INTRODUCTION

INTRODUCTION 

Growth is permanent and irreversible increase in size. It is brought about by the increase in the number of cells, cell division, cell enlargement and cell differentiation.

Growth is measured using a growth curve.

This is a curve obtained when data collected during stages of growth is plotted against time.

Growth in many organisms tends to be similar whereby there is rapid growth, average growth and finally slow growth.

This pattern gives an S  shaped curve known as sigmoid curve. When sigmoid curve is closely analyzed, four distinct phases are obtained. These are;

• Lag phase
• Log phase
• Exponential phase
• Linear or decelerating phase
• Stationary phase

The phases are described below;

1.Lag phase.

Is the phase where the rate of growth is very slow.

During this period, called the lag phase, the cells are metabolically active and increase only in cell size.

They are also synthesizing the enzymes and factors needed for cell division and population growth under their new environmental conditions.

2.Exponential phase

This phase involves very rapid or exponential growth. The number of dividing cells is very high than the shed off cells. New tissues are formed.

3.Decelerating phase

This involves the decline in the rate of growth. As maturity approaches, the rate of cell divison decreases. The ability of cells to divide declines as the cells mature.

4.Plateau /stationary phase 

Marks the period where there is no change in the size of the organism. The organism has attained maturity. The cells are formed only to replace those which are worn out.