BackBIO 255 Chapters 6 & 7 Microbial Growth and Control Study Guide – Step-by-Step Guidance
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Q1. Most bacteria grow by the process of _____________ meaning they each split into __________ cells.
Background
Topic: Bacterial Cell Division
This question tests your understanding of how bacteria reproduce and increase their population.
Key Terms:
Binary fission: The most common method of bacterial reproduction, where one cell divides into two.
Daughter cells: The two cells resulting from the division.
Step-by-Step Guidance
Recall the main method by which most bacteria reproduce. This process involves the cell duplicating its genetic material and splitting.
Think about how many cells result from one division event.
Fill in the blanks with the correct terms describing the process and the number of resulting cells.
Try solving on your own before revealing the answer!
Final Answer:
Most bacteria grow by the process of binary fission, meaning they each split into two cells.
This is the primary method of asexual reproduction in bacteria.
Q2. For each generation the population of cells increases by a factor of _____.
Background
Topic: Exponential Growth in Bacteria
This question is about how bacterial populations grow during binary fission.
Key Terms and Formula:
Generation: One complete round of cell division.
Exponential growth: Each cell divides to form two cells, doubling the population each generation.
Step-by-Step Guidance
Consider what happens to the population after each cell divides once.
Think about the mathematical factor by which the population increases with each generation.
Fill in the blank with the correct factor.
Try solving on your own before revealing the answer!
Final Answer:
For each generation, the population of cells increases by a factor of 2.
This is because each cell divides into two new cells during binary fission.
Q3. With a generation time of 30 minutes, how many cells will be in a population of bacteria that started with 200 cells and grew exponentially for 3 hours?
Background
Topic: Calculating Bacterial Population Growth
This question tests your ability to use exponential growth equations to determine the final population size after a certain number of generations.
Key Formula:
= final number of cells
= initial number of cells
= number of generations
Step-by-Step Guidance
Identify the initial number of cells (), which is 200.
Calculate the total time of growth (3 hours) in minutes.
Determine the number of generations by dividing the total time by the generation time (30 minutes).
Set up the exponential growth formula using your values for and .
Plug the values into the formula but do not calculate the final value yet.
Try solving on your own before revealing the answer!
Final Answer:
There will be 1,600 cells after 3 hours.
Calculation: 3 hours = 180 minutes; 180/30 = 6 generations; .
Correction: The correct calculation is cells.
Q4. What are the optimum temperatures of growth for each of the temperature groups (-philes) of bacteria?
Background
Topic: Microbial Growth and Temperature Preferences
This question asks you to recall the temperature ranges at which different groups of bacteria grow best.
Key Terms:
Psychrophiles: Cold-loving bacteria
Mesophiles: Moderate temperature-loving bacteria
Thermophiles: Heat-loving bacteria
Hyperthermophiles: Very high temperature-loving bacteria
Step-by-Step Guidance
List each temperature group (-phile) mentioned in your notes.
Recall or look up the typical optimum temperature range for each group.
Write down the temperature range or specific optimum temperature for each group.
Try solving on your own before revealing the answer!
Final Answer:
Psychrophiles: Optimum below 15°C
Mesophiles: Optimum 20–45°C (most human pathogens)
Thermophiles: Optimum 55–65°C
Hyperthermophiles: Optimum above 80°C
Q5. Where in a deep tube of agar will the various “oxygen” groups of bacteria grow (there is only oxygen in just the top 1-2 centimeters of the agar medium)?
Background
Topic: Oxygen Requirements of Bacteria
This question tests your understanding of how different bacteria respond to oxygen and where they grow in a tube with an oxygen gradient.
Key Terms:
Obligate aerobes: Require oxygen
Obligate anaerobes: Killed by oxygen
Facultative anaerobes: Can grow with or without oxygen
Microaerophiles: Require low oxygen
Aerotolerant anaerobes: Do not use oxygen but tolerate it
Step-by-Step Guidance
Recall the oxygen requirements for each group.
Think about where oxygen is present in the tube (top 1–2 cm).
Predict where each group would grow based on their oxygen needs or tolerance.
Try solving on your own before revealing the answer!
Final Answer:
Obligate aerobes: Grow only at the top (where oxygen is present)
Obligate anaerobes: Grow only at the bottom (no oxygen)
Facultative anaerobes: Grow throughout but more at the top
Microaerophiles: Grow just below the top (low oxygen)
Aerotolerant anaerobes: Grow evenly throughout the tube
Q6. What are the toxic forms of oxygen and how do bacteria detoxify them?
Background
Topic: Oxygen Toxicity and Bacterial Defense Mechanisms
This question is about reactive oxygen species and the enzymes bacteria use to neutralize them.
Key Terms:
Superoxide (O2•-)
Hydrogen peroxide (H2O2)
Catalase
Superoxide dismutase (SOD)
Peroxidase
Step-by-Step Guidance
List the main toxic forms of oxygen produced during metabolism.
