Compare respiratory systems of the earthworm, frog, and squid. Explain how the specimen breathes and which organs are involved.

Earthworm: Gas exchange through skin - - tubular shape gives it a large surface area, moist skin promotes gas exchange. Frog: Diffusion (if enough oxygen is present), external gills can be used to increase surface area where there is less oxygen. Snake: Evolution of the trachea, epiglottis, and nostrils - - breathe almost entirely through lungs (some through skin). Breathing takes place by lungs changing size. Squid: The water and oxygen enter the squid's body through the mantle. The respiratory exchange between the carbon dioxide and the oxygen occurs in the gills. The oxygen is then carried through the tissues by the blood and the carbon dioxide and the water are expelled from the body through the siphon.