The Human Body (Ken Jennings’ Junior Genius Guides) - Softcover

Über die Autorinnen und Autoren

Ken Jennings is the New York Times bestselling author of Brainiac, Maphead, Because I Said So!, Planet Funny, and 100 Places to See After You Die. In 2020, he won the “Greatest of All Time” title on the quiz show Jeopardy! and later succeeded Alex Trebek as the show’s host. He lives in Seattle with his family.

Mike Lowery is an author and bestselling illustrator who has worked on more than eighty books for children, including the Mac B., Kid Spy series with Mac Barnett, They Call Me No Sam! with Drew Daywalt, and more. He is also the creator of the Everything Awesome and Bug Scouts books. He lives in Decatur, Georgia, with his wife and kids, and his daily sketchbook can be seen at MikeLowery.com.

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The Human Body

BEING HUMAN

Junior Geniuses, your body is a wonderland. Nothing personal! I just mean that if you are human, you are an amazing piece of biological machinery. If you are not human, please let me know immediately. We would like to dissect and study you for the upcoming Junior Genius Guides: Alien Beings.

The chemicals in your body are nothing special—common stuff you could buy with a little allowance money. In fact, you could recreate most of your body just by turning on a faucet. More than half of you is actually water!



So, if you are an eighty-pound human looking to rebuild your body with a chemistry set, buying the elements shown in the chart would set you back about $160. More than half the money would go to buying potassium, a kind-of-rare mineral found in foods such as oranges and bananas. Your body needs potassium to keep your blood pressure healthy and your muscles working.



EXTRA CREDIT

Your body doesn’t need gold to survive, but you do have some in your tissues, from tiny traces of it in the food you eat and water you drink. But you’re not going to strike it rich by selling your boogers and earwax to a late-night gold infomercial! The total amount of gold in your body is about the size of a grain of sand.

But when you combine the elements in your body, your value skyrockets. Let’s say you sold every part of you on the open market—your organs, your bone marrow, your DNA, your antibodies. I would advise against this, however. Not only is it illegal, but you sort of need some of that stuff. But if you had a clearance sale and everything had to go, your body could bring in about $45 million!

That’s because your body is made of very ordinary elements combined in extraordinary ways.

LADDER PERFECT

Like all other life on earth, human beings are carbon-based. This means that the big, complicated molecules that power us, like proteins and carbohydrates, are all based on the element carbon. Yup, the same stuff that charcoal and diamonds and graphite are made out of. Your body has enough carbon in it to provide the graphite for more than six thousand pencils!



One of the most important of these carbon-based molecules is deoxyribonucleic acid. Most people call it DNA to save time, and because it’s much easier to spell. DNA is a long, skinny molecule shaped like a twisted ladder (or a “double helix,” as a biologist would say).



Why is DNA so complicated? Because it contains all the information necessary to make you . . . you. It’s how a skin cell knows how to divide itself into new skin cells, and how a liver cell knows how to make new liver cells. There’s a reason why dogs don’t give birth to kittens and cats don’t give birth to puppies, and that reason is DNA. The DNA ladder is divided into long sections called genes, which contain instructions on how to pass along heredity information. Do you have brown eyes? Eye color is a gene. Curly hair? The ability to roll your tongue? Morton’s Toe? (That’s when your second toe is longer than your big toe.) Those traits are all in your genes.



EXTRA CREDIT

There’s even a human gene named for Sonic the Hedgehog! The SHH gene makes sure that your body grows your fingers and brain tissues in the right places.



The rungs of the ladder in each molecule of DNA are chemicals called bases. There are four different bases: adenine, guanine, thymine, and cytosine. You know what? Let’s keep it simple and call them A, G, T, and C. The pattern of As, Gs, Ts, and Cs on your DNA molecules is like a secret code that contains all the instructions your cells needed to grow into a person. Your whole genome—the entire code—is three billion base pairs long. That’s enough space to encode an entire shelf of encyclopedias!

MR. GREEN GENES

DNA isn’t just a human thing, Junior Geniuses. Pretty much all life on earth is based on DNA. Don’t get me wrong, I love humans. We are the only organisms on earth with speech, opposable thumbs, video games, and pizza. But not everything in our genome is so special. Did you know that . . .

99% of your DNA is the same as a chimpanzee’s?

97% of your DNA is the same as an orangutan’s?

80% of your DNA is the same as a mouse’s?

50% of your DNA is the same as a banana’s?

You may not be yellow, potassium-rich, and delicious on cereal, but you and bananas are distant branches on the same family tree–the tree of life on earth.

PIECES OF ME

Your DNA is found in every single cell of your body. In fact, there are almost six feet of DNA crammed into each tiny cell. Since the human body has about forty trillion cells in it, that means that you contain more than forty-five billion miles of DNA . . . enough to stretch between the sun and Pluto twelve times!



But what is a cell exactly? In 1665 the British scientist Robert Hooke was looking through a microscope at a thin slice of cork. He was surprised to see this:



The wood was divided into boxy structures, which reminded him of small rooms. He called them cells, like the small rooms where monks or prisoners lived, and the name stuck. Cells are the building blocks of life. All the tissues that make up life on earth, from rose petals to jellyfish tentacles to human brains, are made out of cells.



Human cells aren’t boxy like the ones Hooke saw. Only plant cells, it turns out, have rigid walls. Under a very powerful microscope, one of your cells might look more like this.



You have many different types of cells. A bone cell is very different from a brain cell, which is very different from a blood cell. This is a good thing, or you would be a very strange-looking person indeed.

YOUNG AT HEART

Keeping all the cells of your body up-to-date is a never-ending job. Every minute, cell division replaces ninety-six million dead cells all over your body. Blink your eyes once. Go ahead. Guess what? During that blink you got half a million new cells! Congratulations!

Are you around ten years old? Maybe a little less, maybe a little more? Here’s a secret: so am I, and so are your grandparents, and so is every other adult you know. Because human cells die and get replaced every decade or so, that means that the average age of my cells is about ten years. Most of me isn’t old enough to drive!

SMALL WONDER

Your body didn’t always have forty trillion cells. At first you had only one!

The path toward human life begins when the largest cell in the human body, a female egg cell, is fertilized by the smallest cell in the human body, a male sperm cell. These two are a real odd couple. A sperm cell weighs 175,000 times less than the egg, which is the only human cell so large it can be seen with the naked eye. For the first half hour of existence, you were...