Cellular Respiration
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50 free Cellular Respiration trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Every living thing faces the same problem: the energy locked in food has to be turned into a form its cells can spend. Cellular respiration is the solution, a chain of reactions that runs in almost every organism on Earth, from yeast in a brewing vat to the muscles of a sprinter. This quiz covers the whole process: glycolysis, the reactions inside the mitochondria, the electron transport chain and the making of ATP, plus fermentation, the route cells take when oxygen runs short. Alongside the core biology are the people who worked it out, the poisons that shut it down, and the animals and plants that push it to extremes. It is pitched for biology students revising for a test, teachers who want a ready-made review, and anyone curious about where their energy comes from. The questions run from the basics to tougher biochemistry, and every answer comes with a short explanation.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which nickname, popularized by a 1957 Scientific American article, do mitochondria carry for making most of our ATP?
Powerhouse of the cell
Powerhouse of the cell was the title of Philip Siekevitz's article, and the phrase stuck. A single liver cell can hold more than 2,000 mitochondria.
Q 02Which poison jams the last enzyme of the electron transport chain, leaving cells unable to use oxygen?
Cyanide
Cyanide blocks complex IV, so cells suffocate with oxygen all around them. Victims can turn cherry red because their veins still carry the oxygen that the tissues could not use.
Q 03Which gas, released as yeast ferments the sugars in dough, makes a loaf of bread rise?
Carbon dioxide
Carbon dioxide bubbles get trapped in the stretchy dough, leaving the air pockets seen in every slice. Bakers use the same yeast species that brews beer.
Q 04Which change after death happens because muscle fibers, starved of ATP, can no longer release their grip?
Rigor mortis
Rigor mortis sets in because muscle needs ATP to relax, not just to contract. It peaks about 13 hours after death and fades as the tissue starts to break down.
Q 05Which organ is only about 2% of human body weight yet burns roughly a quarter of the body's glucose?
Brain
Brain tissue also takes about a fifth of the oxygen the body uses. It runs mostly on glucose, which is why very low blood sugar can cause a blackout.
Q 06Which compound do human muscle cells make by fermentation when a hard sprint outruns their oxygen supply?
Lactic acid
Lactic acid was long blamed for next-day muscle soreness, a theory now largely rejected. Chemists first isolated it in 1780 from sour milk.
Q 07Mitochondria carry their own DNA because they descend from which free-living microbes, engulfed by an ancient cell?
Bacteria
Bacteria swallowed by a larger cell became permanent lodgers. Mitochondria still multiply by splitting in two, as free-living microbes do, and keep a circular chromosome.
Q 08Which burrowing African rodent can survive 18 minutes without oxygen by fueling glycolysis with fructose?
Naked mole-rat
Naked mole-rat colonies live in crowded tunnels where oxygen runs low. The animal can also carry on as normal for five hours in air that holds only 5% oxygen.
Q 09Which tissue, abundant in newborn babies and hibernating mammals, burns fuel to make heat instead of ATP?
Brown fat
Brown fat is crammed with mitochondria that let protons leak back across their inner membrane, turning the energy into warmth. That keeps a baby warm without shivering.
Q 10Which disease's cells often ferment glucose even when oxygen is plentiful, a quirk known as the Warburg effect?
Cancer
Cancer cells take up glucose so greedily that PET scans find tumors by tracking a radioactive sugar. The effect is named for Otto Warburg, who studied tumor metabolism in the 1920s.
Q 11Oxygen collects the spent electrons at the end of the electron transport chain and becomes which molecule?
Water
Water forms when oxygen takes on the electrons along with two protons. Without oxygen waiting at the end of the line, the whole chain backs up and stops.
Q 12Which process in plants is, in outline, the opposite of cellular respiration, building sugar instead of burning it?
Photosynthesis
Photosynthesis stores the sun's energy in sugar, and respiration releases it again. Plants do both, since their cells need ATP just as animal cells do.
Q 13Which human cell type has no mitochondria at all and so makes its ATP by glycolysis alone?
Red blood cells
Q 21Which stage of cellular respiration, a loop of reactions that begins with citric acid, honors a 1953 Nobel laureate?
Krebs cycle
Krebs cycle honors Hans Krebs, whose first write-up was turned down by the journal Nature for lack of space. He had fled Nazi Germany for England four years earlier.
