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The Scientific Study of Life Chapter 1 BIOL114 Dave Werner 1.1 What is Life? We understand life by thinking about nature at different levels of organization Nature’s organization begins at the level of atoms, and extends through the biosphere The quality of life emerges at the level of the cell Making Sense of the World Nature is everything in the universe except what humans have manufactured A Pattern in Life’s Organization Atoms • Fundamental building blocks of all substances Molecules • Consisting of two or more atoms Cell • The smallest unit of life Organism • An individual consisting of one or more cells A Pattern in Life’s Organization Population • Individuals of the same species in the same area Community • Populations of all species in the same area Ecosystem • A community and its environment Biosphere • All regions of the Earth where organisms live Levels of Organization in Nature Levels of Organization in Nature Emergent Properties Each level of organization in nature has emergent properties – a characteristic of a system that does not appear in any of its component parts Overview of Life’s Unity All living things have similar characteristics • Continual inputs of energy and the cycling of materials maintain life’s complex organization • Organisms sense and respond to change • DNA inherited from parents is the basis of growth and reproduction in all organisms Energy and Life’s Organization Energy • The capacity to do work Nutrients • Atoms or molecules essential in growth and survival that an organism cannot make for itself Producers and Consumers Producers • Acquire energy and raw materials from the environment • Make their own food (photosynthesis) Consumers • Cannot make their own food • Get energy by eating producers and other organisms Homeostasis Homeostasis • Organisms use receptors to help keep conditions in their internal environment within ranges that their cells can tolerate Organisms Grow and Reproduce Organisms grow, develop, and reproduce using information in their DNA, a nucleic acid inherited from parents Information encoded in DNA is the source of an individual’s distinct features (traits) Same Materials, Many Products 20 amino acids are the building blocks used to build a great variety of proteins Instructions in DNA Guide Development Life’s Underlying Unity All organisms consist of one or more cells, which stay alive through ongoing inputs of energy and raw materials All sense and respond to change; all inherited DNA, a type of molecule that encodes information necessary for growth, development, and reproduction Animation: One-way energy flow and materials cycling Overview of Life’s Diversity Of an estimated 100 billion kinds of organisms that have ever lived on Earth, as many as 100 million are with us today 1.2 The Tree of Life Includes Three Main Branches Scientific Naming - Each type of organism is given a two-part name that includes genus and species names Genus • A group of species that share unique features Species • Individuals that share one or more heritable traits and can interbreed (if sexually reproducing) Scientific Naming The heavy-beaked parrotfish, Scarus gibbus Classification Systems Classification systems group species by their shared, heritable traits All organisms are classified into three domains • Bacteria, archaea, and eukaryotes • Eukaryotes include plants, animals, protists and fungi Comparison of Life’s Three Domains Diversity of Life Diversity of Life Life’s Diversity Many millions of kinds of organisms, or species, have appeared and disappeared over time Each kind is unique in some aspects of its body form or behavior Animation: Life’s diversity One-Way Flow of Energy and Cycling of Materials through an Ecosystem energy input, mainly from sunlight PRODUCERS plants and other self-feeding organisms nutrient cycling CONSUMERS animals, most fungi, many protists, bacteria A Energy inputs from the environment flow through producers, then consumers. B Nutrients become incorporated into the cells of producers and consumers. Some nutrients released by decomposition cycle back to producers. C All energy that enters an ecosystem eventually flows out of it, mainly as heat. energy output, mainly heat Fig. 1-3, p. 6 energy input, mainly from sunlight PRODUCERS plants and other self-feeding organisms nutrient cycling CONSUMERS animals, most fungi, many protists, bacteria energy output, mainly heat A Energy inputs from the environment flow through producers, then consumers. B Nutrients become incorporated into the cells of producers and consumers. Some nutrients released by decomposition cycle back to producers. C All energy that enters an ecosystem eventually flows out of it, mainly as heat. Stepped Art Fig. 1-3, p. 6 An Evolutionary View of Diversity A theory of evolution by natural selection is an explanation of life’s diversity Variation and Mutation Information encoded in DNA is the basis of traits an organism shares with others of its species Mutations are the original source of variation in traits Adaptation Some forms of traits are more adaptive than others, so their bearers are more likely to survive and reproduce Over generations, adaptive traits tend to become more common in a population; less adaptive forms of traits become less common or are lost Evolution and Natural Selection Evolution is change in a line of descent • Traits that characterize a species can change over generations in evolving populations Natural selection is an evolutionary process • Differential survival and reproduction among individuals that vary in the details of their shared, heritable traits Artificial and Natural Selection 1.3 Key Concepts: Explaining Unity in Diversity Theories of evolution, especially a theory of evolution by natural selection, help explain why life shows both unity and diversity Evolutionary theories guide research in all fields of biology 1.5 Critical Thinking and Science Critical thinking is judging the quality of information Science is limited to that which is observed • Helps minimize bias in judgments by focusing on testable ideas about observable aspects of nature A Guide to Critical Thinking 1.6 How Science Works Scientists make and test potentially falsifiable predictions about how the natural world works Observations, Hypotheses, and Tests Researchers make observations, form hypotheses (testable assumptions), and make predictions about what might occur if the hypothesis is correct A Scientific Approach Research in Laboratory and Field About the Word “Theory” A hypothesis that is inconsistent with results of scientific tests (evidence) is modified or discarded A scientific theory is a long-standing hypothesis that is used to make useful predictions Examples of Scientific Theories Some Terms Used in Experiments Experiments • Tests that can support or falsify a prediction Variable • A single characteristic in a set of individuals that differs from the control group in an experiment Some Terms Used in Experiments Experimental group • Group with a single variable characteristic to be tested against a control group in an experiment Control group • Group identical to the control group, except for the variable 1.7 The Power of Experimental Tests Researchers unravel cause and effect in complex natural processes by studying the effects of one variable at a time Potato Chips and Stomach Aches Researchers tested the prediction that Olestra® in potato chips causes cramps • Experimental group: Olestra chips • Control group: regular chips Experiment: Olestra and Stomach Cramps Hypothesis Olestra® causes intestinal cramps. Prediction People who eat potato chips made with Olestra will be more likely to get intestinal cramps than those who eat potato chips made without Olestra Experiment Control Group Eats regular potato chips Experimental Group Eats Olestra potato chips Results Control Group Eats regular potato chips Experimental Group Eats Olestra potato chips Conclusion Percentages are about equal. People who eat potato chips made with Olestra are just as likely to get intestinal cramps as those who eat potato chips made without Olestra. These results do not support the hypothesis. Stepped Art Fig. 1-10, p. 14 Butterflies and Birds Why does the peacock butterfly flick its wings when birds are near? Researchers tested two hypotheses • Wing spots deter predatory birds • Hissing and clicking sounds deter predatory birds Peacock Butterfly Defenses against Predatory Birds Fig. 1-11a, p. 15 Fig. 1-11b, p. 15 Fig. 1-11c, p. 15 Results: Peacock Butterfly Experiment Asking Useful Questions Scientists try to design single-variable experiments that yield quantitative results When studying humans, isolating a single variable is not often possible 1.8 Sampling Error in Experiments Researchers experiment on subsets of a group • Results may differ from results of the same experiment performed on the whole group Sampling error is a difference between results from a subset and results from the whole • Small sample size increases the likelihood of sampling error in experiments Animation: Sampling error Summary of Life’s Characteristics 1.5-1.8 Key Concepts: How We Know Biologists make systematic observations, predictions, and tests in the laboratory and in the field They report their results so others may repeat their work and check their reasoning Animation: Insect development Animation: Three domains Video: Finding new species