Which factor does NOT influence microbiome composition?

A. Genetics: Host genetics influence immune factors, mucosal receptors and other host traits that shape which microbes colonize and persist.
B. Eye Color: Eye color is a physical trait determined by pigment and is not known to be a determinant of overall microbiome composition.
C. Diet: Diet strongly shapes the gut and oral microbiomes by providing different substrates for microbial growth.
D. Age: Age influences microbiome composition across the lifespan (infant → adult → elderly shifts).

A. Nucleus: Contains the cell’s genetic material and regulates gene expression and cell activities, but does not act as the selective barrier for material exchange with the external environment.
B. Lysosome: Membrane-bound organelle with hydrolytic enzymes that digests macromolecules and damaged organelles; not responsible for controlling entry/exit of substances.
C. Plasma membrane: A phospholipid bilayer with embedded proteins that provides selective permeability, transport channels, pumps, and mechanisms (endocytosis/exocytosis) controlling passage of materials into and out of the cell.
D. Cytoplasm: The intracellular fluid and organelle-containing matrix where metabolic reactions occur; it does not determine what crosses the cell boundary.