On page 103, Shubin provides a very nice diagram of the development of organs from three germ layers: mesoderm, ectoderm, and endoderm. On page 659 of Cambell, further discussion about these germs layers are discussed. Differentiate between diploblastic and triploblastic and the organs and tissues associated with each germ layer. Further discuss the animal kingdom and the differences we see between different phyla based on germ layer and other associated features. Discuss how the theme of evolution has affected the categorization of each of these animal phyla. Lastly, discuss the differences between the molecular tree and morphological tree. What are the similarities between these trees and what are the differences?
(Bobby Muttilainen, rmuttilainen@gmail.com)
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ReplyDeleteThe body plan of many animals can be different depending on the organization of its tissues. Sponges and a few other organisms lack true tissue (collections of specialized cells isolated from other tissues by membranous layers), but in all other animals, the embryo begins to form layers as it goes through gastrulation. These layers are called germ layers, which go on to form various tissues/organs throughout the body. Animals that have two germ layers - such as cnidarians (corals, jellies, etc..) - are said to be diploblastic while animals that have three germ layers are said to be triploblastic.
ReplyDeleteDiploblastic organisms have only an ectoderm (the outermost germ layer) and an endoderm (the innermost germ layer) while triploblastic organisms have an ectoderm, endoderm, and a mesoderm (which is the germ layer between the ectoderm and endoderm). The ectoderm gives rise to the outer covering of an animal and in some organisms, the outer covering of the central nervous system. In humans specifically, the ectoderm forms the epidermis of the skin and epithelial lining of the mouth/anus, the cornea of the eye, the nervous system, tooth enamel, etc... The mesoderm gives rise to muscles and most of the organs that lie between the digestive tract and the outer covering of an animal. In humans specifically, the mesoderm forms the notocord, skeletal system, muscular system, excretory system, circulatory and lymphatic systems, reproductive system, lining of the body cavity, etc... The endoderm gives rise to the lining of the developing digestive tube (archenteron) and the digestive tract, as well as organs like the liver and lungs. In humans specifically, the endoderm forms the epithelial lining of the digestive tract and respiratory system, the liver, pancreas, thymus, thyroid glands, etc...
Taking a look at all of the different animal phyla, evolution over many generations and millions of years has brought some extremely significant changes in organisms from phyla porifera (sponges) - which have no true tissues - to phyla cnidaria - which are diploblastic - to phylums annelida, mollusca, arthropoda, and nematoda - which are all triploblastic. Evolution has changed organisms in phylum porifera, which had no true tissues and no germ layers (and therefore no real organs or bodily systems) to diploblastic organisms, which had an endoderm and ectoderm (therefore being able to form basic protective outer layers as well as linings of the digestive tube) and but no mesoderm (therefore not muscles and complex systems such as the digestive, respiratory, circulatory, and excretory system. Over another million years and many generations, evolution went further and animals became triploblastic - not only having an endoderm and ectoderm, but a mesoderm, therefore being able to create basic bodily systems, such as the digestive, excretory, respiratory, and circulatory system. These phylums with triploblastic organisms - such as annelida, mollusca, and nematoda - did not have nearly as advanced systems of the body as humans do, since these organisms were still invertebrates. But after evolution over millions of years and generations again, mammals with more complex digestive. respiratory, and circulatory systems formed and eventually, humans became the organisms with the most complex and efficient bodily systems.
ReplyDeleteA molecular tree is a map of animal phylogeny based on molecular data, such as different ribosomal genes, Hox genes, and other protein-coding nuclear genes. A morphological tree is a map of animal phylogeny based on morphological and developmental characteristics such as symmetry, body plans and germ layers. Although both the morphological and molecular trees have a similar basis, the molecular tree branches off into more categories based on some specific molecular data that may not necessarily match morphological and developmental data. The morphological tree is very accurate, but the molecular tree is said to be even more accurate and specific. Also, the morphological tree has less animal phyla branching off of it than the molecularl tree, which means that there is a whole different phylum of animal just based on molecular data.
Sujin Ko (sujinko93@gmail.com)
Sources: Campbell - page 659, 661-663, figure 47.14
http://waynesword.palomar.edu/trnov01.htm#animals