Write an account of the growth curve analysis of a microorganism.
The growth of cultured microorganisms can be analysed by plotting the logarithm of the number of viable cells versus the incubation time, which results in a curve with four distinct phases: lag phase, exponential phase, stationary phase, and decline phase.
In the lag phase, there is no immediate increase in cell number or net increase in mass. During this period, the cell is metabolically active and synthesising new components required for cell division.
During the exponential phase, unicellular organisms divide by binary fission. This leads to an exponential increase in the number of cells, where one cell divides into two, two into four, and so on.
In the stationary phase, population growth ceases and the growth curve becomes horizontal. The total number of viable microorganisms remains constant due to a balance between cell division and cell death. This phase occurs due to factors like limited nutrient availability.
Finally, in the decline phase, the accumulation of metabolic waste products leads to a decline in population growth. For example, Streptococci produce lactic acid from sugar fermentation, making the medium acidic and inhibiting growth.
Explanation
The answer is derived from the section '6.6 THE GROWTH CURVE'. It defines the growth curve analysis method (plotting log of viable cells vs time) and systematically describes the four phases mentioned in the text: Lag, Exponential, Stationary, and Decline. Specific details like the synthesis of components in the lag phase, binary fission in the exponential phase, the balance of division and death in the stationary phase, and the effect of waste products like lactic acid in the decline phase are included to ensure the 5-mark requirement is met.