Chapter 1 Invitation to Biology Albia Dugger • Miami Dade College 1.1 The Secret Life of Earth • Human activities are profoundly changing life on Earth • Hundreds of new species are discovered each year – about 20 species become extinct every minute in rain forests alone • What is a species, and why should discovering a new one matter to anyone other than a scientist? • These questions are part of biology, the scientific study of life Foja Mountain Cloud Forest New Cloud Forest Species New Species of Spider 1.2 Life Is More Than the Sum of Its Parts • Biologists study life by thinking about it 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 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 Same Parts, Different Organization • Complex properties, including life, often emerge from the interactions of much simpler parts Stepped Art p4 ANIMATION: Building blocks of life To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 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 • Tissue • Specialized cells organized to perform a collective function A Pattern in Life’s Organization • Organ • Structural unit of interacting tissues. • Organ system • A set of interacting organs • Multicelled 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 Life’s Levels of Organization atom molecule cell tissue organ organ system ANIMATED FIGURE: Life’s levels of organization To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Take-Home Message: How do living things differ from nonliving things? • All things, living or not, consist of the same building blocks— atoms; atoms join as molecules. • The unique properties of life emerge as certain kinds of molecules become organized into cells. • Higher levels of life’s organization include multicelled organisms, populations, communities, ecosystems, and the biosphere. • Emergent properties occur at each successive level of life’s organization. 1.3 How Living Things Are Alike • Continual inputs of energy and the cycling of materials maintain life’s complex organization • Organisms sense and respond to change • All organisms use information in the DNA they inherited from their parent or parents to develop and function Energy and Life’s Organization • Energy • The capacity to do work • Not cycled; flows through the world of life in one direction • Nutrients • Atoms or molecules essential in growth and survival that an organism cannot make for itself • Cycled between organisms and the environment 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 A Producers harvest energy from the environment. Some of that energy flows from producers to consumers. sunlight energy Producers plants and other self-feeding organisms B Nutrients that become incorporated into the cells of producers and consumers are eventually released by decomposition. Some cycle back to producers. Consumers animals, most fungi, many protists, bacteria C All of the energy that enters the world of life eventually flows out of it, mainly as heat released back to the environment. Stepped Art Figure 1-3b p6 ANIMATED FIGURE: One-way energy flow and materials cycling To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Organisms Sense and Respond to Change • Organisms sense and respond to change both inside and outside the body • The body’s internal environment consists of all body fluids outside of cells • The internal environment must be kept within certain ranges of composition, temperature, and other conditions • By sensing and adjusting to change, organisms keep conditions in the internal environment within a range that favors cell survival (homeostasis) Response to a Stimulus Organisms Use DNA • DNA is the basis of similarities in form and function among organisms • Details of DNA molecules differ – the source of life’s diversity • DNA • Deoxyribonucleic acid • Carries hereditary information that guides development and functioning Development and Growth • DNA guides ongoing metabolic activities that sustain the individual through its lifetime • Development • Multistep process by which the first cell of a new individual becomes a multicelled adult • Growth • In multicelled species, an increase in the number, size, and volume of cells Reproduction and Inheritance • All organisms receive their DNA from one or more parents • Reproduction includes various processes by which individuals produce offspring • Inheritance refers to the transmission of DNA to offspring Take-Home Message: How are all living things alike? • A one-way flow of energy and a cycling of nutrients sustain life’s organization. • Organisms sense and respond to conditions inside and outside themselves; they make adjustments that keep conditions in their internal environment within a range that favors cell survival, a process called homeostasis. • Organisms develop and function based on information encoded in their DNA, which they inherit from their parents. DNA is the basis of similarities and differences in form and function 1.4 How Living Things Differ • Living things differ in their observable characteristics • Various classification schemes help us organize this variation, which we call Earth’s biodiversity • biodiversity • Scope of variation among living organisms Basics of Classification • Organisms can be classified into broad groups depending on whether they have a nucleus • Nucleus • A sac with two membranes that encloses and protects a cell’s DNA Organisms With No Nucleus • Bacteria and archaea are two types of organisms whose DNA is not contained within a nucleus • Bacteria • The most diverse and well-known group of single-celled organisms that lack a nucleus • Archaea • Single-celled organisms that lack a nucleus but are more closely related to eukaryotes than to bacteria Bacteria Archaea ANIMATED FIGURE: Life's diversity To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Eukaryotes • Eukaryotes are organisms whose DNA is contained within a nucleus • Some eukaryotes live as individual cells; others are multicelled • Eukaryotic cells are typically larger and more complex than bacteria or archaea Protists • Protists are the simplest eukaryotes • As a group they vary a great deal, from single-celled consumers to giant, multicelled producers • Many biologists view “protists” as several major groups Protists Fungi • Fungi are multicelled eukaryotes such as mushrooms • Many are decomposers • All are consumers that secrete substances that break down food outside of the body and absorb the released nutrients Fungi Plants • Plants are multicelled eukaryotes that live on land or in freshwater environments • Most are photosynthetic producers • Plants and other photosynthesizers also serve as food for most of the other organisms in the biosphere Plants Animals • Animals • Multicelled consumers that ingest tissues or juices of other organisms • Herbivores graze; carnivores eat meat; scavengers eat remains of other organisms; parasites withdraw nutrients from the tissues of a host • Develop through stages that lead to the adult form • Actively move about during at least part of their lives Animals Take-Home Message: How do organisms differ from one another? • Organisms differ in their details; they show tremendous variation in observable characteristics, or traits • Various classification systems group species on the basis of shared traits 1.5 Organizing Information About Species • Each type of organism, or species, is given a unique name • We define and group species based on shared traits • Taxonomy is the science of naming and classifying species The Binomial System • Carolus Linnaeus standardized a two-part naming system that we use today • The first part is the genus, a group of species that share a unique set of features • The second part is the specific epithet • Genus name plus specific epithet designate one species • Example: the dog rose Rosa canina Taxonomic Classification • We rank species into ever more inclusive categories: genus, family, order, class, phylum, kingdom, and domain • Each rank, or taxon is a group of organisms that share a unique set of features • Each higher taxon consists of a group of the next lower taxon Taxonomic Classification The Three-Domain System The Six-Kingdom System ANIMATED FIGURE: Classification systems To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE A Rose by Any Other Name . . . • A species is assigned to higher taxa based on some subset of heritable traits it shares with other species • Morphological traits (observable characteristics) • Physiological traits (functional characteristics) • Behavioral traits (responses to certain stimuli) Traits • Traits vary a little within a species • There can be tremendous differences between species; such species look very different, so it is easy to tell them apart • Species that share a more recent ancestor may be harder to tell apart The Biological Species Concept • Evolutionary biologist Ernst Mayr defined a species as groups of individuals that potentially can interbreed, produce fertile offspring, and do not interbreed with other groups • This “biological species concept” is useful in many cases, but it is not universally applicable • For now it is important to remember that a “species” is a convenient but artificial human construction Four Butterflies, Two Species Take-Home Message: How do we keep track of all the species we know about? • Each species has a unique, two-part scientific name. • Classification systems group species on the basis of shared, inherited traits 1.6 The Science of Nature • Judging the quality of information before accepting it is called critical thinking • Scientists practice critical thinking by testing predictions about how the natural world works Thinking About Thinking • Critical thinking is the deliberate process of judging the quality of information before accepting it • Critical thinking considers the supporting evidence, alternative interpretations, and biases contained in a message • Being conscious about learning can help you decide whether to allow new information to guide your beliefs and actions How Science Works • Science is the systematic study of the observable world and how it works • Generally, a researcher observes something in nature and uses inductive reasoning to form a hypothesis (testable explanation) for it • The researcher then uses deductive reasoning to make a prediction about what might occur if the hypothesis is correct Experiments • Experiments are tests designed to support or falsify a prediction • Researchers investigate cause-and-effect relationships by changing or observing variables • An independent variable is defined or controlled by the person doing the experiment • A dependent variable is an observed result that is supposed to be influenced by the independent variable The Scientific Method • Experiments are performed on an experimental group as compared with a control group, and sometimes on models • Conclusions are drawn from experimental results (data); a hypothesis that is not consistent with data is modified • Making, testing, and evaluating hypotheses is called the scientific method The Scientific Method ANIMATION: Bacteriophage mice experiment Examples of Research Take-Home Message: What is science? • The scientific method consists