Study GuideBiology–Blood and Circulation1. Circulatory SystemsAll living organisms need a way to move important materials—such asnutrients, gases, andwastes—to and from their cells. How this transport happens depends on the size andcomplexity ofthe organism.1.1 Simple Organisms: No Transport System NeededSingle-celled organisms live in constant contact with their environment. They can take inoxygen andnutrientsand releasewastesdirectly across their cell surface.The same is true for small and simple organisms such asalgae, bryophytes, sponges, cnidarians,and flatworms. Because their bodies are thin or small, materials do not have to travel far.1.2 Larger Organisms: Transport Becomes EssentialAs plants and animals becomelarger and more complex, many cells are located far from theoutside environment. Diffusion alone is no longer enough. To solve this problem, these organismshave evolvedtransport systems, known ascirculatory systems, to move materials efficientlythroughout the body.1.3Circulatory Systems: The Big PictureA circulatory system is responsible for:•Deliveringnutrients and oxygento cells•Carryingwaste materialsaway from cells•Helping coordinate activities throughout the organismBecause plants and animals have different lifestyles and needs, they have developeddifferent typesof circulatory systems.Preview Mode
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