* Cells are the fundamental unit of life. They have all the necessary machinery to carry out life processes, including:

* A membrane that separates the cell from its environment.

* Genetic material (DNA or RNA) that carries instructions for building and maintaining the cell.

* Ribosomes for making proteins.

* Energy production mechanisms (e.g., mitochondria).

* Viruses lack many of these key components. They consist of a core of genetic material (DNA or RNA) surrounded by a protein coat (capsid). Some viruses may also have an outer envelope derived from the host cell membrane.

* Viruses are obligate intracellular parasites. This means they can only replicate inside living cells. They lack the ability to produce their own energy or proteins independently. They hijack the host cell's machinery to make copies of themselves.

In short, viruses are not considered living organisms because they cannot reproduce or carry out metabolic processes on their own. They are more like complex molecules that require a host cell to function.