Question

A greater scattering of light in a bacterial sample, when measured by UV spectrophotometer, indicates
A. Decreased bacterial growth
B. Greater bacterial growth
C. Stable Bacterial growth
D. None of the above

Answer 1

Hint: UV spectroscopy involves the use of absorption spectroscopy and its range is 400-700nm. In this, the molecules absorb light from the ultraviolet region which causes excitation of the electrons from the ground state to higher energy states.

Complete answer: Bacterial growth culture has four phases- lag phase, log phase or exponential phase, stationary phase and death phase. Log phase is the multiplication phase of the bacteria. In this period, the number of cells and the rate of population increase of the bacteria doubles. Growth conditions and nutrients supplied in the culture medium are the factors that control this phase.
UV spectroscopy is based on the Beer-lambert law. As per this law, the rate of decrease of intensity of radiation with the thickness of absorbing solution of a monochromatic light passing through a solution of absorbing substance, is directly proportional to the incident light radiation and the concentration of the solutions.
The spectrophotometer helps in measuring the turbidity or optical density of a substance.
The culture with greater bacterial growth will have more turbidity which is the measure of the amount of light absorbed by bacterial suspension. So the degree of turbidity tells us about the number of microorganisms or bacteria present which is also called the microbial density.
So, the correct answer is “Option B”.

Note: This is a simple method for measuring the rate of increase in cell growth of an organism. Increased microbial mass of solution is reflected by the increased turbidity of broth medium. There is an increase in the absorbance value, with the decrease in the amount of transmitted light.