Nokea
Fossils of prokaryotes go back __________ billion years.
- A. 4.0 to 5.0
- B. 3.5 to 4.0
- C. 2.5 to 3.0
- D. 2.2 to 2.7
Correct Answer: B
Rationale: The correct answer is B: 3.5 to 4.0 billion years. Prokaryotic fossils date back to around 3.5 to 4.0 billion years ago, based on scientific evidence. This timeframe aligns with the earliest known evidence of life on Earth. Choices A, C, and D have incorrect timelines that do not correspond to the established age range of prokaryotic fossils. Choice A is too broad and includes a range that extends beyond the known fossil record. Choices C and D have much younger timelines, which do not match the historical evidence of prokaryotic life dating back billions of years.
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Which of the following is a host-dependent bacterium?
- A. Mycoplasma
- B. Ureaplasma
- C. Rickettsia
- D. Micrococcus
Correct Answer: C
Rationale: The correct answer is C: Rickettsia. Rickettsia is a host-dependent bacterium because it requires living cells of a host organism to survive and replicate. This bacterium is an obligate intracellular pathogen, meaning it cannot grow outside of a host cell.
A: Mycoplasma and B: Ureaplasma are not host-dependent as they can grow and reproduce in cell-free environments due to possessing their own unique cell wall structures.
D: Micrococcus is a free-living bacterium that can survive and reproduce independently without relying on a host organism.
A patient's blood culture revealed Gram-positive rods capable of spore formation. They were also motile and produced gas in nutrient broth. What is the causative agent?
- A. Clostridium perfringens
- B. Bacillus anthracis
- C. Clostridium tetani
- D. Bacillus cereus
Correct Answer: A
Rationale: The correct answer is A: Clostridium perfringens. This bacterium fits all the characteristics mentioned: Gram-positive rods with spore formation, motile, and gas production in nutrient broth. Clostridium perfringens is known to cause gas gangrene, which aligns with the gas production in nutrient broth. Bacillus anthracis (B) causes anthrax and does not typically produce gas. Clostridium tetani (C) causes tetanus and does not form spores that are motile. Bacillus cereus (D) is a common cause of food poisoning and does not cause gas gangrene.
Researchers of a bacteriological laboratory examine tinned meat for botulinic toxin. For this purpose a group of mice was injected with an extract of the material under examination and antitoxic antibotulinic serum of A, B, E types. A control group of mice was injected with the same extract but without antibotulinic serum. What serological reaction was applied?
- A. Neutralization
- B. Precipitation
- C. Complement binding
- D. Double immune diffusion
Correct Answer: A
Rationale: The correct answer is A: Neutralization. In this experiment, the researchers used antitoxic antibotulinic serum of different types to neutralize the botulinic toxin in tinned meat extract injected into mice. Neutralization is the process of rendering a toxin harmless by combining it with specific antibodies. The purpose of injecting the antitoxic serum was to neutralize the toxin and prevent it from causing harm to the mice. This serological reaction of neutralization directly aligns with the objective of the experiment.
Summary of other choices:
B: Precipitation - Precipitation involves the formation of a visible insoluble complex when an antigen reacts with its corresponding antibody. This process was not described in the scenario.
C: Complement binding - Complement binding involves the activation of the complement system by antigen-antibody complexes. This was not the main focus of the experiment described.
D: Double immune diffusion - This technique is used to detect the presence of specific antigens or antibodies
Which bacterium is known as a common cause of hospital-acquired infections?
- A. Clostridium botulinum
- B. Staphylococcus aureus
- C. Treponema pallidum
- D. Mycobacterium leprae
Correct Answer: B
Rationale: The correct answer is B: Staphylococcus aureus. This bacterium is known as a common cause of hospital-acquired infections due to its ability to colonize the skin and mucous membranes of healthcare workers and patients. Staphylococcus aureus can cause various infections, including surgical site infections and bloodstream infections, in healthcare settings.
Rationale:
1. Clostridium botulinum is known for causing foodborne botulism, not hospital-acquired infections.
2. Treponema pallidum causes syphilis, which is primarily transmitted through sexual contact, not hospital settings.
3. Mycobacterium leprae causes leprosy, which is not commonly associated with hospital-acquired infections.
In summary, Staphylococcus aureus is the correct answer as it is a common cause of hospital-acquired infections due to its prevalence in healthcare environments, unlike the other choices which are not typically associated with hospital-acquired infections.
Gram (-) bacteria have basal structure consisting of:
- A. 20-25% of all materials building the cell wall
- B. 1-4% of all materials building the cell wall
- C. 4-10% of all materials building the cell wall
- D. 10-20% of all materials building the cell wall
Correct Answer: C
Rationale: The correct answer is C: 4-10% of all materials building the cell wall. Gram (-) bacteria have a thin peptidoglycan layer making up 4-10% of the cell wall. This is in contrast to Gram (+) bacteria which have a thicker peptidoglycan layer. Choice A is too high a percentage for Gram (-) bacteria. Choice B is too low as it would not provide enough structural support. Choice D is also too high and would not accurately reflect the composition of Gram (-) bacteria.