Evolution of Animals and Their Organ Systems

Topics: Nervous system, Digestion, Reproductive system Pages: 11 (4172 words) Published: June 10, 2012
Organ Systems Project

(Digestive, Excretory, Circulatory, Reproductive, Nervous)
There is an enormous variety of life on our planet Earth ranging from simple cell bacteria to complex multicellular animals. Animals are creatures in the kingdom Animilia, one of the kingdoms in Whitakers 5 kingdom system. Their bodies consist of 555tanimal eukaryotic cells. Meaning their cell or cells contain a nucleus, are surrounded by a cell membrane (phospholipid bilayer) and can self-reproduce in a free medium. However, not all animals are anatomically the same. They have evolutionized, inside and out, from the ancestral protozoa all the way to the most complex animals chordates. As the animals evolved, cells became tissue, tissues became organs, and organs became organ systems to be able to function as a single organism. The organ systems include: integumentary, digestive, excretory, reproductive, nervous, muscular, skeletal, circulatory, respiratory, immune, and endocrine. Yet, not all organ systems are found in all the ten phyla of animals, but the animals with absent organ systems, have cells or tissues that work together to replace the organ system. The simplest animals include Protozoan. They are microscopic unicellular organisms that commonly show characteristics usually associated with animals of the other phyla. Since they have only cell level of organization, the organelles with in the cell are responsible for the functions the organ systems would perform. For example, in reality, the functions of the digestive system are to capture and physically or chemically disintegrate food, absorb, detoxify, alternate, store and control the release of products of digestion and metabolism. Using a paramecium as the representative ciliated protozoa, the digestive system can be replaced with the oral groove, mouth pore, gullet, developing food vacuole, circulating food vacuole and anal pore. Food particles enter the ciliated oral groove pass through the mouth pore and form a developing food vacuole at the tip of the gullet. The food vacuole circulates through the endoplasm, while diffusing nutrients to the cell. Just as the digestive system would do, the cell absorbs the nutrients and the waste exists the cell via the anal pore. Characteristics of the excretory system are also observed in protozoa. The function of the excretory system is to chemically, and to a lesser extent physically, maintain homeostasis in the cell. That is, by excreting toxic and metabolic waste products, maintaining water balance, proper concentration of salts in the blood, and maintain proper acid-base equilibrium in the body fluids. The paramecium is able to perform these functions by using its contractile vacuoles, feeder canals and excretory pore. The contractile vacuoles are responsible for holding excess water that enters the cell via the feeder canals. Once the contractile vacuoles are filled with enough excess water, the water is released through the excretory pore. The circulatory system is closely related to the digestive and excretory system in the protozoa. The function of the circulatory system is to transport materials to and from cells, form and store blood cells for oxygen transport and defense and drain fluids between cells and return it to the regular circulatory system from which it leaked. It is similar to the digestive and excretory systems because it must transport the nutrients and also drain fluids. The same organelles mentioned before and diffusion are also responsible for replacing the circulatory system. The reproductive system is the first fully functional system in protozoan. The reproductive system is responsible for forming zygotes by the union of two gametes to produce new individuals of the same biological species. Asexual and sexual reproduction can be found in the protozoa, and in both cases the actual events are usually very complicated. In asexual reproduction, many of the complex surface features need to be...
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