Identify the enzymes that bacteria use to detoxify each form.
Match each enzyme to the specific toxic oxygen species it neutralizes.
Try solving on your own before revealing the answer!
Final Answer:
Toxic forms: Superoxide radical (O2•-), hydrogen peroxide (H2O2)
Detoxification: Superoxide dismutase converts superoxide to H2O2; catalase and peroxidase convert H2O2 to water and oxygen.
Q7. Describe the 3 forms of bacteria/host symbioses.
Background
Topic: Symbiotic Relationships
This question asks you to define the main types of symbiotic interactions between bacteria and their hosts.
Key Terms:
Mutualism
Commensalism
Parasitism
Step-by-Step Guidance
List the three main types of symbiotic relationships.
Define each type in terms of benefit or harm to the host and the bacteria.
Give an example of each, if possible.
Try solving on your own before revealing the answer!
Final Answer:
Mutualism: Both host and bacteria benefit.
Commensalism: Bacteria benefit; host is unaffected.
Parasitism: Bacteria benefit; host is harmed.
Q8. What are the 4 phases of growth of bacteria in a broth culture? Which one has the fastest growth rate (doublings)?
Background
Topic: Bacterial Growth Curve
This question is about the stages of bacterial population growth in a closed system and which phase has the highest rate of cell division.
Key Terms:
Lag phase
Exponential (log) phase
Stationary phase
Death phase
Step-by-Step Guidance
List the four phases of the bacterial growth curve in order.
Briefly describe what happens in each phase.
Identify which phase is characterized by the fastest rate of cell division (doublings).
Try solving on your own before revealing the answer!
Final Answer:
Lag phase
Exponential (log) phase – fastest growth rate
Stationary phase
Death phase
The exponential (log) phase has the fastest growth rate.
Q9. Why is the 3rd phase called “stationary”? What causes the death phase?
Background
Topic: Bacterial Growth Curve – Stationary and Death Phases
This question asks you to explain why the stationary phase occurs and what leads to the death phase in a closed culture.
Key Terms:
Stationary phase: Growth rate equals death rate
Death phase: Cells die faster than they divide
Step-by-Step Guidance
Consider what happens to nutrients and waste products as the culture grows.
Explain why cell division slows and stops during the stationary phase.
Describe what causes the death phase to begin.
Try solving on your own before revealing the answer!
Final Answer:
The 3rd phase is called “stationary” because the rate of cell growth equals the rate of cell death, so the population size remains constant. The death phase is caused by depletion of nutrients and accumulation of toxic waste products.
Q10. What is meant by “serial dilution”? Why do we use the term “cfu/ml” to label cell concentration values?
Background
Topic: Measuring Microbial Populations
This question is about laboratory techniques for quantifying bacteria and the meaning of colony-forming units.
Key Terms:
Serial dilution: Stepwise dilution of a sample
cfu/ml: Colony-forming units per milliliter
Step-by-Step Guidance
Define serial dilution and explain why it is used in microbiology labs.
Explain what a colony-forming unit (cfu) represents.
Describe why “cfu/ml” is used instead of “cells/ml.”
Try solving on your own before revealing the answer!
Final Answer:
Serial dilution is the process of stepwise diluting a sample to reduce the concentration of cells for easier counting. “cfu/ml” is used because each colony may arise from a single cell or a group of cells, so it measures viable units capable of forming colonies, not individual cells.
Q11. How can a culture’s turbidity be used to quantitate (measure) a microbial population?
Background
Topic: Measuring Bacterial Growth by Turbidity
This question is about using optical density (turbidity) to estimate cell concentration in a liquid culture.
Key Terms:
Turbidity: Cloudiness of a culture
Spectrophotometer: Instrument to measure optical density
Step-by-Step Guidance
Explain what happens to the appearance of a broth culture as bacteria grow.
Describe how a spectrophotometer is used to measure turbidity.
Discuss how turbidity readings can be correlated with cell concentration using a standard curve.
Try solving on your own before revealing the answer!
Final Answer:
Turbidity increases as the number of cells increases. A spectrophotometer measures the optical density (OD) of the culture, which can be compared to a standard curve to estimate the microbial population.
Q12. What “additive” could be added to the culture media to encourage the growth of osmophiles? for acidophiles? for halophiles?
Background
Topic: Specialized Growth Requirements
This question asks you to identify substances that promote the growth of bacteria adapted to high osmotic pressure, acidic environments, or high salt concentrations.
Key Terms:
Osmophiles: Thrive in high solute concentrations
Acidophiles: Thrive in acidic conditions
Halophiles: Thrive in high salt concentrations
Step-by-Step Guidance
Recall what each group requires for optimal growth.
Identify the additive that would create the necessary environment for each group.
List the appropriate additive for each type of organism.
