Diatoms
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40 free Diatoms trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Diatoms are single-celled algae that live almost anywhere there is water and light, from open seas and rivers to damp soil. Each one sits inside an ornate, glass-like shell, and together they do a remarkable share of the planet's photosynthesis. This quiz covers the core ideas: how the shell is built and why cells get smaller as they divide, the two main shape groups, where diatoms sit on the tree of life, and the part they play in the sea's food webs and chemistry. It also takes in their history, from the first drawings made under early microscopes to the fossil deposits people have mined for industry, forensics and the home. It suits biology and marine science students revising for a test, microscopy hobbyists, and anyone who enjoys finding out how much a speck of pond life can matter.
30 of 40 questions with answers and explanations. Play the quiz
Q 01Diatoms generate an estimated 20 to 50 percent of which gas produced on Earth each year?
Oxygen
Oxygen is a by-product of their photosynthesis, and diatoms also make up nearly half of the organic material found in the oceans.
Q 02A 1961 incident in Capitola, later linked to a diatom toxin, helped inspire which Hitchcock film?
The Birds
The Birds drew on the night disoriented seabirds slammed into Capitola homes. Toxic algae were later blamed, though nobody knew that in the 1960s.
Q 03Alfred Nobel soaked unstable nitroglycerin into diatomaceous earth to create which safer explosive?
Dynamite
Dynamite was patented in 1867 after Nobel found the porous powder made nitroglycerin stable enough to transport and handle.
Q 04Dust from ancient diatom shells crosses the Atlantic to fertilize the Amazon from which desert?
Sahara
Sahara dust reaching the Amazon comes in large part from the Bodélé Depression in Chad, an ancient lake bed whose diatom-rich sediment carries phosphorus the rainforest needs.
Q 05Forensic scientists test a body's tissues for diatoms to help confirm which cause of death?
Drowning
Drowning is suggested when diatoms matching the local water turn up inside a body, because their hard shells do not readily decay and never occur there naturally.
Q 06Diatoms pull which glassy compound out of the water to build their intricately patterned cell walls?
Silica
Silica in a hydrated form makes up the two-part shell, and diatoms take in over 6.7 billion tonnes of silicon from the water every year to build it.
Q 07The invasive river diatom Didymosphenia geminata forms slimy mats known by which blunt nickname?
Rock snot
Rock snot, also called didymo, is native to the Northern Hemisphere but became an invader in New Zealand, where it had never been found before.
Q 08Diatomite has long served as a mild abrasive in metal polishes and which bathroom product?
Toothpaste
Toothpaste, metal polishes and some facial scrubs have all used the crumbly powder, which is made of fossil diatom shells built up over millions of years.
Q 09Whalers nicknamed which giant 'sulphur bottom' after the yellowish diatom film on its belly?
Blue whale
Blue whale bellies can carry a coating of huge numbers of diatoms, which tinges some individuals yellow. Herman Melville mentions the nickname in Moby-Dick.
Q 10Diatom shells are made of the same mineral as which gemstone, earning them a 'living' nickname?
Opal
Opal is the hard mineral of the shell, and its shimmering structural color is why diatoms are called living opals and jewels of the sea.
Q 11Makers of wine and which other popular drink filter it through diatomaceous earth?
Beer
Beer and wine are both clarified this way, and the powder can also filter syrups and honey without altering their color, taste or nutritional properties.
Q 12Diatomaceous earth kills bed bugs and other insects mainly by causing which fatal effect?
Dehydration
Dehydration follows because the fine powder soaks up oily lipids from the waxy outer layer of the insect's exoskeleton, the barrier that normally holds water in.
Q 13Diatoms and cyanobacteria are among the most important groups in which drifting, sunlit community?
Phytoplankton
Phytoplankton in nutrient-rich coastal waters are often dominated by diatoms, because diatoms can divide more rapidly than the other groups.
Q 21Centric diatoms, one of the two main shape groups, are built with which kind of symmetry?
