Physiology
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50 free Physiology trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Physiology is the science of how living bodies work: how a heart keeps time, how a meal becomes energy, how a nerve carries a message faster than a blink. It is anatomy set in motion, and it explains everyday mysteries, from why knuckles pop to why holding your breath gets so uncomfortable. This quiz covers the ground a first physiology course does. There are questions on breathing and blood, the heart and circulation, nerves and muscles, digestion, the kidneys and the chemical messengers that keep everything in balance. The discoverers are here too, along with a few animals whose bodies solve the same problems in stranger ways. The first questions are fun facts that anyone curious about the body can try. The later ones are closer to what a nursing, biology or pre-med student meets before a test. Every answer comes with a short explanation, so even a miss teaches you something.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which gas building up in the blood, rather than a lack of oxygen, triggers the human urge to breathe?
Carbon dioxide
Carbon dioxide is what the brainstem's sensors track, so free divers who over-breathe before a dive can black out underwater without ever feeling a need for air.
Q 02Which Russian physiologist won a 1904 Nobel Prize for work on digestion, not for his famous salivating dogs?
Ivan Pavlov
Ivan Pavlov was the first Russian Nobel laureate. He was measuring the digestive juices of dogs when he noticed them drooling before any food arrived, which led him to the conditioned reflex.
Q 03Which sea animal has three hearts and blue blood, coloured by a copper-rich protein instead of an iron-rich one?
Octopus
Octopus blood is pumped by one main heart for the body and two smaller ones that push it through the gills. The main heart goes quiet whenever the animal swims.
Q 04Which gas from ordinary compressed air dissolves in a diver's tissues and forms the bubbles that cause 'the bends'?
Nitrogen
Nitrogen makes up most of the air in a scuba tank and is not used up by the body. If a diver surfaces too fast, it comes out of solution like the fizz in a freshly opened bottle of soda.
Q 05Which lubricant inside a human joint holds the gas bubbles behind the pop of a cracked knuckle?
Synovial fluid
Synovial fluid takes about 20 minutes to reabsorb the gas, which is why the same knuckle will not crack twice in a row. Studies have found no link between the habit and arthritis.
Q 06Which nightly brain state brings the most vivid dreams while leaving nearly all of the body's muscles paralysed?
REM sleep
REM sleep shuts down the motor neurons so that dreamers do not act out their dreams. People whose paralysis fails can punch, kick or leap out of bed while still fast asleep.
Q 07Which human organ can regrow to its full size after surgeons remove more than half of it?
Liver
The liver is the only internal organ that can regenerate this way. In Greek myth the punished Prometheus has his eaten by a bird each day, only for it to grow back overnight.
Q 08Which hormone, released by glands sitting on top of the kidneys, drives the body's fight-or-flight response?
Adrenaline
Adrenaline widens the pupils, speeds the heart and sends extra blood to the muscles within seconds. In the United States it is usually called epinephrine, from the Greek for 'upon the kidney'.
Q 09Which enzyme do most mammals stop making after weaning, though many adult humans keep it and can digest milk?
Lactase
Lactase stays switched on for life in people who carry a mutation that spread once humans began dairy farming. Without it, milk sugar reaches the gut bacteria undigested.
Q 10Which African mammal needs about double a human's blood pressure, plus tight leg skin to stop blood pooling?
Giraffe
Giraffe leg skin holds blood in place so well that scientists have studied it as a model for astronaut and fighter-pilot suits. The high pressure is needed to reach a brain far above the heart.
Q 11Which word did physiologist Walter Cannon coin in 1926 for the body keeping its inner conditions steady?
Homeostasis
Homeostasis joins the Greek words for 'similar' and 'standing still'. Cannon also gave English the phrase 'fight or flight', which he used for an animal's response to a threat.
Q 12Which almond-sized region of the human brain acts as the body's thermostat, triggering shivering and sweating?
Hypothalamus
The hypothalamus turns its own setting up during an infection, and that raised setting is what a fever is. It also controls hunger, thirst and the daily body clock.
Q 13Which iron-containing protein in red blood cells carries oxygen from the lungs and gives blood its colour?
Hemoglobin
Q 21Which gland hanging beneath the brain is nicknamed the 'master gland' because it directs so many other hormone glands?
Pituitary
The pituitary is only about the size of a kidney bean, yet the growth hormone it releases decides how tall a child will become.
