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50 free Mitochondria trivia questions with answers — science & nature quiz, new questions added Aug 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 50 questions with answers and explanations. Play the quiz
Q 01Mitochondria are popularly nicknamed the what of the cell?
Powerhouse
The phrase was popularised by Philip Siekevitz in a 1957 magazine article of that name.
Q 02Which energy-carrying molecule do mitochondria generate through aerobic respiration?
ATP
Making it aerobically yields far more energy than fermentation does.
Q 03How many membranes does a mitochondrion have?
Two
The outer one is leaky to small molecules; the inner one is highly impermeable and packed with proteins.
Q 04What are the folds of the inner mitochondrial membrane called?
Cristae
They boost surface area; muscle mitochondria, which need more ATP, have more of them.
Q 05What is the fluid-filled space inside the inner membrane called?
The matrix
It holds about two-thirds of the organelle's protein, its ribosomes and several copies of its DNA.
Q 06Which of these components of the human body has no mitochondria at all?
A mature red blood cell
A liver cell, by contrast, has a great many.
Q 07Roughly how many mitochondria can a single liver cell contain?
More than 2,000
Numbers vary hugely by tissue and by how much energy the cell needs.
Q 08Which hypothesis holds that mitochondria descend from free-living bacteria engulfed by an ancestral cell?
The endosymbiotic theory
The relationship began deep in the Precambrian and gave the host cell the ability to respire.
Q 09Which biologist popularised the endosymbiotic origin of mitochondria?
Lynn Margulis
The idea gained acceptance once it was clear mitochondria have bacteria-like genomes and 70S-type ribosomes.
Q 10The ancestor of mitochondria was probably closely related to which order of bacteria?
Rickettsiales
That places it among the alphaproteobacteria, though the exact relationship is still argued over.
Q 11Roughly how long ago did the symbiotic relationship that produced mitochondria probably begin?
1.7 to 2 billion years ago
Respiring bacteria would have been a huge advantage to a host that only knew glycolysis and fermentation.
Q 12What shape is the mitochondrial chromosome in most organisms?
Circular
That is another bacterial trait; a mitochondrion may hold two to ten copies of it.
Q 13How many genes does the human mitochondrial genome encode?
37
That is 13 protein subunits, 22 tRNAs and 2 rRNAs.
Approximately how long is the human mitochondrial genome?
Q 21Which molecule, made from pyruvate or fatty acids, is the only fuel that enters the citric acid cycle?
Acetyl-CoA
One is consumed per turn and, unlike the cycle's intermediates, is never regenerated.
Q 22Which citric acid cycle enzyme is bound to the inner membrane as part of Complex II?
Succinate dehydrogenase
All the other cycle enzymes are dissolved in the interior.
Q 23What is the final acceptor of electrons at the end of the mitochondrial electron transport chain?
Oxygen
At complex IV it reacts with a reduced iron-carrying protein to make water, releasing 218 kJ per mole.
16 kilobases
It is a double-stranded circle with almost no non-coding DNA and no introns.
Q 15From which parent do humans normally inherit their mitochondrial DNA?
The mother only
The sperm's mitochondria enter the egg but are tagged for destruction.
Q 16What molecular tag marks paternal mitochondria for destruction in the embryo?
Ubiquitin
Some conifers, by contrast, normally pass mitochondria down the paternal line, though not pines and yews.
Q 17The most recent common matrilineal ancestor of living humans is nicknamed 'Mitochondrial' what?
Eve
The date is often taken as support for a recent modern-human expansion out of Africa.
Q 18In 1979 researchers found that human mitochondrial genes use what?
An alternative genetic code
AUA, AUC and AUU can all serve as start codons; most plant mitochondria stick to the standard code.
Q 19The mitochondrial genome of which parasite is unusually split into 18 tiny minichromosomes?
The human body louse
The same pattern is found in other sucking lice but not in chewing lice.
Q 20The citric acid cycle at the heart of mitochondrial metabolism is also named after which biochemist?
Krebs
Each turn produces three NADH, one FADH2 and one GTP.
Q 24The electron transport chain pumps which particles into the intermembrane space?
Protons
The resulting gradient drives them back through a rotary enzyme, which spins out ATP.
Q 25What process uses the proton gradient across the inner membrane to drive ATP synthesis?
Chemiosmosis
The scientist who described it won the 1978 Nobel Prize in Chemistry.
Q 26Who received the 1978 Nobel Prize in Chemistry for the chemiosmotic theory?
Peter Mitchell
Boyer and John Walker shared part of the 1997 prize for working out how the ATP-making enzyme itself operates.
Q 27Which enzyme complex in the inner membrane actually makes ATP from ADP and phosphate?
ATP synthase
The small round F1 particles studding the inner membrane folds are its heads.
Q 28What is the name of the proton channel that lets some mitochondria release energy as heat instead of ATP?
Thermogenin
Also called UCP1, it drives non-shivering thermogenesis in newborns and hibernating animals.
Q 29Which tissue, rich in heat-generating mitochondria, is present at birth in humans and declines with age?
Brown fat
It is at its highest in early life and in hibernating mammals.
Q 30Which protein, released from the intermembrane space, triggers apoptosomes and programmed cell death?
Cytochrome c
Mitochondria have long been recognised as central to the intrinsic pathway of apoptosis.