The passage of salts into and out of cells is most closely associated with the life process of transport.

Here's why:

* Transport refers to the movement of substances across cell membranes. This includes both the uptake of nutrients and the removal of waste products.

* Salts are essential for many cellular functions, including maintaining cell volume, nerve impulse transmission, and muscle contraction.

* Cells use various mechanisms to transport salts, including:

* Passive transport: Movement of substances across the membrane without the use of energy (e.g., diffusion).

* Active transport: Movement of substances across the membrane requiring energy (e.g., sodium-potassium pump).

While other life processes like metabolism and growth are important, they are not directly related to the movement of salts across cell membranes.