Protists
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40 free Protists trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Protists are the misfits of biology: living things with complex cells that are not animals, plants or fungi. Most are single cells too small to see, yet the group also takes in seaweeds taller than a house, and its members feed whole oceans, build rock and cause some of the deadliest infections on Earth. This quiz covers what a biology class covers and then some: how protists are classified and who named them, the amoebas, Paramecium and algae you meet under a school microscope, the structures they use to move, feed and stay alive, and the parasites behind malaria and other illnesses. It also tells the stranger stories, from a brainless blob that plans transport routes to the fossils hidden in famous monuments. The questions run from middle school basics to a few stretch questions for AP and college biology. Every answer comes with a short explanation, so the quiz works as a study check before a test as well as a round for quiz night.
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Q 01Rats infected with the protist Toxoplasma gondii lose their instinctive fear of the scent of which predator?
Cats
Cats are the only hosts in which Toxoplasma can reproduce sexually, so a fearless rat may be the parasite's ticket home. Infected rats stop avoiding the smell of cat urine.
Q 02The "brain-eating amoeba" Naegleria fowleri infects swimmers when warm fresh water enters which part of the body?
The nose
The nose gives the amoeba a route along the smell nerves into the brain, where the infection is almost always fatal. Swallowing the same water causes no infection.
Q 03Which country lost a million lives in the 1840s when the protist Phytophthora infestans rotted its potato crop?
Ireland
Ireland leaned on a single potato variety, the Lumper, so the blight destroyed the staple food of millions. The culprit looks like a fungus but belongs to a separate group, the oomycetes.
Q 04What kind of protist is Physarum polycephalum, the brainless yellow blob that solved a maze and copied Tokyo's railways?
A slime mold
A slime mold has no brain or nerves, yet it linked oat flakes laid out like Tokyo's towns with a network as efficient as the real railway. It is a single giant cell that can grow a foot or more across.
Q 05Which Egyptian monuments are built of limestone full of nummulites, the coin-like shells of giant fossil protists?
The Giza pyramids
The Giza pyramids are built of stone that formed on an ancient seabed. The Greek geographer Strabo took the fossils for lentils left behind by the workers who built them.
Q 06Which wood-eating insects rely on gut protists such as Trichonympha to break down the cellulose they swallow?
Termites
Termites shelter Trichonympha in the hindgut, and it lives nowhere else except in wood-eating roaches. The protist gets food and a home, and the insect gets wood it can digest.
Q 07Which bitter extract of cinchona bark, the flavoring in tonic water, kills the protist that causes malaria?
Quinine
Quinine was so bitter that British officials in India mixed their dose with soda and sugar, inventing tonic water. Adding gin to mask the taste gave the world the gin and tonic.
Q 08Which marine mammal protects forests of kelp, a giant protist, by eating the sea urchins that graze them bare?
Sea otter
The sea otter is a keystone species: where it disappears, urchins multiply and turn kelp forests into barrens. Some kelp can grow half a meter in a day.
Q 09Which rock, famous in the cliffs at Dover, is made of plates shed by tiny armored protists called coccolithophores?
Chalk
Chalk is made mostly of plankton shells, and each coccolithophore is a single cell wrapped in plates only a few thousandths of a millimeter wide.
Q 10Which term describes the blue glow that dinoflagellates such as Noctiluca give off when waves disturb the sea at night?
Bioluminescence
Bioluminescence is light made by a cell's own chemistry, unlike fluorescence and phosphorescence, which need light shone on them first. Noctiluca flashes whenever it is jostled.
Q 11Alfred Nobel made dynamite safe to handle by soaking nitroglycerin into the fossil shells of which glassy protists?
Diatoms
Diatoms pile up on lake and sea floors as a soft powder called diatomaceous earth, or kieselguhr in German. The same powder filters swimming pools and beer.
Q 12A Paramecium swims by beating which structures, arranged in tightly spaced rows around the outside of its body?
Cilia
Cilia beat like oars, with a stiff power stroke and a floppy recovery stroke, and a Paramecium spends over half its energy on swimming. To back away from an obstacle it reverses the stroke.
Q 13Which temporary bulges of the cell does an amoeba push out in the direction it wants to crawl?
Pseudopods
Q 21Which Dutch draper first saw swimming microbes, later nicknamed animalcules, through microscopes he made himself?
