homeostasis. DNA replication is essential for cell division and genetic continuity; ATP is the energy currency used in many cellular processes but does not directly control the permeability of the membrane; and mitosis is the process of cell division rather than a mechanism for maintaining internal balance.