Synovial cavities are exposed to the external environment.

A. Help in the formation of cell membranes: Lysosomes do not participate in building cell membranes. Their main role is to digest cellular waste, foreign particles, and damaged organelles, not to synthesize structural components like membranes.

B. Digesting particles taken in by endocytosis: Lysosomes contain hydrolytic enzymes that break down materials brought into the cell via endocytosis, helping the cell recycle nutrients and eliminate debris.

C. Degrading worn-out or nonfunctional organelles: Lysosomes perform autophagy, digesting damaged or obsolete organelles to maintain cellular health and prevent accumulation of dysfunctional components.

D. Breaking down bone to release calcium ions into the blood: Specialized lysosomes in osteoclasts secrete enzymes that degrade bone matrix, releasing calcium and phosphate ions into circulation, which is part of normal bone remodeling.

A. Most important steroid; cholesterol: Cholesterol is a steroid that serves as a key component of cell membranes and as a precursor for other steroid hormones.

B. Nucleotide; nucleic acid: Nucleotides are the building blocks of nucleic acids such as DNA and RNA, so this pairing correctly represents the relationship between the monomer and polymer.

C. Eicosanoid; triglyceride: Eicosanoids are signaling molecules derived from fatty acids, not triglycerides. Triglycerides are energy-storage molecules, so this pairing is incorrect.

D. Monosaccharide; carbohydrate: Monosaccharides, such as glucose and fructose, are the simplest units of carbohydrates, correctly linking the monomer to the macromolecule.