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?
Question: What could explain the gradual consumption of oxygen, even though no glucose has yet been added to the culture?
Answer: The gradual consumption of oxygen in the absence of glucose can be attributed to the cells in the culture utilizing other carbon sources present in the medium. Bacteria like Escherichia coli have the ability to utilize alternative carbon sources, such as amino acids or organic acids, for energy production through various metabolic pathways. Therefore, the bacteria may still consume oxygen as they metabolize these carbon sources.
To confirm this, you can perform a control experiment where you provide a medium without any carbon sources other than oxygen. If there is no oxygen consumption observed in this control, it would support the hypothesis that alternative carbon sources are being utilized by the bacteria.
Question: 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?
Answer: Yes, the rate of oxygen consumption can be determined by examining the change in dissolved oxygen (DO) levels over a given time period. In this scenario, if the DO levels drop by 0.5 mg/l in 1 minute and by 1.0 mg/l in the following 2 minutes, the rate of oxygen consumption during the first minute would be (0.5 mg/l) per minute, while the rate during the subsequent 2 minutes would be (1.0 mg/l) per 2 minutes.
To calculate the rate of oxygen consumption more precisely, you can convert the changes in DO levels to a rate per unit time. For example, if the DO levels drop by 0.5 mg/l in 1 minute, the rate of oxygen consumption would be 0.5 mg/l per minute. Similarly, if the DO levels drop by 1.0 mg/l in 2 minutes, the rate would be 0.5 mg/l per minute. Therefore, the rates of oxygen consumption are the same in this case.
Question: 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?
Answer: The delay in the change of oxygen consumption rate after injecting glucose can be explained by the time required for bacterial cells to recognize the presence of glucose and activate the necessary metabolic pathways for glucose utilization. This delay is often referred to as the "lag phase."
During this lag phase, the bacterial cells need to adjust their gene expression patterns, switch from utilizing alternative carbon sources to glucose metabolism, and optimize their metabolic machinery for efficient glucose utilization. These processes take some time, leading to the observed delay before a significant change in the oxygen consumption rate occurs.
Question: 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?
Answer: If the cells in the culture grow and increase in number during the lab period, it is likely to affect the measurements of oxygen consumption rate. As the number of cells increases, the overall metabolic activity of the culture increases as well. Consequently, more oxygen will be consumed due to the higher metabolic demand of a larger cell population.
To accurately measure the oxygen consumption rate, it is important to consider and control for the cell growth during the experimental period. This can be achieved by measuring the oxygen consumption rate per unit of biomass or per unit of cell density (e.g., oxygen consumption rate per OD unit). This normalization allows you to compare the metabolic activity of the cells, accounting for differences in cell number or growth.
Question: 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?
Answer: Absorbance (A650) is a measure of the optical density of a culture, often used as an indirect estimate of cell density. To determine the absorbance of a culture when its volume is increased, you need to consider the dilution factor caused by adding fresh medium.
In this case, the initial culture has a volume of 10 ml and an absorbance of 0.5 A650 units. If you bring the volume up to 50 ml with fresh medium, you are essentially diluting the culture by a factor of 5 (50 ml / 10 ml = 5).
During dilution, the absorbance is also diluted by the same factor. Therefore, to calculate the final absorbance of the diluted culture, you need to divide the initial absorbance by the dilution factor. In this case, dividing 0.5 A650 by 5 (dilution factor) gives you a final absorbance of 0.1 A650 units when the volume is brought up to 50 ml with fresh medium.