Final answer:
Viruses are not considered living organisms because they lack cells and the necessary cellular structures for life processes. They rely on a host cell for replication and cannot carry out essential functions on their own.
Step-by-step explanation:
Viruses are not considered living organisms because they do not consist of cells. They lack the cellular structures and organelles necessary for life processes such as metabolism, homeostasis, and growth. Instead, viruses depend on a host cell to replicate and carry out essential functions.
Although viruses have genetic material and can evolve, they do not meet the criteria for being classified as living organisms.