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112lect24 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Proterozoic Life forms Lecture Goals : A) Eukaryote Life forms (Acritarchs) B) Metazoans (Ediacaran Fauna) Textbook reference: Levin 7 th edition (2003) Chapter 7; Levin 8 th edition (2006), Chapter 9 A) Eukaryotes The first life forms on this planet were rather primitive. This is not to say that they were unimportant, rather that they were simple in their makeup. The prokaryotes resembled the bacteria pictured to the left (from http://micro.magnet.fsu.edu/cells/bacteriacell.html), were small (less than 0.020 mm), and lacked nuclei and organelles. In other words, DNA was spread throughout the cell rather than localized to the nucleus. Eukaryotes probably first evolved in the Archean. They differed from the prokaryotes in several ways (see image to right from http://www.earthlife.net) 1. they had nuclei 2. they has organelles 3. they were larger (>0.060 mm) 4. they had sex (yahoo!) I have told you several times that I am not a biologist, so my understanding of the origin of eukaryotes is a bit weak. However, it seems likely that the earliest eukaryotes formed from the assimilation of 2 prokaryotic cells. It is tempting to envision that one cell simply ate the other, but for reasons unknown, just didn’t digest it. My stomach sometimes behaves the same way, but back in the Archean, these two cells developed a unique relationship. The digested cell resided within the other and mutated into what biologists call a mitochondrion . This is the structure that helps cells to produce energy by producing ATP through respiration. A similar assimilation may also have occurred between a eukaryote and a cyanobacteria cell to form chloroplasts which regulate photosynthesis in plants. Both of these events were
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GY 112 Lecture Notes D. Haywick (2006) 2 critical to all future evolutionary changes on this planet, because they allowed multicellular organisms to develop.
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