EBIO 1010-02 EBIO 1010-02
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This 8 page Class Notes was uploaded by Claire Jacob on Thursday February 11, 2016. The Class Notes belongs to EBIO 1010-02 at Tulane University taught by Doosey, Michael in Summer 2015. Since its upload, it has received 29 views. For similar materials see Diversity of Life in Biological Sciences at Tulane University.
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Date Created: 02/11/16
Chapter 1: The Science of Biology 1.1 The Science of Life Biology unifies much of natural science ● No new laws of nature can be gleaned from the study of biologybut that study does illuminate and illustrate the workings of those natural laws ● Biology is at the heart of this multidisciplinary approach because biological problems often require many different approaches to arrive at solutions Life defies simple definition ● In its broadest sense, biology is the study of living things→ the science of life ● A series of seven characteristics shared by living systems: 1. Cellular organization 2. Ordered complexity 3. Sensitivity 4. Growth, development, and reproduction 5. Energy utilization 6. Homeostasis 7. Evolutionary adaptation Living Systems show hierarchical organization ● The Cellular Level ○ atoms→ the fundamental elements of matter ○ molecules→ clusters of atoms ○ organelles→ tiny structures within cells formed by complex biological molecules ○ cells→ membrane-bounded units. the most basic unit of life ● The Organismal Level ○ tissues→ groups of similar cells that act as a functional unit ○ organs→ body structures composed of several different tissues that act as a structural and functional unit ○ organ systems→ organs that work together. i.e. the nervous system consists of sensory organs, the brain, spinal cord, and neurons that convey signals ● The Populational level ○ populations→ a group of organisms of the same species living in the same place ○ species→ all populations of a particular kind of organism together ○ biological community→ all the populations of different species living together in one place ● The Ecosystem Level ○ ecosystem (ecological system) → a biological community and the physical habitat within which it lives together ● The Biosphere ○ the entire planet as an ecosystem ...As you move up this hierarchy, novel properties emerge. These emergent properties result from the way in which components interact, and they often cannot be deduced just from looking at the parts themselves. Examining individual cells, for example, give little hint about the whole animal. The Nature of Science ● Science is concerned with developing an increasingly accurate understanding of the world around us using observation and reasoning ● there is no one “scientific method” Much of science is descriptive ● The study of biodiversity is an example of descriptive science that has implications for other aspects of biology in addition to societal implications ● One of the most important accomplishments of molecular biology at the dawn of the 21st century was the completion of the sequence of the human genome. The determination of the sequence itself was descriptive science Science uses both deductive and inductive reasoning ● Deductive reasoning applies general principles to predict specific results ○ example: if all mammals by definition have hair, and you find an animal that does not hair hair, then you may conclude that the animal is not a mammal ● Inductive reasoning: the logic flows from specific to general ○ uses specific observations to construct general scientific principles ■ example: if poodles hair hair, and terriers have hair, and every dog that you observe has hair, then you may conclude that all dogs have hair ■ an example in modern biology is the role of homeobox genes in development→ studied genes in fruit flies that led to mutations. found the same genes in other animals, including humans. homeobox genes act as switches to control developmental fate Hypothesisdriven science makes and tests predictions ● Scientists establish which general principles are true through the process of systematically testing alternative proposals. If these proposals prove inconsistent with experimental observations, they are rejected as untrue ● Hypothesis→ a suggested explanation that accounts for observations. a proposition that might be true ● iterative process→ a hypothesis can be changed and refined with new data Testing hypotheses ● We call the test of a hypothesis an experiment. ● A successful experiment is one in which one or more of the alternative hypotheses is demonstrated to be inconsistent with the results and is thus rejected. Establishing controls ● Variables→ factors that influence processes ● Test hypotheses by carrying out two experiments in parallel: ○ 1. Test experiment→ one variable is altered in a known way to test a particular hypothesis ○ 2. control experiment→ the variable is left unaltered ● Much of the challenge of experimental science lies in designing control experiments that isolate a particular variable from other factors that might influence a process Using predictions ● A successful scientific hypothesis needs to be not only valid but also useful→ it needs to tell us