TOPIC 01-GROWTH AND DEVELOPMENT
GROWTH
Refers to the irreversible (permanent) increase in size and mass of an organism.
Reproduction results in the formation of new organisms. Every newly produced organism is usually small in size, with time the organism increase in size and weight.
In multicellucar organisms the increase in size and weight is a result of the increase in the number and size of body cells. As the number of cells increases various organs are formed. - The changes can take place only if energy and raw materials are available. The energy and raw materials are derived from food. Because raw materials are used, growth brings about an increase in the mass of an organism.
In some multicellular organisms as new cells are formed some old cells usually die off. In such cases there is therefore a continuous addition and less of cells. But for growth to occur the rate of cell increase must exceed the rate of cell less.
When the rate of cell increase is higher than the rate of cell less growth is referred to as
POSITIVE GROWTH.
When the rate of cell increase is lower than the rate at which cells are lost from the body, the organism decrease in size and weight. This is also growth and it is referred to as NEGATIVE GROWTH. It may be caused by an illness or starvation.
It should be noted however that negative growth cannot go on indefinitely. An organism cannot resume the size , weight and body shape of a newly born body. For this reason growth is said to be irreversible.
IMPORTANCE OF GROWTH IN LIVING THINGS
Life usually starts as a single cell e.g a human zygote (fertilized egg) give rise to billions of different cells etc.
During growth and development the cells divide and enlarge giving rise to a more complex and elaborate multicellular organism.