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60 free Bacteria trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Bacteria trivia covers the oldest and most numerous living things on Earth: roughly two nonillion single cells that put the oxygen in the air, fix the nitrogen in the soil, ferment your yogurt, make the vitamin B12 in your food, and occasionally cause plague, cholera and botulism. This quiz treats them as organisms in their own right rather than as a chapter of medicine. You will meet the rods, cocci and commas of the microscope slide, the peptidoglycan wall that penicillin attacks, endospores that can survive space, plasmids and conjugation, the CRISPR memory that became a gene-editing tool, and the flagellar motor. Then the characters: cyanobacteria and the Great Oxidation Event, stromatolites at Shark Bay, Streptomyces and the smell of rain, the squid-lighting Aliivibrio fischeri, Wolbachia versus dengue, magnetic bacteria, Yersinia pestis in Hong Kong, Pacini's cholera comma, Escherich's E. coli, golden staph, Helicobacter and the Nobel Prize, and the Bulgarian yogurt cultures. Easy questions suit a curious teenager; the expert tier is for people who know who coined the word 'bacterium'. If you want the scientists rather than the microbes, our microbiology quiz covers Pasteur, Koch and Leeuwenhoek in depth. Every answer here was checked against Wikipedia's articles on the organisms, and the supporting sentence is attached to each question.
30 of 60 questions with answers and explanations. Play the quiz
Q 01The word 'bacterium' comes from an Ancient Greek word meaning what?
Staff or cane
The first ones discovered were rod-shaped, hence the walking-stick image; the spherical kind got a separate word meaning 'grain'.
Q 02Bacteria are prokaryotes. Which of these do their cells lack?
A nucleus
Their single circular chromosome sits in an irregular region of the cytoplasm called the nucleoid.
Q 03Roughly how many bacteria are thought to exist on Earth?
About 2 x 10^30
Their combined biomass is exceeded only by that of plants.
Q 04Comma-shaped or slightly curved rod bacteria are known by what name?
Vibrio
The cholera bacterium is the classic vibrio; Robert Koch described it as 'a little bent, like a comma'.
Q 05Staphylococci group together in clusters likened to what?
A bunch of grapes
The name itself comes from the Greek for 'grape-cluster berry'; streptococci, by contrast, form chains.
Q 06Bacterial cell walls are made of which polymer, which penicillin stops them building?
Peptidoglycan
Plants use cellulose and fungi use chitin, which is why penicillin harms neither.
Q 07In a Gram stain, what colour do Gram-negative bacteria appear?
Pink
The thick walls of Gram-positive cells hold the purple dye; thin-walled Gram-negatives lose it and take up the pink counterstain.
Q 08Inhaling the endospores of which bacterium causes anthrax?
Bacillus anthracis
Clostridium tetani spores in deep puncture wounds cause tetanus in much the same way, and both illnesses come from toxins the germinated cells release.
Q 09Bacteria reproduce asexually by splitting in two. What is this process called?
Binary fission
Some populations can double as quickly as every 17 minutes.
Q 10When bacteria enter a fresh nutrient-rich medium, what is the first stage of growth called, before rapid division begins?
Lag phase
The cells spend it building the proteins they need for the exponential burst that follows.
Q 11The transfer of DNA between two bacteria through direct cell contact via a pilus is called what?
Conjugation
Transformation is taking up loose DNA from the environment, and transduction is delivery by a virus.
Q 12Which small extra-chromosomal DNA molecules often carry antibiotic-resistance genes in bacteria?
Plasmids
They can hop between species by horizontal gene transfer, which is how resistance spreads.
Q 13Bacteria keep fragments of past viral invaders' genomes as an immune memory in which system, later turned into a gene-editing tool?
CRISPR
The 2020 Nobel Prize in Chemistry went to Charpentier and Doudna for turning this bacterial defence into genetic scissors.
Q 21Which health-food supplement is actually a bacterium, not a true alga, sold as food?
Spirulina
Chlorella and nori are true algae; the supplement's producer was long placed in the genus Arthrospira.
Q 22Which layered rock mounds built by microbes still grow at Shark Bay in Western Australia?
Stromatolites
They peaked about 1.25 billion years ago and were probably grazed into decline once complex animals appeared.
Q 23Which soil bacteria, famous for the earthy smell of rain, produce over two-thirds of clinically useful natural antibiotics?
Streptomyces
The smell comes from geosmin, a volatile compound they release, and streptomycin takes its name from them.
Q 14A bacterium with a single flagellum is described by which term?
Monotrichous
Peritrichous cells such as E. coli are covered all over, which lets them alternate swimming with tumbling.
Q 15The bacterial flagellum is built from roughly how many different proteins?
About 20
Around another 30 proteins are needed just to assemble and regulate it, all powering a rotary motor at the base.
Q 16Bacteria that decide to act only when their population is dense enough use which signalling process?
Quorum sensing
It controls things like glowing or secreting digestive enzymes that only pay off in a crowd.
Q 17Bacteria in biofilms can be how much more resistant to antibacterial agents than free-floating cells of the same species?
Over 500 times
This is why infections on implanted devices such as catheters are so hard to clear.
Q 18Bacteria that swim along Earth's magnetic field lines contain crystals of which iron mineral inside organelles called magnetosomes?
Magnetite
Some species make greigite, an iron sulphide, instead; the chains of crystals act as a compass needle.
Q 19Magnetotactic bacteria were first noticed in 1963 by which Italian, whose work was forgotten until Richard Blakemore rediscovered them in 1975?
Salvatore Bellini
Blakemore's paper in Science did not mention him, and Blakemore's term 'magnetotaxis' is the one that stuck.
Q 20Which group of bacteria is credited with the Great Oxidation Event, the first flood of free oxygen into Earth's atmosphere?
Cyanobacteria
The same lineage was later swallowed by early eukaryotes and became the chloroplasts of algae and plants.
Q 24Which glowing bacterium lights up the light organ of the Hawaiian bobtail squid?
Aliivibrio fischeri
The two-species partnership is the textbook model for how bacteria count their neighbours, since they glow only when packed densely enough.
Q 25Wolbachia, a bacterium that manipulates insect reproduction, has been released into mosquitoes to suppress which disease?
Dengue
After infected mosquitoes were released in Townsville, Australia, in 2014, the city reported no cases for four years.
Q 26Roughly what share of all insect species are estimated to be potential hosts of Wolbachia?
25 to 70%
In some woodlice it feminises males so thoroughly that populations have lost their female-determining chromosome.
Q 27Yersinia pestis, the plague bacterium, was isolated in 1894 during an epidemic in which city?
Hong Kong
Alexandre Yersin and Kitasato Shibasaburō found it independently within days of each other; Yersin got the naming rights.
Q 28Before it got its modern name in 1944, what did Yersin call the plague bacillus in honour of his institute?
Pasteurella pestis
Its main vector is the oriental rat flea, though the pneumonic form spreads by airborne droplets.
Q 29The word 'botulism' comes from a Latin word meaning what?
Sausage
The disease was first traced to spoiled blood sausages in Württemberg in the early 1800s.
Q 30Which Belgian microbiologist discovered Clostridium botulinum in 1895 after a fatal outbreak at a funeral where guests ate pickled ham?
Émile van Ermengem
Justinus Kerner's 1817-22 descriptions of the illness had already suggested the toxin might be useful medically.