of making, testing, and evaluating hypotheses • It is a way of critical thinking, or systematically judging the quality of information before allowing it to guide one’s beliefs and actions • Experiments measure how changing an independent variable affects a dependent variable 1.7 Examples of Experiments in Biology • Researchers unravel cause-and-effect relationships in complex natural processes by changing one variable at a time • When studying humans, isolating a single variable is not often possible Potato Chips and Stomach Aches • Researchers tested the prediction that Olestra® in potato chips causes cramps • Experimental group: Olestra chips • Control group: regular chips A Hypothesis Olestra® causes intestinal cramps. B 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. C Experiment D Results E Control Group Eats regular potato chips Experimental Group 93 of 529 people get cramps later (17.6%) 89 of 563 people get cramps later (15.8%) 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 Figure 1-10 p14 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 Results: Peacock Butterfly Experiment Take-Home Message: Why do biologists perform experiments? • Natural processes are often very complex and influenced by many interacting variables • Experiments help researchers unravel causes of complex natural processes by focusing on the effects of changing a single variable 1.8 Analyzing Experimental Results • Biology researchers often experiment on subsets of a group • Results from such an experiment may differ from results of the same experiment performed on the whole group • Science is, ideally, a self-correcting process because scientists check one another’s work Sampling Error in Experiments • Researchers often test or survey a subset of a population, area, or event, then use the results to make generalizations • 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 Sample Size Affects Sampling Error A Natalie, blindfolded, randomly plucks a jelly bean from a jar. The jar contains 120 green and 280 black jelly beans, so 30 percent of the jelly beans in the jar are green, and 70 percent are black. B The jar is hidden from Natalie’s view before she removes her blindfold. She sees one green jelly bean in her hand and assumes that the jar must hold only green jelly beans. C Still blindfolded, Natalie randomly picks out 50 jelly beans from the jar. She ends up picking out 10 green and 40 black ones. D The larger sample leads Natalie to assume that one-fifth of the jar’s jelly beans are green (20 percent) and four-fifths are black (80 percent). This sample more closely approximates the jar’s actual green-to-black ratio of 30 percent to 70 percent. The more times Natalie repeats the sampling, the greater the chance she has of guessing the actual ratio. Stepped Art Figure 1-13 p16 Probability • In cases like flipping a coin, it is possible to calculate probability of an expected result • Probability • The measure, expressed as a percentage, of the chance that a particular outcome will occur • Depends on the total number of possible outcomes • Analysis of experimental data often includes calculations of probability Statistical Significance • If a result is very unlikely to have occurred by chance alone, it is said to be statistically significant • Statistically significant refers to a result that is statistically unlikely to have occurred by chance • In science, every result – even a statistically significant one – has a possibility of being incorrect Variability • Variation in a set of data is often shown as error bars on a graph • Error bars may indicate variation around an average for one sample set, or the difference between two sample sets Error Bars in a Graph Bias in Interpreting Results • Experimenting with a single variable is not often possible, particularly when studying humans • Experiments are designed to yield quantitative results that minimize the potential for bias • Other scientists repeat the experiments and check the conclusions drawn from them How do scientists reduce sampling error and bias in research? Take-Home Message: • Researchers minimize sampling error by using large sample sizes and by repeating their experiments • A statistical analysis can show the probability that a result has occurred by chance alone • Science is a self-correcting process because it is carried out by an aggregate community of people systematically checking one another’s ideas 1.9 The Nature of Science • Scientific theories are our best descriptions of reality • Science helps us to be objective about our observations, in part because it is limited to the observable “Theories” and “Laws” • A scientific theory is a long-standing hypothesis that has not been disproved after many years of rigorous testing • Like all hypotheses, a scientific theory can be disproven by a single observation that falsifies it • A law of nature describes a phenomenon that has been observed to occur consistently, but for which we do not have a complete scientific explanation The Limits of Science • Science deals with observations of the natural world which produce objective data that can be measured without bias • Science does not measure moral, aesthetic, or philosophical standards vary from one society to the next • Neither does science address the supernatural, or anything that is “beyond nature” Take-Home Message: Why does science work? • Checks and balances inherent in the scientific process help researchers to be objective about their observations • Because a scientific theory is revised until no one can prove it wrong, it is our best way of measuring reality