Explain how three of the most common elements found in living things are important to the human body

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?

What are 3 reasons that natural selection occurs

Polar zones are cold and tend to be dry because of a pressure system of cold. low high