Viruses: Acellular Organisms
Viruses are often classified as acellular or organisms that exist in a gray area between living and non-living entities due to their unique characteristics. Here's why viruses are considered as such:

Structure:
- Viruses lack cellular structure and organelles, which are essential components of living organisms.
- They consist of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid.

Reproduction:
- Viruses cannot reproduce on their own and require a host cell to replicate.
- They invade host cells, hijack their cellular machinery, and use it to produce more virus particles.

Metabolism:
- Viruses do not have metabolic processes or the ability to generate energy on their own.
- They rely on the host cell's metabolism to carry out their replicative functions.

Evolution:
- Viruses are constantly evolving through mutation and genetic recombination.
- They exhibit a high degree of genetic variability, allowing them to adapt to changing environments and host defenses.

Host Specificity:
- Viruses have a specific host range and can only infect certain types of cells.
- This specificity is due to the interactions between viral surface proteins and host cell receptors.
In conclusion, viruses blur the line between living and non-living organisms due to their unique characteristics. While they exhibit some properties of living entities, such as genetic material and the ability to evolve, they lack essential features like cellular structure and independent metabolism. This classification as acellular organisms highlights the distinct nature of viruses in the biological world.

Because they are called living when present on host but they are called dead without host body that's why viruses are called organism between living and non living.