If you can get the mouth of the balloon over the mouth of the bottle, then you will not need the cork. Make sure it is tight. If you have trouble catching hold of the balloon, put a small piece of tape on the center of the balloon to make a handle. 39 Easy Animal Biology Experiments by Robert Wood Gas exchange in the lungs. To supply oxygen to the blood and remove carbon dioxide from it, the lungs need to draw in fresh gas and expel stale gas.
Fresh gas is drawn in when the diaphragm and other muscles in the chest wall contract.
The expansion lowers the pressure in the lungs, and air from the atmosphere flows in. When the muscles relax, the lungs return to a smaller volume, and gas flows out into the atmosphere. This action is called expiration or exhalation. Diaphragm , pronounced DY uh fram , the large muscle attached to the lower ribs, separates the chest from the abdomen. Only human beings and other mammals have complete diaphragms.