Which pair of groups contain the greatest number of organisms?

Which experiment would most likely contain experimental bias

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?

When the oxygen produced by photosynthetic plants in the water dissolves in the water, which of these is being formed?