The Study of Life Chapter 1 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. Which of these are characteristics of living organisms? 90% 1. Responds to stimuli. 2. Maintains homeostasis. 3. Has an organized structure. 4. Only 1 and 3 5. All of these 5% 0% 1 2 2% 3 3% 4 5 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.” 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 Inquiry. • Scientific Laws and Theories are products of scientific inquiry. Hypothesis Testing • Scientific Inquiry is often used to test hypotheses. • A hypothesis is a tentative explanation for an observation. • A valid hypothesis must be specific, testable, and falsifiable. Scientific Evidence • Based on natural causes. • Uniform in time and space. • Perceived similarly by many people. • Objective, measurable. Forming Hypotheses • Scientific Inquiry is often used to test hypotheses. • A hypothesis is a tentative explanation for an observation. • A valid hypothesis must be specific, testable, and falsifiable. 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.” Let’s test it! Which kind of licorice do you prefer? 33% 33% 33% 1. Black licorice 2. Red licorice 3. No preference 1 2 3 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.” Observation • What’s happening in this picture? Question Hypothesis Prediction Experiment or Observation Conclusion • Write an IF – THEN hypothesis and prediction based on the picture. W O R K T O G E T H E R Experiments are one type of scientific inquiry. Experiments test variables to try to find the cause of natural events. Observational studies are also part of scientific inquiry. Much of Astronomy and Paleontology, for example, involves observational science. In order to test a hypothesis, a scientist must conduct: 33% 33% 33% 1. An experiment. 2. An observation. 3. A study, using an appropriate type of inquiry for the hypothesis. 1 2 3 Laws and Theories • In general: • Scientific Laws and Theories are both products of Scientific Inquiry. • Laws tend to be descriptions of natural phenomena in given circumstances. • Theories tend to be explanations of how natural phenomena work. 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 scientific explanation based on many observations that have been tested and supported by many scientists is a: 33% 33% 33% 1. Law 2. Theory 3. Hypothesis 1 2 3 Scientific laws are: 33% 33% 33% 1. Proven theories. 2. Proven hypotheses. 3. Descriptions of natural phenomena. 1 2 3 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.