R18 – How does the biological clock tick?


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1Our life span is restricted. 2Everyone accepts this as ‘biologically’ obvious. 3‘Nothing lives for ever!’ 4However, in this statement we think of artificially produced, technical objects, products which are subjected to natural wear and tear during use. 5This leads to the result that at some time or other the object stops working and is unusable (‘death’ in the biological sense). 6But are the wear and tear and loss of function of technical objects and the death of living organisms really similar or comparable?


1Our ‘dead’ products are ‘static’, closed systems. 2It is always the basic material which constitutes the object and which, in the natural course of things, is worn down and becomes ‘older’. 3Ageing in this case must occur according to the laws of physical chemistry and of thermodynamics. 4Although the same law holds for a living organism, the result of this law is not inexorable in the same way. 5At 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. 6Destruction of old material and formation of new material are thus in permanent dynamic equilibrium. 7The material of which the organism is formed changes continuously. 8Thus 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.


1Thus ageing and death should not be seen as inevitable, particularly as the organism possesses many mechanisms for repair. 2It is not, in principle, necessary for a biological system to age and die. 3Nevertheless, a restricted life span, ageing, and then death are basic characteristics of life. 4The reason for this is easy to recognise: in nature, the existent organisms either adapt or are regularly replaced by new types. 5Because 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. 6Immortality would disturb this system – it needs room for new and better life. 7This is the basic problem of evolution.


1Every organism has a life span which is highly characteristic. 2There are striking differences in life span between different species, but within one species the parameter is relatively constant. 3For example, the average duration of human life has hardly changed in thousands of years. 4Although 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. 5A 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.


1If 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. 2Like the life span, the metabolic rate has for different organisms a fixed mathematical relationship to the body mass. 3In comparison to the life span this relationship is ‘inverted’: the larger the organism the lower its metabolic rate. 4Again 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).


1Animals which behave ‘frugally’ with energy become particularly old, for example, crocodiles and tortoises. 2Parrots and birds of prey are often held chained up. 3Thus they are not able to experience life’ and so they attain a high life span in captivity. 4Animals which save energy by hibernation or lethargy (e.g. bats or hedgehogs) live much longer than those which are always active. 5The metabolic rate of mice can be reduced by a very low consumption of food (hunger diet). 6They then may live twice as long as their well fed comrades. 7Women become distinctly (about 10 per cent) older than men. 8If 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. 9That means that they live life ‘energetically’ – more intensively, but not for as long.


1It follows from the above that sparing use of energy reserves should tend to extend life. 2Extreme high performance sports may lead to optimal cardiovascular performance, but they quite certainly do not prolong life. 3Relaxation lowers metabolic rate, as does adequate sleep and in general an equable and balanced personality. 4Each of us can develop his or her own ‘energy saving programme’ with a little self-observation, critical self-control and, above all, logical consistency. 5Experience will show that to live in this way not only increases the life span but is also very healthy. 6This final aspect should not be forgotten.


Questions 27-32

Reading Passage 3 has seven paragraphs, A-G.

Choose the correct heading for paragraphs B-G from the list of headings below.

Write the correct number, i-x, in boxes 27-32 on your answer sheet.

List of Headings

i   The biological clock

ii   Why dying is beneficial

iii   The ageing process of men and women

iv   Prolonging your life

v   Limitations of life span

vi   Modes of development of different species

vii   A stable life span despite improvements

viii   Energy consumption

ix   Fundamental differences in ageing of objects and organisms

x   Repair of genetic material


Paragraph A




32  Paragraph B

33  Paragraph C

34  Paragraph D

35  Paragraph E

36  Paragraph F

37  Paragraph G


Questions 33-36

Complete the notes below.

Choose NO MORE THAN TWO WORDS from the passage for each answer.

Write your answers in boxes 33-36 on your answer sheet.

  • Objects age in accordance with principles of 33 ………………and of 34 ……………..
  • Through mutations, organisms can 35…………………..better to the environment
  • 36 …………………….. would pose a serious problem for the theory of evolution


Questions 37-40

Do the following statements agree with the views of the writer in Reading Passage?

In boxes 37-40 on your answer sheet, write

YES                 if the statement agrees with the views of the writer

NO                   if the statement contradicts the views of the writer

NOT GIVEN    if it is impossible to say what the writer thinks about this

37  The wear and tear theory applies to both artificial objects and biological systems.

38  In principle, it is possible for a biological system to become older without ageing.

39  Within seven years, about 90 per cent of a human body is replaced as new.

40  Conserving energy may help to extend a human’s life