Theory of Ageing – Gerontology Biology

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Ageing is a slow deterioration in the structure or function of tissues, body cells, or organs of an animal and starts after the adulthood. Aging was first described by Huxley.

The branch of biology which is dealing the study of processes of ageing is known as gerontology.

Characteristics of Aging

(a) The power of replacing the worn out cells are decrease.

(b) The metabolic activities are decline gradually.

Theories of Ageing

(a) Wear or Tear theory-It states that tissues or cells of the body are always subjected to wear and tear process according to intrinsic or extrinsic factors.

(b) Metabolic theory-According to this theory those organisms which have higher metabolic rate, maturity, age or die earlier than those organisms that have low metabolic rate or they take years to age or years to mature.

(c) Mutation theory-This theory says that ageing is due to somatic mutations which is caused by unsuitable environmental factors such as X-rays that produce defective protein leading to ageing.

(d) Collagen theory-It says that ageing is induced by changes in the collagen protein which is in the interstitial fluid that surrounding the body cells.

(e) Genetic theory- According to this, ageing is an intrinsic phenomena that is controlled by some genetic timetable of genome that induces ageing at specific time or period.

Changes in Ageing

(A)Morphological and physiological changes

(1) Lung-Vital capacity of lungs in old age is decrease to 44%.

(2) Heart-The efficiency of heart is also decreases with age, that’s why heart pumps only 65% blood per minute in his comparison to young age. So blood supply to the various organs like kidney, brain also decrease because of this efficiency of these organs is highly affected.

(3) Kidneys-The numbers of nephrons in kidneys in old age is also decrease to 56%, rate of glomerular filtration falls to 69%, so the amount of urine output during old age is also decrease.

(4) Number of taste buds falls to 36% in old age.

(5)Skin problems are also occoured like dry or wrinkled skin as water holding capacity of body cells decreases.

(6) Blood volume is decreas in old age as rate of haemopoiesis decreases.

(7) Body becomes shriveled, thin or stooping.

(8) After the age of 10 years decline in hearing power is begin.

(9) Increased of mineral deposition in the bones that becomes easily or brittle fracturable.

(10) Changes in the immune system can be important in the ageing process .During ageing the immunity system loses the ability to react to the antigen. The resistance of disease is decrease, T-lymphocytes reduced in function.

(11) Weight of brain is decreased to 56%, number of axons reduce to 63% while speed of nerve impulses in nerve fiber reduced to 90%.Memory is impaired.


Death is the final stopping and permanent breakdown of vital functions. Death is an essential biological phenomena because it control or prevent the overcrowding of a members of a specific species on earth.

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