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The Study of Life Chapter 1 Bio logy Life Knowledge Biology is the branch of science that studies living things So.... What is “life?” How do scientists study it? Living vs. Non-living or Alive vs. Dead When talking about the qualities of “living things,” we are often talking about the species level rather than the individual level. “Skunks are living things,” rather than, “That skunk is living, the one on the road is dead.” Activity! • Observe the items in the green trays. Discuss with others: • Is it alive? How do we know? • At what level of organization should this item be placed? Why? Scientific Inquiry • Science is an investigation of the natural world, using evidence from nature to support explanations. • The methods used by scientists to investigate the natural world are called _________________________. • Scientific Laws and Theories are products of scientific inquiry. Scientific Evidence • Based on _______ ________________. • Uniform in time and space. • Perceived similarly by many people. • ________, ___________. Forming Hypotheses • Scientific Inquiry is often used to test hypotheses. • A hypothesis is a ____________________ for an observation. • A valid hypothesis must be __________, ____________, and ________________. Specific • A hypothesis is specific if it addresses particular observations and has specific variables. • Not specific: “Toxins in water make fish populations decline.” • Specific: “The herbicide glyphosate causes trout embryos to die in the egg when present in water at levels of 100 parts per million or more.” Falsifiable • A hypothesis is falsifiable if it can be “true or false,” either supported or rejected by evidence. Note we do not say “proven” or “disproven.” • Not falsifiable: “Black licorice is the best kind of licorice.” (Opinions cannot be true or false.) • Falsifiable: “Over half of WOU students in our biology class prefer black licorice over red.” Testable • A hypothesis is testable if involves specific variables in the real, physical world that can be measured directly or indirectly. • Not testable: “Students do poorly on exams because of bad luck.” • Testable: “Biology students who make outlines and concept maps while studying their textbook score 10% better on exams than students who only read the textbook.” A hypothesis does not… • …have to be “true” at the start of the experiment. We don’t know until the experiment is over whether the hypothesis is supported or not. • …have to explain everything. It only has to address one variable at a time. If you try to write a hypothesis that explains everything, it is no longer specific. Hypotheses often begin with an observation that leads to questions. Questions invite possible explanations. These possible explanations are hypotheses. To be valid, a hypothesis must be specific, testable, and falsifiable – but it doesn’t have to be correct! In fact, you don’t know if it is correct or not until you test it. Each possible explanation — hypothesis — can give rise to a prediction, often stated in an IF...THEN format. A good prediction suggests a procedure that can test the hypothesis. Scientists test hypotheses and accept or reject hypotheses based on data. They do not set out to prove hypotheses or they may bias their results. Once the procedures are carried out, scientists use the data to reach a conclusion regarding the hypothesis. Notice that the hypothesis is supported rather than “proven.” Testing Hypotheses • Scientific inquiry is used to test hypotheses. • Scientific inquiry can be carried out by: • Experiments • Observational studies Experiments • Scientists design experiments when their questions ask, “What is the natural cause of what I am seeing?” • Variables must be _____________. Results must be ___________ to be dependable. • Experiments use controls and replication. “Does this fertilizer cause crops to mature faster?” “Does pond water pH affect Daphnia survival?” Experiments are one type of scientific inquiry. Experiments test variables to try to find the cause of natural events. Observational Studies • Scientists design observational studies when their questions ask, “What is happening here?” • Observational studies may be needed to establish which variables to test in an experiment. “What lived here long ago?” • In some fields, observation may be all that is possible. “What lives here now?” Much of Astronomy and Paleontology involves observational science. We can’t do experiments on things out in space or that went extinct long ago. Laws and Theories • In general: • Scientific Laws and Theories are both products of Scientific Inquiry. • Laws tend to be _____________ of natural phenomena in given circumstances. • Theories tend to be _____________ of how natural phenomena work. Two misconceptions to avoid! • Laws are NOT ideas or theories that are “proven.” They are NOT “better” than theories. • Theories are NOT guesses that have not been “proven” yet. Scientists to NOT form theories and then “desperately” try to “prove” them! Law of Gravity describes what happens when you drop a rock or launch a rocket at the moon. Gravitational Theory explains why dropped objects fall toward the center of the mass of the Earth. Mendel’s Laws of Heredity: Describe patterns of inheritance in terms of probability. Darwin’s Theory of Natural Selection: Explains why inherited traits change in populations over generations. A Unifying Theory • The gene pool of populations changes over time. Changing environmental conditions favor different gene combinations at different times. • Change in the genetics of a population from generation to generation is called “evolution.” • Evolution explains species diversity and underlies all of modern Biology. Modern evolutionary theory explains why organisms are so diverse, yet all are related. Three processes underlie evolution: genetic variability, inheritance, and selection. Genetic variability in populations is normal. Genetic variation is inherited when DNA is passed from one generation to the next. Our DNA contains the code for all of our inheritable traits. Natural Selection, one mechanism that causes evolution, is a tendency for genes for traits that help an organism survive and reproduce to be passed on from generation to generation. Traits that interfere with reproductive success tend not to be passed on. What is Life? • The concept of “living” can be difficult to define, since many qualities of living things can be seen in non-living things: • Crystals (non-living) can grow. • A thermostat (non-living) responds to the environment. Qualities of Living Things • Living things: • are complex, organized, and made up of cells. • maintain homeostasis. • respond to stimuli. • reproduce and grow. • use materials and energy. • as species, adapt and evolve. Complex and organized All living things have DNA, which contains information to build cell parts. Cells are the basic unit of living things. Organisms can be single-celled, or cells can organize into tissues and organs. Maintain Homeostasis Living organisms need to maintain an internal environment, such as maintaining temperature. Respond to stimuli All living things have ways of sensing the environment that allow them to respond to threats and find food or favorable environments. Reproduce and grow Living things produce more of their kind through reproduction. The young grow to maturity and the cycle begins again. Use materials and energy In order to maintain complexity, maintain homeostasis, to grow, and to respond to the environment, organisms must take in energy and materials. Living things have a metabolism and give off waste products as they use materials. Still a relevant question “What is life?” isn’t just a question that you left behind in Kindergarten. Astrobiologists who search for signs of life on other planets look for many of the same characteristics of terrestrial life. Microbiologists studying nanobacteria may challenge our current understanding of “life.” Life can be studied on many different levels. What is the smallest level of organization that meets our criteria for “living organism?” Living? • The classification systems described are applied to living organisms. • Some particles are “proto-living” – having a few of the characteristics of living things, but not quite alive. Viruses HIV Virus • A virus has: • _______________ • _______________ Viruses • A virus lacks a metabolism and cannot reproduce on its own. • Much, much smaller than bacteria. Bacteria Viruses infecting a bacteria cell. Viroid • A viroid is only ____________, often in a ring. • Viroids can, however, act as infectious agents. Several plant diseases are caused by viroids. Prions • Prions are ____ ___________________ ___ that cause disease (such as “mad cow” disease). • How prions replicate is still not fully understood. Recap • Living things are complex, organized, and maintain homeostasis. • Scientists study living things using scientific inquiry to make observations and test hypotheses. • Laws and theories are the products of science. • Evolution is the unifying theory of modern biology.