The amount of water on Earth has for billions of years.

Which of the following is not a way in which a vascular plant's xylem and phloem are similar?

An easy way to calculate the amount of energy available at each level is to what?

Use the phylogenetic tree to the right to determine which statement below is true. organisms a and f are not related. organism e is more closely related to organism b than organism f. organisms c and d are more closely related than organisms a and b. phylogenetic trees