98% of People Can't Ace This Human Biology Quiz. Can You?

Able to support 30 times the weight of your body, it's your femur -- a bone in your leg -- that's the largest bone in your body. The shortest bone, in contrast, is found in your ears, and is shorter than a grain of rice.

The normal human body temperature is 98.6 degrees F. But based on things such as your age, gender, physical activity, time of day and, of course, whether or not you're sick, it can naturally range from 97.7 degrees F to 99.5 degrees F.

All humans are born with around 300 bones. But with time, some fuse together, and by the time you're an adult you have 206 bones, of many different shapes and sizes, making up your skeleton.

Your spinal cord is the bundle of nerves that runs from your brain stem down your spine and to your lower back. It's responsible for your reflexes, which is important, but it's also responsible for all the incoming and outgoing communications between your brain to your body.

The size of your heart can vary, especially if you're an athlete, but the average human heart is about the size of a large fist, and weighs about 8 to 10 ounces in women and 10 to 12 ounces in men.

The largest organ of the human body is its skin -- in fact, it's both the largest external organ and the largest organ overall. The pineal gland, located near the center of the brain, is actually the smallest organ in the human body.

Your bones may stop growing by age 25, but the parts of your body that are made of cartilage -- including your ears and your nose, continue to grow from birth until death. (And gravity isn't helping, either.) Your eyes, on the other hand, are the same size now as the day you were born.

Your ribcage protects your heart, lungs and liver. But it also provides support and framework for your body's muscles, and is a key component of the respiratory system.

The strongest muscle in the human body is the masseter, or the jaw muscle, which allows you to chew and clench. There's nothing special about the masseter when you look at it, but, it's the muscle that exerts the most pressure (that's the force exerted per unit area) -- your jaw can close with a force as great as 55 pounds on your incisors or 200 pounds on your molars. (In comparison, Tyrannosaurus Rex had a bite force of 8,000 pounds.)

Its the vessels of the vascular system -- the arteries, capillaries and veins that are also known as the body's circulatory system, that circulate blood throughout your body. In total, humans have about 1.2 to 1.5 gallons of blood -- since about the age of 6 and up.

From your collarbone to the end of your rib cage -- that's how big your lungs are. Together, they weight just shy of 3 pounds, but the pair aren't identical. Unlike the left lung which has two lobes and shares space in your chest with your heart, your right lung is larger, with three lobes, and doesn't have to share its space at all.

Bones are always busy making new bone and repairing themselves, communicating with other parts of the body and making a jelly-like substance called bone marrow. There are two types, red and yellow marrow, and each type produces specific stem cells. Red bone marrow, known as myeloid tissue, produces blood cells (red blood cells, platelets, and white blood cells). And yellow marrow is responsible for producing fat, cartilage, and bone.

Enzymes are made up of hundreds of amino acids strung together -- which you might recognize as the building blocks of proteins. These proteins, acting as a catalyst, can speed up the rate of all biochemical reactions within cells.

The human body's pulmonary system includes: the lungs, plus the alveoli, bronchi, bronchioles, larynx, thoracic diaphragm (or just "diaphragm"), and trachea. Your esophagus is part of your body's digestive system.

Your nose is capable of smelling at least 1 trillion distinct scents. Some of our favorite smells as a species include, vanilla, as well as some orange scents, cinnamon, crayons and cookies. And did you know? Humans can also smell feelings of fear and disgust through the smell of sweat.

A human adult's stomach can expand to hold more than 2 quarts of your favorite foods and beverages. That's about the equivalent of 8 eight-ounce glasses of water.

Every human has one of four blood types: A, B, AB and O. These four groupings are based on your red blood cells, and how the glycoprotein coating on the cells varies among humans. In blood type A, for instance, A oligosaccharide is present. In blood type B, B oligosaccharide is present. Similarly, AB blood has A and B oligosaccharides present. But in O blood type, neither A nor B is present, although the precursor to them (H oligosaccharide) is detected.

The average adult breathes more than 20,000 breaths a day -- which is equivalent to roughly 2,905 gallons of air per day.

