Bio 105 1st Edition Lecture 9 Outline of Last LectureI. How do we know that new species have evolved?II. What are species?III. How are new species formed?IV. What factors influence how fast new species form?Outline of Current LectureI. How did life on Earth first evolve?II. How did the Earth get oxygen?III. What kinds of prokaryotes do we have on Earth now?IV. What are the eukaryotic microbes and what do they do?Current LectureBiology 105 Origin of Life and Microbial Diversity Essential Questions 1. How did life on Earth first evolve? 2. How did the Earth get oxygen? 3. What kinds of prokaryotes do we have on Earth now? 4. What are the eukaryotic microbes and what do they do?Interactive Class Notes How did life on Earth first evolve? I. Origin of Life A. Science provides evidence to explain the origin of life, based on evolution and knowledge of chemistry and physics. B. Early Earth conditions 1. The Earth formed about 4.6 bya (billion years ago), and conditions then were very different than they are now. a. The atmosphere was thought to include hydrogen gas, ammonia, methane, carbon These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.dioxide, carbon monoxide, and water vapor, but no oxygen. b. Severe lightning storms, strong UV radiation, and constant volcanic eruptions supplied energy to these atmospheric chemicals. 2. A Russian scientist, Oparin, hypothesized that these atmospheric gasses plus energy would react to form organic (cellular) molecules. 3. An American scientist, Miller tested the idea by putting gasses into an apparatus with circulating water using sparks to simulate lightning. In a few weeks he succeeded in making many organic molecules, similar to those found in cells, in his ‘primitive earth’ apparatus. C. Scientists now believe that similar cellular molecules were formed on the primitive Earth and slowly built up in the oceans, forming a mixture called the “primordial soup”. 1. Many also believe that significant amounts and types of chemicals were contributed by meteorites and comets striking the Earth. 2. How the small molecules were able to form the large molecules needed for cells, and then how cells themselves were formed has proven more difficult, but not impossible, to study. a. clay surfaces can attract small molecules and hold them in the right orientation to allow reaction. They can also participate in reactions. i. Experiments have shown that if clays are repeatedly wet and dried with solutions containing nucleotides, they can produce nucleic acid-like molecules b. Other experiments by Miller suggest that ice may have played an important role in helpingsmall molecules come together to form the first organic polymers. The freezing water excludes other molecules, trapping them in very small unfrozen space where they could react. 3. Somehow primitive cells evolved in the primordial soup and lived by eating these molecules. a. Nobody knows exactly how it happened, but natural selection would have been important. Cells or proto-cells that were good at getting what they needed would persist and reproduce, while others would fall apart or be eaten. 4. The minimum requirements for something to be a cell seem to be a. a boundary, or membrane, between the cell and its environment b. controlled chemical activity, or some sort of metabolism in the cell, and c. a way to store and use the biological information needed to produce the metabolic enzymes and membrane (evidence suggests this was RNA in the first cells) 5. The first primitive cells formed in this way were anaerobic (non oxygen-using), prokaryotic cells -- small primitive cells lacking a nucleus or other internal parts, like bacteria today. How did the Earth get oxygen?I. Solving the energy crisis A. After these first prokaryotic cells evolved, the Earth's first ecological crisis occurred. 1. Cells consumed the organic molecules faster than they could be made. Life was limited by the small supply of abiotically-formed organic molecules. The future of life on Earth appeared extremely limited. B. The solution to this crisis was the evolution of photosynthesis In this process, the energy of the sun is used to make organic molecules. 1. Photosynthesis provided a new source of biological molecules and saved the future of life. 2. A byproduct of photosynthesis is oxygen. When photosynthesis evolved, there was nooxygen in the atmosphere. Since then, the oxygen concentration of the atmosphere has varied a lot; currently it is about 21%. C. Eukaryotic cells, found in animals, plants, and people, evolved due to this change in the atmosphere. 1. Oxygen is toxic to anaerobic cells, so this change in the atmosphere set up a strong selection pressure for cells immune to oxygen toxicity. 2. In response to this pressure, cells were selected for that had the ability to use oxygen in their metabolic reactions. a. This was a new set of reactions called respiration and it opened up a new realm of possibilities for life. b. These reactions used up the dangerous oxygen in the cell, and produced much more energy than the old, anaerobic-type metabolic reactions. 3. Not all cells could carry out this new reaction. Some that couldn't died out, or were limitedto living in unusual habitats. a. Others, however, were able to develop symbiotic relationships in which a smaller aerobic cell lived inside a bigger, anaerobic cell. i. The small aerobe removed oxygen from the larger cell, and provided it energy in the process. ii. The larger cell protected the smaller one from the environment. b. The two cell types coevolved together and became completely dependent on one another. The smaller cells became mitochondria, energy-producing organelles within eukaryoticcells. 4. Some cells also engulfed photosynthetic bacteria, which became chloroplasts in their cells, and these organisms became plants. 5. Cells of higher plants and animals, therefore, contain endosymbionts, which were once free-living bacterial cells. D. Evidence for endosymbiosis 1. Mitochondria and chloroplasts have their own DNA and make RNA and some of their own proteins -- no other parts of a cell can do that