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Questions and Answers
What is the primary process by which most bacteria reproduce?
Which of the following physical requirements affects the shape of proteins?
What is a biofilm?
Which of the following is NOT a chemical requirement for microbial growth?
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How does low temperature affect cell membranes?
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Which of the following is a trace element required for microbial growth?
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What term describes an aggregation of microbial cells arising from a single cell?
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What occurs during binary fission?
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Which group of organisms is specifically known for causing food spoilage in refrigeration temperatures?
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What is the optimum growth temperature range for thermophiles?
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Which organism is commonly linked to foodborne illnesses and can cross the placenta in pregnant women?
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What pH range do most bacteria, classified as neutrophiles, prefer for optimal growth?
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Which of the following is an example of an acidophile?
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What characteristic of Helicobacter pylori allows it to survive in the acidic environment of the stomach?
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Which group of microorganisms typically grows best at high alkaline pH levels?
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What is a common characteristic of psychrotrophs in relation to food preservation?
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What are halophiles primarily known for?
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Which type of halophiles requires high osmotic pressure for survival?
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Which of the following is a characteristic of barophiles?
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What is the osmotic pressure in the salt ponds near San Francisco compared to seawater?
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Which of the following groups includes halotolerant microorganisms?
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What type of pressure increases by 1 atm for every additional 10 m of water depth?
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What chemical element is NOT typically required for the growth of prokaryotes?
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Which of the following is NOT a physical requirement for organism growth?
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Which enzyme is responsible for breaking down superoxide radicals?
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What type of relationship do synergistic associations represent?
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How do biofilms contribute to increased resistance to treatments?
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Which of the following statements about obligate anaerobes is true?
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What is a common characteristic of medical devices contaminated with biofilms?
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In which of the following areas are biofilms commonly found?
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What is the role of quorum sensing in biofilms?
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Which type of infections is most commonly associated with biofilms?
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What is the primary role of nitrogen in living organisms?
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Which of the following is NOT a characteristic of obligate aerobes?
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How do chemoheterotrophs obtain their energy?
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What is a common source of nitrogen for most bacteria?
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Which statement about trace elements is true?
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What role does phosphorus play in living organisms?
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Why is nitrogen fixation important for life on Earth?
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Which of the following growth factors must be obtained from the environment by certain organisms?
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Study Notes
Microbial Growth
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Increase in a population of microbes, not the size of an individual microbe.
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A colony is an aggregation of cells arising from a single cell.
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A biofilm is a complex, diverse community of microbes living on a surface.
Requirements for Microbial Growth
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Physical requirements:
- Temperature
- pH
- Osmotic pressure
- Hydrostatic pressure
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Chemical requirements:
- Carbon
- Nitrogen, sulfur, and phosphorus
- Trace elements
- Oxygen
- Organic growth factors
Physical Requirements for Microbial Growth
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Temperature affects the shape (3D structure) of proteins and the fluidity of cell membranes and organelles.
- Too low: membranes become rigid and fragile.
- Too high: membranes become too fluid, unable to contain the cell or organelles.
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Categories of microbes based on temperature ranges for growth:
- Psychrophiles: cold-loving
- Mesophiles: moderate-temperature-loving
- Thermophiles: heat-loving (optimal growth temperature of 50° to 60°C), found in hot springs and organic compost.
- Hyperthermophiles: optimal growth temperature >80°C
- Psychrotrophs: grow between 0°C and 20° - 30°C, cause food spoilage.
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Psychrotrophs (grow between 0°C and 20° - 30°C) cause food spoilage:
- Can degrade food over time (mold mycelium, slime on food surfaces, off-tastes or off-colors in foods).
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Listeria monocytogenes: a common food pathogen that grows within the psychrotroph range.
- Gram-positive rod, causes meningitis (20% mortality).
- Affects immunocompromised people and the elderly.
- Can cross the placenta, leading to miscarriage, stillbirth, or fatal neonatal infection in pregnant women.
- Pregnant women advised to avoid soft cheeses, refrigerated cold cuts, smoked seafood, and unpasteurized dairy products.
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pH profoundly affects the structure of macromolecules and cellular functions:
- Extreme pH affects molecules stabilized by hydrogen bonds (e.g., proteins) and cellular respiration (chemiosmosis).
- Important for food preservation (controlling microbial growth) and the survival of microorganisms in the stomach (human microbiota).
