In reality, electrons are confined to specific orbits, as if they ran on rails. They cannot exist anywhere between these orbits but have to make a “quantum leap” from one to another. What’s more, as quantum particles, electrons exist as a collection of probabilities rather than at specific locations, so a better picture is to show the electrons as a set of fuzzy shells around the nucleus.
11. Red blooded
When you see blood oozing from a cut in your finger, you might assume that it is red because of the iron in it, rather as rust has a reddish hue. However, the presence of the iron is a coincidence. The red color arises because the iron is bound in a ring of atoms in hemoglobin called porphyrin and it is the shape of this structure that produces the color. Just how red your hemoglobin is depends on whether there is oxygen bound to it. When there is oxygen present, it changes the shape of the porphyrin, giving the red blood cells a more vivid shade.
12. Going viral
Surprisingly, not all the useful DNA in your chromosomes comes from your evolutionary ancestors — some of it was borrowed from elsewhere. Your DNA includes the genes from at least eight retroviruses. These are a kind of virus that makes use of the cell’s mechanisms for coding DNA to take over a cell. At some point in human history, these genes became incorporated into human DNA. These viral genes in DNA now perform important functions in human reproduction, yet they are entirely alien to our genetic ancestry.
13. Other life
On sheer count of cells, there is more bacterial life inside you than human. There are about 10 trillion of your own cells, but 10 times more bacteria. Many of the bacteria that call you home are friendly in the sense that they don’t do any harm. Some are beneficial.
In the 1920s, a US engineer investigated whether animals could live without bacteria, hoping that a bacteria-free world would be a healthier one. James “Art” Reyniers made it his life’s work to produce environments where animals could be raised bacteria-free. The result was clear. It was possible. However, many of Reyniers’ animals died and those that survived had to be fed on special food. This is because bacteria in the gut help with digestion. You could exist with no bacteria, but without the help of the enzymes in your gut that bacteria produce, you would need to eat food that is more loaded with nutrients than a typical diet.
14. Eyelash invaders
Depending on how old you are, it’s pretty likely that you have eyelash mites. These tiny creatures live on old skin cells and the natural oil (sebum) produced by human hair follicles. They are usually harmless, though they can cause an allergic reaction in a minority of people. Eyelash mites typically grow to a third of a millimeter and are near-transparent, so you are unlikely to see them with the naked eye. Put an eyelash hair or eyebrow hair under the microscope, though, and you may find them, as they spend most of their time right at the base of the hair where it meets the skin. Around half the population have them, a proportion that rises as we get older.