Which of the following is NOT a life function?

The correct answer highlights the distinction between excretion and other vital life functions. Excretion of waste is indeed a life function; however, when the term is limited to "excretion of waste only," it suggests a narrow focus, excluding other essential processes that contribute to an organism's overall biological functions.

Life functions, such as metabolism, reproduction, and defecation, are integral to maintaining life. Metabolism encompasses all biochemical processes that occur within an organism, including energy production and utilization. Reproduction is crucial for the continuation of species, allowing for genetic material to be passed to the next generation. Defecation, as a process of eliminating undigested food and other waste, is vital for maintaining a healthy balance within the organism.

By contrast, defining life function solely in terms of excretion excludes the broader array of physiological processes that sustain life, indicating why "excretion of waste only" does not fulfill the criteria for being classified as a comprehensive life function.