The organs and tissues that make up your immune system are your body's defense system. They work together to keep pathogens, such as bacteria, viruses, fungi and parasites, from making you sick.

On average, by the time you reach adulthood, your body is composed of 100 trillion cells. And that translates to 7 octillion atoms (that's 7,000,000,000,000,000,000,000,000,000 atoms).

It used to be believed that bacteria and other microorganisms outnumbered our own human cells by a huge ratio of 10 microbes to 1 human cell. In 2016, scientists discovered the ratio is far more likely to be closer to 1:1 or 2:1, microbes to human cells. Regardless, either way you're not all human.

The sympathetic nervous system is one of the two branches of the autonomic nervous system, which regulates involuntary functions of your body such as your heart rate. It's the part of the system that's responsible for your "fight or flight" response -- also known as "hyperarousal," which includes raising your blood pressure and your heart rate, and slowing down your digestion.

Known as both the "love hormone" and the "bonding hormone," oxytocin is the hormone responsible for kittens, puppies, rainbows, and anything that makes your heart melt. It's released by your hypothalamus, and it plays a role in our social and sexual interactions, reproduction and childbirth, as well as mother-infant bonding. It also has a role in some of our behavior, such as how empathetic or generous we are.

Of the more than 200 bones in the human body, more than half of them are being used by your hands and feet. Specifically, there are 27 in each hand and 26 in each foot.

The cells in your body are organized into tissues, and it's these tissues that form your organs. Different parts of your body are made up of different types of tissue. There are four basic types, including connective, epithelial, muscle and nerve tissues -- and it's epithelial cells that make up your skin (as well as the coverings of your throat and other cavities).

Your gastrointestinal tract is made up of your mouth, esophagus, stomach and both large and small intestines. But it takes more than that to handle the complete process of human digestion -- your digestive system is your gastrointestinal tract plus what's called accessory organs, which include your gallbladder, liver, pancreas, salivary glands and tongue. In fact, even though your small intestine handles most of the heavy lifting, digestion begins as soon as the food you're chewing mixes with your saliva.

With all the neurons in your brain working together, you're generating enough electricity to power a 10-watt light bulb.

Although it's part of the autonomic nervous system, the enteric nervous system (ENS) also acts independently -- in fact, it's part of the reason the ENS is known as the body's second brain. Like the brain, it uses neurotransmitters such as acetylcholine, dopamine, and serotonin, but unlike the brain, your gut contains more than 90 percent of the body's serotonin and about 50 percent of its dopamine.

When your brain and body communicate, it's fast. Not as fast as the speed of sound (767 mph) or the speed of light (671 million mph), but communication speeds of up to 200 mph make your nervous system a speedy machine.

Deoxyribonucleic acid, or DNA for short, contains the genetic instructions -- the building blocks -- for your human self. It's stored in pairs, 23 pairs to be exact, inside the nucleus of every cell in your body.

When you're donating blood, it's O - that's the universal donor -- which means that it can be given safely to people with other blood types, without fear of triggering an immune response. People with blood type AB + are considered universal recipients. And when it comes to plasma donation, it's the AB blood type that's the universal donor.

Your kidneys are a filtering system, and the pair is responsible for filtering water and toxins from your blood. It handles about 120 to 152 quarts of blood every day, from which about 1 - 2 quarts of urine is produced.

Humans have balance, hearing, sight, smell, taste and touch -- as well as others we're not even aware of, like spatial awareness. But, it's pit vipers that have a special organ between the eye and the nostril that allows them to detect infrared radiation -- a built-in heat sensor.

Mitochondria are tiny structures called organelles that are the powerhouses within a cell -- literally, they generate power by converting oxygen (O2) and nutrients into chemical energy, adenosine triphosphate (ATP). ATP is known as molecular "currency."

If you donate 50 percent of your liver to someone who is in need of a transplant, you can expect that your remaining liver will be back to its original size in about two weeks. It needs only one-quarter of its original tissue to completely regenerate.