Which enzyme copies DNA?

When listening the levels of orginization in orginisims from the smallest to most complex , which level is just below organs in complexity

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?

People with one sickle cell allele are not likely to get malaria. what is this an example of?