Which of the following types of microscopy is valuable in the identification of crystals that are able to rotate light?

Correct Answer: C

Rationale: The correct answer is C: Polarizing microscopy. Polarizing microscopy is valuable in identifying crystals that rotate light because it can distinguish between isotropic and anisotropic materials, such as crystals. When polarized light passes through an anisotropic material like crystal, the light waves are split into ordinary and extraordinary rays, causing the crystals to rotate light. This phenomenon, known as birefringence, is observed under polarizing microscopy. Incorrect Choices: A: Compound brightfield microscopy does not provide the necessary contrast to identify crystals that rotate light. B: Darkfield microscopy is used for observing light scattering, not for identifying crystals that rotate light. D: Phase-contrast microscopy is used to enhance contrast in transparent samples, not specifically for identifying crystals that rotate light.

Correct Answer: C

Rationale: The correct answer is C: Glycoprotein. Glycoproteins are the most common type of protein found in the cell membrane because they play crucial roles in cell signaling, adhesion, and recognition. They have sugar molecules attached to them, which help in cell-cell interactions. Lipoproteins (choice A) have lipids attached to them and are found in cell membranes but are not as common as glycoproteins. Mucoproteins (choice B) are proteins with carbohydrate chains but are not as prevalent in cell membranes. Nucleoproteins (choice D) are proteins associated with nucleic acids and are not typically found in the cell membrane.

Correct Answer: C

Rationale: The correct answer is C (70+). Chronic lymphoblastic leukemia typically affects older adults, with the median age of diagnosis around 70 years old. This is due to the gradual accumulation of genetic mutations over time. Older patients are more likely to develop this type of leukemia compared to younger individuals. Choices A, B, and D are incorrect because they suggest younger age groups, which are less commonly associated with chronic lymphoblastic leukemia. Additionally, younger individuals are more likely to be affected by acute lymphoblastic leukemia rather than the chronic form.

Correct Answer: B

Rationale: The correct answer is B: slow-reacting substance A (leukotrienes). In severe asthma, leukotrienes are potent inflammatory mediators that cause bronchoconstriction, mucus production, and airway inflammation. Antihistamines target histamine, which is not the primary mediator in asthma. Interleukin-2 is involved in immune response modulation, not asthma symptoms. Serotonin plays a role in smooth muscle contraction, but it is not a major player in asthma pathophysiology. Bradykinin is a potent vasodilator and increases vascular permeability, but it is not the primary mediator in asthma. Therefore, the lack of relief from antihistamines suggests that leukotrienes are likely the cause of the symptoms in this patient with severe asthma.

Correct Answer: B

Rationale: The correct answer is B: immunoglobulin heavy-chain class. After binding to its specific antigen, a B lymphocyte can undergo class switching to change the type of antibody it produces while maintaining the same antigen specificity. This process involves recombination events that switch the constant region of the immunoglobulin heavy chain, leading to the production of antibodies with different effector functions. Choices A, C, and D are incorrect because they do not accurately describe the process of class switching in B lymphocytes. Light-chain isotypes, variable region of the heavy chain, and constant region of the light chain do not undergo class switching.