Answer: A. the gravitational pull of the Sun
The sun is providing a centripetal force pulling the earth inward toward the sun. At the same time, the inertia of the earth is making it want to move forward in a straight line. The two forces work together to create the net effect of the earth orbiting around the sun. Other planets, moons, asteroids, and celestial objects exert gravitational forces on the earth as well, but nowhere near the amount of what the sun does.
The two stages of photosynthesis: Photosynthesis takes place in two stages: light-dependent reactions and the Calvin cycle (light-independent reactions). Light-dependent reactions, which take place in the thylakoid membrane, use light energy to make ATP and NADPH.
Double layer phospholipids.
