Immunodeficiency diseases occur when individuals have defects in leukocyte adhesion to inflamed endothelial cells, thereby impeding the extravasation of phagocytes into infected tissues. When neutrophils from one class of these patients were isolated and tested using in vitro assays for neutrophil-endothelial cell interactions and extravasation, it was found that the neutrophils could slowly roll along the endothelial vessel wall but were unable to arrest and migrate across the endothelium. The most likely protein deficient in these neutrophils is:

Correct Answer: D

Rationale: Integrins mediate neutrophil arrest; rolling (selectins, B/C) occurs, but without integrins, migration fails; ICAMs are on endothelium.

Correct Answer: A

Rationale: Food chains describe the linear transfer of energy and nutrients from one organism to another in an ecosystem.

Correct Answer: C

Rationale: Clonal selection is the antigen-driven proliferation of specific B and T cells, not involving NK cells, leukocytes, or complement.

Correct Answer: C

Rationale: The figure (assumed) shows an active plasma B cell at part C, as per the text, typically depicted as antibody-producing.

Correct Answer: C

Rationale: T cells (CD4+) recognize MHCII-antigen complexes and help B cells, unlike antigenic shift (viral reassortment), immature DCs (antigen uptake), or soluble proteins.