Twenty questions about the body you live in: bones, the brain, the heart, the senses and the strange things they do, each with the fact behind the answer. Play them as a quiz, or read the list with the answers marked.
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The same questions as the quiz, right answer highlighted and the fact under it. Print the page for a quiz night: the print layout keeps the questions and answers only. The Human Body topic in Lock&Learn holds 121 facts in all.
Are you more human or more bacteria?
You carry more bacterial cells than human cells. Current estimates put the ratio at roughly 1.3 bacterial cells for every human cell, most of them living in your gut.
Source: NIH
Who has more bones, you or a newborn?
Babies are born with ~300 bones; adults have 206. Many of a baby's bones are separate pieces of cartilage that fuse together as they grow.
Source: Britannica
Which organ rebuilds itself every few days?
Your stomach lining renews itself every few days. Stomach acid is strong enough to digest the stomach itself, so the body constantly replaces the protective lining.
Source: Scientific American
How far would your blood vessels stretch?
Your blood vessels could stretch nearly halfway around Earth. Laid end to end, the body's arteries, veins and capillaries would run an estimated 9,000 to 19,000 kilometres, enough to reach nearly halfway around the planet.
Source: Physiology research
Which organ is the body's biggest energy hog?
Your brain burns 20% of your energy at 2% of your weight. Thinking is expensive: the brain consumes about a fifth of your calories while making up a fiftieth of your body mass.
Source: Scientific American
How many times will your heart beat today?
Your heart beats about 100,000 times a day. That's roughly 35 million beats a year, pumping around 7,500 litres of blood every single day.
Source: American Heart Association
What household liquid matches your stomach acid?
Stomach acid is strong enough to corrode metal. With a pH of 1-2, gastric acid is comparable to battery acid. Lab tests show it can corrode razor blades.
Source: Gastrointestinal research studies
Do humans glow in the dark?
Your body literally glows, just too faintly for eyes to see. Humans emit a tiny amount of visible light from chemical reactions in our cells, about 1,000 times weaker than our eyes can detect.
Source: PLOS ONE (2009)
Where is your pound-for-pound strongest muscle?
The strongest muscle for its size is in your jaw. The masseter can close teeth with a force of up to 90 kg on the molars.
Source: Guinness World Records
When are you at your tallest?
You're about a centimetre taller in the morning. The discs in your spine compress slightly under gravity during the day and re-expand while you sleep.
Source: NASA & spine research
Which grows faster, fingernails or toenails?
Fingernails grow about three times faster than toenails. A fingernail takes around six months to fully regrow; a toenail can take a year or more.
Source: American Academy of Dermatology
Why aren't your lungs the same size?
Your left lung is smaller to make room for your heart. The left lung has two lobes instead of three, with a notch carved out where the heart sits.
Source: Britannica
How long is the tube inside you?
Your small intestine is about six metres long. Coiled inside your abdomen is a tube longer than a car, and its inner surface, unfolded, would cover a badminton court.
Source: NIH
Why do you get goosebumps?
Goosebumps are a leftover from when we had fur. The reflex fluffs up fur to trap heat or look bigger when threatened. Useful for our ancestors, mostly decorative now.
Source: Scientific American
How often do you get a whole new layer of skin?
Your skin completely replaces itself about every month. The outer layer of your skin renews itself roughly every four weeks, shedding tens of thousands of dead cells a minute as it goes.
Source: Dermatology research
Where does your 'happiness chemical' mostly live?
Over 90% of your serotonin lives in your gut. The 'happiness chemical' is mostly made down in your intestines, not your brain, where it helps run digestion at least as much as mood.
Source: Wikipedia
Why aren't your fingers webbed?
Your fingers were carved apart by programmed cell death. Human embryos start with webbed hands and feet. The cells between the digits are told to die on cue, sculpting your fingers and toes apart.
Source: Wikipedia
Are all your movements learned, or born in?
Some basic movements may be wired in before birth. Children blind from birth still smile and pull the same facial expressions as sighted ones, a hint that some movements are inherited, not learned.
Source: Wikipedia
How does a wound physically pull itself smaller?
Special cells shrink a wound by gripping its edges. Myofibroblasts latch onto the sides of a wound and contract like muscle, physically hauling the edges together as it heals.
Source: Wikipedia
Your heart pumps blood, but what moves your lymph?
Your lymph has no pump, your own movement drives it. Blood has the heart, but lymph relies on you moving: contracting muscles squeeze the fluid along, which is why staying active helps ease swelling.
Source: Wikipedia
This page has 20, each with three answers and the fact that settles it. They are the first 20 of the 121 facts in the Human Body topic of Lock&Learn, which holds the rest.
Yes. Read them out, print the page (the right answers are marked) or play the quiz on a shared screen. Each question has one right answer and two plausible wrong ones, and the fact under it gives you something to say after the reveal. Please do not republish the questions elsewhere.
Every fact names its source under the answer, from space agencies and museums to encyclopedias and published research. Lock&Learn writes each one as a teaser question with three answers, and the fact that settles it.
Install Lock&Learn, then touch and hold your Lock Screen, tap Customize, tap the widget area and choose Lock&Learn. A question waits on every screen-wake; you guess, tap, and reveal the verified fact behind the answer. Pick the topics you like and the widget rotates through them.
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