Viruses Trivia
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100 free Viruses trivia questions with answers — science & nature quiz, new questions added Oct 2026.
There are about ten million viruses in a teaspoon of seawater, roughly 800 million land on every square metre of the planet each day, and biologists still cannot agree whether they are alive. This quiz covers what a virus actually is: capsids and envelopes, DNA and RNA genomes, the six stages of the replication cycle, the Baltimore classification, and the reason RNA viruses mutate faster than DNA ones. It then moves into the parts everyone has lived through: the 1918 flu, HIV, SARS and COVID-19, the viruses that cause cancer, how vaccines and antiviral drugs work, and the smallpox stocks still kept in two freezers on opposite sides of the world. Along the way there are giant viruses visible under a light microscope, viruses that infect other viruses, and a pond ciliate that eats them for lunch. It is written for biology students, science readers and pub-quiz regulars. Every answer was checked against Wikipedia's article on viruses, and each question carries the sentence that supports it.
30 of 100 questions with answers and explanations. Play the quiz
Q 01Where can a virus replicate?
Only inside a living cell
Viruses have no metabolism of their own, so they hijack a host cell's machinery to build copies.
Q 02What is the study of viruses called?
Virology
It is a subspeciality of microbiology, dating from Beijerinck's work in the 1890s.
Q 03What is a single virus particle outside a cell called?
A virion
The term dates from 1959 and describes the released particle capable of infecting another cell.
Q 04What is the protein coat that surrounds a virus's genetic material called?
The capsid
It is built from repeating protein subunits called capsomeres; some viruses add an outer envelope of lipids.
Q 05Which plant pathogen, found in filtered sap in the 1890s, was the first of its kind ever described?
Tobacco mosaic virus
Dmitri Ivanovsky showed that sap from diseased plants stayed infectious after passing through a filter fine enough to trap bacteria.
Q 06Which Dutch scientist coined the modern use of 'virus' in 1898 after studying diseased tobacco plants?
Martinus Beijerinck
Ivanovsky had run the filter experiment six years earlier, but the 1898 work argued the agent could reproduce only inside living cells.
Q 07The word "virus" comes from a Latin word meaning what?
Poison
It shares a root with the Sanskrit and Ancient Greek words for poison; the sense of "agent causing infectious disease" is first recorded in 1728.
Q 08Why do many biologists hesitate to call viruses alive?
They lack a cell structure
They have genes, evolve by natural selection and self-assemble, which is why they are called "organisms at the edge of life".
Q 09What genetic material can a virus carry?
Either DNA or RNA
Most viruses have RNA genomes; retroviruses convert theirs into DNA at one stage of the cycle.
Q 10Roughly what size are most studied spherical viruses?
20 to 300 nanometres
More than a thousand of them would fit inside a single E. coli cell.
Q 11Which instrument, invented in 1931, finally allowed the complex structures of viruses to be seen?
The electron microscope
Wendell Stanley had already shown that viruses were particles rather than a fluid.
Q 12How few norovirus particles can be enough to infect a person?
Fewer than 100
Norovirus and rotavirus spread by the faecal-oral route, in food, water or hand-to-mouth contact.
Q 13What term describes which cell types a given virus is able to infect?
Host range
Rabies can take hold in many mammal species, while other viruses are restricted to a single one.
Q 21What are viroids, the subviral agents that attack plants?
RNA molecules with no protein coat
They are significant plant pathogens and are often called subviral agents.
Q 22What are viruses that can only replicate in a cell already infected by another virus called?
Satellites
The sputnik virophage, for instance, can only replicate in an amoeba that is already infected by a giant virus.
Q 23Which biologist devised the classification system that sorts viruses by how they make messenger RNA?
David Baltimore
His scheme is used alongside the ICTV's taxonomic classification.
Q 14What are viruses that infect bacteria called?
Bacteriophages
At up to 250 million per millilitre, they are the most abundant biological entity in seawater.
Q 15Roughly how many viruses are there in a teaspoon of seawater?
About ten million
Most of them attack bacteria and cyanobacteria, and they kill an estimated 20% of ocean microbial biomass every day.
Q 16What is the "viral shunt" in ocean ecosystems?
Recycling of nutrients from lysed bacteria
Organic molecules from the dead cells feed fresh bacterial and algal growth, and boost nitrogen cycling.
Q 17How many viruses were reported in 2018 to fall from the atmosphere onto every square metre of Earth daily?
800 million
They circulate above the weather but below usual airline altitude, spreading around the planet.
Q 18Which pond ciliate was reported in 2022 to eat viruses, the first observed case of 'virovory'?
Halteria
It multiplied on a diet of chlorovirus once all other microbial food was removed from the water.
Q 19Which giant virus, with a 400 nm particle, helped overturn the idea that all viruses are tiny?
Mimivirus
Megavirus chilensis, found off Chile in 2011, is big enough to be seen with a basic optical microscope.
Q 20Which giant virus genus, found in 2013, has genomes about twice the size of the previous record?
Pandoravirus
Their two-megabase genomes code for roughly 2,500 proteins; all giant viruses have double-stranded DNA.
Q 24How many groups does the Baltimore classification place viruses into?
Seven
They range from double-stranded DNA viruses to reverse-transcribing viruses such as retroviruses and hepadnaviruses.
Q 25Which enzyme lets retroviruses turn their RNA genome into DNA?
Reverse transcriptase
Drugs such as zidovudine and lamivudine work by inhibiting it.
Q 26Why do RNA viruses generally have smaller genomes than DNA viruses?
Their replication is more error-prone
Beyond a certain size, copying mistakes would render the particle useless, so many RNA viruses split their genome into segments.
Q 27Which viruses have the smallest known genomes, coding for just two proteins?
Circoviruses
Their genome is about two kilobases, roughly a thousand times smaller than the largest known viral genomes.
Q 28What is the first stage of a virus's replication cycle?
Attachment to a host cell receptor
HIV's gp120 protein binds the CD4 molecule, which is why it targets a narrow set of human leucocytes.
Q 29What is the bursting process that kills a host cell as new viruses escape?
Lysis
Enveloped viruses such as HIV usually leave more gently, by budding through the cell membrane.
Q 30What is a viral genome called once it has integrated into a bacterium's chromosome?
A prophage
In other hosts the integrated genome is called a provirus; it is copied every time the cell divides.