Biology: Science for Life, with Physiology Sixth Edition Chapter 1 Can Science Cure the Common Cold? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Introduction to the Scientific Method Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Learning Outcomes • Describe the characteristics of a scientific hypothesis. • Compare and contrast the terms scientific hypothesis and scientific theory. • Explain why the truth of a hypothesis cannot be proven conclusively via deductive reasoning. • Describe the features of a controlled experiment, and explain how these experiments eliminate alternative hypotheses for the results. • Compare and contrast primary and secondary sources. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. What advice do you receive from friends and family to treat your cold? A. Take vitamin C. B. Use zinc lozenges. C. Drink echinacea tea. D. Meditate. E. Get more rest. F. Wear a warm hat. G. Eat chicken soup. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Science is… ‒ a body of knowledge E.g., biology, the study of living organisms ‒ the discovery of something new and unknown Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Science is NOT… ‒ recalling specific facts about the world. ‒ memorizing what is already known. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The scientific method ‒ ‒ ‒ ‒ Making observations Proposing ideas Testing the ideas Discarding or modifying ideas based on results ‒ What is a hypothesis? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Observations lead to questions. • Hypotheses are proposed explanations for those observations. Chance Logic Experience Intuition Previous scientific results Imagination HYPOTHESIS OBSERVATION QUESTION Scientific theory Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Your mom’s observation: People are more likely to get colds when it is cold outside. Chance Logic Experience Intuition Previous scientific results Imagination HYPOTHESIS OBSERVATION QUESTION Scientific theory Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Your mom’s observation: People are more likely to get colds when it is cold outside. • Your mom’s hypothesis: Becoming chilled makes you more susceptible to illness. Chance Logic Experience Intuition Previous scientific results Imagination HYPOTHESIS OBSERVATION QUESTION Scientific theory Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The Nature of hypotheses ‒ Scientific hypotheses Testable: possible to evaluate Falsifiable: potentially false Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Is this a testable statement? Colds are caused by differences in personal auras. A. Yes B. No Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Examples of a testable statement? A. ______________________________ B. ______________________________ C. ______________________________ Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Everyday use of “theory” ‒ Untested ideas based on little information • Scientific theory ‒ Powerful, broad explanation for related observations Based on well-supported hypotheses Supported by different, independent lines of research Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. (a) 1.1 The Process of Science • Chronic stomach ulcers ‒ Common belief: Ulcers are caused by acids and spicy foods. ‒ Treatment: drugs to reduce acid; avoiding spicy food ‒ New observation: Helicobacter pylori bacteria were found in most samples of ulcer tissue. (b) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. (a) 1.1 The Process of Science • Chronic stomach ulcers ‒ Accepted fact: H. pylori infections cause stomach ulcers. 1. No reasonable alternative hypotheses are supported. (b) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. (a) 1.1 The Process of Science • Chronic stomach ulcers ‒ Accepted fact: H. pylori infections cause stomach ulcers. 1. No reasonable alternative hypotheses are supported. 2. The hypothesis has not been rejected by carefully designed experiments. (b) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Chronic stomach ulcers ‒ Accepted fact: H. pylori infections cause stomach ulcers. 1. No reasonable alternative hypotheses are supported. 2. The hypothesis has not been rejected by carefully designed experiments. 3. The relationship between H. pylori and stomach ulcers follows the germ theory of disease. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Fact 1: Fruits and vegetables contain much vitamin C. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Fact 1: Fruits and vegetables contain much vitamin C. • Fact 2: People with diets rich in fruits and vegetables are generally healthier. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Fact 1: Fruits and vegetables contain much vitamin C. • Fact 2: People with diets rich in fruits and vegetables are generally healthier. • Fact 3: Vitamin C is an anti-inflammatory agent that reduces throat and nose irritation. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Fact 1: Fruits and vegetables contain much vitamin C. • Fact 2: People with diets rich in fruits and vegetables are generally healthier. • Fact 3: Vitamin C is an anti-inflammatory agent that reduces throat and nose irritation. • Hypothesis: Consuming vitamin C decreases the risk of catching a cold. ‒ Inductive reasoning: combining specific observations to a general principle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • Hypothesis: Consuming vitamin C decreases the risk of catching a cold. ‒ Sensible ‒ Needs to be tested ‒ May be proven false Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The logic of hypothesis tests Hypothesis (that is testable and falsifiable) Consuming vitamin C reduces the risk of catching a cold. Make prediction If vitamin C decreases the risk of catching a cold, then people who take vitamin C supplements will experience fewer colds than people who do not. Test prediction Conduct experiment or survey to compare number of colds in people who do and do not take vitamin C supplements. