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Every element that exists on Earth is also part of you. But just six elements make up 99 percent of your body’s mass. What are they, and why do you need them?

Use the clues to choose the elements from the list below.

Choices:

Potassium
Oxygen
Sodium
Nitrogen
Chlorine
Hydrogen
Magnesium
Carbon
Iron
Calcium
Phosphorus
Fluorine        

Element 1 - 61%

Clue: Like all animals, we need a minute-by-minute supply of the gas form of this element in order to stay alive. It’s also a component of water, which makes up about 65 percent of your body’s total weight.

Answer: Oxygen

Oxygen makes up 61 percent of your body’s mass. Oxygen is essential to life as it’s a component of DNA and most important compounds in the body. Oxygen is present in your body mostly as water (H2O), so the actual amount may vary. When you inhale, oxygen is absorbed through your lungs and picked up by the iron in your red blood cells. From there, it is carried to wherever it’s needed throughout the body.

Health fact: Although water is essential to life, giving too much water to someone who is badly dehydrated can upset the balance of sodium and potassium ions in the heart muscle, leading to a heart attack.

More about oxygen.

Element 2 - 23%

Clue: Without this element, you would just be a pile of loose atoms. It gives structure to the molecules that you’re made of, and is the basis for all life on Earth.

Answer: Carbon

We are carbon-based life forms. This is because carbon is a very sociable element — it forms strong chemical bonds not only to itself but also to other atoms. Carbon’s stability makes possible the long chains and rings of atoms that form everything from your DNA to the steroids and proteins in your body. About 23 percent of your body mass is made of carbon.

Health fact: Although carbon on its own is harmless, some compounds of carbon are highly toxic. Carbon monoxide (CO) is an odourless, colourless gas found in combustion fumes such as car exhaust. Red blood cells pick up CO faster than oxygen, so if the air contains high amounts of CO, the body may not get enough oxygen. This can lead to illness or death.

More about carbon.

Element 3 - 10%

Clue: This element is number one in several ways — it’s the first element of the Periodic Table of the Elements, and was the first element created after the Big Bang. It’s also a crucial component of the water that makes up about 65 percent of your body’s weight.

Answer: Hydrogen

Although hydrogen is the most abundant element in the universe, it makes up only about 10 percent of your body mass. Its most important role is as a component of water (H2O). Water carries nutrients to your cells and removes toxins from the environment. Almost all reactions in the body take place in water. We need about 2.5 litres of water every day to keep healthy. About half of this comes from the liquids we drink, and half from food.

Without hydrogen, you couldn’t digest food. The acid in your stomach is a compound of hydrogen and chlorine (hydrochloric acid).

Health fact: Magnetic resonance imaging (MRI), a technology for scanning the body non-invasively, depends on the distribution of water throughout the body. Without water and the hydrogen it contains, MRI scans would not be possible. 

More about hydrogen.

Element 4 - 2.6%

Clue: The gas form of this element makes up 78 percent of the air we breathe. In its liquid form, it can be used to quickly freeze just about anything, including tissue samples or genetic material.

Answer: Nitrogen

Nitrogen makes up 2.6 percent of your body’s weight. It’s a component of DNA and of important molecules such as haem (part of the haemoglobin that carries oxygen in your blood). It’s also a component of the amino acids that form enzymes and other proteins. Nitrogen is important for growth, especially during pregnancy.

Although the air we breathe contains plenty of nitrogen, we don’t absorb it in this form. Instead, we get most of our nitrogen from the foods we eat. Many foods contain nitrogen, especially protein sources such as meat and dairy products.

Health fact: During World War I, doctors found that workers who were packing ammunition shells with the explosive nitroglycerine (made of carbon, nitrogen, hydrogen and oxygen) had very low blood pressure. This led to the use of nitroglycerine to dilate blood vessels. It’s often used to treat angina — chest pain caused by reduced blood flow to the heart.

More about nitrogen.

Element 5 - 1.4%

Clue: This element is a major component of your skeleton and teeth. 

Answer: Calcium

Calcium accounts for about 1.4 percent of your body weight. Calcium is a metal, and the most abundant metal in the body. It’s mostly found in bone but it also has other important functions, such as controlling cell division, aiding in the conduction of nerve impulses and contraction of muscles, and keeping blood pH stable. It’s also important for blood clotting.

Health fact: Bone is constantly being created and broken down in the body, which helps to keep the level of calcium in the blood steady. When the body runs low on calcium, it makes up the deficiency from bone and replaces it later when there is excess calcium in the blood. As people get older, the calcium isn’t replaced as easily, which can lead to osteoporosis.

More about calcium.

Element 6 - 1.1%

Clue: Dangerously flammable in its elemental form, this element is also part of the body’s system for storing energy.

Answer: Phosphorus

Phosphorus makes up about 1.1 percent of your body weight. In the form called white phosphorus, it is highly flammable and poisonous. Luckily, in the natural world phosphorus is found only in the form of phosphate, which is a phosphorus atom bonded to four oxygen atoms. Although it’s a small component of DNA, phosphorus is found in the body mostly as calcium phosphate in bone.

Phosphorus also makes it possible for your body to move. When the energy molecule, adenosine triphosphate (ATP), releases a phosphate molecule, this creates the energy needed for contracting muscles. The body creates, uses and recycles about one kilogram of ATP every hour.

Health fact: A new family of drugs called bisphosphonates, which contain phosphorus, is being used to treat osteoporosis. These drugs bind to the calcium in bone and slow down the action of bone-eroding cells, so that bone-building cells can work more effectively.

More about phosphorus.

Source: Nature’s Building Blocks: An A-Z Guide to the Elements, by John Elmsley

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