History of Invertebrates - Welcome to Mr. Walker's Class Website

History of Invertebrates - Welcome to Mr. Walker's Class Website

History of Invertebrates Bonneville High School Mr. Walker Water and Life The origin and maintenance of life on earth depends on water. Allows the basic biomolecules.

Lipids Carbohydrates Nucleic Acids Proteins How life began Two Theories: Spontaneous Generation: Living things can come from other nonliving things Biogenesis: Living things can come from other living things.

Experiments: Experiments by Louis Pasteur in the 1860s convinced scientists that organisms do not arise repeatedly from inorganic matter. About 60 years later, A. I. Oparin and J. B. S. Haldane provided an explanation for how a common ancestor of all living forms could have arisen from nonliving matter almost 4 billion years ago. The origin of life followed a long period of abiogenic molecular evolution on earth in which organic molecules slowly accumulated in a primordial soup. The atmosphere of the primitive earth was reducing, with little or no free oxygen present. Ultraviolet radiation, electrical discharges of lightning, or energy from hydrothermal vents could have provided energy for early formation of organic molecules. Stanley Miller and Harold Urey demonstrated the plausibility of the Oparin-Haldane hypothesis by simple but ingenious experiments. The concentration of reactants necessary

for early synthesis of organic molecules might have been provided by damp surfaces, clay particles, iron pyrite, or other conditions. RNA might have been the primordial biomolecule, performing the functions of both genetic coding of information and catalysis. When selfreplicating systems became established, evolution by natural selection could have increased their diversity and complexity. Prokaryotes The earliest bacterium like organisms developed about 3 billion years ago. These bacterium (cyanobacteria) were capable of producing oxygen through photosynthesis. These organisms rules the

oceans for 1-2 billion years. They evolved into true bacteria (eubacteria) and algae. PRECAMBRIAN LIFE The Precambrian period covers the geological time before the beginning of the Cambrian period some 570 to 600 million years ago. Most major animal phyla appear in the fossil record within a few million years at the beginning of the Cambrian period. This appearance has been called the Cambrian explosion because before this time, fossil deposits

are mostly devoid of any organisms more complex than single-celled bacteria. Appearance of Eukaryotes These cells have a nucleus and membrane bound organelles. They contain chromatin (DNA wrapped around proteins called histones). Single celled eukaryotes arose at least 1.5 billion years ago. The first eukaryotes evolved to be carnivorous and photosynthetic.

This ended the Precambrian period and the beginning of the Cambrian period. Phylogentic Relationships of Animals Porifera Platyhelminthes Cnideria Mollusca Nematoda

Arthropoda Annelida Echinodermata pseudoc oelom acoelom segmentation Protostome: schizocoelem

Deuterostomes: eucoelom radial symmetry bilateral symmetry no true tissues true tissue Ancestral Protist Chordata Origins of Animal Diversity

Based on anatomical and embryological criteria, there are about 35 phyla. Most major animal body plans appeared between 525 million to 545 million years ago during the late Precambrian and Paleozoic eras. A lot of the more advanced invertebrates appeared in the Cambrian and Ordovician periods within the Paleozoic Era. Why not evolve quickly?

The burst of evolutionary activity that followed at the end of the Precambrian period and beginning of the Cambrian period was unprecedented. Some investigators hypothesize that the explanation for the Cambrian explosion lies in the accumulation of oxygen in the atmosphere to a critical threshold level. Larger, multicellular animals required the increased efficiency of oxidative metabolism; these pathways could not be supported under conditions of limiting oxygen concentration.

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