Question

Please devise an experiment that you could use to quantify bacterial growth using only light. Be sure to include all materials, methods, and how you will determine results.

.Please discuss the evidence supporting the endosymbiont theory.

Answer 1

Principle :The bacterial growth can be quantified using only light via spectrophotometer. Spectrophotometer helps to measure bacterial growth based on the turbidity of the medium/cell suspensions in which the bacterial cells grow.Cells are known to absorb and scatter the light and more the cell concentration, the higher the turbidity.Optical density (OD) is always known to be directly proportional to the biomass present in the cell suspension in a given range which is usually specific for a given bacterial cell type. The amount of transmitted light through a turbid broth will go on to decrease with a subsequent increase in the absorbance value. Spectrophotometer scan thus helps to measure the intensity of light very accurately and thereby helping to quantify the bacterial growth.

Materials : Test tubes ,Bacterial cell culture in broth kept under different duration of growth conditions, spectrophotometer, cuvette.

Method :Using a spectrophotometer, take the absorbance reading at particular wavelength (specific for that bacteria say for example 650nm)) of light for blank and experimental tubes(in an increasing order of duration for growth ).Record the absorbance values

Results:Results can be determined from the absorbance values recorded.Next plot a graph with the optical density values recorded vs time of growth.This will give you the growth curve for the bacteria.We can calculate the generation time from the growth curve.