Question

this is a bacterial growth curve experiment . please explain rhe results

Procedure: You will follow the growth of E. coli over the course of the period (3 hrs) by making direct counts of the bacterial suspension by measuring the turbidity of a sample at a given time with a spectrophotometer. The data obtained from the direct counts will be used to plot a partial growth curve. Summary: Turbidity Counts with the Spectrophotometer to measure absorbance at 600. Direct Counts with a Hemocytometer and cells stained with crystal violet. 1. Turn on the spectrophotometer at least 15 minutes prior to use. Set the unit to "absorbance" and the wavelength to OD.00. 2. The class is provided a 250 ml Erlenmeyer flask of with 190 ml nutrient media. Add 10ml of 40% glucose for a final concentration of 2% glucose and final volume of 200 ml. 3. Remove 10 ml of the growth media-glucose mixture from the flask and place into a separate spectrophotometer tube to use as a blank for the spectrophotometer (no bacteria). 4. Insert the media blank into the spectrophotometer and adjust the spectrophotometer dial to zero. **Do not adjust the dials on the spectrophotometer after you blank it or your future readings will be incorrect. 5. Add 10 ml of E. coli stock culture provided to the 190 ml media-glucose mixture for a 1:20 dilution and homogenize. 6. Remove 7 ml of the E. coli growth mixture from the flask, place in a spectrophotometer tube and immediately measure the OD600. This is the T-O absorbance. 7. Add one drop of crystal violet to the spectrophotometer tube. (At about T3 first dilute the culture 1:100) Mix well and let sit for 5 min. Fill a hemocytometer counting chamber and let sit for 5 min. Count at least 100 cells and 3 of the smallest boxes. Record current direct count concentration - (Ave. cell count x 2.5*10-?)/Dilution. 8. Keep the flask containing the E. coli growth media-glucose mixture in the 37°C orbital shaker

Answer 1

When more time will be spent , the turgidity of the solution will be increased as the numbers of the bacteria will also be increased .

And thus the absorbance will also be increased and when this will go to the maximum it means the bacteria has been grown to a saturation level then when you are diluting the sample it is again getting more place and it will then be divided again and similar pattern of ABSORBANCE will be seen.