something we want to know ● If an experiment produces results inconsistent with the predictions, the hypothesis must be rejected or modified ● The more experimentally supported predictions a hypothesis makes, the more valid the hypothesis is Reductionism breaks larger systems into their component parts ● Scientists use the philosophical approach of reductionism to understand a complex system by reducing it to its working parts ● Reductionism has limits when applied to living systems, however→ one of which is that enzymes do not always behave exactly the same in isolation as they do in their normal cellular context. A larger problem is that the complex interworking of many interconnected functions lead to emergent properties that cannot be predicted based on the working of the parts Biologists construct model to explain living systems ● Models provide a way to organize how we think about a problem. Models can also get us close to the larger picture and away from the extreme reductionist approach ● In systems biology, this modeling is being applied on a larger scale to regulatory networks during development, and even to modeling an entire bacterial cell The nature of scientific theories ● Scientists use the word theory in two main ways: ○ 1. a proposed explanation for some natural phenomenon, often based on some general principle ○ 2. the body of interconnected concepts, supported by scientific reasoning and experimental evidence, that explains the facts in some area of study ■ Such a theory provides an indispensable framework for organizing a body of knowledge ● To a scientist, theories are the solid ground of science, expressing ides of which we are most certain ● Again, the key is how well a hypothesis fits the observations→ evolution is a scientific theory Research can be basic or applied ● British philosopher Karl Popper: “successful scientists without exception design their experiments with a pretty fair idea of how the results are going to come out” → this is known as imaginative preconception ● Some scientists perform basic research, which is intended to extend the boundaries of what we know ○ The information generated by basic research contributes to the growing body of scientific knowledge, and it provides the scientific foundation utilized by applied research. ● The process of of careful evaluation called peer review lies at the heart of modern science 1.3: An Example of Scientific Inquiry: Darwin and Evolution ● Darwin’s theory of evolution explains and describes how organisms on Earth have changed over time and acquired a diversity of new forms The idea of evolution existed prior to Darwin ● A number of earlier naturalists and philosophers had presented the view that living things must have changed during the history of life on Earth ● Darwin’s contribution was a concept he called natural selection Darwin observed differences in related organisms ● 1831 part of a 5year navigational mapping expedition around the coasts of South America ● Darwin had the chance to study a wide variety of plants and animals on continents and islands and in distant seas ● Repeatedly, Darwin saw that the characteristics of similar species varied somewhat from place to place, These geographical patterns suggested to him that lineages change gradually as species migrate from one area to another ○ 14 species of Galápagos finches off the coast of Ecuador, although related, differed slightly in appearance, particularly in their beaks ■ birds had descended from a common ancestor→ “descent with modification” or evolution ● Darwin was struck by the fact that the plants and animals on these relatively young volcanic islands resembled those on the nearby coast of South America Darwin proposed natural selection as a mechanism for evolution Darwin and Malthus ● Thomas Malthus’s An Essay on the Principle of Population (1798) ○ populations of plants and animals (including human beings) tend to increase geometrically, while humans are able to increase their food supply only arithmetically ○ populations of species remain fairly constant year after year because death limits population numbers ■ although every organism has the potential to produce more offspring than can survive, only a limited number actually do survive and produce further offspring ● Darwin’s proposal: individuals possessing physical, behavioral, or other attributes that give them an advantage in their environment are more likely to survive and reproduce than those with less advantageous traits. As the frequency of these characteristics increase in the population, the nature of the population as a whole will gradually change. Natural Selection ● animal breeders selected certain varieties of pigeons and other animals, such as dogs, to produce certain characteristics, a process Darwin called artificial selection ● Artificial selection often produces a great variation in traits ● If pigeon breeders could foster variation by artificial selection, nature could do the same→ a process Darwin called natural selection Darwin drafts his argument ● Alfred Russel Wallace (18231913) wrote an essay in Indonesia ○ it concisely set forth the hypothesis of evolution by means of natural selection, a hypothesis Wallace had developed