Respiration

This requires energy released by respiration, the chemical reactions in cells that release energy from glucose. Transport proteins in the cell membrane use this energy to move substances across the membrane. Unlike diffusion and osmosis, active transport is not a passive process.

Carbon moves into plants through photosynthesis, passes between organisms through feeding, and returns to the atmosphere through respiration and combustion. A material cycle is therefore a network of routes, not necessarily one simple loop.