A student is reading about the chemical composition of a category of molecules. The molecules are found as repeating units of proteins. What type of molecule are the repeating units?
amino acids
fatty acids
monosaccharides
nucleotides

Ivan is looking at a cross section of a stem taken from a vascular plant. he sees two different types of vascular tissue: the xylem, which is closer to the center of the stem, and the phloem, located around the xylem, closer to the outside of the stem. how do these two structures work together in a living plant?