Answers to these questions can be found in Appendix: Self-Quiz Answers. THE PROC

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Answers to these questions can be found in Appendix: Self-Quiz Answers. THE PROCESS OF SCIENCE 12. Mammals have a four-chambered heart, with two ventricles and two atria. So do birds, alligators, and crocodiles, but other living reptiles have a three-chambered heart, with just one ventricle. Paleontol ogists debate whether dinosaurs had a three-chambered or a four-chambered heart. Long-necked sauropod dinosaurs could have had unusual circulatory demands because their head may have been raised far above the heart. The farther the head is above the heart, the greater the systolic pressure needs to be for blood to reach the brain. For example, the 2 2 long-necked dinosaur Brachiosaurus may have carried its head as much as 6 m (20 feet) above its heart. It is estimated that such an anatomy demanded a systolic blood pressure of 500 mm of mercury for blood to reach the brain! Some paleontologists consider this evidence that dinosaurs had a four-chambered heart that supported a dual circulatory system similar to that of birds and mammals, rather than the three- chambered heart of most nonbird reptiles. Can you explain why?

Explanation / Answer

The dual circulatory system is the one in which there would be two individual pathways for blood circulation. This is done first through the pulmonary circuit followed by the systemic circuit. Thus helps in release of carbon dioxide. The double circulation helps in direct oxygenation via the pulmonary circuit which has been developed. This would result in the blood passing twice from the heart with no mixture, thus helping to maintain a greater pressure as a result of greater blood flow to tissues. If the heart of brachiosaurus had only a single pump, or did not have a double chambered hear, in order to draw blood to heights as high as 20 ft would have put huge strain on the heart and the blood pressure would not have been stable or even worked properly.

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