independently of Darwin The Predictions of Natural Selection have been tested ● Fossil Record ○ Yield intermediate links between the great groups of organisms ○ Although truly intermediate organisms are hard to determine, paleontologists have found what appear to be transitional forms and found them at the predicted positions in time ○ Life began approximately 3.5 BYA ○ For vertebrate animals especially, the fossil record is rich and exhibits a graded series of changes in form, with the evolutionary sequence visible for all to see ● The age of the Earth ○ Using evidence obtained by studying the rates of radioactive decay, we now know that the physicists of Darwin’s time were very wrong: the Earth was formed about 4.5 BYA ● The mechanism of heredity ○ at the time of Darwin, no one had any concept of genes or how heredity works, so it was not possible for Darwin to explain completely how evolution occurs. ● Comparative anatomy ○ In many different types of vertebrates for examples, the same bones are present, indicating their evolutionary past… constructed from same basic array of bones, modified for different purposes ○ homologous structures→ have the same evolutionary origin, but they now differ in structure and function ○ analogous structures→ have similar function but different evolutionary origins ● Molecular evidence ○ by comparing the genomes of different groups of animals or plants, we can more precisely specify the degree of relationship among the groups. A series of evolutionary changes over time should involve a continual accumulation of genetic changes in the DNA ○ The sequences of some genes, such as the ones specifying the hemoglobin proteins, have been determined in many organisms, and the entire time course of their evolution can be laid out with confidence by tracing the origins of particular nucleotide changes in the gene sequence. ■ phylogenetic tree→ represents the evolutionary history of the gene, its “family tree”. Molecular phylogenetic trees agree well with those derived from the fossil record, which is strong direct evidence of evolution. Unifying Themes in Biology Cell theory describes the organization of living systems ● Cells were discovered by Robert Hooke in England in 1665 ● Dutch scientist Anton van Leeuwenhoek used microscopes capable of magnifying 300x and discovered an amazing world of singlecelled life in a drop of pond water ● In 1839, the German biologists matthias Schleiden and Theodor Schwann concluded that organisms consist of cells. Their conclusion has come to be known as cell theory. Later, biologists added the idea that all cells come from preexisting cells. The molecular basis of inheritance explains the continuity of life ● The information that specifies what a cell is likeits detailed planis encoded in deoxyribonucleic acid (DNA), a long, cablelike molecule. Each DNA molecule is formed from two long chains of building blocks, called nucleotides, wound around each other. Four different nucleotides are found in DNA, and the sequence in which they occur encodes the cell’s information. Specific sequences of several hundred to many thousand nucleotides make up a gene, a discrete unit of information. The relationship between structure and function underlies living systems ● One of the unifying themes of molecular biology is the relationship between structure and function. Function in molecules, and larger macromolecular complexes, is dependent on their structure. ● This knowledge gives us clues as to what kinds of structures may be involved in a process if we know about the functionality The diversity of life arises by evolutionary change ● The underlying unity of biochemistry and genetics argues that all life has evolved from the same origin event ● Biologists divide life’s great diversity into three groups; Archaea, Bacteria, and Eukarya ○ Eukarya: ■ Kingdom Protista→ consists of all the unicellular eukaryotes which are fungi, as well as the multicellular algae ■ Kingdom Plantae→ consists of organisms that have cell walls of cellulose and obtain energy by photosynthesis Evolutionary conservation explains the unity of living organisms ● Biologists agree that all organisms alive today have descended from some simple cellular creature that arose around 3.5 BYA ● The storage of hereditary information in DNA, for example, is common to all living things ○ The retention of these conserved characteristics in a long line of descent usually reflect that they have a fundamental role in the biology of the organism→ one not easily changed once adopted Cells are informationprocessing systems ● The information stored in DNA is used to direct the synthesis of cellular components, and the particular set of components can differ from cell to cell ● The control of gene expression allows differentiation of cell types in time and space, leading to changes over developmental time into different tissue types→ even though all cells in an organism carry the same genetic information ● Cells also process information that they receive from their environment Living systems exist in a nonequillibrium state ● A constant supply of energy is necessary to maintain a stable nonequillibrium state.
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