Here are five important roles of diffusion in animals: 1. Gas Exchange: Oxygen diffuses from the alveoli in the lungs into the blood, and carbon dioxide diffuses from the blood into the alveoli. 2. Nutrient Absorption: Digested nutrients diffuse from the small intestine into the bloodstream. 3. Waste Removal: Waste products like urea diffuse from body cells into the blood to be transported to the kidneys. 4. Oxygen Transport to Tissues: Oxygen diffuses from red blood cells into the body's tissues. 5. Carbon Dioxide Transport from Tissues: Carbon dioxide diffuses from body tissues into the blood.