Page 16 - Herlihy: The Human Body in Health and Illness, 3rd Edition

23 HYDROGEN

Brief description: hydrogen is the lightest
element. It is by far the most abundant
element in the universe and makes up about
about 90% of the universe by weight.
Hydrogen as water (H 2O) is absolutely
essential to life and it is present in all
organic compounds.

24 OXYGEN

Brief description: While about one fifth of
the atmosphere is oxygen gas, the
atmosphere of Mars contains only about
0.15% oxygen. Oxygen is the third most
abundant element found in the sun, and it
plays a part in the carbon-nitrogen cycle,
About two thirds of the human body, and
nine tenths of water, is oxygen. The gas is
colourless, odourless, and tasteless. Liquid
and solid oxygen are pale blue (see picture
above) and strongly paramagnetic (contains
unpaired electrons).

25 POTASSIUM

Brief description: potassium is a metal and
is the seventh most abundant and makes up
about 1.5 % by weight of the earth's crust.
Potassium is an essential constituent for
plant growth and it is found in most soils. It
is also a vital element in the human diet.