Please help with these questions
question: Oxygen consumption by a growing culture of Escheri...
oxygen consumption by a growing culture of Escherichia coli bacteria.
What could explain the gradual consumption of oxygen, even though no glucose has yet been added to the culture?
If the DO levels drop by 0.5 mg/l in a period of 1 min, and by 1.0 mg/l during
the following 2 min, do those represent different rates of O2 consumption?
You may have observed that after injecting the glucose there was a slight
delay before the rate of O2 consumption changed significantly. What might
be responsible for that delay
If the cells in your culture grow and increase in number during the course of
the lab period, how might your measurements of oxygen consumption rate be
affected?
If you have 10 ml of a culture of cells that has an absorbance of 0.5 A650 units,
what would its absorbance be if you brought its volume up to 50 ml with fresh
medium?
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To answer these questions, let's start with some background knowledge on oxygen consumption by Escherichia coli (E. coli) bacteria cultures.
1. What could explain the gradual consumption of oxygen, even though no glucose has yet been added to the culture?
The gradual consumption of oxygen in the absence of glucose could be due to E. coli bacteria utilizing other carbon sources present in the culture media, such as amino acids or organic acids. These alternative carbon sources can undergo metabolic processes that consume oxygen.
2. If the Dissolved Oxygen (DO) levels drop by 0.5 mg/l in a period of 1 min, and by 1.0 mg/l during the following 2 min, do those represent different rates of O2 consumption?
Yes, the difference in DO levels dropping by 0.5 mg/l in 1 minute and by 1.0 mg/l in the subsequent 2 minutes implies different rates of oxygen consumption. The rate calculation can be done by dividing the change in DO level by the time taken. In this case, the first scenario has a rate of 0.5 mg/l per minute, while the second scenario has a rate of 0.5 mg/l per minute. Therefore, the rates are different.
3. You may have observed that after injecting glucose, there was a slight delay before the rate of oxygen consumption changed significantly. What might be responsible for that delay?
The delay before the rate of oxygen consumption changed significantly after injecting glucose could be attributed to the time required for the E. coli bacteria to take up and metabolize the glucose. The bacteria need to activate the necessary transporters and enzymes to utilize the glucose as an energy source, leading to a delay in the increased oxygen consumption rate.
4. If the cells in your culture grow and increase in number during the course of the lab period, how might your measurements of oxygen consumption rate be affected?
As the cells in the culture grow and increase in number, the oxygen consumption rate may increase. This is because a larger number of cells will require more oxygen for their metabolic processes. Therefore, the measurements of oxygen consumption rate will be influenced by the growth of the culture.
5. If you have 10 ml of a culture of cells that has an absorbance of 0.5 A650 units, what would its absorbance be if you brought its volume up to 50 ml with fresh medium?
To calculate the absorbance of the culture when its volume is increased, you need to understand Beer-Lambert's Law. According to this law, absorbance is directly proportional to the concentration of a solute in a solution. Therefore, if you dilute the culture by increasing its volume to 50 ml with fresh medium while keeping the same concentration of cells, the absorbance will remain the same at 0.5 A650 units.