Chapter 42 Dr. Gleason

Chapter 42 Dr. Gleason - Chapter 42: Circulation and Gas...

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Chapter 42: Circulation and Gas Exchange Why are animals multicellular rather than just one big cell? o Answer: Dissolved substances exchanges with environment by diffusion or being transported across cell plasma membranes o Surface area/volume critical!!! Diffusion (Figure 7.11A) o Time of diffusion is proportional to square of distance Example: If it takes 1 second for given quantity of glucose to diffuse 100 μm. Will take 100 seconds to go 1 mm; 3 hours to go 1 cm. Solution to Diffusion Problem o Circulatory and Respiratory Systems Guarantee substances diffuse over short distances to get in/out of cells Invertebrate Circulation o Cnidarians (hydroids and anemones): body wall is two cells thick and encloses gastrovascular cavity Cavity functions in digestion and distribution of substances o Animals with many cell layers have either: Open circulatory system (grasshopper, cockroaches) Hemolymph- body fluid that bathes tissues
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o Like blood but not called blood because not confined to vessels
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Chapter 42 Dr. Gleason - Chapter 42: Circulation and Gas...

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