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, we need to understand the process of oxygen consumption in a growing culture of Escherichia coli bacteria. Let's break down each question and explain how to get the answers:

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 could be due to the bacteria utilizing alternative carbon sources present in the culture media, such as amino acids or organic compounds. To confirm this, you can perform an experiment by adding glucose to the culture and observe if the oxygen consumption rate increases significantly.

2. 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?
In this case, we need to calculate the rates of oxygen consumption. Rate is defined as the change in quantity (in this case, DO levels) per unit time. The consumption rates can be calculated by dividing the change in DO levels by the corresponding time intervals. For the first case, the rate would be 0.5 mg/l per min, while for the second case, the rate would be 0.5 mg/l per min as well because the change in DO levels is the same even though the time interval is longer.

3. What might be responsible for the slight delay in the rate of O2 consumption after injecting glucose?
The slight delay in the rate of oxygen consumption after injecting glucose could be attributed to the time required for the bacteria to initiate the metabolic pathways involved in utilizing glucose. The cells may need some time to adjust and activate enzymes necessary for glucose metabolism, leading to the observed delay.

4. How might your measurements of oxygen consumption rate be affected if the cells in your culture grow and increase in number during the lab period?
As the number of cells in the culture increases, the oxygen consumption rate may also increase. This is because a larger population of cells requires more oxygen for metabolic activities. Therefore, if the cells in the culture are growing and increasing in number during the lab period, the measurements of oxygen consumption rate could be higher compared to an initial time point when the cell population was smaller.

5. If you have 10 ml of a culture of cells with 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 diluted culture, you need to understand the relationship between absorbance and concentration. Absorbance is directly proportional to the concentration of the absorbing substance. Therefore, if you dilute the culture by bringing its volume up to 50 ml with fresh medium, the absorbance will remain the same. So the absorbance would still be 0.5 A650 units.