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 from 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.
Increasing the Rate of Diffusion
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Specification: OCR Biology A (H020), AS-level, 3.1.1 Exchange surfaces. Topic: Exchange Surfaces and Breathing.
Key terms in this lesson
- diffusion
- The net movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.
- osmosis
- The net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.
- water potential
- A measure of the tendency of water molecules to move out of a solution; pure water has a water potential of zero and adding solute lowers it.
- surface area to volume ratio
- The ratio of an organism's outer surface area to its volume; it decreases as size increases, which limits the rate of exchange achievable by diffusion alone.
More in Exchange Surfaces and Breathing
- Gas Exchange in Unicellular Organisms
- Gas Exchange in Insects
- Diffusion Gradient
- Mass Transport
- Limitations of the Tracheal System
- Gas Exchange in Fish
- Structure of the Gills
- Counter Current Exchange
All 24 lessons in Exchange Surfaces and Breathing · All OCR AS-level Biology topics