In the Iron cycle, the transferrin receptor carries:

Correct Answer: D

Rationale: The correct answer is D because the transferrin receptor is responsible for transporting transferrin-bound iron into cells, particularly erythrocytes. This process allows for the delivery of iron to cells for various biological functions, such as hemoglobin synthesis. Choice A is incorrect as iron is typically absorbed into duodenal cells, not transported out. Choice B is incorrect as it does not align with the role of the transferrin receptor in importing iron. Choice C is incorrect as the transferrin-bound iron in the plasma is not directly handled by the transferrin receptor but rather serves as a carrier for iron transport.

Correct Answer: B

Rationale: The correct answer is B: P. ovale. P. ovale can cause relapses of malaria due to the presence of dormant liver stages (hypnozoites) that can reactivate weeks to years after the initial infection. P. falciparum, P. malariae, and P. knowlesi do not have hypnozoites and therefore do not cause relapses. P. falciparum is known for its severe manifestations, P. malariae has a long incubation period but does not cause relapses, and P. knowlesi mainly infects monkeys and rarely causes human malaria.

Correct Answer: D

Rationale: The correct answer is D: delayed hypersensitivity. Hemolytic disease of the newborn caused by Rh incompatibility is a type II hypersensitivity reaction. Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive fetus, leading to the mother producing antibodies against the Rh antigen. This immune response is delayed and involves sensitized T cells. This results in the destruction of Rh-positive red blood cells in the newborn. Choice A (atopic or anaphylactic) refers to type I hypersensitivity, which involves immediate IgE-mediated reactions like allergies. Choice B (cytotoxic) is a close contender, as it also involves antibodies targeting specific antigens on cell surfaces, but it typically involves antibody-dependent cell-mediated cytotoxicity rather than delayed responses. Choice C (immune complex) relates to type III hypersensitivity, where immune complexes deposit in tissues and activate complement, causing inflammation. However, this mechanism is not the primary process in hemolytic disease of the newborn caused by

Correct Answer: D

Rationale: The correct answer is D (bovine serum albumin). Bovine serum albumin can act as a carrier protein, allowing hapten (penicillin) to bind and form a complex, triggering an immune response. This complex induces memory B cells, leading to a secondary response upon re-exposure to penicillin. Penicillin alone (choice A) is a hapten and cannot induce a secondary response without a carrier protein. Penicillin bound to egg albumin (choice B) is specific to egg albumin, not penicillin, and would not generate a response to penicillin. Egg albumin (choice C) is a protein unrelated to penicillin. Bovine serum albumin (choice D) is the correct carrier protein for penicillin in this context.

Correct Answer: B

Rationale: The correct answer is B: increased numbers of severe bacterial infections. Severely reduced C3 levels indicate a deficiency in the complement system, which plays a key role in immune defense against bacteria. Without C3, the ability to opsonize bacteria and enhance phagocytosis is impaired, leading to an increased susceptibility to severe bacterial infections. The other choices are incorrect because low gamma globulin levels are associated with antibody deficiencies, severe viral infections are typically more common with T-cell deficiencies, and hemolytic anemia is linked to issues with red blood cell destruction rather than bacterial infections.