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You need to know
about three things:
Try to avoid using simple words like
"breathing" if this does not make it absolutely clear what you
mean. Tissue Respiration, Ventilating the Lungs and Gaseous Exchange are
terms with precise meanings and you must know what these are.
Tissue
Respiration.
Tissue respiration is the release of energy,
usually from glucose, in the tissues of all animals, green plants, fungi
and bacteria. All these living things require energy for other processes
such as growth, movement, sensitivity, and reproduction.
The most efficient form of respiration is aerobic
respiration: this requires oxygen. When oxygen is not available, some
organisms can respire anaerobically i.e. without air or oxygen. Yeast can
respire in both ways. Yeast gets more energy from aerobic respiration, but
when it runs out of oxygen it does not die. It can continue to respire
anaerobically, but it does not get so much energy from the sugar. Yeast
produces ethanol (alcohol) when it respires anaerobically and ultimately
the ethanol will kill the yeast.
We can respire in both ways too. Normally we use
oxygen, but when we are running in a race, we may not get enough oxygen
into our blood, so our muscles start to respire anaerobically. Unlike
yeast we produce lactic acid. Of course if we produced alcohol in our
muscles it would make us drunk! Fine thing if you are running away from a
predator and you end up drunk! Making lactic acid is not much better.
Lactic acid causes cramp.
Glucose + Oxygen = Carbon
Dioxide + Water + Energy
This word equation means: "sugar
and oxygen are turned into carbon dioxide and water releasing energy".
You must memorise the word equation (and the balanced chemical equation if
you want a grade A, B or C). Get help
memorising the equations
Glucose = Carbon Dioxide +
Ethanol + Energy
This word equation means: "glucose
is turned into carbon dioxide and ethanol releasing energy".
You must memorise this word equation.
Back to index
Ventilating
the Lung.
This is the proper term for what many people call
breathing. If you open a window, you can ventilate a room and get rid of
all the nasty smells of BO, cigarette smoke, and cooking; but if you open
your mouth it is not enough to ventilate your lungs. You must actually
suck air into your lungs. We do this by contracting the diaphragm when we
are sitting down and "breathing" gently, and by raising and
expanding our rib cage when we are "breathing" deeply. Sucking
air into the lungs is called inhaling. Inhaled air is
mixed with the stale air already in our lungs; so although the air we
inhale contains 20% Oxygen, the air in our alveoli (alveolar air) only
contains 14% Oxygen.
Don't expect all the stale used air to come out
just by opening your mouth, it must be pushed out. This happens when the
diaphragm relaxes and the muscles of the abdomen (tummy) push the lungs
up. The rib cage can also be pulled down and in. So this is how you exhale.
Although alveolar air only contains 14% Oxygen, it gets mixed
with rather fresher air in your trachea. This means that exhaled air may
contain 16% Oxygen.
When I inhale and exhale as deeply as I possibly
can, about 5.5 Litres of air comes in and out.
Back to index
Gaseous
Exchange.
All forms of respiration require
some form of gaseous exchange. In aerobic respiration, Oxygen must enter
our blood and Carbon Dioxide must leave the blood through our lungs.
Gaseous exchange is the exchange of Oxygen and Carbon Dioxide
across a respiratory surface. Many animals which live in water or
very wet places use gills for gaseous exchange. Animals which live on dry
land use lungs. Our lungs have an enormous surface area
so that Oxygen can get into the blood quickly enough and Carbon Dioxide
can get out of our blood quickly enough. Our lungs contain billions of
very tiny sacs called alveoli. Each alveolus is microscopic; but if we
took all the alveoli in someone's lungs and laid them flat side by side we
would end up with a sheet the size of a tennis court. As well as having a
very, very, very large surface area, the walls of out alveoli are incredibly
thin, so the distance between the air in our lungs and the blood
in our capillaries is very, very, very small.
So in your exam remember that
respiratory surfaces:
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have a very large surface area
and
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are very thin.
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These two things allow the
respiratory gases (Oxygen and Carbon Dioxide) to get in or out of the
blood fast enough. If you don't believe this, find someone who has been
smoking cigarettes for fifty years. They might have a disease called emphysema.
What happens is that instead of having billions of very tiny alveoli, they
have millions of larger ones; this means that the surface area of their
lungs is not the size of a tennis court but just the size of a dining room
table. People with emphysema get out of breath very quickly. Even getting
out of the chair to change channels on the TV makes them puff and pant as
though they had run the marathon. Perhaps that is why we need remote
controls for our TVs and radios.
Gaseous exchange is also necessary
for photosynthesis. Green plants do respire: at night time they exchange
gases just as we do, Oxygen in and Carbon Dioxide out. In the daytime they
do just the opposite. Carbon Dioxide enters a plant because it is needed
for photosynthesis, and Oxygen leaves. This is still called gaseous
exchange.
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