A level Biology exam revision resources written by A level Examiners


Senescence is the deterioration of bodily functions and the appearance of features associated with old age.

  • There are effects on skin which cause the characteristic wrinkling associated with ageing. This occurs because collagenase is produce which alters the structure of collagen in the skin. The altered collegen makes to skin less elastic due to the presence of cross-links in the elastin and collagen fibres. This cross linking occurs in all connective tissues and is one of the main causes of the reduced organ efficiency associated with ageing.
  • Genetic errors accumulate in all tissues - this leads to an increased incidence of cancers.
  • Degeneration of tissues - due to 'wear & tear' especially on joints. Arthritis and a reduction in ease of movement are the main two results of this.
  • With increasing age there is a natural increase in the amount of arteriosclerosis / atherosclerosis which reduces the efficiency of the circulatory system.
  • Decreased organ function, metabolic rate and lung capacities.
  • The immune system efficiency decreases and the incidence of autoimmune diseases increases.
  • In women osteoporosis can occur due to loss of calcium from bones.
  • The is a lower rate of nervous conduction which leads to reduced reaction times.
  • As brain cells are not replaced after adolescence there is a loss of brain cells which causes slower responses, slower learning ability and loss of memory.

There are two main types of investigation used to investigate growth and aging. These are:

  1. Cross Sectioned Studies = Studying large samples of people at several ages. In the case of research into ageing measurements of physical and physiological features are taken and averages for the different age groups established.

    The advantages of this technique are that it can be performed in a short period of time and the data collected can be analysed immediately. Also it is easy to monitor large numbers of people, and you don't lose track of subjects as measurements only need to be taken once.

    There is one main disadvantage of this type of study in that the data collected are averages, and do not necessarily give a good representation of what happens to individuals.

  2. Longitudinal Studies = Studying a small sample of people and taking measurements on them at several intervals over time (the time period involved is normally several years).

    The advantages of this technique are that it is more representative of the individuals involved and detail is not lost by averaging the data.

    The main disadvantages of this technique are that it takes a long time before the data generated can be analysed. Also individuals may drop out of the study at any time reducing the amount of data that can be obtained.

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