Lab 7 Quiz Multiple Choice

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Questions and Answers

What classification of bacteria are specifically adapted to thrive in very low temperatures?

Psychrophiles (correct)

Mesophiles

Thermoduric

Thermophiles

Which type of microorganism would likely have the highest optimal growth temperature?

Mesophiles

Hyperthermophiles (correct)

Thermophiles

Psychrophiles

Which temperature range is characteristic for mesophiles?

20 to 45°C (correct)

-10 to 0°C

0 to 20°C

45 to 100°C

What effect do low temperatures have on bacterial growth?

Slow down enzyme activity Signup and view all the answers

What defines the maximum temperature for a microorganism?

The temperature at which growth ceases completely Signup and view all the answers

Thermoduric bacteria are distinguished by which characteristic?

They can survive brief high-temperature exposure but prefer colder habitats Signup and view all the answers

Which statement accurately describes thermophiles?

They thrive at temperatures between 45 and 80°C Signup and view all the answers

Which of the following categories includes organisms that can grow at very high temperatures, above 80°C?

Hyperthermophiles Signup and view all the answers

The effect of temperature on prokaryotic growth can be characterized as:

Having species-specific optimal ranges Signup and view all the answers

What is the primary role of low temperatures in controlling bacterial populations?

Inhibiting metabolic activity Signup and view all the answers

What is the main reason for using low temperatures in food preservation?

To inhibit bacterial growth Signup and view all the answers

Which heating method is specifically designed to achieve sterilization by using steam under pressure?

Autoclave Signup and view all the answers

What is the temperature setting of an autoclave that allows for effective sterilization?

121.5oC at 15 lbs/in2 pressure Signup and view all the answers

Which bacterial species is likely to require the longest exposure time at boiling temperature to ensure effective microbial control?

Bacteria producing spores Signup and view all the answers

What is the critical drawback of using boiling water as a method of sterilization?

Some bacteria can produce spores resistant to boiling. Signup and view all the answers

Which pasteurization method is capable of achieving sterilization under proper conditions?

Ultra-high temperature (UHT) method Signup and view all the answers

What is the defining characteristic of dry heat sterilization compared to moist heat sterilization?

Takes longer and is less penetrating Signup and view all the answers

What is measured by the thermal death time (TDT)?

The minimum time to kill a population at a specific temperature Signup and view all the answers

At what temperature is the holding method of pasteurization typically conducted?

63oC Signup and view all the answers

Which temperature represents the optimal growth temperature for most mesophilic bacteria?

37oC Signup and view all the answers

What property allows bacterial endospores to survive in dry conditions?

Thick outer membrane Signup and view all the answers

What is the wavelength range of UV radiation?

100 - 400 nm Signup and view all the answers

What type of DNA damage is primarily caused by UV radiation?

Pyrimidine dimers Signup and view all the answers

How can UV radiation lead to cell death after prolonged exposure?

By overwhelming repair mechanisms Signup and view all the answers

In what environments is UV radiation typically used to control microbial growth?

Sterile hoods and operating rooms Signup and view all the answers

Which component of DNA is affected by the formation of pyrimidine dimers?

Thymine and cytosine Signup and view all the answers

What precaution should humans take when using UV radiation for sterilization?

Limiting skin exposure Signup and view all the answers

What happens to DNA when it forms pyrimidine dimers?

It distorts the DNA structure Signup and view all the answers

Which method is NOT mentioned as a function of UV radiation?

Repairing DNA damage Signup and view all the answers

What type of microorganisms can persist in the environment aside from endospore formers?

Non-spore formers with specific properties Signup and view all the answers

Study Notes

Temperature and Microbial Growth

Temperature affects bacterial growth - different bacterial species have different temperature requirements for growth.
Microbial growth is strongly influenced by temperature and can be used to control bacterial growth.
Temperature ranges for different bacterial species:
- Psychrophiles: -10°C to 20°C.
- Mesophiles: 20°C to 45°C.
- Thermophiles: 45°C to 80°C.
- Hyperthermophiles: 80°C to 110°C.
Thermoduric bacteria - can survive short bursts of heat but will only grow at lower temperatures.
Temperature control methods:
- Low temperatures: Primarily bacteriostatic - inhibit bacterial growth and/or reduce the total number of bacteria.
- High temperatures: Bactericidal - can kill bacteria.
Sterilization: using high temperatures to kill all forms of life.
- Methods of sterilization:
  - Incineration: high-temperature flames for materials that can withstand it.
  - Dry heat: uses oxidation of cellular molecules and desiccation (drying) of bacteria.
  - Moist heat: denatures nucleic acids and enzymes, rendering bacteria incapable of metabolizing or reproducing.
- Moist heat methods:
  - Boiling: 100°C at sea level, kills many vegetative cells, but not all bacteria.
  - Pasteurization: Heat treatment used for food items
    - Holding method (63°C for 30 min)
    - Flash pasteurization (71.6°C for 15 sec)
    - Ultra-high temperature (UHT) (140°C for 3 sec)
  - Autoclave: uses steam under pressure (121.5°C), capable of sterilizing materials.
Factors affecting sterilization efficiency:
- Thermal death time (TDT): minimum time required to kill a population of microbes at a specific temperature.
- Thermal death point (TDP): lowest temperature required to kill a population of microbes in a specific amount of time.

Other Factors Affecting Microbial Growth

Moisture: All living organisms, including bacteria, require water to survive.
UV radiation: Damages DNA by forming pyrimidine dimers, which disrupt DNA replication and transcription.
- UV radiation can be used for controlling microbial growth in specific areas.
- However, UV radiation can damage skin cells.
Endospores: Resistant to dryness, can survive for extended periods in dry environments and germinate to form vegetative cells when moisture is available.
Cell wall properties and glycocalyx: Affect the ability of certain non-spore-forming bacteria to persist in dry environments.

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Description

Explore how temperature impacts microbial growth in various bacterial species such as psychrophiles, mesophiles, thermophiles, and hyperthermophiles. Understand the significance of temperature in controlling bacterial growth and the methods of sterilization utilized in microbiology. Test your knowledge on the vital temperature ranges and how they influence microbial life.