Q 22In which innermost compartment of a mitochondrion, home to the organelle's own DNA, does the citric acid cycle run?
Matrix
Matrix is the name of that inner space, where nearly all the enzymes of the cycle float free. Only one of them sits elsewhere, fixed in the membrane that surrounds it.
Q 23Which folds of a mitochondrion's inner membrane multiply the surface available for the electron transport chain?
Cristae
Red blood cells discard their mitochondria as they mature, so they use none of the oxygen they carry. They throw out the nucleus too, leaving more room for hemoglobin.
Q 14In which part of a cell, outside the mitochondria, do the ten enzyme steps of glycolysis take place?
Cytoplasm
Cytoplasm holds the whole pathway, which needs no oxygen and no organelle. Glycolysis turns up across the living world, a sign that it is an ancient way of making ATP.
Q 15ATP, the energy carrier that cellular respiration exists to make, is short for which chemical name?
Adenosine triphosphate
Adenosine triphosphate is spent and rebuilt so fast that an average adult recycles around 50 kilograms of it every day.
Q 16When ATP gives up one phosphate group to power a cell's work, which molecule is left behind?
ADP
ADP is the flat battery to ATP's charged one. Cellular respiration recharges it by bolting a third phosphate group back on.
Q 17Which chemist overturned the idea that fermentation is mere decay by showing that living yeast makes the alcohol?
Louis Pasteur
Louis Pasteur was drawn in when a Lille manufacturer asked why his beetroot alcohol kept souring. He later described fermentation as life without air.
Q 18Glycolysis splits each six-carbon glucose molecule into two molecules of which three-carbon compound?
Pyruvate
Pyruvate sits at a crossroads: with oxygen it moves into the mitochondria to be burned completely, and without oxygen it is fermented instead.
Q 19Glycolysis invests ATP to split one glucose molecule, then earns back more, for a net gain of how many ATP?
2
A net gain of 2 ATP is all glycolysis offers, because it makes four but spends two getting started. The big payoff comes later, inside the mitochondria.
Q 20Which alcohol do yeast cells make when they ferment sugar without oxygen, as in brewing beer?
Ethanol
Ethanol is not only a yeast product: goldfish and carp make it too, to get energy when oxygen is scarce. Yeasts switch to it whenever oxygen is absent.
Cristae give the membrane its wrinkled look, and they are not fixed: the folds are remodeled with stress and nutrition. Cells hungry for ATP, such as muscle, pack in even more of them.
Q 24Which enzyme in the inner mitochondrial membrane, honored by a 1997 Nobel Prize, spins as protons pass through?
ATP synthase
ATP synthase earned Paul Boyer and John Walker their share of the prize. Part of the enzyme turns like a rotor in the membrane while the rest stamps out fresh ATP.
Q 25Which term names the flow of protons down a gradient across a membrane, the push behind most ATP production?
Chemiosmosis
Chemiosmosis works like a dam: pumps pile protons up on one side of a membrane, and their rush back does the work. Chloroplasts use the same trick, with light driving the pumps.
Q 26Which B vitamin, whose shortage causes pellagra, do cells need to build the main electron carrier of respiration?
Niacin
Niacin is vitamin B3. Pellagra killed more than 100,000 Americans between 1906 and 1940, an epidemic tied to diets built on corn.
Q 27Which molecule, used up by glycolysis, does fermentation in muscle and yeast exist to regenerate?
NAD+
NAD+ picks up electrons during glycolysis and must be emptied before it can be used again. Fermentation does that by dumping the electrons onto a waste product, so the sugar-splitting can go on.
Q 28Which molecule delivers two-carbon fragments from sugars, lipids and proteins alike into the citric acid cycle?
Acetyl-CoA
Acetyl-CoA is the hub of metabolism: whatever the fuel, its carbon arrives here before the final burn. Cells also use it as the starting material for cholesterol.
Q 29Cellular respiration breaks big molecules into smaller ones to release energy, making it which kind of pathway?
Catabolic
Catabolic pathways tear molecules down, while anabolic ones build them up, which is how muscle-building anabolic steroids got their name.
Q 30What do chemists call the loss of electrons that glucose undergoes as cellular respiration breaks it down?
Oxidation
Oxidation is the O in the student mnemonic OIL RIG, whose first three letters spell out the loss. The electrons that glucose gives up end their journey on oxygen.