Try solving on your own before revealing the answer!
Final Answer:
Osmophiles: Add sugar (high solute concentration)
Acidophiles: Add acid (lower pH)
Halophiles: Add salt (NaCl)
Q13. Distinguish between sterilization and disinfection.
Background
Topic: Microbial Control Methods
This question is about the definitions and differences between two key methods of controlling microbial growth.
Key Terms:
Sterilization: Complete destruction of all forms of microbial life
Disinfection: Destruction of most microbes, but not necessarily all
Step-by-Step Guidance
Define sterilization and what it achieves.
Define disinfection and what it achieves.
Compare the two in terms of effectiveness and typical use.
Try solving on your own before revealing the answer!
Final Answer:
Sterilization destroys all forms of microbial life, including spores. Disinfection eliminates most pathogens but may not kill all spores or viruses.
Q14. Distinguish between a disinfectant and an antiseptic.
Background
Topic: Types of Chemical Agents
This question asks you to differentiate between chemicals used on inanimate objects and those safe for living tissue.
Key Terms:
Disinfectant: Used on non-living surfaces
Antiseptic: Used on living tissue
Step-by-Step Guidance
Define what a disinfectant is and where it is used.
Define what an antiseptic is and where it is used.
Compare their safety and application.
Try solving on your own before revealing the answer!
Final Answer:
Disinfectants are chemicals used on inanimate objects to kill microbes. Antiseptics are chemicals safe for use on living tissue to reduce microbial load.
Q15. What are the times and temperatures of the 3 methods of pasteurization (batch, continuous, ultra)?
Background
Topic: Physical Methods of Microbial Control
This question is about the different pasteurization methods and their specific time and temperature parameters.
Key Terms:
Batch pasteurization
Continuous (HTST) pasteurization
Ultra pasteurization
Step-by-Step Guidance
List each method of pasteurization.
Recall or look up the time and temperature for each method.
Write down the correct values for each method.
Try solving on your own before revealing the answer!
Final Answer:
Batch: 63°C for 30 minutes
Continuous (HTST): 72°C for 15 seconds
Ultra: 140°C for less than 1 second
Q16. Why was hexachlorophene use discontinued in newborn nurseries in the hospital? Why is triclosan no longer allowed in soaps?
Background
Topic: Chemical Agents and Safety
This question is about the risks associated with certain antimicrobial chemicals and why their use was restricted.
Key Terms:
Hexachlorophene: Antimicrobial agent, toxic effects
Triclosan: Antimicrobial, resistance concerns
Step-by-Step Guidance
Recall the reason hexachlorophene was considered unsafe for newborns.
Explain why triclosan was banned from soaps.
Summarize the main safety or resistance concerns for each chemical.
Try solving on your own before revealing the answer!
Final Answer:
Hexachlorophene was discontinued due to its neurotoxicity in newborns. Triclosan was banned from soaps because of concerns about bacterial resistance and environmental impact.
Q17. What alcohols are used for routine disinfection? What range of alcohol content is effective against most microbes?
Background
Topic: Alcohols as Disinfectants
This question is about the types of alcohols used and the effective concentration range for microbial control.
Key Terms:
Ethanol
Isopropanol
Effective concentration
Step-by-Step Guidance
List the two main alcohols used for disinfection.
Recall the effective concentration range for these alcohols.
Explain why concentrations below a certain percentage are less effective.
Try solving on your own before revealing the answer!
Final Answer:
Ethanol and isopropanol are used for routine disinfection. The effective range is 60–95% alcohol; below 50% is less effective.
Q18. Why were silver nitrate drops used in newborn baby eyes? What is used today for the same purpose?
Background
Topic: Prevention of Neonatal Infections
This question is about the historical and current methods for preventing eye infections in newborns.
Key Terms:
Silver nitrate
Erythromycin
Neisseria gonorrhoeae
Step-by-Step Guidance
Recall the infection that silver nitrate was used to prevent.
Identify the current agent used for the same purpose.
Explain why the change was made.
Try solving on your own before revealing the answer!
Final Answer:
Silver nitrate drops were used to prevent gonococcal eye infections in newborns. Today, erythromycin ointment is used for the same purpose.
Q19. How is ethylene oxide used to control microbial contamination?
Background
Topic: Chemical Sterilization
This question is about the use of ethylene oxide gas as a sterilizing agent for heat-sensitive materials.
Key Terms:
Ethylene oxide: Alkylating agent
Gas sterilization
Step-by-Step Guidance
Describe what ethylene oxide is and its mode of action.
Explain why it is used for sterilizing certain materials.
List examples of items that might be sterilized with ethylene oxide.
Try solving on your own before revealing the answer!
Final Answer:
Ethylene oxide is a gas used to sterilize heat-sensitive medical equipment by alkylating proteins and DNA, effectively killing all microbes, including spores.
