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eval_testing_mns

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Accumulation of lactic acid results in muscular pain. If we take walk,
brisk walk, slow jogging, running for same distance we feel that there an
increase in pain levels this is because of lactic acid accumulation.
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It seems as if the lactic acid was being produced rapidly by the active
muscles, and then only gradually removed from the blood after exercise.
What is surprising is that the athlete needs a great length of time to recover.
The simplest explanation we can produce at-this stage is that the sugar in
the working muscles was being changed to lactic acid. The energy stored
LA
in lactic acid molecules is less than that in sugar molecules, and if the acid
comes from the sugar then the energy released could be used to rebuild
ATP from ADP and phosphate.
During a 100 m race a well-trained athlete can hold his breath all the
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time it is not until afterwards that he pants. In this case, the muscles are
using the energy released during the anaerobic breakdown of glucose. It is
not until afterwards that the athlete obtains the oxygen needed in order to
remove the lactic acid. Therefore, when we under-take strenuous exercise
we build up what is called an oxygen debt which has to be repaid later. In a
longer race athletes have to breathe all the time, so some lactic acid is
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removed while they are running, and they can go on for longer before
becoming exhausted. The presence of lactic acid in the blood is the main
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cause of muscle fatigue, but if the body is rested for long enough the
tiredness goes.
Anaerobic respiration
We have found that living things produce carbon dioxide and give out
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energy. If these processes are caused by an oxidation process, what happens
if the oxygen supply is cut off? If human muscles can go on releasing
energy when they are short of oxygen, what can cells of other living
organisms do?
Let us find out by doing some experiments.
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36 X Class Respiration - The energy releasing system
Lab Activity
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Some experiments with yeast
To test this idea we can see whether it is possible to detect any rise in
temperature and the production of carbon dioxide, when living organisms
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are kept away from a supply of oxygen.
Yeast grows rapidly if it is supplied with thermometer
glucose in solution. Indeed, wild yeasts are
normally found growing on the skins of fruits
like grapes and apples, from which they derive
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their food supplies. Our immediate problem is
to remove the oxygen from the glucose
solution and yeast.
Arrange the apparatus as shown in fig. 12 liquid paraffin
lime water
1. You can remove dissolved oxygen from glu-
cose solution by heating it for a minute, and yeast in boiled and
LA cooled glucose
then cooling it without shaking. Now put in
some yeast; the supply of oxygen from the
fig-12: Testing for production of heat and
air can be cut off by pouring one centimetre
CO2 under anaerobic respiration
layer of liquid paraffin on to the mixture.
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2. If you wish to check that the oxygen has been removed from the mix-
ture, add a few drops of diazine green (Janus Green B) solution to the
yeast suspension before you pour the liquid paraffin (wax) over it.
This blue dye turns pink when oxygen is in short supply around it.
3. Arrange for any gas produced by the yeast to escape through a wash