Mitochondria Trivia
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100 free Mitochondria trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Mitochondria trivia starts with the one line every biology student remembers, 'the powerhouse of the cell', and then finds out who actually said it (a 1957 Scientific American article) and how much more there is. These are former bacteria, swallowed about two billion years ago, that still carry their own circular DNA, use a slightly different genetic code, divide by fission and are inherited only from your mother. This quiz covers the anatomy (outer membrane, porins, the intermembrane space, cristae, the matrix, cardiolipin), the chemistry (pyruvate, acetyl-CoA, the citric acid cycle, complexes I to IV, the proton gradient, ATP synthase and Peter Mitchell's chemiosmosis), the sidelines (calcium storage, heat from brown fat via thermogenin, cytochrome c and apoptosis, reactive oxygen species and ageing), the genetics (37 genes, 16 kilobases, mitochondrial Eve, the body louse's minichromosomes), the diseases and mitochondrial replacement therapy, and the history from Kölliker and Benda to Lynn Margulis and the 1978 and 1997 Nobel Prizes. Easy questions suit anyone who took school biology; the expert tier is for people who know which lipid gives the inner membrane four fatty-acid tails. Every answer was checked against Wikipedia's article on the mitochondrion, and the supporting sentence is attached to each question.
30 of 100 questions with answers and explanations. Play the quiz
Q 01Mitochondria are popularly nicknamed the what of the cell?
Powerhouse
Powerhouse fits because mitochondria generate most of the chemical energy a cell runs on; the cell biologist Philip Siekevitz spread the phrase with a 1957 magazine article of that title.
Q 02Which gas does the citric acid cycle inside mitochondria release as waste?
Carbon dioxide
Carbon dioxide: the cycle strips the carbon out of food molecules, so when the body burns off fat, much of that fat ends up leaving through the lungs.
Q 03Like a mitochondrion, which of these has a double membrane?
Nucleus
Nucleus: its double membrane is pierced by pores, because the RNA copied from the DNA inside has to reach the rest of the cell, where proteins are built.
Q 04What are the folds of the inner mitochondrial membrane called?
Cristae
Cristae greatly enlarge the inner membrane's surface, making room for more energy-producing machinery; mitochondria in muscle cells, which need more power, have more of them.
Q 05What is the fluid-filled space enclosed by a mitochondrion's inner membrane called?
The matrix
The matrix is where the citric acid cycle turns, and it also holds the organelle's own DNA and ribosomes, leftovers from its free-living past.
Q 06Which of these components of the human body has no mitochondria at all?
A mature red blood cell
A mature red blood cell throws out its mitochondria as it develops, leaving more room for haemoglobin; from then on it lives by fermenting sugar.
Q 07Which of these parts of the body has cells most densely packed with mitochondria?
The heart
The heart never rests, so its muscle cells are more densely packed with mitochondria than any other tissue; the kidneys, which filter the blood around the clock, come second.
Q 08Which hypothesis holds that mitochondria descend from free-living bacteria engulfed by an ancestral cell?
The endosymbiotic theory
The endosymbiotic theory holds that the swallowed bacterium was kept rather than digested, trading energy for shelter until neither partner could live without the other.
Q 09Which biologist, Carl Sagan's first wife, argued that mitochondria began as bacteria?
Lynn Margulis
Lynn Margulis set out the case in a 1967 paper that, by her own count, about fifteen journals rejected before one printed it; genetic evidence later turned her idea into textbook science.
Q 10Which plant-cell organelle shares the mitochondrion's origin, having started out as a free-living microbe swallowed by a larger cell?
The chloroplast
The chloroplast began as a cyanobacterium swallowed by a cell that already had mitochondria, which is why plants and algae carry both organelles while animals have only one.
Q 11The cell that engulfed the mitochondrion's ancestor belonged to which group of microbes, famous for thriving in hot springs?
Archaea
Archaea: the host was probably a relative of the Asgard archaea, first identified in 2015 in mud from near an Arctic vent field named Loki's Castle; all complex life descends from that merger.
Q 12What shape is the mitochondrial chromosome in most organisms?
Circular
Circular, like a bacterium's chromosome and unlike the cell's own linear ones, which is one of the clues that mitochondria were once free-living microbes.
Q 13How many genes does the human mitochondrial genome encode?
37
37 genes are all that remain: most of the ancestral microbe's genes were lost or moved into the cell's main genome, which now codes for about a thousand mitochondrial proteins.