Radial
Radial symmetry gives centric diatoms their typically circular outline, but they are the minority: most diatoms belong to the other, elongated group.
Q 22Many open-water diatoms grow spines or link into long chains mainly to slow down which process?
Sinking
Sinking is a constant risk because the dense shell drags cells down out of the sunlit surface, so spines and chains add drag that keeps them up longer.
Q 23Diatoms of the family Rhopalodiaceae carry a bacterial partner that lets them fix which gas?
Nitrogen
Nitrogen fixing is the job of the spheroid body, a former cyanobacterium that has lost its ability to photosynthesize but still feeds its diatom host.
Q 14Open-ocean diatom blooms, later ended by a nutrient shortage, typically peak at which time of year?
Spring
Spring brings the main bloom. A smaller, shorter-lived autumn bloom can follow when the summer layering of the water breaks down and stirs nutrients back up.
Q 15The slippery film of diatoms coating submerged river stones typically shows which color?
Brown
Brown coatings on stones and sticks are frequently diatoms, and the color comes from the yellowish chloroplasts where they photosynthesize.
Q 16Which naturalist found diatom remains in dust at Cape Verde and later puzzled over their beauty?
Charles Darwin
Charles Darwin called the tiny cases among the most beautiful of objects, doubted they were made for humans to admire, and put their beauty down to symmetry of growth.
Q 17The name diatom traces back, by way of Neo-Latin diatoma, to a Greek word with which meaning?
Cut in half
Cut in half suits the shell, which is built from two overlapping sections. The Greek word was diatomos, from a verb meaning to cut through.
Q 18Neither plants nor animals, diatoms belong to which catch-all group of mostly single-celled life?
Protists
Protists such as diatoms are eukaryotes, with a nucleus wrapped in its own envelope, which separates them from bacteria and archaea.
Q 19Diatoms help drive the ocean's biological pump, which locks which element away in the deep sea?
Carbon
Carbon fixed by diatoms comes to 10 to 20 gigatonnes a year, and the small share that reaches the deep ocean stays out of the atmosphere for thousands of years.
Q 20Diatoms belong to the heterokonts, making the tiny cells surprising relatives of which seaweed?
Kelp
Kelp and golden algae share the group with diatoms, as do water moulds, and many of its members have plastids rich in chlorophylls a and c.
Q 24The world's largest deposit of diatomite is worked near the town of Lompoc in which US state?
California
California holds the deposit in Santa Barbara County, part of the Sisquoc Formation, while Nevada and Colorado have beds several hundred meters thick in places.
Q 25Which London scientific body published the first known drawings of diatoms in its Transactions?
Royal Society
Royal Society readers saw drawings of Tabellaria in 1703, sent by an unnamed English gentleman who had wondered whether the chains of tiny parallelograms were salt crystals or a plant.
Q 26Seafloor mud made of diatom shells builds up fastest in the deep waters of which ocean?
Southern
Southern waters hold a continuous belt of the mud that stretches around the globe, and the tiny shells that build it can take 20 to 50 years to settle to the seabed.
Q 27The earliest known diatom fossils, including one in amber from Thailand, date from which period?
Jurassic
Jurassic fossils are the oldest found so far, though molecular clocks hint that diatoms arose earlier, perhaps after the end-Permian mass extinction opened up marine niches.
Q 28Until World War I, nearly all diatomaceous earth came from Lüneburg Heath in which country?
Germany
Germany owes the find to a peasant, Peter Kasten, who struck the powder while digging a well in the 1830s. Extraction on the heath went on until 1994.
Q 29Berkefeld filters made of diatomaceous earth proved their worth in an 1892 Hamburg epidemic of what?
Cholera
Cholera struck Hamburg in 1892, and the tubular filter candles developed by the Celle engineer Wilhelm Berkefeld were used successfully during the outbreak.
Q 30Diatom research belongs to which branch of biology, which also covers seaweeds and pond scum?
Phycology
Phycology is the study of algae, and its specialists use the pores, ribs and spines patterned into each shell to tell diatom genera and species apart.