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The logic of hypothesis tests ‒ Hypothesis testing based on Deductive reasoning – General principle to predict observations If/then statements for making predictions Hypothesis (that is testable and falsifiable) Consuming vitamin C reduces the risk of catching a cold. Make prediction If vitamin C decreases the risk of catching a cold, then people who take vitamin C supplements will experience fewer colds than people who do not. Test prediction Conduct experiment or survey to compare number of colds in people who do and do not take vitamin C supplements. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The logic of hypothesis tests If people who take vitamin C suffer fewer colds than those who do not . . . If people who take vitamin C suffer the same number of colds or more than those who do not . . . Conclude that prediction is true Conclude that prediction is false Do not reject the hypothesis Reject the hypothesis Conduct additional tests Consider alternative hypotheses Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.1 The Process of Science • The logic of hypothesis tests ‒ Prediction is true Hypothesis is supported but NOT proven ‒ Prediction is false If people who take vitamin C suffer fewer colds than those who do not . . . If people who take vitamin C suffer the same number of colds or more than those who do not . . . Conclude that prediction is true Conclude that prediction is false Do not reject the hypothesis Reject the hypothesis Hypothesis rejected and disproven Conduct additional tests Consider alternative hypotheses Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Hypothesis: Vitamin C prevents colds. Why is it impossible to say that this hypothesis is true? A. Lab experiments are not practical. B. Alternative hypotheses might be possible. C. Experiments with humans are unethical. D. Vitamin C cannot be obtained naturally. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Hypothesis: Vitamin C prevents colds. Why is it impossible to say that this hypothesis is true? A. Lab experiments are not practical. B. Alternative hypotheses might be possible. C. Experiments with humans are unethical. D. Vitamin C cannot be obtained naturally. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • The experimental method ‒ Experiments Collect data or information Test specific hypotheses Example: Scientists will measure the effects of vitamin C on cold prevention Nasal passages Throat Host cell 1 Virus introduces its genetic material into a host cell. 2 The viral genetic material instructs the host cell to make new copies of the virus. Immune system cells target infected host cells. Side effects are increased mucus production and throat irritation. 3 New copies of the virus are released, killing host cells. These copies can infect other cells in the same person or cells in another person (for example, if transmitted by a sneeze). Virus Virus copies Released virus copies Immune system cells Mucus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • The Experiment: To measure the effect of vitamin C on cold prevention • Variables: factors that may change ‒ Independent variables: those manipulated by the researcher Vitamin C intake Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • The Experiment: To measure the effect of vitamin C on cold prevention • Variables: factors that may change ‒ Independent variables: those manipulated by the researcher Vitamin C intake ‒ Dependent variables: those not changed by the researcher; may change during the experiment Susceptibility to illness upon exposure to virus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Controlled experiments ‒ Test the effect of a single variable ‒ Limit possible alternate hypotheses ‒ Differences in results should be due to treatment Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Control or control group ‒ Similar to experimental subjects ‒ Do NOT receive the experimental treatment Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Steps for controlled experiments 1. Random assignment to control or experimental group 2. Identical participation for both groups except for the testing treatment Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Echinacea tea experiment ‒ Hypothesis: Drinking echinacea tea relieves cold symptoms. Experimental group drank echinacea tea 5–6 times daily Control group drank “sham” tea (placebo) Control group Experimental group Experiencing early cold symptoms Experiencing early cold symptoms Sought treatment from clinic Sought treatment from clinic Received placebo tea Received echinacea tea Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Echinacea tea experiment ‒ Hypothesis: Drinking echinacea tea relieves cold symptoms. Independent variable: drinking tea Dependent variable: relief from cold symptoms Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing Independent variable: drinking tea Dependent variable: relief from cold symptoms ‒ Results: Experimental group felt echinacea tea was 33% more effective. Effective 5 Echinacea tea 33% more effective 4 3 2 Not effective ‒ Hypothesis: Drinking echinacea tea relieves cold symptoms. Effectiveness of tea at relieving cold symptoms • Echinacea tea experiment 1 0 Control group Experimental group Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Minimizing bias in experimental design ‒ Bias: influence on results ‒ Blind studies: limit participant knowledge ‒ Double-blind studies: also limit researcher knowledge of participant groups Technician “blind” What they know Participant “blind” • Limited knowledge of experimental hypothesis • Limited knowledge of experimental hypothesis • No knowledge of which group participants belong to • No knowledge of which group he or she belongs to • No difference in instructions to participants • Unbiased reporting of symptoms or effects of treatment • No difference in treatment of participants • No difference in data collection How they behave Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Using correlation to test hypotheses ‒ When controlled experiments on humans may be Impossible Dangerous Unethical Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. (a) 1.2 Hypothesis Testing • Using correlation to test hypotheses (b) ‒ Model systems: used to avoid unethical or impractical tests on humans Bacteria Fruit flies Nematodes Mammals (rodents, dogs, pigs, human cells) (c) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Relationships between factors • Hypothesis: Stress makes people more susceptible to catching a cold. ‒ Is there a correlation between stress and the number of colds people have caught? (a) Does high stress cause high cold frequency? High stress High cold frequency Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Using correlation to test hypotheses Percentage of participants with colds ‒ Results: The number of colds increases as stress levels increase. 