Nokea
What is the primary function of platelets?
- A. Producing hormones
- B. Transporting oxygen and carbon dioxide
- C. Clotting and sealing damaged blood vessels
- D. Protecting the body from foreign substances
Correct Answer: C
Rationale: Platelets primarily function in clotting and sealing damaged blood vessels. Firstly, when a blood vessel is injured, platelets rush to the site to form a plug, preventing excessive bleeding. Secondly, platelets release clotting factors to initiate the coagulation cascade, leading to the formation of a stable blood clot. This process is crucial for wound healing and preventing blood loss. Platelets do not produce hormones (choice A), transport gases (choice B), or protect the body from foreign substances (choice D). These functions are carried out by other components of the body's systems.
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How does an antigen stimulate an immune response?
- A. It is captured, processed, and presented to a lymphocyte by a macrophage.
- B. It circulates in the blood, where it comes in contact with circulating lymphocytes.
- C. It is a foreign protein that has antigenic determinants different from those of the body.
- D. It combines with larger molecules that are capable of stimulating production of antibodies.
Correct Answer: A
Rationale: Antigens are captured, processed, and presented to lymphocytes by antigen-presenting cells like macrophages, initiating an immune response.
Which of the following restriction endonucleases produce fragments with blunt ends?
- A. Sacl
- B. EcoRI
- C. Smal
- D. HindIII
Correct Answer: C
Rationale: The correct answer is C: Smal. Smal is a restriction endonuclease that cuts DNA at specific sequences, producing fragments with blunt ends. Smal recognizes the sequence CCCGGG and cuts between the two C's on both strands, resulting in blunt-ended fragments.
Explanation for incorrect choices:
A: Sacl - Sacl produces sticky ends, not blunt ends.
B: EcoRI - EcoRI produces sticky ends with overhangs.
D: HindIII - HindIII also produces sticky ends with overhangs.
In summary, Smal is the only enzyme among the choices that generates DNA fragments with blunt ends.
Who introduced the concept of discrimination between self and non-self?
- A. Elie Metchnikoff
- B. Louis Pasteur
- C. Paul Ehrlich
- D. Charles Janeway
Correct Answer: C
Rationale: Paul Ehrlich introduced the concept of discrimination between self and non-self through his "horror autotoxicus" theory. He proposed that the immune system can differentiate between harmful non-self antigens and self-antigens. Ehrlich's theory laid the foundation for understanding immune responses and the development of immunology. Metchnikoff focused on phagocytosis, Pasteur on microbiology, and Janeway on innate immunity, not specifically on self vs. non-self discrimination.
In order to grow, all microorganisms require:
- A. liquid water
- B. organic substances
- C. oxygen
- D. warm temperatures
Correct Answer: A
Rationale: The correct answer is A: liquid water. Water is essential for all cellular functions, including metabolism and nutrient transport. Without water, microorganisms cannot grow or survive. Organic substances (choice B) are important as a nutrient source, but water is indispensable for growth. While oxygen (choice C) and warm temperatures (choice D) can enhance growth for some microorganisms, they are not universally required for all microorganisms to grow.
Which disease is an example of Type V hypersensitivity?
- A. Multiple sclerosis
- B. Grave's disease
- C. Rheumatoid arthritis
- D. Type 1 diabetes mellitus
Correct Answer: B
Rationale: The correct answer is B, Grave's disease, for Type V hypersensitivity. In Type V hypersensitivity, antibodies target cell surface receptors, leading to abnormal stimulation or blockage. In Grave's disease, antibodies target the thyroid-stimulating hormone receptor, leading to excessive thyroid hormone production. Multiple sclerosis (A) is an example of Type IV hypersensitivity involving T cell-mediated response. Rheumatoid arthritis (C) is an example of Type III hypersensitivity involving immune complex deposition. Type 1 diabetes mellitus (D) is an example of Type II hypersensitivity involving antibody-mediated destruction of cells.