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Lecture 42

BSC 2010 Lecture 42: BSC 2010 Chapter 42 Notes Dixon

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Florida State University
Biological Science
BSC 2010
Kevin Dixon

Overview: Trading Places ● Every organism must exchange materials with its environment ● Exchanges ultimately occur at the cellular level by crossing the plasma membrane ● In unicellular organisms, these exchanges occur directly with the environment ● For most cells making up multicellular organisms, direct exchange with the environment is not possible ● Gills are an example of a specialized exchange system in animals ● O2 diffuses from the water into blood vessels ● CO2 diffuses from blood into the water ● Internal transport and gas exchange are functionally related in most animals Circulatory systems link exchange surfaces with cells throughout the body ● Diffusion is only efficient over small distances ● In small and/or thin animals, cells can exchange materials directly with the surrounding medium ● In most animals, cells exchange materials with the environment via a fluid-filled circulatory system Gastrovascular Cavities ● Some animals lack a circulatory system ● Some cnidarians, such as jellies, have elaborate gastrovascular cavities ● A gastrovascular cavity functions in both digestion and distribution of substances throughout the body ● The body wall that encloses the gastrovascular cavity is only two cells thick Evolutionary Variation in Circulatory Systems ● A circulatory system minimizes the diffusion distance in animals with many cell layers General Properties of Circulatory Systems ● A circulatory system has ● A circulatory fluid ● A set of interconnecting vessels ● A muscular pump, the heart ● The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes ● Circulatory systems can be open or closed and vary in the number of circuits in the body Open and Closed Circulatory Systems ● In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open circulatory system ● In an open circulatory system, there i
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