This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Bacteria Cultivation – Physical Conditions Required for Growth”.
1. The temperature that allows for most rapid growth during a short period of time is known as __________
a) Minimum Temperature
b) Maximum Temperature
c) Optimum Temperature
d) Growth Temperature
Explanation: The temperature that allows for the most rapid growth during a short period of time(12 to 24 hrs) is known as the optimum temperature. Maximum temperature for growth lies very close to the optimum temperature whereas minimum temperature for growth is usually much lower than the optimum.
2. Mesophiles are group of bacteria that grow within the temperature range of?
a) 0-20 degree Celsius
b) 25-40 degree Celsius
c) 45-60 degree Celsius
d) more than 60 degree Celsius
Explanation: Mesophiles grow best within a temperature range of 25 to 40 degree Celsius. All bacteria that are pathogenic for humans and warm-blooded animals are mesophiles, most growing best at about body temperature(37 degree Celsius).
3. Which of the following factors are responsible for the stability of thermophiles at high temperatures?
a) increased leakage of cell components
b) presence of large no. of polar amino acids and alpha-helix protein
c) thermal stability of ribosomes
d) presence of Inositol diphosphate and thermal stability of ribosomes
Explanation: Factors that have been implicated in the ability to grow at high temperature is increased thermal stability of ribosomes. The cytoplasmic membrane of thermophiles also contains Inositol diphosphate or Inositol triphosphate which can tolerate high temperature and maintains the fluidity of the membrane.
4. The bacterium Staphylococcus aureus is which type of bacteria?
d) Mesophile and psychrophile
Explanation: Staphylococcus aureus is a mesophilic bacteria which can grow in the temperature range of 6.5-46 degree Celsius and has an optimum temperature at 30-37 degree Celsius.
5. Microaerophilic bacteria require low levels of oxygen for growth.
Explanation: Microaerophilic bacteria require low levels of oxygen for growth but it cannot tolerate the level of oxygen present in an air atmosphere.
6. The Reactive Oxygen Species(ROS) produced by some bacteria are degraded by which of the following enzymes?
d) Superoxide dismutase, Catalase and Peroxidase
Explanation: In some cases, oxygen may accept large number of free electrons and produces Reactive Oxygen Species (ROS). They are harmful as they degrade macromolecules required for growth and nutrition. But aerobic bacteria contains three different enzymes-Superoxide dismutase, Catalase and Peroxidase which eliminates the different ROS.
7. Which of the following ROS is a powerful oxidizing agent?
a) Superoxide radical
b) Hydrogen peroxide
c) Hydroxyl radical
d) Singlet oxygen
Explanation: Superoxide radicals form toxic substances such as hydrogen peroxide. Hydrogen peroxide is not a free radical, but it is a powerful oxidizing agent.
8. The GasPak system is suitable for which of the following?
a) Aerobic bacteria
b) Anaerobic bacteria
c) Facultatively anaerobic bacteria
d) Microaerophilic bacteria
Explanation: GasPak Jar is a system for anaerobic bacteria. In this jar media is inoculated and placed in the jar. To this water is added, causing the evolution of Hydrogen gas and Carbon dioxide. Hydrogen gas reacts with oxygen on the surface of the palladium catalyst, forming water and establishing anaerobic conditions.
9. Which of the following are functions of phosphates used in the preparation of media?
a) they act as buffer
b) source of phosphorous
c) act as “reserve alkali”
d) they act as buffer and is a source of phosphorous
Explanation: The phosphates are used widely in the preparation of media because they are the only inorganic agents that buffer in the physiologically important range around neutrality and that are relatively non-toxic to microorganisms. In addition, they provide a source of phosphorous, which is an essential element of growth.
10. The optimum pH for the growth of most bacteria lies between _______
Explanation: pH is an important physical condition controlling the growth of bacteria. For most bacteria, the optimum pH for growth lies between 6.5 and 7.5. This pH of the media is maintained by using a buffer into the medium.
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