Energy flow through an ecosystem is
A. completely random
B. a one-way pathway
C. always towards the Sun
D. a dual-directional pathway

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?

Which statement is true for bacteria a. bacteria have complex internal structures b. all bacteria are spiral in shape c. all bacteria cause disease in animals d. bacteria break down some foods

Substances that can pass through cell membranes by diffusion include a. na ions. b. proteins c. glucose. d. oxygen.