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Page 206
PHYSICAL SCIENCE AND LIFE SCIENCE
Elements of Life
8.3.a Students know
the structure of the
atom and know it is composed
of protons, neutrons, and
electrons.
There are more than 25 different types of
atoms in the cells of your body. The table
below shows the amount of atoms of some of the elements in a
50-kilogram human. For example, atoms of oxygen account for
about 61 percent of a person’s mass. Atoms of carbon account for
about 23 percent of a person’s mass. The atoms and ions of other
elements may be present only in very small amounts, but they play
important roles in the chemical processes that occur in your cells.
Blood and Other Fluids
Iron ions are part of the hemoglobin that gives blood its red color
and carries oxygen to cells throughout the body. Sodium and potassium ions help regulate the amount and location of the water in
the body. Sodium and potassium ions also make up part of the
sweat the body produces to regulate temperature.
Mass of Elements in 50 kg Human
Element
Amount (kg)
Oxygen (O)
30.5
Carbon (C)
11.5
Bones and Teeth
The sturdier structures of the body get their
strength from calcium, magnesium, and phosphorus. An average body has a little less than a
kilogram of calcium, almost all of which is in the
bones and teeth. Fluoride ions make up part of
the hard coating on the teeth. This is why you’ll
often find fluorine added to toothpaste.
Hydrogen (H)
5.0
Nitrogen (N)
1.3
Calcium (Ca)
0.7
Phosphorus (P)
0.6
Elements to Avoid
Potassium (K)
0.1
In some way, every element plays a role in
human lives. Many elements, however, can be
harmful or even poisonous. Arsenic is harmful
if swallowed. Mercury is dangerous even to
handle. While sodium may be necessary for
many processes inside cells, too much sodium
can be a serious health risk.
Sodium (Na)
> 0.1
Chlorine (Cl)
> 0.1
Other elements are in the body in very
small amounts.
SOURCE: CRC Handbook of Chemistry and Physics
EXPLORE
1. CALCULATE What percentage of your body is made up of
oxygen, carbon, hydrogen, and nitrogen?
2. CHALLENGE Salt, made of sodium ions and chloride ions,
is an essential part of your diet. However, too much salt
can cause health problems. Use the Internet to find out
about the problems caused by too much or too little salt
in your diet.
This photo shows a false-color
x-ray of the human skull. X-rays
show the bones in the human
body. Bones contain calcium.
206 Unit 2: The Structure of Matter
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