Name the two molecules which alternative to make the side portions or backbone of a dna model.

Which represents a negative impact of technology

Why is it important to study each branch of earth science?

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?