Question
TOPIC 8.4 Effect of Density on Populations
(a) – TOPIC 8.4 Effect of Density on Populations
(b) – TOPIC 8.4 Effect of Density on Populations
(c) – TOPIC 8.4 Effect of Density on Populations
(d) -TOPIC 8.4 Effect of Density on Populations
Bacteria can be cultured in media with a carefully controlled nutrient composition. The graph above shows the growth of a bacterial population in a medium with limiting amounts of two nutrients, I and II.
(a) Estimate the maximum population density in \(\frac{cells}{mL}\) for the culture. Using the data, describe what prevents further growth of the bacterial population in the culture.
(b) Using the data, calculate the growth rate in \(\frac{cells}{mL\times hours}\) of the bacterial population between hours 2 and 4.
(c) Identify the preferred nutrient source of the bacteria in the culture over the course of the experiment. Use the graph to justify your response. Propose ONE advantage of the nutrient preference for an individual bacterium.
(d) Describe how nutrient I most likely regulates the genes for metabolism of nutrient I and the genes for metabolism of nutrient II. Provide TWO reasons that the population does not grow between hours 5 and 6.
Answer/Explanation
Ans:
(a) Estimate the maximum population density in \(\frac{cells}{mL}\) for the culture. Using the data, describe what prevents further growth of the bacterial population in the culture. (2 points)
Estimate (1 point)
• 108
Description (1 point)
• When both nutrients are depleted
(b) Using the data, calculate the growth rate in \(\frac{cells}{mL\times hours}\) of the bacterial population between hours 2 and 4. (1 point).
Calculation (1 point)
• 4,995
(c) Identify the preferred nutrient source of the bacteria in the culture over the course of the experiment. Use the graph to justify your response. Propose ONE advantage of the nutrient preference for an individual bacterium. (3 points)
Identification (1 point)
• Nutrient I is the preferred nutrient.
Justification (1 point)
• When both nutrients are present in the growth medium, only nutrient I is used.
• Nutrient II is only used after nutrient I is depleted.
Proposed advantage (1 point)
• Do not spend energy making enzymes/proteins that the cell doesn’t need.
• Do not have to express all metabolic genes at once.
• The preferred nutrient provides more energy.
(d) Describe how nutrient I most likely regulates the genes for metabolism of nutrient I and the genes for metabolism of nutrient II. Provide TWO reasons that the population does not grow between hours 5 and 6. (4 points)
Description (2 points)
• Nutrient I promotes expression of genes required for metabolism of nutrient I.
• Nutrient I represses expression of genes required for metabolism of nutrient II.
Reasoning (2 points)
• Nutrient I is depleted from the growth medium OR neither nutrient is being consumed.
• Takes time to produce proteins/enzymes required to metabolize nutrient II.
The maximum bacterial population density is 108 cells/ml in this allele. Further grow beyond this point is prevented by limited resources; both nutrient 1 and nutrient 2 are entirely depleted.
The grow rate between users 2 and y is
\(\frac{10^{4}cels/mL -10^{1}cels/mL – }{2h/s}= \frac{4995 cells}{mL\times hr}\)
The bacteria prefer nutrient 1, as evidenced by the fact that they consume nutrient I first, as shown by nutrient I’s depletion prior to nutrient II’s depletion. The amount of nutrient II only begins so decline, or be consumed, once nutrient I is already gone. Nutrient I probably is a more efficient source of energy, d, in oval welds, requires the bacteria to expend less energy relative to the energy gained from the nutrient. This preference could be an advantage to an individual bacterium because it could then expand more energy on preproduction.
When nutrient I is present in the environment, it turns on the genes that allow the bacteria to digest nutrient I. It presently dues this by activity a phosphorylation cascade that practices a mole ale that binds to the promoter and allow RNA polymerase to bind. This allows the genes to be transcribed, leading to the upto the and consumption of nutrient I. As the same time, nutrient I probably also prevents the genes for digesting nutrient II from being dronouribed, giving the bacteria a preference for nutrient I, It probably does this through a phosphorylation wocade that an inhibitions that prevent RNA polyomas, from bindery s the genes for nutrient II. Only when nutrient I is absent will nutrient II be absolved.
The population does not grow between hours 5 and 6 because it is not consuming nutrients. It could not be consuming nutrient II because it takes time so the inhibitor caused by nutrient I to be released so that the goes for consuming nutrient II can be transcribed. alternately, the inhibition could be released quickly but the proteins to update nutrient II could take a long time so produce, and thus the population does not consume nutrients for that now. Perhaps the bacteria have a mechanism for waiting after the depletion of nutrient I to see if more nutrient will become available before turning to nutrient II.