01Size2.00 µm
Bacterium
Single-celled life, no nucleus required.
BiologyMicrobeMicro-World
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CDC / Public Health Image Library
Picture this
Magnify a virus to the size of a marble in your palm — at that scale, a single human cell would be a beach ball next to it.
A virus is not strictly alive. It has no metabolism, can't reproduce on its own, and shows no behaviour outside a host. What it carries is a packet of genetic instructions — DNA or RNA — inside a protein shell. Once inside a cell, those instructions hijack the host's machinery and turn it into a copy factory.
Did you know?
There are an estimated 10³¹ virus particles on Earth — about ten million times more than there are stars in the entire observable universe.
Last updated 2026-05-17
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Scale
Strands of code wrapped in protein.
Size
100 nm
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