Which of the following is most likely to cause a mutation? 1. the fact that ribosomes are located on the rough ER
2. the insertion of a nucleotide into a DNA strand
3. the movement of tRNA to the ribosome
4. the release of mRNA from DNA after it is copiped

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?