The Fundamental Unit of Life — Science STD 9 — Question

Diffusion is important to organisms because it is the process by which useful molecules enter the body cells and waste products are removed.
The intestines: Digested food molecules (amino acids, glucose) move down a concentration gradient from the intestine to the blood. Waste products such as carbon dioxide or urea travel by diffusion from body cells into the bloodstream.
The lungs: Oxygen moves from high concentration (in the air sac) to a lower concentration (in the blood). Carbon dioxide moves from high concentration (in the blood) to a lower concentration (in the air sac).