Which of the following statements about animal connective tissues is true?
(a) Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly.
(b) In connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load.
(c) Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein.
(d) Proteoglycans can resist compression in the extracellular matrix.
Choice (d) is correct. Collagen is synthesized within the cell and reaches the extracellular environment through exocytosis [choice (a)]. In connective tissues, the extracellular matrix carries the mechanical load [choice (b)]. Cells attach to the collagen matrix with the use of integrins, which span the plasma membrane; integrins then interact with fibronectin, which binds to collagen [choice (c)].
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