How to use this quiz: choose an answer before opening the explanation. Each answer is supported by two independent sources checked on 2026-08-27.
10 microscopic life questions
1 · Warm-up
Which microscopic animal has survived direct exposure to the vacuum of space in an experiment?
- A tardigrade
- A fruit fly
- A dust mite
- A brine shrimp
Show the answer, explanation, and sources
Answer: A tardigrade. Tardigrades have survived direct exposure to the vacuum of space.
In ESA's TARDIS experiment, dehydrated tardigrades endured vacuum and cosmic radiation outside a spacecraft. Some reproduced after returning.
Sources: European Space Agency and Smithsonian National Air and Space Museum.
2 · Warm-up
As yeast feeds on dough sugars, which gas inflates the web of bubbles in bread?
- Oxygen
- Carbon dioxide
- Hydrogen
- Nitrogen
Show the answer, explanation, and sources
Answer: Carbon dioxide. Yeast produces the carbon dioxide that inflates bread dough.
Yeast ferments sugar, producing carbon dioxide and alcohol. Gluten traps the gas in elastic pockets, which expand in the oven before the bread's structure sets.
Sources: Exploratorium and American Chemical Society.
3 · Core
How do bacteria detect that their population has reached the density needed for group behavior?
- By measuring shadows from nearby cells
- By comparing the ages of neighboring cells
- By detecting accumulated chemical signals
- By lining up and counting cell divisions
Show the answer, explanation, and sources
Answer: By detecting accumulated chemical signals. Bacteria use chemical signals in a process called quorum sensing.
Cells release signaling molecules whose concentration rises as the population grows. Crossing a threshold can activate bioluminescence, biofilm formation, or other coordinated behavior.
Sources: National Institutes of Health and American Society for Microbiology.
4 · Core
Roughly 20% of the oxygen produced on Earth each year comes from which microscopic organisms?
- Amoebas
- Yeasts
- Bacteriophages
- Diatoms
Show the answer, explanation, and sources
Answer: Diatoms. Diatoms produce about one-fifth of Earth's oxygen.
Diatoms are photosynthetic algae enclosed in intricate silica shells. In oceans and fresh water, their combined photosynthesis produces roughly 20 percent of global oxygen.
Sources: Royal Botanic Garden Edinburgh and Natural History Museum of Los Angeles County.
5 · Core
Where are Demodex mites most likely to live on a healthy adult?
- In hair follicles around the eyelashes
- Inside the tear fluid over the cornea
- Between the layers of tooth enamel
- Under the surface of the fingernails
Show the answer, explanation, and sources
Answer: In hair follicles around the eyelashes. Demodex mites commonly inhabit hair follicles near the eyelashes.
Demodex folliculorum spends much of its life in hair follicles, especially around the eyelashes. Small populations are a normal component of adult facial skin ecosystems.
Sources: American Academy of Ophthalmology and Archives of Medical Science.
6 · Core
What is notable about the size of Thiomargarita magnifica?
- See it only with a phone's macro lens
- See a single cell with the naked eye
- See it only when thousands form a colony
- See it only after staining it bright blue
Show the answer, explanation, and sources
Answer: See a single cell with the naked eye. A single Thiomargarita magnifica cell can be as long as an eyelash.
Thiomargarita magnifica can exceed one centimeter, thousands of times larger than an average bacterium. Each threadlike specimen is a single cell.
Sources: Natural History Museum and U.S. Department of Energy Joint Genome Institute.
7 · Core
A particle has a geometric head, a tail, and a genome it delivers into a bacterium. What is it?
- A fungal spore
- A diatom
- A bacteriophage
- A pollen grain
Show the answer, explanation, and sources
Answer: A bacteriophage. A bacteriophage uses its tail to deliver genetic material into a bacterium.
Many phages package their genome in a capsid head and use a tail to recognize and penetrate a bacterial host. The empty shell stays outside after delivery.
Sources: American Society for Microbiology and National Center for Biotechnology Information.
8 · Core
Magnetotactic bacteria align with Earth's field using chains of which material?
- Calcium carbonate crystals
- Sodium chloride crystals
- Silicon dioxide crystals
- Iron oxide crystals
Show the answer, explanation, and sources
Answer: Iron oxide crystals. They form chains of magnetite crystals inside magnetosomes.
They grow magnetite crystals inside structures called magnetosomes. Chains of those iron-rich crystals align the whole cell with Earth's magnetic field.
Sources: MIT News and University of California, Santa Barbara.
9 · Challenge
Bdellovibrio catches a larger bacterium. What does this microscopic predator do next?
- Invades beneath its outer wall and consumes it
- Stays outside and steals energy from sunlight
- Trades DNA with it, then swims away unharmed
- Builds a spore shell around both cells
Show the answer, explanation, and sources
Answer: Invades beneath its outer wall and consumes it. Bdellovibrio enters a bacterium's periplasm and digests it from within.
The predator enters the prey's periplasm, seals the entry, and digests the contents while multiplying. New cells eventually emerge from the depleted host.
Sources: American Society for Microbiology and Microbiology Society.
10 · Challenge
After exploring a maze with food at two exits, what did a slime mold do?
- Keep identical tubes in every corridor
- Retract to the shortest food route
- Keep only the widest corridor open
- Split into one blob at each exit
Show the answer, explanation, and sources
Answer: Retract to the shortest food route. The slime mold withdrew from inefficient paths, leaving the shortest route.
Physarum first spreads through the maze, then withdraws from dead ends and inefficient routes. Its surviving tube traces the shortest path between food sources.
Sources: PBS and Museum Wales.
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