Growth is defined as an increase in the size and weight of an organism due to synthesis of new protoplasm.
The growth of multi-cellular organisms is of four kinds with regard to the growth and multiplication of the body cells.
Two patterns of growth are commonly seen in animals regarding the proportion of the various body parts.
If the tail of a house lizard is cut, the missing part develops again from the remaining part of the tail. In some cases, regeneration is so advanced that an entire multicellular body is reconstructed from a small fragment of tissue. Our body spontaneously loses cells from the surface of the skin and replaced by newly formed cells. This is due to regeneration.
Ageing can be defined as the progressive deterioration in the structure and function of the cells, tissues, organ and organ systems of the organism with advancing age.
Many theories have been proposed to explain the process of ageing.
Growth is an irreversible increase in size and weight of an organism. The cells of the body do not grow uniformly but differentially. The main types of growth are auxetic, multiplicative and accretionary. The human growth curve is sigmoid and is controlled by hormones.
Accretionary growth: Post embryonic growth in some special cells to reinforce and replace the worn out differentiated cells.