Living characters:
1. Presence of nucleic acid and protein.
2. Capable of mutation.
3. Ability to multiply within living cells.
4. Able to infect and cause diseases in living beings.
5. Show irritability. 6. Host – specific.
Non – living characters:
1. Can be crystallized.
2. Absence of metabolism.
3. Inactive outside the host.
4. Do not show functional autonomy,
5. Energy producing enzyme system is absent.
