Why is surface area an important feature of both digestion and respiration?

Digestion

The surface area of the digestive system is important for the absorption of nutrients. The larger the surface area, the more nutrients can be absorbed. This is why the small intestine has so many folds and villi. The folds increase the surface area of the small intestine by a factor of 10, and the villi increase the surface area by a factor of 100.

Respiration

The surface area of the respiratory system is important for the exchange of gases. The larger the surface area, the more oxygen can be taken in and the more carbon dioxide can be released. This is why the lungs have so many alveoli. The alveoli are tiny sacs that increase the surface area of the lungs by a factor of 100.

In both digestion and respiration, the surface area is important for the movement of molecules across a membrane. The larger the surface area, the faster the molecules can move across the membrane. This is why the small intestine and the lungs have such large surface areas.