Leeuwenhoek
Leeuwenhoek wanted better lenses to inspect the thread in his cloth shop, then turned them on pond water and found it alive. He was also the first to describe bacteria.
Q 22Which protist genus, whose deadliest species is named falciparum, causes malaria by invading human red blood cells?
Plasmodium
Plasmodium falciparum alone kills hundreds of thousands of people a year. Four other species of the genus also regularly infect humans.
Q 23After a mosquito bite, malaria parasites multiply silently in which organ before bursting out to attack red blood cells?
Liver
Pseudopods, literally false feet, are not unique to protists: human white blood cells crawl through tissue on them too. An amoeba can push out several at once.
Q 14Which organelle does a freshwater Paramecium squeeze every few seconds to pump out water that floods in by osmosis?
Contractile vacuole
The contractile vacuole works like a bilge pump, stopping a freshwater cell from swelling until it bursts. Some marine and soil protists have one as well.
Q 15Which green pond protist puzzled early taxonomists by photosynthesizing like a plant yet swimming with a whip-like tail?
Euglena
Euglena feeds like a plant in sunlight but can live in the dark by absorbing nutrients, as an animal would. Its red eyespot helps it find the light.
Q 16The pond protist Paramecium earned an 18th-century nickname for its resemblance to which item of footwear?
A slipper
A slipper is what French microscopist Louis Joblot called it in 1718, and the name slipper animalcule stuck for two centuries.
Q 17Unlike bacteria, every protist keeps its DNA inside which membrane-wrapped compartment, the mark of a eukaryotic cell?
Nucleus
The nucleus can come in multiples: a Paramecium carries a large macronucleus for daily business and at least one tiny micronucleus reserved for sex.
Q 18Which organelles, gained when an ancient cell swallowed a cyanobacterium, let algae and other protists live on sunlight?
Chloroplasts
Chloroplasts still carry their own DNA, a leftover from their free-living days. Many algae got theirs second-hand, by swallowing another alga that already had them.
Q 19Which process strikes reef corals when warm seas make them expel zooxanthellae, the protists that feed and color them?
Bleaching
Bleaching can end in starvation, because the lost protists supply up to 90 percent of a coral's energy. Corals can survive a short spell without them, but not a long one.
Q 20What name is given to blooms of toxic dinoflagellates such as Karenia brevis that kill fish and poison shellfish?
Red tide
A red tide is misnamed twice over: the blooms vary widely in color, and they have nothing to do with the tides.
The liver hides the parasites at first, with no symptoms, and a single infected cell there can end up holding 40,000 of them. Some species lie dormant in it for more than a year.
Q 24Which blood-feeding African insect spreads Trypanosoma brucei, the protist behind the deadly disease sleeping sickness?
Tsetse fly
The tsetse fly injects the parasites as it feeds, and in time they reach the brain and flip the sleep cycle: victims doze by day and lie awake at night.
Q 25Which gut protist, the cause of "beaver fever", infects backpackers who drink untreated water from lakes and streams?
Giardia
Giardia leaves the body as tough cysts that stay infectious for up to three months in cold water. Fever is rare, striking only about 15% of patients, despite the nickname.
Q 26Which sea, the only one with no land boundaries, is named for the golden-brown algae that float across its surface?
Sargasso Sea
The Sargasso Sea is fenced in by four ocean currents instead of coasts. European eels cross the Atlantic to breed beneath its drifting weed.
Q 27Which dark sheets of dried red algae, farmed on nets in the sea, are wrapped around sushi rolls and rice balls?
Nori
Nori is made by shredding the algae and drying the pulp on racks, a process that resembles papermaking. A British scientist's study of Welsh seaweed once rescued Japan's nori farms.
Q 28Which name, coined for what seemed the simplest animals, covers protists that eat rather than photosynthesize?
Protozoa
Protozoa means first animals, and Georg Goldfuss coined it in 1818 for a class he filed inside the animal kingdom. Biologists now use the word only loosely, since protists are not animals.
Q 29Which freshwater alga forms hollow green spheres of up to 50,000 cells, each cell beating two whip-like tails?
Volvox
Volvox takes its name from the Latin for "to roll". Its cells divide the labor: most only swim, while a few are set aside to reproduce.
Q 30Carrying one copy of the gene for which blood disorder protects against malaria, keeping the gene common in Africa?
Sickle cell disease
Sickle cell disease strikes only people who inherit two copies of the gene. Those with one copy usually stay well and resist the parasite, so the gene persists wherever it is a threat.