National Science Bee Practice Test

Gas exchange between the body and the environment is performed by the respiratory system. It starts with the nose, which filters and warms or humidifies incoming air, then the air moves down the trachea into the lungs. In the lungs, tiny air sacs called alveoli sit next to a network of capillaries, and this is where the exchange happens. Oxygen moves from the air in the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli to be exhaled. This exchange relies on differences in partial pressures and occurs across a very thin alveolar membrane. The circulatory system is essential for transporting these gases to and from tissues, but the actual transfer of gases occurs in the lungs. The digestive system handles nutrients from food, and the nervous system coordinates and controls body functions.