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Hox Gene And Cambrian Explosion Essay

4945 words - 20 pages

Session 1.3: The Evolution of Cellular Life

Exam review

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In this session we focus on the natural history of cells and the evolutionary timelines of their appearance.  The modern phylogenetic classification of domains is used to categorize the different types of cells: bacteria, archea, and eukarya.  The names of periods and organisms and certain dates are often helpful in remembering or understanding events that occur in the natural history of evolution.  However, we do not expect you to know the names of all organisms mentioned nor all dates (you may find some of the sound attachments on complicated figures useful for review).  Those names and dates mentioned ...view middle of the document...

  Dates for these processes are relevant.
3. Since all life forms originated from common ancestor, there should be fundamental properties of life.  You will find these briefly outlined in the assigned readings from Chapter 1 of your text and reiterated throughout the material in-class.
4. The endosymbiont hypothesis is an additional key feature of the development of eukaryotic life.  The details for chloroplasts are presented more than those for mitochondria- both endosymbionts have significant impact on the evolution of life forms.  Why?
5. Significant time was spent describing photosynthesis and chloroplasts.  There were multiple reasons for this example. 
1. First, it is a classic example of starting from a simple form of anaerobic, cyclic synthesis to generate energy and metabolites used for construction of prokaryotic cells to the modern representation of non-cyclic photosynthesis.  (Hint: You do not need to describe these processes in detail but you should understand how they function.) The process changed gradually over 0.5-1.0 BY into a process of non-cyclic photosynthesis that combined features of the cyclic process with a new process probably started by gene duplication of the original genes.  The non-cyclical photosynthesis process is used in modern plants, algae and cyanobacteria.  Being able to convert light energy into chemical energy allowed for the development of complexity (remember session 2 and entropy versus complexity).  The fossil record (stromatolites) indicates the timing (3.0 BYA) and role of cyanobacteria in development of oxygenic photosynthesis (2.5 BYA).  The fact that cyanobacteria are the only bacteria to have both photosystem I and II is relevant as is the fact that the chloroplast has properties similar to those of cyanobacteria (endosymbiont hypothesis).
2. Second, during the evolution of photosynthesis the anaerobic process changed to a process that generated oxygen (over a time span of 1.5 BY).  The slow increase in the percent oxygen in the atmosphere is seen in the banded iron formations found in the fossil record.  The oxygen environment caused a cataclysm for anaerobic organisms which retreated to special protective niches in the Earth’s environment.  The main mode of respiration became aerobic starting around 2 BYA.
6. What major events do I need to remember?  There are two slides in the in-class material (slides 26 and 39 up through colonization of land) that cover dates, periods, and significant events.  I think you should know these as it is easier to discuss the events if you know the names.  The videos of the Cambrian explosion and the post-Cambrian evolution are significant in adding a visual perspective to events.  The names of organisms are less important and we would name and describe something if we asked a question about it on an exam.  However, the audio buttons on the slides often name and describe organisms.
7. The video “Snowball Earth” provides a...

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