L3: Population Growth

What does the growth of individual cells refer to?

Increase in cell size and division of individual cells.

What’s population growth?

Increase in the number of many individual cells in a particular environment.

What’s population growth dependent on?

The division and death of individual cells.

How many phases in population growth?

7

What’s a heterotroph?

A heterotroph is an organism that cannot produce its own food; instead, it must obtain organic carbon molecules from the environment.

What does population growth mean in the lab. (cultures)

Change in the density of cells (cells/mL) in a lab culture.

When examining population growth in the lab, what’s the environment like typically?

A test tube or flask containing media that supports growth.

What’s media?

A liquid, solid or semi-solid material that provides nutrients for the growth of microorganisms in the lab.

How can population growth in a test tube with medium be quantified?

Estimating the number of living cells per mL of media OR measuring how CLOUDY the media is.

How is the measure of “cloudiness” in population growth termed?

Optical density (OD): The more bacteria in the culture, the cloudier the media and the higher the OD.

What’s a cell line?

Lab culture derived from a single source and maintained in the lab.

What do heterotrophic bacteria cells need in order to grow and divide?

1. Medium: Provides nutrients for the growth of microorganisms

2. Environment: To sustain bacterial cells for reproduction.

   • Temperature, availability of water, light (no UV), and oxygen.

What are the major types of molecules that bacterial cells take up from nutrient media?

• Carbon source → generally a sugar.

  • Energy source → typically the sugar.

• Nitrogen source.

• Minerals (in trace quantities)

• Oxygen, hydrogen → also seen in the sugar

• Make macromolecules from these

How does population growth in eukaryotes differ compared to prokaryotes?

Cell division in eukaryotes is more complicated.

In the lag phase, what is happening? (4)

• No growth.

• Population not actively dividing.

• Cells require time to acclimatize to the new conditions. Need to adjust gene expression.

• Medium concentration constant.

In the acceleration phase, what is happening? (4)

• Cells actively dividing.

• Increasing population growth rate.

• More cells added than lost from death.

• Medium concentration decreasing.

In the log phase, what is happening? (4)

• Cells dividing at maximum rate.

• Maximum population growth rate.

• More cells produced than lost.

• Medium concentration rapidly decreasing.

In the deceleration phase, what is happening? (2, 3 mini)

• Population growth rate decreases.

  • Less medium concentration (limiting)

  • Metabolic waste (acetate) accumulating

  • Environment full of cells.

• Cells gained still greater than lost.

What is happening in the stationary phase?

• Growth rate is zero → constant number of cells.

• No overall change in number of cells

  • Cell division = cell death

  • Cells stop actively dividing

• 0 medium concentration and metabolic waste limit.

In the death phase, what is happening?

• Population growth is negative.

• More cells are dying than dividing.

• Environment is toxic (metabolic waste) and nutrient-depleted.

In the long-term stationary phase, what is happening?

• Population growth rate fluctuates.

  • Overall negative.

• Cell division and death occurring at a low rate.

• Metabolic rate is low.

• Cultures can stay in this phase without additional nutrients for a long time depending on the species and conditions.

  • Living cells use dead cells and “waste” as nutrients

How does the lag phase start?

A sample of bacterial cells is added (inoculated) into sterile media.

When is DNA replication occurring in population growth?

Every stage INCLUDING the lag phase; however, very little replication in the death phase and long-term stationary phase.

When are transcription and translation occurring in population growth?

• Occurring in all places; very little in death and long-term stationary phase.

• Most prominent in lag phase, as cells adjust gene expression to acclimatize to new environments.