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I always respected Dennis and Brian the most in the FE field, and I valued their integrity above all else. Their great hearts attracted me to them, not their talent, genius, or fame. I have written plenty about my days with and , and interested readers can discover more if they wish. I hope to convey what the learning experience of carrying their spears was like. My and comprised the kind of education that few survive for long. Although my education with Brian was far gentler, I learned important lessons from him. If not for my adventures, I would not have much worth saying. Even though much of this essay “merely” deals with mainstream science theory and data, . This essay is obviously not the work of a professional scientist, historian, or economist.

Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness

The Heart and Circulation of Blood - CU Boulder

- Lymphatic System research papers look into the part of the circulatory system that is comprised of a network of conduits that carry lymph, a clear fluid, towards the heart.

Respiratory system plays a major role of transporting oxygen to the circulatory system which in turn ..

But plants had to migrate before animals did, as they formed the terrestrial food chain’s base. Along with desiccation issues, plants needed structures to raise them above the ground, roots, a circulatory system, and new means of reproduction. Large temperature swings between day and night also accompanied life on land. Plants developed to conserve moisture, a that piped water from the roots up into the plant and transported nutrients where they were needed, and plant to function. Vascular plants pumped water through their tissues in tubes by tissues and pulling up more new water behind the evaporating water via the “chain” of water’s . The last common ancestor of plants and animals , and sexual reproduction is how nearly all eukaryotes reproduce today, although many ways exist to . The first vascular plants are considered to have attained their height in order to .The in Scotland is the most famous fossil bed that records complex life’s early colonization of land.

Factual essay about the circulatory system Very goodThe Circulatory SystemThe circulatory system in anatomy and physiology is the course taken by …

Biology Exam Custom Essay – Focus Essays

But the branch of the that readers might find most interesting led to humans. Humans are in the phylum, and the last common ancestor that founded the Chordata phylum is still a mystery and understandably a source of controversy. Was our ancestor a ? A ? Peter Ward made the case, as have others for a long time, that it was the sea squirt, also called a tunicate, which in its larval stage resembles a fish. The nerve cord in most bilaterally symmetric animals runs below the belly, not above it, and a sea squirt that never grew up may have been our direct ancestor. Adult tunicates are also highly adapted to extracting oxygen from water, even too much so, with only about 10% of today’s available oxygen extracted in tunicate respiration. It may mean that tunicates adapted to low oxygen conditions early on. Ward’s respiration hypothesis, which makes the case that adapting to low oxygen conditions was an evolutionary spur for animals, will repeatedly reappear in this essay, as will . Ward’s hypothesis may be proven wrong or will not have the key influence that he attributes to it, but it also has plenty going for it. The idea that fluctuating oxygen levels impacted animal evolution has been gaining support in recent years, particularly in light of recent reconstructions of oxygen levels in the eon of complex life, called and , which have yielded broadly similar results, but their variances mean that much more work needs to be performed before on the can be done, if it ever can be. Ward’s basic hypotheses is that when oxygen levels are high, ecosystems are diverse and life is an easy proposition; when oxygen levels are low, animals adapted to high oxygen levels go extinct and the survivors are adapted to low oxygen with body plan changes, and their adaptations helped them dominate after the extinctions. The has a pretty wide range of potential error, particularly in the early years, and it also tracked atmospheric carbon dioxide levels. The challenges to the validity of a model based on data with such a wide range of error are understandable. But some broad trends are unmistakable, as it is with other models, some of which are generally declining carbon dioxide levels, some huge oxygen spikes, and the generally relationship between oxygen and carbon dioxide levels, which a geochemist would expect. The high carbon dioxide level during the Cambrian, of at least 4,000 PPM (the "RCO2" in the below graphic is a ratio of the calculated CO2 levels to today's levels), is what scientists think made the times so hot. (Permission: Peter Ward, June 2014)

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appeared in the Ediacaran, and Cambrian Period skeletons became a key aspect of the coming arms race between predator and prey. appeared in which about was transferred to the animal that ate it. Unlike the internal skeletons that characterized fish, amphibians, reptiles, birds, and mammals, the first skeletons were external. Hard shells protected from predation, and the bigger the animal, the more likely it would survive (but a bigger animal also meant a bigger energy windfall if it could be eaten). But size presented immense challenges. Similar to how complex cells needed to , increasing size presented numerous problems to early complex life. How could a large organism supply energy and other nutrients to its cells? Remove waste? Move? Life solved the problems by making structures and organs from specialized cells. By the Cambrian Period’s end, animals had developed skeletons, gills, muscles, brains, circulatory systems, digestive and eliminative systems, nervous systems, respiratory systems, and internal organs which included eyes, livers, kidneys, etc.