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Every living creature must breathe in
some way. All animal life
breathes by taking in oxygen.
Man gets his oxygen by taking air into the lungs.
It seems a simple thing for us to
breathe. We do not even think about it as we do it. But I involve quite a
complicated process when a
person breathes in, air passes into the body through a series of tubes called
"the upper respiratory tract".
This starts with the nose. Here, particles which could be harmful to the lungs
are stopped or strained out. The nose also warms the air.
From the nose the air turns down through
the "pharynx", or throat. From here, the air goes through two smaller
tubes called "bronchi", one of which enters each lung. The lungs are large, soft organs. Around the
entire lung is a thin covering called "the pleura!'
The lung tissue is like a fine sponge in
some ways. But in the lung there are spaces, or air sacs, and it is here that air is received from
the bronchi, the proper gases are used, and unwanted gases are forced out.
These air spaces are called "alveoli".
The air we take in contains oxygen,
nitrogen, carbon dioxide, and water vapor.
These same gases are present in the blood but in different amounts. When a
fresh breath is drawn in, there is more oxygen in the alveoli than in the
blood. So the oxygen passes through the very thin walls of the blood vessels (capillaries)
and into the blood. Carbon dioxide goes from the blood into the air sacs of the
lung and is exhaled.
While there is much more to the process
of breathing, of course, this is the most vital part of it—the exchange of
gases that enables all the cells to obtain oxygen and to get rid of carbon
dioxide.
Source
: July 11, 2013 http://www.blurtit.com/q546386.html
The text above is an explanation text in written form. It functions to explain each step of the process (how) and to give reasons (why). In other words, it tells how or why something happens. Some examples of explanation texts are how something occurs, why something happens, why things are alike or different, how to solve a problem, and how something works.
This type of text has the following structure :
- general statement : states the phenomenon to be explained.
- sequenced explanation : states a series of steps which explain the phenomena.
