Lecture 9: Population growth Flashcards
What is the formulation for population growth during active growth.
2^n
What is the difference between synchronous and asynchronous growth?
Asynchronous growth is when the timing of cell division is random, and it produces a smooth exponential growth plot. Synchronous growth is when cells divide at the same time, and it produces a stepwise growth plot.
What are the two ways to plot asynchronous growth?
Along an exponential curve with time on the x axis and population on the y axis or along a linear curve with time on the x axis and the logarithm of population on the y axis.
Describe the growth curve of a synchronous culture.
It is a stepwise curve. As time passes, the steps begin to lose their definition as the cells fall out of synch. `
Growth rate is also called […] or [..]
Doubling time, generation time
What is the definition of generation time?
The period required for a cell just after division to enlarge, divide, and produce two daughter cells.
All cells in a population have [the same/a different] doubling time assuming the same growth condition for all.
The same
Generation time can vary with […]
The availability of nutrients
Explain how generation time varies with the availability of nutrients.
In a closed environment, a population will grow quickly when there are a lot of nutrients. As this happens, there will be an accumulation of toxic metabolic compounds and nutrient availability will go down, slowing generation time.
We would expect the growth time of E. coli in the lab to be [longer/shorter] than it is in the gut, because […]
Shorter, because in the gut it has to compete with other organisms for limited nutrients.
Doubling time is determined by looking at the […] portion of the growth curve.
Exponential phase, which is the (logarithmic) linear portion
Name the four major phases of growth.
Lag phase, exponential phase, stationary phase, death phase
Explain what happens in the lag phase of growth.
It is time for cells to adjust to a fresh or new medium and restart their metabolism and start dividing
Explain what happens in the exponential phase of growth
This is the period where nutrients are not in limiting amounts and where cells divide at their maximum speed (where they have their lowest doubling time).
Explain what happens in the stationary phase of growth.
The culture switches over once the nutrient concentration has become limiting and toxic waste begins to accumulate. Cells divide slower and eventually stop growing (doubling time gradually increasing)
Explain what happens in the death phase of growth.
Nutrients have been completely consumed and cells are starting to burst and die, although not all cells die.
The stopping of growth occurs in the […] phase of growth.
Stationary
Name 5 reasons why the lag phase of growth might be longer than standard.
- Inoculum taken from an old culture
- Inoculum taken from a rich medium and added to a poorer one
- Inoculum taken from a chemically different medium
- Inoculum taken from refrigerated cells
- Cells inoculated into a cold medium
Explain how inoculum taken from an old culture causes a longer lag phase.
An old culture will have few live cells left, and they will have nearly completely stopped their metabolism If you inoculute them into a fresh culture it will take longer before they start growing again.
Explain how inoculum taken from a rich medium and added to a poorer one causes a longer lag phase.
If we go from a medium where all the amino acids are provided for the cells to a new one where they have to make everything themselves, there will be a growth delay
What will the effect be of inoculum taken from a poor medium to a rich medium on the lag phase?
There will be no lag.
