Which of the following best describes diffusion? *
a)movement of water molecules across a selectively permeable membrane
b)movement of molecules from an area of higher concentration to lower concentration
c)movement of materials across a cell membrane using cellular energy
d)movement of materials across a cell membrane without using the cell's energy

Drag each tile to the correct box. the body monitors the levels of oxygen in the blood to regulate breathing. isabel is running in a marathon and is near the finish line. she feels out of breath. how will her nervous system work to generate a reaction? arrange the tiles in chronological order. isabel's breathing rate increases. sensory receptors in the arteries detect low oxygen levels. the brain sends signals through motor neurons. sensory neurons generate an impulse. the central nervous system relays an impulse to certain brain regions.