Which of the following statements best characterizes an antibody?

Correct Answer: D

Rationale: Rationale for Correct Answer D: 1. Antibodies are composed mainly of proteins, specifically immunoglobulins. 2. Antibodies are synthesized in response to foreign proteins or polysaccharides, known as antigens. 3. This process involves B cells recognizing antigens and producing antibodies. 4. The statement accurately reflects the nature of antibody structure and synthesis. Summary of Incorrect Choices: A: Antibodies do not contain RNA as their basic structure; they are primarily composed of proteins. B: Antibodies can be distinguished from albumin fraction as they have specific functions in the immune system. C: Antibodies consist of two heavy and two light chains, not four identical protein subunits, and are not typically dissociated by urea.

Correct Answer: A

Rationale: The correct answer is A because a consistent exercise routine is important for managing rheumatoid arthritis. Performing exercises every day helps improve joint mobility and strength without causing excessive strain. Option B is incorrect as exercising during inflammation can worsen symptoms. Option C is incorrect as exercising past the point of pain can lead to injury. Option D is incorrect as overcompensating the following day can also lead to injury and disrupt the exercise program's consistency.

Correct Answer: D

Rationale: Effector T cells are fully activated, expanded, and capable of carrying out their functions, such as killing infected cells or assisting in immune responses. The correct choice (D) accurately describes the characteristics of effector T cells. They are not naïve cells (A), as they have encountered their specific antigen. They are not just starting to proliferate (B), as they have already undergone extensive proliferation. They have not only been energized (C), but have also completed the necessary steps for full activation and functionality.

Correct Answer: A

Rationale: The dark zone of germinal centers is composed of rapidly proliferating B cells. This is because during the dark zone phase of the germinal center reaction, B cells undergo rapid proliferation and somatic hypermutation to generate high-affinity antibodies. T cells and dendritic cells are typically found in the light zone of the germinal centers where B cells interact with them to receive signals for selection. Rapidly proliferating T cells are not typically found in the dark zone. Follicular dendritic cells are present in the light zone where they present antigens to B cells but not in the dark zone where B cell proliferation mainly occurs.

Correct Answer: B

Rationale: Step 1: The current Influenza vaccine is designed to provide protection against multiple strains to increase effectiveness. Step 2: Option B includes a combination of different strains (H1N1, H5N1, and B), covering a broader spectrum of the virus. Step 3: Including different strains helps to address potential mutations and variations in circulating viruses. Step 4: Option B is the most comprehensive choice compared to others, offering a more robust protection against various strains. Summary: Option A is too limited with only 3 type A strains, while option C focuses only on 2009 H1N1 strain. Option D is also limited to only the most common seasonal H1N1 strain. Option B stands out as the correct choice for its broad coverage of different strains.