- Neutrophiles: most bacteria grow between pH 6.5 - 7.5 (e.g., intestinal pathogens like Salmonella are resistant to stomach acid).
- Acidophiles: grow in acidic environments (e.g., Lactobacillus in the vagina microbiota contributes to acidity, inhibiting other less tolerant microbes).
- Alkalinophiles: grow best between pH 8-11.5.
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Surviving the Low pH of the Stomach:
- Helicobacter pylori: gram-negative, flagellated, helical bacterium, common cause of stomach ulcers (peptic ulcers).
- H. pylori is a neutrophile. It survives in the stomach because it secretes urease, which converts urea to ammonia, raising the pH around the bacterium.
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Osmotic Pressure
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Halophiles: "salt-loving" organisms that live in high-salt environments (e.g., salt ponds).
- Extreme or obligate halophiles: require high osmotic pressure (high salt).
- Facultative halophiles: tolerate high osmotic pressure (e.g., Staphylococcus, Micrococcus, and Corynebacterium, which colonize human skin).
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Halophiles: "salt-loving" organisms that live in high-salt environments (e.g., salt ponds).
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Hydrostatic Pressure
- Water exerts pressure in proportion to its depth (for every 10 m of depth, water pressure increases by 1 atm).
- Barophiles: organisms that live under extreme pressure. Their membranes and enzymes depend on this pressure to maintain their functional 3-D shape.
Chemical Requirements for Microbial Growth
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Carbon: the structural backbone of organic molecules.
- Chemoheterotrophs: use organic molecules as energy sources.
- Autotrophs: use CO2 as their carbon source.
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Nitrogen: a component of proteins, DNA, and ATP.
- Most bacteria decompose protein material for their nitrogen source.
- Some bacteria use NH4+ or NO3- from organic material.
- A few bacteria use N2 in nitrogen fixation, a process essential for life on Earth.
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Phosphorus: a component of phospholipid membranes, DNA, RNA, ATP, and some proteins.
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Sulfur: a component of sulfur-containing amino acids (disulfide bonds critical to tertiary structure of proteins and in vitamins like thiamin and biotin).
- Some bacteria use SO4 or H2S.
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Trace elements: required in small amounts, usually found in sufficient quantities in tap water.
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Growth factors: necessary organic chemicals that cannot be synthesized by certain organisms (e.g., vitamins, certain amino acids, purines, pyrimidines, cholesterol, NADH, and heme).
Oxygen Requirements
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Obligate aerobes: require oxygen for growth (final e- acceptor in electron transport chain).
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Obligate anaerobes: oxygen is deadly (lack the enzymes to detoxify reactive oxygen species).
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Detoxification of Reactive Oxygen Species:
- Oxygen radicals are produced during cellular respiration and from atmospheric oxygen.
- Three main enzymes break down these toxic byproducts:
- Superoxide dismutase: breaks down superoxide radicals (O2-).
- Peroxidase: breaks down peroxide anions (O22-).
- Catalase: also breaks down peroxide anions (O22-).
- Obligate anaerobes lack all three enzymes.
Associations and Biofilms
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Organisms live in association with different species:
- Antagonistic: one organism inhibits the growth of another.
- Synergistic: two organisms work together for growth, but neither is dependent on the other for survival.
- Symbiotic: two organisms live together, and at least one is dependent on this relationship for survival (e.g., nitrogen-fixing bacteria in plant roots).
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Biofilms: a collection of microbes that live in a complex community, adhering to surfaces (such as medical devices, mucous membranes, etc.).
- They form an extracellular matrix that adheres cells to one another, allows attachment to a substrate, sequesters nutrients, and may protect individuals in the biofilm.
- Quorum sensing is a key mechanism in biofilm formation.
- Slime or hydrogels: the matrix that forms on surfaces.
- Often implicated in infections.
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Harmful Effects of Biofilms:
- Biofilm formation on medical devices: (catheters, heart valves, contact lenses) often leads to infections (more than 70% of infections).
- Biofilms can be resistant to microbicides and antibiotics.
- Biofilms can form in digestive systems, sewage treatment systems, and clog pipes.
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Description
Test your knowledge on microbial growth concepts including the physical and chemical requirements necessary for different types of microbes. Understand the role of temperature, pH, and other factors in the growth and survival of microorganisms. This quiz covers categories of microbes based on temperature preferences and their characteristics.
