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50 free Plankton trivia questions with answers — nature quiz, new questions added Aug 2026.
Plankton make half the oxygen you breathe and most of the biomass in the sea, and this quiz takes them seriously. It starts with the word itself (Greek for drifter, coined in 1887), the difference between plankton, nekton, benthos and neuston, and the four trophic groups from phytoplankton to the newly recognised mixoplankton. Then it works through the cast: diatoms in their glass houses, whip-spinning dinoflagellates and their red tides, chalk-plated coccolithophores blooming visibly from space, one-eyed copepods, Antarctic krill by the half-billion tonnes, the smallest photosynthesiser on Earth and the commonest bacterium in the sea. There are questions on what plankton do for the planet (the biological pump, marine snow, iron and blooms, the viral shunt, the largest migration on Earth every night) and on the people and tools that study them, from Victor Hensen to the silk ribbon of the Continuous Plankton Recorder. And because search engines are honest about what people mean, there are a few questions on Sheldon J. Plankton, Karen and the Chum Bucket. Easy questions suit anyone who has heard of krill; the expert tier asks about the mycoloop and Langmuir circulation. Every answer was checked against Wikipedia's articles on plankton and its many groups, and the supporting sentence is attached to each question.
30 of 50 questions with answers and explanations. Play the quiz
Q 01The word 'plankton' comes from a Greek word meaning what?
Drifter or wanderer
Plankton are defined by their inability to swim against currents, not by what species they are.
Q 02What is a single individual plankton organism called?
A plankter
And the study of plankton is planktology.
Q 03Which German marine biologist coined the word 'plankton' in 1887?
Victor Hensen
He shortened 'halyplankton', from the Greek for 'sea' and 'I drift', and founded quantitative biological oceanography.
Q 04Organisms such as fish and squid that can swim against currents, unlike plankton, are called what?
Nekton
Bottom-dwellers are the benthos.
Q 05Roughly what share of Earth's oxygen production comes from phytoplankton?
About half
They do this despite making up only about 1% of global plant biomass.
Q 06Photosynthesising plankton are phytoplankton. What are the animal-like consumers called?
Zooplankton
A third group does both, and a fourth are decomposers such as fungi, bacteria and viruses.
Q 07What are plankton that are planktonic only as larvae called?
Meroplankton
Sea urchin, starfish, crab and most fish larvae fall into this group before settling or swimming off.
Q 08What are the drifting organisms of the atmosphere, such as spores and pollen, called?
Aeroplankton
They rain hundreds of millions of viruses and tens of millions of bacteria on every square metre of the planet daily.
Q 09What is the shower of organic detritus that sinks from the sunlit ocean to feed deep-sea life called?
Marine snow
The term was coined by explorer William Beebe, watching from his bathysphere.
Q 10Marine viruses are estimated to kill what proportion of ocean microplankton biomass every day?
20%
They are the main agents that wipe out harmful algal blooms.
Q 11Which micronutrient is missing in the ocean's 'HNLC' regions?
Iron
It arrives mostly as dust, which is why the eastern Atlantic downwind of the Sahara teems with phytoplankton.
Q 12Diatoms are encased in a cell wall made of what?
Silica
The glassy frustule produces structural colours that earned them the names 'jewels of the sea' and 'living opals'.
Q 13Diatoms are estimated to generate what share of the oxygen produced on the planet each year?
20 to 50 percent
They also draw more than 6.7 billion tonnes of silicon a year out of the water they live in.
Q 21Roughly how many species of copepod are known?
13,000
About 2,800 of them live in fresh water; most are only 1-2 mm long.
Q 22The word 'krill' comes from which language, where it means 'small fry of fish'?
Norwegian
Krill are shrimp-like crustaceans that filter phytoplankton and feed whales, seals and penguins.
Q 23Antarctic krill has a total biomass of roughly how much?
500 million tonnes
Whales, seals, birds, squid and fish together eat between 152 and 313 million tonnes of it a year.
Q 24Antarctic krill swarms can reach densities of how many animals per cubic metre?
Q 14Fossilised diatom shells form a soft rock used in cat litter, toothpaste and to stabilise what explosive?
Dynamite
Alfred Nobel patented the nitroglycerine-and-kieselguhr mixture in 1867.
Q 15Dinoflagellates take their name from Greek and Latin words meaning what?
Whirling whip
They carry two flagella and can bloom into red tides or glow blue-green in the dark.
Q 16A 'red tide' is a harmful bloom of which kind of plankton?
Dinoflagellate
Eating shellfish contaminated by such blooms can cause poisoning; Karenia brevis is the Florida culprit.
Q 17Which glowing organism, whose name means 'light at night', makes seawater glow bright blue after dark?
Noctiluca
Ernst Haeckel moved it out of the jellyfish and in with the dinoflagellates in 1873.
Q 18Coccolithophores cover themselves in plates made of what?
Calcium carbonate
They are the most productive calcifying organisms on the planet; their coccoliths are essentially chalk.
Q 19Which coccolithophore, the most abundant in modern oceans, forms milky blooms visible from space?
Emiliania huxleyi
Now often called Gephyrocapsa huxleyi, it blooms in nutrient-poor water after the summer thermocline forms.
Q 20Copepods, the tiny crustaceans of the plankton, typically have how many eyes?
One
Most have a single, usually bright red, compound eye in the middle of a transparent head, and no heart.
10,000 to 30,000
Their 12-hour vertical migrations help mix nutrient-rich deep water up to the surface.
Q 25Which cyanobacterium, found in 1986, is probably Earth's most abundant and smallest photosynthetic organism?
Prochlorococcus
Its discoverer Sallie Chisholm won the 2019 Crafoord Prize; it is a major producer of the ocean's oxygen.
Q 26Which bacterium, perhaps Earth's most abundant, makes up a third of surface-ocean microbes?
Pelagibacter ubique
It is unusually small and busy recycling nutrients in the microbial loop.
Q 27What is the name for the daily rise and fall of drifting animals, the largest synchronous movement on Earth?
Diel vertical migration
Some plankton swim hundreds of metres up and down in a single day.
Q 28What is the plankton-driven ocean process that carries carbon from the atmosphere to the deep sea called?
The biological pump
Marine microbes make up the great majority of ocean biomass.
Q 29In the 'viral shunt', viruses do what to bacteria in the plankton?
Break them open, returning nutrients to the water
This keeps nutrients in the microbial loop instead of passing them up to grazers and fish.
Q 30Foraminifera, or 'forams', are single-celled plankton whose Latin name means what?
Hole bearers
They build shells called tests, some with many elaborate chambers.