Which statement best describes the function of the cytoskeleton?

A. Microvilli: Microvilli are small, finger-like projections on the apical surface of epithelial cells that increase surface area for absorption and secretion. They are abundant in the intestines and kidney tubules but do not play a primary role in clearing mucus or trapped particles from the respiratory tract.

B. Flagella: Flagella are long, whip-like structures used for motility in certain single-celled organisms, such as sperm cells or bacteria. Human respiratory epithelial cells do not possess flagella, so they are not involved in airway mucus clearance.

C. Cilia: Cilia are hair-like projections on the apical surface of respiratory epithelial cells that beat in a coordinated manner to move mucus, trapped dust, and pathogens toward the pharynx for clearance. Chronic cigarette smoking damages ciliary structure and function, impairing mucociliary clearance and leading to mucus accumulation, chronic productive cough, and recurrent infections.

D. Desmosomes: Desmosomes are intercellular junctions that provide mechanical adhesion between epithelial cells. While important for tissue integrity, they do not facilitate movement of mucus or debris along the airway epithelium.

E. Tight junctions: Tight junctions are specialized connections between epithelial cells that prevent paracellular leakage of fluids and solutes. They maintain barrier function but are not involved in the active transport of mucus or particulate matter along the respiratory tract.

A. Yeasts are multicellular fungi that reproduce by spore fragmentation: Multicellular fungi, such as molds, have hyphal structures and can reproduce via spore formation or fragmentation of mycelia. Yeasts, however, are unicellular and do not form multicellular hyphae under normal conditions.

B. Yeasts are unicellular fungi that reproduce by budding: Yeasts are single-celled eukaryotic fungi that reproduce primarily through asexual budding, where a new daughter cell forms as an outgrowth from the parent cell. Their unicellular structure and budding reproduction distinguish them from filamentous fungi.

C. Yeasts are prokaryotic organisms that divide by binary fission: Prokaryotic organisms, such as bacteria, lack a nucleus and organelles and reproduce primarily by binary fission. Yeasts are eukaryotic, containing a true nucleus and membrane-bound organelles, and although some yeast species may divide by fission, they are classified as eukaryotes.

D. Yeasts are photosynthetic eukaryotes with chloroplasts: Photosynthesis is carried out by plants and certain protists possessing chloroplasts. Yeasts lack chloroplasts and do not perform photosynthesis; they obtain energy through fermentation or aerobic respiration, depending on environmental conditions.