Everyday Biology, Surprisingly Handy (Part 1)

[C] AIDS | Sharing needles can transmit HIV and hepatitis faster than gossip in a small town. This is why medical professionals treat needles like toxic waste, because technically they are.

[C] Deoxyribonucleic Acid | DNA contains instructions for building you, written in just four letters. If typed out, your DNA would fill 175,000 pages, making it history's longest instruction manual nobody reads.

[B] Karl Landsteiner | Landsteiner figured out why some blood transfusions killed people while others didn't. Before him, getting a transfusion was basically medical roulette with terrible odds.

[B] Human Skin | Your skin is your largest organ at 20 square feet. It completely replaces itself every month, meaning you've worn about 1,000 different skin suits in your lifetime.

[A] Adrenaline | Adrenaline can make mothers lift cars off babies and gives you superhuman strength for about 60 seconds. Side effects include shaky hands and questioning reality afterward.

[A] Stapes | The stapes is smaller than a rice grain but amplifies sound 20 times. Without this tiny bone, conversations would sound like Charlie Brown's teacher to everyone.

[C] Insulin | Insulin acts like a doorman for sugar, letting it into cells. Type 1 diabetics' doormen quit, while Type 2's doormen need hearing aids.

[C] Iris | Your iris color is determined by melanin, same stuff in your skin. Blue eyes aren't actually blue; they're just brown eyes with less furniture in them.

[A] Bacille Calmette-Guérin | BCG vaccine is made from weakened cow tuberculosis. Humans literally learned disease prevention from cows, making them history's first immunology professors.

[C] Femur | Your femur can support 30 times your body weight vertically. It's basically a biological steel beam that occasionally reminds you it exists when you hit furniture.

[A] Charles Darwin | Darwin spent 20 years thinking about his theory before publishing because he knew it would upset literally everyone. He was right about both the theory and the upset.

[C] Thallophyta | Thallophytes are plants that never figured out how to grow proper roots, stems, or leaves. They're basically the minimalists of the plant kingdom.

[C] Ligaments | Ligaments are like biological rubber bands holding your skeleton together. Stretch one too far and you'll spend weeks explaining how you injured yourself doing something mundane.

[B] Plasma | Plasma is 92% water and 8% everything else your body needs delivered. It's basically biological Amazon Prime, but faster and more reliable.

[A] Mosquito | Mosquitoes have 47 teeth to saw through your skin. They're basically flying dental equipment that nobody asked for, complete with anesthetic and anticoagulants.

[D] Eye | Your pupils dilate when you see someone attractive, making them literally windows to your soul and also your dating preferences.

[A] Convex lens | Your eye's lens changes shape 100,000 times a day to focus. It's doing more workouts than most people's gym memberships.

[A] Testosterone | Testosterone peaks in the morning, which explains both morning mood and why hardware stores are busiest on Saturday mornings.

[D] Liver | Jaundice turns you yellow because your liver stops processing bilirubin properly. You basically become a human highlighter, but not in a good way.

[D] Rod-shaped | Bacillus bacteria look like tiny hot dogs under a microscope. Some cause disease, others make yogurt, proving shape doesn't determine personality.

[B] Vena cava | The vena cava is wide as a garden hose and returns blood from your entire body. It's the main highway back to your heart's recycling center.

[A] Brain | Your brain processes senses but doesn't sense anything itself. It has no pain receptors, which is why brain surgery can happen while you're awake and chatting.

[B] Monosaccharide | Glucose is your brain's favorite food, using 20% of your body's supply. Your brain is basically running on sugar, explaining both creativity and crashes.

[B] Epidermis | Your epidermis is technically dead cells stacked like shingles. You're basically wearing a suit made of your own expired cells.

[D] 22 | Your skull bones are held together by sutures that look like jigsaw puzzles. Babies have more pieces that fuse together, like biological IKEA furniture.

[D] Ethyl Alcohol | Ethanol is the only alcohol that won't blind or kill you in small doses. Your liver processes it at exactly one drink per hour, no matter how much you beg.

[B] Polynucleotides | Genes are instruction manuals written in a four-letter alphabet. Every human shares 99.9% of their genes, making that 0.1% responsible for all our arguments.

[B] Hansen's disease | Leprosy is one of the least contagious diseases despite its reputation. 95% of people are naturally immune, making historical panic particularly ironic.

[D] Ductless Glands | Endocrine glands release hormones directly into blood like dropping messages into a river. It's slower than texting but way more dramatic.

[D] Amphibious Plants | Bryophytes like moss need water to reproduce, making them the plant kingdom's helicopter parents who never let their kids leave the pool.