Q 21Which molecule, made from pyruvate or fatty acids, is the main fuel fed into the citric acid cycle?
Acetyl-CoA
Acetyl-CoA is the point where the breakdown of sugars, fats and proteins converges, which is why the body can burn all three in a single cycle.
Q 22The Warburg effect is the habit of which cells to ferment sugar even when their mitochondria could burn it fully?
Cancer cells
Cancer cells mostly ferment glucose even when they could burn it completely, as Otto Warburg first noticed; the wasteful habit seems to free up raw materials for building new cells.
Q 23What is the final acceptor of electrons at the end of the mitochondrial electron transport chain?
Oxygen
Q 14The first complete human mitochondrial genome, published in 1981, is named after which English university city?
Cambridge
Cambridge: Fred Sanger's laboratory there read all 16,569 letters, and geneticists still describe a person's mitochondrial DNA by how it differs from a corrected version of that sequence.
Q 15Mitochondrial DNA passes only from mother to child, so which of these relatives shares yours?
Mother's mother
Mother's mother: the same mitochondrial DNA runs down the female line from her to your mother to you, while your father's copy, inherited from his own mother, stops with him.
Q 16What molecular tag marks a sperm's mitochondria for destruction in the mammalian embryo?
Ubiquitin
Ubiquitin is the cell's 'dispose of this' label, and sperm mitochondria carry it into the egg; once they are broken down, a child's mitochondria normally all come from its mother.
Q 17The most recent common matrilineal ancestor of living humans is nicknamed 'Mitochondrial' what?
Eve
Eve was one woman among many in her day; she is singled out only because her mother-to-daughter line alone never broke, so everyone alive carries her mitochondrial DNA.
Q 18Which supposedly universal system do human mitochondria break by reading a few three-letter words differently?
The genetic code
The genetic code was assumed to be the same in all life until a 1979 study found that human mitochondria read UGA, a stop signal in the standard code, as the amino acid tryptophan.
Q 19Which notorious poison kills by jamming the final enzyme of the mitochondrial electron transport chain?
Cyanide
Cyanide binds the chain's last enzyme, so cells can no longer turn fuel into usable energy and suffocate from the inside, however well the blood supplies them.
Q 20The citric acid cycle that drives mitochondrial metabolism is also named after which biochemist?
Krebs
Krebs worked out the cycle at Sheffield in 1937, four years after the Nazi government dismissed him from his German hospital post and he moved to England; it won him a Nobel Prize.
Oxygen takes up the spent electrons at the end of the chain and is turned into water; this single reaction is the reason animals have to breathe.
Q 24The mitochondrial electron transport chain pumps which particles into the intermembrane space?
Protons
Protons, the positively charged cores of hydrogen atoms, pile up outside the inner membrane, creating a difference in both charge and acidity that the cell then taps for power.
Q 25Which process uses an ion gradient across the inner mitochondrial membrane to power the making of ATP?
Chemiosmosis
Chemiosmosis was first received with scepticism, since it explained the cell's power supply by a mere build-up of ions across a membrane, yet it won its author a Nobel Prize.
Q 26Who won the 1978 Chemistry Nobel for showing how mitochondria store energy as a membrane gradient?
Peter Mitchell
Peter Mitchell pursued the idea in a private laboratory he built inside a restored Cornish mansion, Glynn House, after stomach ulcers led him to resign from Edinburgh University.
Q 27Which rotary enzyme in the inner mitochondrial membrane makes the cell's main energy-carrying molecule?
ATP synthase
ATP synthase is a true rotary motor: ions streaming through it spin a central shaft, and each turn presses ADP and phosphate together into fresh ATP.
Q 28Which channel protein lets the mitochondria of some cells release their stored energy as heat instead of making ATP?
Thermogenin
Thermogenin short-circuits the usual energy-storing step so that fuel is burned straight into heat, which is how newborn babies keep warm without shivering.
Q 29Which tissue, rich in heat-generating mitochondria, is present at birth in humans and declines with age?
Brown fat
Brown fat owes its colour to the iron in its densely packed mitochondria; newborns carry it around the back, neck and shoulders, and it switches on in the cold.
Q 30Which protein, when it leaks out of a mitochondrion, sets off the cell's programmed self-destruction?
Cytochrome c
Cytochrome c normally just ferries electrons along the energy chain; once it escapes into the rest of the cell, it switches on the enzymes that take the cell apart.