Nitrogen enters the food chain: a. primarily through soil-dwelling bacteria that "fix" it by attaching it to other atoms. b. through methane produced by herbivores as a by-product to the breakdown of plant material. c. through soil erosion followed by runoff into streams and ponds. d. when rocks dissolved by rainwater become soil and are used by plants as they grow. e. from the atmosphere when "fixed" by the photosynthetic machinery of plants.

What is the significance of the protein-lined pits? a. protein attracts other proteins needed for atp synthesis within the cell. b. protein-lined pits are able to transport one molecule at a time down the concentration gradient within the cell. c. the polarity of proteins allows other polar molecules to attach and be transported in the cell by transport channels. d. receptors within the pits allow ligands to fuse and be transported into the cell by endocytosis.