Q 22Which butterfly-shaped gland in the neck needs iodine to make hormones that set how fast the body burns energy?
Thyroid
The thyroid can swell into a lump at the front of the neck, called a goitre, when a diet is short of iodine. That is one reason iodine is added to table salt.
Q 23Which 'love hormone' triggers contractions in childbirth and the let-down of milk during breastfeeding?
Oxytocin
Oxytocin runs on a rare positive feedback loop: each contraction releases more of it, which makes the next contraction stronger, and so on until the baby is born.
Hemoglobin lets blood carry about 70 times more oxygen than could simply dissolve in its watery plasma. Each molecule can hold up to four oxygen molecules at once.
Q 14Which hormone from the pancreas lowers blood sugar by telling cells to absorb glucose after a meal?
Insulin
Insulin was first injected into a patient in 1922, a 14-year-old boy who lay dying in a Toronto hospital. Until then there was no effective treatment for type 1 diabetes.
Q 15Which dome-shaped sheet of muscle beneath the lungs contracts and flattens each time a person breathes in?
Diaphragm
The diaphragm also walls off the chest from the abdomen. A sudden involuntary spasm of it, followed by the vocal cords snapping shut, is what makes the sound of a hiccup.
Q 16Which English physician showed in 1628 that the heart pumps blood around the body in a continuous loop?
William Harvey
William Harvey worked out that the heart moves far more blood in half an hour than the body could possibly make, so the same blood had to be going round again. He was physician to two kings.
Q 17Which hormone does the pineal gland release in darkness to help set the body's sleep-wake cycle?
Melatonin
Melatonin production is held back by light, and blue light most of all, which is why a bright screen at bedtime can delay sleep. Travellers take it as a remedy for jet lag.
Q 18In which part of the human digestive tract, lined with finger-like villi, are most nutrients absorbed?
Small intestine
The small intestine is small only in width. Its folds and villi give it an absorbing surface of about 30 square metres, roughly the floor of a studio flat.
Q 19Which fifth basic taste did Japanese chemist Kikunae Ikeda identify in 1908 while studying seaweed broth?
Umami
Umami is the savoury taste of glutamate, strong in ripe tomatoes, mushrooms and aged cheese. The year after Ikeda identified it, it went on sale as the seasoning MSG under the brand name Ajinomoto.
Q 20Which nutrient does human skin make when sunlight hits it, and which children need to avoid rickets?
Vitamin D
Vitamin D is the one vitamin that sunshine can supply: for most people the skin makes more of it than food provides. It lets the gut absorb the calcium that growing bones need.
Q 24Which tiny cell fragments in human blood clump together at a wound to begin forming a clot?
Platelets
Platelets have no nucleus: they are chips that break off giant cells in the bone marrow. Each one circulates for only eight or nine days before it is replaced.
Q 25Which snail-shaped chamber of the human inner ear turns sound vibrations into nerve signals?
Cochlea
The cochlea sorts sound by pitch along its spiral. High notes are picked up near the entrance, where the membrane is stiff, and low notes travel on towards the far tip.
Q 26Which fatty sheath around nerve fibres speeds up their signals and is damaged in multiple sclerosis?
Myelin
Myelin makes a nerve impulse hop from gap to gap along the fibre instead of travelling as one slow continuous wave. Being rich in fat, it is also what makes the brain's white matter white.
Q 27Which natural painkillers made in the brain bind the same receptors as morphine and are released during hard exercise?
Endorphins
Endorphins take their name from 'endogenous morphine', morphine made within. They were long credited with the runner's high, though blocking them in experiments does not stop it.
Q 28Which sea animal's giant nerve fibre let Alan Hodgkin and Andrew Huxley work out how nerve impulses travel?
Squid
Squid have a nerve fibre up to a millimetre and a half thick, wide enough for the pair to slide an electrode inside it. The work earned them the 1963 Nobel Prize.
Q 29Which word did Charles Sherrington introduce in 1897 for the junction where one nerve cell signals another?
Synapse
Synapse comes from Greek words meaning 'to fasten together', and it was a classical scholar who suggested it. Most are in fact tiny gaps that a signal crosses as a burst of chemicals.
Q 30Which Italian scientist found in 1780 that a dead frog's leg muscles twitch when struck by an electrical spark?
Luigi Galvani
Luigi Galvani called the effect animal electricity, and his name survives in the verb 'galvanize'. Mary Shelley knew of his experiments before she wrote Frankenstein.