Increasing the Rate of Diffusion

Tracheoles are the small tubes that form the terminal endings of the tracheal system and range from 1 to 0.1 μm in diameter.Tracheole walls are capable of transporting oxygen at high rates by diffusion because they are thin (usually <0.1 μm) and have a very large surface area to volume ratio.Thus, the tracheoles are the major site of gas exchange between the tissues and the tracheal system.During periods of intense exercise, the muscles around the tracheoles respire anaerobically and produce lactic acid.This lowers the water potential in muscle cells and water moves form the ends of the tracheoles into the muscle cells by osmosis enabling the final diffusion pathway to be in a gas rather than in water.The reliance on mostly diffusion limits the size of insects because the length of the diffusion pathway has to be short for diffusion to be fast enough to supply the insect's metabolic needs.