50 45 40 People with higher stress levels were more likely to become infected with the cold virus. 35 30 25 3-4 5-6 7-8 11-12 9-10 Psychological stress index Low High Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. A correlation exists between stress and colds, but stress may NOT cause the increase in the number of colds. A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. A correlation exists between stress and colds, but stress may NOT cause the increase in the number of colds. A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Using correlation to test hypotheses Percentage of participants with colds ‒ Results: The number of colds increases as stress levels increase. ‒ Caution! Correlation does not imply causation. 50 45 40 People with higher stress levels were more likely to become infected with the cold virus. 35 30 25 3-4 5-6 7-8 11-12 9-10 Psychological stress index Low High Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.2 Hypothesis Testing • Using correlation to test hypotheses ‒ The correlation might be due to other reasons (a) Does high stress cause high cold frequency? High cold frequency High stress (b) Or does one of the causes of high stress also cause high cold frequency? Other illness Poor diet High stress Little exercise Little sleep High cold frequency Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. (a) Average hair length in this snapshot is shorter ... 1.3 Understanding Statistics • What statistical tests can tell us ‒ Statistical tests Examine differences between groups Results from sample may extend to entire population Class of 1962 • • Little variability High probability of reflecting average of all women in the class (b) ... than average hair length in this snapshot ... Sample - Small subgroup used in experimental tests Class of 2018 • • High variability Low probability of reflecting average of all women in the class ... so, is hair longer today than in 1962? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.3 Understanding Statistics • What statistical tests can tell us ‒ Statistically significant Results show a true difference between groups Low probability that difference between groups is due to random chance Probability of 5% or less Researchers may infer that treatment had an effect Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. What factor influences statistical significance? A. The number of variables B. The sample size C. The number of researchers D. The population size Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. What factor influences statistical significance? A. The number of variables B. The sample size C. The number of researchers D. The population size Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.3 Understanding Statistics • What statistical tests cannot tell us ‒ If an experiment was designed and carried out properly ‒ If observer error occurred ‒ can only evaluate the probability of sampling error Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Manuscript 1.4 Evaluating Scientific Information • Primary Sources ‒ Primary source: original research ‒ Peer review: critique by other scientists before publication to increase confidence in results Peer reviewers Reject Revise OR Primary source Published Secondary sources Media Comments published in later issues of the journal Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. Manuscript 1.4 Evaluating Scientific Information • Secondary Sources ‒ Secondary source: story about the original research Peer reviewers Reject Revise OR Primary source ‒ Book ‒ News report ‒ Advertisement Published Secondary sources Media Comments published in later issues of the journal Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.4 Evaluating Scientific Information • Anecdotal evidence ‒ Based on one person’s experience, not on experimental data. ‒ Example: a testimonial from a celebrity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.4 Evaluating Scientific Information • Science in the News ‒ Consider the source. ‒ ‒ ‒ ‒ ‒ Reputable? Science background? Advertisements? Current? References? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.4 Evaluating Scientific Information • The Big Question • Use this checklist to evaluate science in the news. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. What is the best way to prevent the common cold? A. Take vitamin C. B. Wash your hands. C. Take zinc lozenges. D. Get a cold vaccine. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. What is the best way to prevent the common cold? A. Take vitamin C. B. Wash your hands. C. Take zinc lozenges. D. Get a cold vaccine. Explanation: Washing hands is the only method that has been shown to prevent the common cold. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved. 1.5 Is There a Cure for the Common Cold? • No cure or vaccine • Best prevention: Keep your hands clean! • No effect on cold susceptibility: ‒ Vitamin C ‒ Diet quality ‒ Exposure to cold temperatures ‒ Exercise • But may reduce cold symptoms: ‒ Vitamin C ‒ Echinacea tea ‒ Zinc lozenges Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved.
