Here's why:
* Viruses are obligate intracellular parasites: This means they absolutely need a host cell to survive and reproduce. They lack the necessary machinery to do so independently.
* They hijack cellular processes: Once inside a cell, viruses use the host's resources and machinery to replicate their own genetic material and proteins, effectively taking over the cell's functions.
* They can cause a wide range of diseases: From the common cold to HIV/AIDS, viruses are responsible for a vast array of human illnesses.
Examples of viruses that live only by invading cells:
* Influenza virus: Causes the flu
* HIV: Causes AIDS
* Hepatitis viruses: Cause inflammation of the liver
* Measles virus: Causes measles
* Poliovirus: Causes polio
Let me know if you have any other questions!
