![]() ![]() Diffusion is insufficient over distances of more than a few millimeters, because the time it takes for a substance to diffuse from one place to another is proportional to the square of the distance.Diffusion alone is not adequate for transporting substances over long distances in animals-for example, for moving glucose from the digestive tract and oxygen from the lungs to the brain of a mammal.At the same time, carbon dioxide diffuses out into the water.Ĭoncept 42.1 Circulatory systems reflect phylogeny.Oxygen dissolved in the surrounding water diffuses across the thin epithelium covering the gills and into a network of tiny blood vessels (capillaries).For aquatic organisms, structures such as gills present an expansive surface area to the outside environment.Most animals have organ systems specialized for exchanging materials with the environment, and many have an internal transport system that conveys fluid (blood or interstitial fluid) throughout the body.Metabolic wastes, such as carbon dioxide, move out of the cell.The resources that they need, such as nutrients and oxygen, move across the plasma membrane to the cytoplasm.Every organism must exchange materials and energy with its environment, and this exchange ultimately occurs at the cellular level.Chapter 42 Circulation and Gas Exchange Lecture Outline ![]()
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