Atmospheric nitrogen varies widely from location to location, and local shortages occur frequently. b. atmospheric nitrogen cannot be used by most organisms. c. there is very little free nitrogen in the air. d. atmospheric nitrogen exists primarily in the stratosphere and does not come into contact with terrestrial ecosystems.

Factors that can increase mutation rates a. high temps b. low temps c. food additives d. uv rays

According to the cell theory, which describes cells? a. all organisms are composed of multiple cells. b. all cells have the same structure and function. c. cells are found in everything on earth. d. living organisms are not created spontaneously

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.