Questions 27-32 - Few words to say about this book

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READING PASSAGE 6
HOW DOES THE BIOLOGICAL CLOCK TICK?
A
Our life span is restricted. Everyone accepts this as ‘biologically’ obvious. ‘Nothing lives for ever!’ However,
in this statement we
think of artificially produced, technical objects, products which are subjected to natural
wear and tear during use. This leads to the result that at some time or other the object stops working and is
unusable (‘death’ in the biological sense). But are the wear and tear and loss of function of technical objects
and the death of living organisms really similar or comparable?
B
Our ‘dead’ products are ‘static’, closed systems. It is always the basic material which constitutes the object and
which, in the natural course of things, is worn down and becomes ‘older’. Ageing in this case
must occur according to the laws of physical chemistry and of thermodynamics. Although the same law
holds for a
living organism, the result of this law is not inexorable in the same way. At least as long as a
biological system has the ability to renew itself it could actually become older without ageing; an organism is
an open, dynamic system through which new material continuously flows. Destruction of old material and
formation of new material are thus in permanent dynamic equilibrium. The material of which the organism is
formed changes continuously. Thus our bodies continuously exchange old substance for new, just like a
spring which more or less maintains
its form and movement, but in which the water molecules are always
different.
C
Thus ageing and death should not be seen as inevitable, particularly as the organism possesses many
mechanisms for repair. It is not, in principle, necessary for a biological system to age and
die. Nevertheless, a restricted life span, ageing, and then death are basic characteristics of life.
The reason
for this is easy to recognise: in nature, the existent organisms either adapt or are regularly replaced by new
types. Because of changes in the genetic material (mutations) these have new characteristics and in the course
of their individual lives they are tested for optimal or better adaptation to the environmental conditions.
Immortality would disturb this system - it needs room for new and better life. This is the basic problem of
evolution.
D
Every organism has a life span which is highly characteristic. There are striking differences in life span
between different species, but within one species the parameter is relatively constant. For example, the
average duration of human life has hardly changed in thousands of years. Although more and more
people attain an advanced age as a result of developments in medical care
and better nutrition, the
characteristic upper limit for most remains 80 years. A further argument against the simple wear and
tear theory is the observation that the time within which organisms age lies between a few days (even a few
hours for unicellular organisms) and several thousand years, as with mammoth trees.
E
If a life span is a genetically determined biological characteristic, it is logically necessary to propose
the existence of an internal clock, which in some way measures and controls the ageing process and which
finally determines death as the last step in a fixed programme. Like
the life span, the metabolic rate has for
different organisms a fixed mathematical relationship to the body mass. In comparison to the life span this
relationship is ‘inverted’: the larger the organism the lower its metabolic rate. Again this relationship
is valid not only for birds, but also, similarly on average within the systematic unit, for all other
organisms (plants, animals, unicellular organisms).
F
Animals which behave ‘frugally’ with energy become particularly old, for example, crocodiles and tortoises.
Parrots and birds of prey are often held chained up. Thus they are not able to ‘experience life’ and so
they attain a high life span in captivity. Animals which save energy by hibernation or lethargy (e.g. bats or
hedgehogs) live much longer than those which are always active. The metabolic rate
of mice can be reduced by
a very low consumption of food (hunger diet). They then may live twice as long as their well fed
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comrades. Women become distinctly (about 10 per cent) older than men. If you examine the metabolic rates of
the two sexes you establish that the higher male metabolic rate roughly accounts for the lower male life span.
That means that they live life ‘energetically’ - more intensively, but not for as long.
G
It follows from the above that sparing use of energy reserves should tend to extend life. Extreme high
performance sports may lead to optimal cardiovascular performance, but they quite certainly do not prolong
life. Relaxation lowers metabolic rate, as does adequate sleep and in general an equable and balanced
personality. Each of us can develop his or her own ‘energy saving programme’ with a little self-observation,
critical self-control and, above all, logical consistency. Experience will show that to
live in this way not only
increases the life span but is also very healthy. This final aspect should not be forgotten.