On Earth, oxygen is more common than any other element. It
is an invisible, odourless gas that makes up 21 per cent of air. Oxygen is
found in water, minerals, and almost all living things. It is essential to
life. Ordinary oxygen molecules contain two oxygen atoms. Ozone, a three-atom
form, is found high up in the atmosphere. Oxygen moves through the environment
via the OXYGEN CYCLE.
Divers wear a SCUBA (self-contained underwater breathing apparatus),
so they can breathe under water. The SCUBA contains a cylinder of compressed
air, which divers carry on their backs. The air is compressed (or squeezed)
into the cylinder to increase the amount of air the divers can carry. Divers
breathe through a regulator, which decompresses the air as it comes out of the
cylinder.
BIOGRAPHY: JOSEPH PRIESTLEY British, 1733-1804
In 1774, this chemist announced his discovery of oxygen. He
didn’t realize that Swedish chemist Carl Scheele (1742–1786) had
found it first, a year or two previously. They both showed that air is not one
element. Priestley also discovered how to combine carbon dioxide with water to
make fizzy water.
Almost all living things, including humans, need oxygen
to survive. Both plants and animals take in oxygen from their surroundings to
release energy. Underwater plants and animals cannot use the oxygen in air
– instead they use oxygen dissolved in water. The oxygen cycle
continuously circulates oxygen through the environment, so it is always
available to all living things.
Plants are able to use the energy of sunlight to convert carbon
dioxide (CO2) and water (H2O) into carbohydrates and
oxygen (O2) in a process called photosynthesis. This oxygen is taken
in by plants and animals to provide energy, releasing carbon dioxide and water.
This process is called respiration.
