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UMass Amherst BIOLOGY 152 - Exam 1 Study Guide

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Exam # 1 Study Guide Lectures: 1 - 7 Lecture 1 (January 21) !What does the “Drunkards Walk” refer to? The random changes that underlie evolution !So, is evolution directed? How does the concept of the Drunkards Walk apply to evolution? -Evolution is not directed, it is random. There is no “goal” of organisms developing from simple to complex. -The Drunkard’s Walk towards complexity explains that evolution does not “progress”, organisms are randomly evolving. Because it is impossible for organisms to become less complex than single-celled bacteria, they automatically become more complex. -“descent with modification” !Instead, evolution comes from a series of processes, such as mutation and genetic drift —> leads to largely random variations among individuals and natural selection (acts upon those variations) !!Lecture 2 (January 23) !Be able to interpret graphs and understand what they mean Experiments using E.coli: example -some e.coli can grow on citrate, not just glucose (Cit+) and some cannot grow on citrate (Cit-) -the Cit+ E.coli that were graphed showed an adaptation that better allowed them to survive in their environment than the the Cit -. They were able to utilize the citrate in the place of glucose when glucose was unavailable !Why did it take so many generations for the E.Coli to be able to grow on citrate? -because mutations are random and just need to happen !Bio 152!!!Know the difference between adaptation and acclimation -adaptation = trait that allows an individual to survive in certain environments relative to individuals without that trait -acclimation = when an individuals physiology changes in response to environmental changes (usually short term) -Did the E.coli adapt or acclimate to the environment? Adapt Prerequisites for natural selection by evolution (what is necessary for evolution by natural selection to occur?) - variation in traits exist in a population -this variation must lead to differences among individuals in lifetime reproductive success -the genes for the adaptations better suited to a particular environment get passed on to offspring, and those offspring then thrive in their environment, so eventually all population has that trait What is the difference between evolution and natural selection? - evolution = through time a species accumulates differences, and because of this descendants differ from their ancestors, and new species arise from existing ones - natural selection = a gradual, non-random process by which heritable traits become more or less common in a species based on differential reproduction What does “fitness” mean in reference to natural selection? -if an organism has good “fitness”, that organism is more successful at passing on their genes — it is the ability of an organism to pass on its heritable traits to the next generation through survival and reproduction (module 1 in Principles, section 1.4 in Morris and 1.3 in Freeman) !Lecture 3 (January 26) Why are there still bacteria even though multicellular organisms have evolved? Because nothing has out-competed them where they live !!What are the three domains? Bacteria, Archaea and Eukaryota What does LCA mean? The last common ancestor in the phylogenetic tree of the three domains: the NODE that all bacteria, archaea and eukaryota stemmed from, or the last organism before adaptations started occurring to differentiate the three domains !Know similarities and differences between Prokaryotes and Eukaryotes Similarities: -basic metabolism -biomolecules (DNA, RNA, etc) Differences: - size (eukaryotes are around 10 times as big) - eukaryotes have a nucleus - eukaryotes have internal membranes - eukaryotes have organelles - multicellular lineages only exist in eukaryotes - prokaryotes can live many more places because they have more energy sources ***there CAN be single celled eukaryotes!!! Advantages What is one of the primary advantages of multicellularity? Defense What is another? They are better able to maintain their position and collect food (examples of this are cheetahs and kelp)! also the experiment with unicellular chlorella gathering to form clusters of around 8 —helped with defense against O. vallescia experiment with snowflake yeast — selected for heaviness so they could sink to the bottom, allows them to maintain position and collect food Lecture 4 (January 28) What are the challenges that a multicellular organism must overcome? -Limits of Diffusion -they must stick together & support the organism -cell —> cell communication -regulate cell division and cell fate (development & reproduction) -Defense Why does surface area to volume ratio matter? DIFFUSION! This becomes more difficult as the organism/cells gets bigger (and we know that eukaryotic cells are bigger than bacteria/archaea). The rate of diffusion is constant in the same medium, so the larger a cell is the longer it will take to get to the center How do eukaryotes deal with the problem of being too large for diffusion? - they actively move using motor proteins - some increase their surface area with folds - they have transport vesicles - there is a local increase of molecules — proteins used to transport them Why was vasculature developed? To move past the stage where every cell was in contact with the outside environment What are cadherins? Proteins in animals involved in cell to cell adhesion What does this graph suggest about cadherins?!- that they did have a role in single cell organisms (the trait did exist prior to the development of multicellular organisms but served different purposes in prokaryotic cell lines) !!!How Genes Control Cell Fate (Development and Differentiation) !Lecture 5 (January 30) What is development controlled by? signaling molecules One way multicellular organisms meet one of the big challenges — signaling from cell to cell to control cell fate Done by morphogens!! What is a morphogen? -Signaling molecules (proteins) -Morphogens determine cell fate. They are usually transcription factors, and they govern the pattern of tissue development, including positioning various cell types within the tissue. The fate of the cells that make up an embryo is determined by morphogens. -Undifferentiated cells get a signal (morphogen) —> cell “turns on” certain genes —>cell begins to specialize —>more regulatory genes are turned on, proteins do their job —> cell becomes completely


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