Which processes are essential for maintaining life?

The four most immediately essential: nutrition, respiration, transportation, and excretion.

• Nutrition: Cells starve without food.
• Respiration: Cellular work stops within seconds without energy.
• Transportation: Circulation failure is immediately life-threatening.
• Excretion: Accumulated toxins rapidly kill cells.

Growth and reproduction are important for species survival but not immediately critical for individual survival.

Summary: Nutrition, respiration, transportation, and excretion are the four most immediately life-sustaining processes.