Growth & Nutrition

Question 1

What are the various ways in which culture media are classified?

Answer 1

Classified as solid or liquid.

Question 2

Bacteria are grown in/ on a medium true or false?

Answer 2

True

Question 3

What are solid media?

Answer 3

-Solid medias are agar, extracted from seaweed.
- Melts at 100 C, solidifies as 45 C.
- It’s a solidifying agent that prevents the growth of bacteria.

Question 4

What is a liquid media?

Answer 4

• It is a broth

Question 5

Defined media

Answer 5

uses pure chemicals, known concentrations and exact composition (ingredients/chemically are known).

Question 6

Complex media

Answer 6

ingredients not chemically defined (chemical composition is unknown and support the growth of the microbes).

Question 7

What are the types of media (composition)?

Answer 7

Defined and complex media

Question 8

What are the classifications of media (function)?

Answer 8

General purpose, differential, selective, and enrichment.

Question 9

General purpose

Answer 9

a medium used for general growth/ many organisms will grow (ex: nutrient agar/nutrient broth/ TSA).

Question 10

Differential

Answer 10

permits growth of many different types of organisms but allows you to differentiate them based on their appearance (ex: blood agar)

Question 11

Selective

Answer 11

permits growth of desired organisms and selects against undesired organisms (ex: MacConkey’s agar/ Bismuth sulfite agar)

Question 12

Enrichment

Answer 12

contain nutrients that enhance the growth of a desired organism (ex: blood agar)

Question 13

What is an example of differential and selective media?

Answer 13

MacConkey’s agar and Mannitol salt agar (selects for staphylococcus species and differentiates S. aureus from others).

Question 14

What is the significance and purpose of the streak plate technique?

Answer 14

The streak plate technique involves spreading a mixture of cells on an agar surface to isolate pure culture of bacteria from the mixed population.

Question 15

What is the correct order of events during binary fission?

Answer 15

Bacterial cell division by binary fission:
1) Cell elongates and DNA is replicated (genomic replicated)
2) Cell wall and plasma membrane begin to divide.
3) Cross-wall forms completely around divided DNA.
4) Cells separate into 2 daughter cells.

Question 16

What is the cell cycle in bacteria?

Answer 16

Cell cycle is sequence of events from formation of new cell through the next cell division (most bacteria are divided by binary fission). (growth, chromosome replication, and cytokinesis).

Question 17

What are the two pathways function during cell cycle?

Answer 17

• DNA replication and partition
• Cytokinesis: separation and daughter cell formation.

Question 18

What is septation (cytokinesis)?

Answer 18

Formation of cross walls between daughter cells.

Question 19

What is FtsZ?

Answer 19

A Z ring is located at the mid-point of the cell followed by formation of the septum.

Question 20

Why does FtsZ polymerize at mid-cell to form the Z ring?

Answer 20

-The FtsZ polymerize forms at the mid-cell rather than anywhere else due to nucleoid occlusion and min proteins. (both help to direct the FtsZ to form in the mid-cell)

Question 21

Z-ring is important for cell division, True or False (if true explain why)?

Answer 21

True the z-ring is important for cell division because it helps to equally divide the DNA among the two-daughter cell.

Question 22

What helps the FtsZ (z-ring) known where to form at the mid-point?

Answer 22

Nucleoid and the min proteins.

Question 23

Lack of min proteins cause what?

Answer 23

Would cause FtsZ to form at an unequal pole creating unequal daughter cells.

Question 24

Nucleoid

Answer 24

Occlusion prevents the z-ring from forming in areas where the DNA is present.

Question 25

Min proteins

Answer 25

prevents the z-ring from polymerizing at the wrong cell poles.

Question 26

Name the 4 methods of measuring bacterial growth as described in class. When would you use each method? State the advantages and disadvantages for each.

Answer 26

4 methods of measuring bacterial growth:
* Turbidity/ Optical density/ Absorbance using a spectrophotometer.
 Cells scatter light that strikes them.
 Amount of light scattered is used to estimate cell numbers.
 Advantage: quick and easy to use.
 Disadvantage: can’t tell if the specimen is alive or dead.

• Viable counts
   Dilute bacterial culture (due to high density).
   Plate on solid medium.
   Count colonies, calculate cell numbers.
   Advantage: only counts live cells and is easy to use.
   Disadvantage: require growth of organism, cell clumping, and time consuming.
• Directs counts (quick count of microbial cell).
   Counting chambers for microscope.
   Stain and count.
   Advantage: inexpensive.
   Disadvantage: can’t tell if the specimen is alive or dead, tedious, and even dispersion (limited measurement).
• Dry weight
   Dry bacteria on a filter paper.
   Weigh
   Gives biomass not cell number (common in fungi).
   Advantage: none
   Disadvantage: can’t tell if the specimen is alive or dead, cumbersome, time consuming.

Question 27

What are the four phases of bacterial growth curve:

Answer 27

Lag phase, exponential log, stationary, and death phase.

Question 28

Lag phase

Answer 28

-No active binary fission
-High metabolic activity
-Preparation phase

Question 28

Exponential Log

Answer 28

-Area where maximum growth happens.

Question 29

Stationary

Answer 29

-Equilibrium: cells are half growing while other cells are dying off.
-Growth is slow down.
-Binary fission is still active.

Question 30

Stationary phases consist of:

Answer 30

-Low nutrient
-Lack of space/ overcrowded.
-Increase of metabolic waste.

Question 31

Death phase

Answer 31

-Some cells remain partially active.
-Doesn’t reach zero.
-Binary fission is not active.

Question 32

What is generation time? How do you calculate population numbers using this?

Answer 32

Generation time is the time it takes for population to double.

Question 33

What is the difference between a constant culture and a batch culture? When is each used?

Answer 33

Constant culture (continuous culture)- can add fresh nutrient at a constant rate/can take put used media (spent media) to create space/dilute toxic waste.
Batch culture- adding set amount of media.