Dynamics of Growth Review

Cells are not dividing but are synthesizing enzymes required for growth

Lag phase

T/F: It is sometimes difficult to obtain pure cultures of microbes that grow naturally in mixed communities.

True

T/F: Microbes will only grow until the least represented (limiting) nutrient is used up.

True

Label the image with the statements that most accurately describe the process of plasmolysis.

1. Higher solute concentration outside the cell; water therefore leaves the cell 2. Higher water concentration inside the cell; water therefore leaves the cell

Identify the phases of a bacterial growth curve:

1. Lag Phase 2. Exponential phase 3. Stationary phase 4. Decline phase

Match the statement to the correct step in the streak place procedure.

1. Start by sterilizing the loop 2. Inoculate loop and streak back and forth in one area 3. Sterilize loop and streak another area, passing over the previous section a few times 4. Sterilize loop and streak the final area of the plate while passing over the previous area a few times

From which of the following would you be most likely to obtain a pure culture?

A single colony on a streak plate

You use the streak-plate method to obtain a pure culture and observe individual colonies following incubation. Consider a single bacterial colony. All of the following statements about the colony are true EXCEPT:

All cells in the colony are expressing the same set of genes and are performing the same metabolic functions

Identify the type of bacterial formation being shown in this image.

Biofilm

Due to nutrient depletion and waste accumulation, cells begin to die at an exponential rate

Death phase

Cells are actively growing, doubling the population with each generation

Exponential/log phase

You observe bacteria growing on the surface of a petri dish of nutrient agar you left on the counter in your lab. You can be confident that your bacteria are NOT which of the following?

Obligate anaerobes

When studying microbes, why is it important to separate mixed communities into individual pure cultures of the different species?

So we can understand the biochemical characteristics of one species without confusing it with another species.

With nutrients depleted, total number of viable cells remains constant, with some dying while others multiply

Stationary phase

You inoculate a flask containing a complex medium with a culture of bacteria and use a spectrophotometer to measure the absorbance of the culture to detect growth. Initial measurements show a modest turbidity (cloudiness) that remains unchanged for the first few hours followed by a steady increase for the rest of the day. Why was there this delay in growth following inoculation?

The bacteria were actively expressing genes and synthesizing enzymes in order to grow in their new environment.

What is the correct statement that best describes the concept behind the enrichment culture method?

The liquid culture enhances the growth of only certain microbes, so their numbers increase in proportion with each transfer.

Microorganisms that have complicated nutritional requirements are:

fastidious