112lect41 - GY 112 lecture notes D Haywick(2004 2005 1 GY...

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GY 112 lecture notes D. Haywick (2004- 2005) 1 GY 112 Lecture Notes Evolution of the Plants Lecture Goals : A) The first “plants” (Archean-Proterozoic) B) Diversification (Paleozoic-Mesozoic) C) Domination (Mesozoic-Cenozoic) Textbook reference: Levin (7 th edition) Chapter 4 (p. 141-142); Chapter 10 (p. 334-338); Chapter 12 (p. 417-422) A) The first plants The question of when the first plants evolved depends upon your definition of what exactly a plant is. Today, most people envision plants to be photosynthetic life forms that you plant in the ground. Most have roots and leaves . These features took time to evolve. The first plants, like the first animals, were far less complex. In fact, they were likely single-celled organisms. Let’s go back to the beginning, when the first prokaryotes were just starting to evolve. This will be review for most of you as we previously talked about this material when we first dealt with evolution. Well, we need to talk about it again. The earliest bacteria were probably heterotrophs , single-celled organisms that were incapable of manufacturing their own food. Instead, they digested other bacteria through the use of enzymes and fermentation reactions. The conversion of sugar into ethanol and carbon dioxide is an example of this type of process. Heterotrophs run the risk of eventually running out of food, so this is not the best strategy for a life form to be locked into. The next step was the evolution of autotrophs , single-celled bacteria that are capable of manufacturing their own food through various chemical reactions. These prokaryotes has a big advantage over their heterotrophic cousins as they could use plentiful chemicals to turn into their own food supply. We now know of 3 major types of autotrophic bacteria: 1) Nitrifying bacteria – use ammonia (NH 3 ) to manufacture their food 2) Sulfur bacteria – use hydrogen sulfide (H 2 S) to manufacture their food 3) Photosynthetic bacteria – use CO 2 and sunlight to manufacture their food. The third type of bacteria are known as photoautotrophs and the basic reaction they used is the same reaction today used by plants: CO 2 + 6 H 2 O + sunlight C 6 H 12 O 6 + 6CO 2 The most well know prokaryotic photoautotrophs are of course the stromatolites which first evolved in the early Archean are still around today. As far as the plants are
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GY 112 lecture notes D. Haywick (2004- 2005) 2 concerned, the next major development probably occurred simultaneously with evolution of eukaryotes . This, as I’m sure you all remember, was the development of larger cells with enclosed nuclei that propagated through sexual reproduction. The most accepted hypothesis for this development is that one prokaryote assimilated another without actually digesting it. Perhaps this was a symbiotic relationship at first, but overtime, the assimilated prokaryote developed into a nucleus and the assimilating prokaryote became the enclosing cell and was contained within a membrane. Those eukaryotes containing an
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112lect41 - GY 112 lecture notes D Haywick(2004 2005 1 GY...

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