Measurement Of Growth : [Cell Density]

Measurement Of Growth -

[III] Cell Density :

Turbidity :

Growth is defined as an increase in mass and one can also measure any growth parameter.

Cell density refers to the number of cells per unit volume. Often cell density is denoted as viable cell density which is the number of living cells per unit volume.

The density (ρ) of a cell is defined by its relative water (ρ = 1 g/ml) content and the composition of its dry mass.

Example :

Cell Number , Turbidity and Protein provided it increases proportionally to the mass of the culture.

You can observe the following photo showing broth media both having liquid media but one different each other because in left of image you can clearly observe the turbidity while other is without bacterial introduction.

The amount of light scattered by bacterial cell is proportional to its mass.If the average mass mass per cell remains constant then one can also use light scattering to measure changes in the cell number.More dense the culture,less light is transmitted this relationship is given by 

Beer's-Lambert Law :

The Beer-Lambert law states that there is a linear relationship between the concentration and the absorbance of the solution, which enables the concentration of a solution to be calculated by measuring its absorbance.

          Expression Of Beer-Lambert Law

Turbidity is directing proportional to cell mass it is measured by colorimeter Spectrophotometer.

In practice one construct a Standard Curve by measuring the turbidity of several different cell suspensions where the cell number is counted independently and generates a straight line graph.

Whenever turbidity measurements are made on unknown sample a standard curve must be constructed to determine thr cell density.

           Spectrophotometer & Sample