Study Notes for Chapters 7 and 8

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Questions and Answers

Which of the following is primarily involved in the synthesis of microbial proteins?

Carbohydrates

Nucleic acids

Amino acids (correct)

Lipids

What type of metabolism generates energy without the use of oxygen?

Fermentation (correct)

Anaerobic respiration (correct)

Photophosphorylation

Aerobic respiration

Which molecule serves as the primary energy currency in microbial cells?

FADH2

ATP (correct)

NADH

DNA

In microbial metabolism, which of the following processes utilizes light energy?

Photosynthesis (A) Signup and view all the answers

Which type of biochemical reaction is characterized by the addition of electrons?

Reduction (B) Signup and view all the answers

Which macromolecule is primarily responsible for catalyzing biochemical reactions in microorganisms?

Proteins (A) Signup and view all the answers

What is the primary byproduct of fermentation in many microbial species?

Lactic acid (C) Signup and view all the answers

Which of the following is NOT a function of lipids in microbial cells?

Enzyme catalysis (A) Signup and view all the answers

Which of the following processes breaks down glucose in the absence of oxygen?

Fermentation (A), Glycolysis (D) Signup and view all the answers

What phase of microbial growth is characterized by little to no increase in cell numbers as the culture adjusts to a new environment?

Lag phase (C) Signup and view all the answers

Which phase of microbial growth shows the maximum growth rate due to active cell division?

Log (exponential) phase (B) Signup and view all the answers

If the generation time (g) is calculated using the formula g = t/n, what do the variables t and n represent?

t is time and n is the number of generations (D) Signup and view all the answers

What does the term 'culture density' refer to in microbial growth analysis?

The number of cells per unit volume (D) Signup and view all the answers

How does environmental condition affect microbial generation times?

Generation times depend on specific microorganisms and their conditions (C) Signup and view all the answers

What does the doubling time in bacterial growth represent?

The duration required for the population to double in number (B) Signup and view all the answers

In the context of bacterial division, what does FtsZ protein primarily assist with?

Directing cytokinesis and forming the division plane (B) Signup and view all the answers

What does the generation time indicate in microbial growth?

The duration for one round of cell replication to occur (C) Signup and view all the answers

Which stage of the growth curve represents a period of slow growth where bacteria adapt to their environment?

Lag phase (D) Signup and view all the answers

What can happen to microbial populations when environmental conditions become unfavorable?

Shift to the stationary phase or death phase (D) Signup and view all the answers

What is the main characteristic of the exponential growth phase in microbial populations?

Bacterial cells undergo binary fission each generation (D) Signup and view all the answers

How does the addition of nutrients typically affect microbial populations during growth?

It can stimulate growth, leading to exponential phase (A) Signup and view all the answers

What does the term 'Measuring Microbial Populations' refer to?

Quantifying the number of microbial cells in a given volume (B) Signup and view all the answers

What is a potential consequence of salt or freshwater eutrophication?

Overgrowth of aquatic algae followed by their death (D) Signup and view all the answers

What characterizes the exponential growth phase in microbial populations?

Cell populations double at regular intervals. (A) Signup and view all the answers

What occurs during the stationary phase of microbial growth?

The rate of cell division equals the rate of cell death. (D) Signup and view all the answers

Which of the following is a reason why cells are less susceptible to antibiotics during the stationary phase?

Formation of spores. (B) Signup and view all the answers

What is the primary reason persister cells are significant in chronic infections?

They can survive antibiotic treatment. (A) Signup and view all the answers

How is the generation time commonly represented in microbial growth curves?

As intervals of time where populations double. (C) Signup and view all the answers

What method is used to measure the turbidity of a microbial culture?

Spectrophotometry. (C) Signup and view all the answers

What is the purpose of using serial dilutions in microbial counting?

To obtain counts within a manageable range. (D) Signup and view all the answers

Why is the pour plate method beneficial in microbial counting?

It counts colonies both on the surface and within the agar. (C) Signup and view all the answers

What is a significant limitation of direct cell count using a Petroff-Hauser chamber?

It cannot distinguish between live and dead cells. (B) Signup and view all the answers

What role do biofilms play in microbial communities?

They protect cells from environmental threats. (A) Signup and view all the answers

In measuring microbial populations, what is the measure known as 'CFU'?

Colony Forming Units. (C) Signup and view all the answers

Which factor most directly affects the rate of microbial growth in a culture?

Nutrient availability. (C) Signup and view all the answers

What does an increase in optical density (OD) indicate in a microbial culture?

Increased turbidity and cell concentration. (D) Signup and view all the answers

Study Notes

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Microbial Growth

Bacterial cells multiply through binary fission, which involves DNA replication, partitioning of cell components, and cytokinesis.
Cytokinesis is directed by protein FtsZ, forming a Z ring on the cytoplasmic membrane, defining the division plane.
Generation time or doubling time refers to the time taken for the population to double in size.
Growth curve is a graphical representation of microbial growth in a closed culture over time.
Four distinct phases can be observed during bacterial growth in a closed culture:
- Lag phase: Minimal cell growth, the cells are adjusting to the environment, repairing damage, and synthesizing proteins.
- Log (exponential) phase: Maximum growth rate where cells divide actively with short generation times.
- Stationary phase: Growth slows down, cell death equals cell division due to limited nutrients and waste accumulation.
- ** Death phase:** Number of dying cells exceeds the number of dividing cells, causing an exponential decline in population.
Microbial growth can be measured using direct and indirect methods:
- Direct methods: Count bacterial cells directly using a microscope, plate count, filtration, or the most probable number (MPN) method.
- Indirect methods: Measure turbidity, dry weight, or metabolic activity.
Direct cell count uses a Petroff-Hauser chamber to observe and count cells under a microscope.
Plate counts determine the number of living cells that can form colonies on agar plates, and the results are expressed as colony-forming units (CFU/mL).
Serial dilution is used to obtain the appropriate number of colonies on the plates (30-300 CFUs) for accurate counting.
Membrane filtration method is used for samples with low bacterial density, where the bacteria are collected on a filter and then transferred to an agar plate for counting.
Turbidity is a measure of cloudiness, while spectrophotometer analyzes light scattering by bacteria to assess cell density.
Biofilms are microbial communities embedded in extracellular polymeric substances (EPS). EPS provides structural integrity and protects bacteria from harmful environmental conditions.

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