Systems Microbiology 1.084J/20.106J PROBLEM SET #1 – Due Monday Sept 18 1. a. Describe the different sorts of evidence for life’s appearance on the early Earth ~ 3.5 bya. b. Which evidence seems most compelling to you, and why? b. What dramatic change ~ 2.5 billion years ago has influenced biology on Earth ever since, and how did it happen? 2. a. Describe how you might determine the stable isotope compositions of different compounds in inorganic, as well as organic or living materials. b. What elements might be useful for investigating biological processes using stable isotope ratios? c. Describe in detail the metric that’s used to differentiate stable isotope content of a specific element in different compounds. 3. a. Draw the general structure of gram negative and gram positive bacterial cell walls. b. What gives these cell walls their structural integrity, how, and why is that important. c.
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