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Scientific Method Guided Reading
Directions: As you read the paragraphs below, highlight any definitions and circle any vocab words. In the margins, write down any questions or comments you might have about the reading. These actions help you comprehend the reading at a deeper level and are called “talking to the text.” After you have read and “talked to the text,” answer the questions at the end of each section. All of the directions must be followed in order to receive full credit on this assignment. Introduction: A Way of Problem Solving Every day of the year there are many problems being investigated by scientists. Sometimes problems are quickly solved. Sometimes they take many years to solve. And sometimes a problem remains unsolved. Whenever scientists try to solve a problem, they search for an answer in an orderly and systematic way called the scientific method. The basic steps of the scientific method are: ➔ State the problem ➔ Form a hypothesis ➔ Perform experiments ➔ Analyze data ➔ State a conclusion 1. What is the scientific method? 2. List the steps of the scientific method. The Scientific Method: 1) State the Problem We are going to look at an example now that shows how a life scientists might use the scientific method to solve a problem. Most people know enough to walk the other way if they should run into a rattlesnake. However, if you could safely observe a rattler, you would discover a curious kind of behavior. 1 With fangs flashing and body arching, the deadly rattler strikes. The snake’s fangs quickly inject poisonous venom into its victim. Then, in a surprise move, the rattler allows the wounded animal to run away! But the rattlesnake will not miss its intended meal. After waiting for its poison to take effect, the rattler follows the trail of the injured animal. Although the rattler cannot see well, somehow it manages to find its victim on the dense, dark, forest floor. Clearly, something leads the snake to its prey. What invisible trail does the snake follow in tracking down its bitten prey? The first step in solving this problem is to find out or review everything important related to it. For example, the scientists trying to solve the rattlesnake mystery knew that a rattlesnake’s eyes are only sensitive to visible light. However, they also knew that a pair of organs located under the animal’s eyes detects invisible light in the form of heat. These heat­sensing pits pick up signals from warm­blooded animals. The signals help the snake locate its intended prey. But the heat­sensing pits cannot help the snake find a wounded victim that has fun many meters away. Some other process must be responsible for that. The scientists knew that a rattler’s tongue “smells” certain odors in the air. The rattler’s tongue picks up these odors on an outward flick. The odors enter the snakes mouth on an inward flick. The scientists also knew that the sight or smell of an unbitten animal did not trigger the rattler’s tracting action. Using all of this information, scientists were able to suggest a possible solution to the problem. 1. What is the first step of the scientific method? 2. What is the problem that needs to be solved in this specific example? Highlight the problem/question in the text above. 3. After the problem is stated, what needs to be done next? 4. What pieces of information did the scientists already know about rattlesnakes? List two. 2) Form a Hypothesis A suggested solution is called a hypothesis. A hypothesis is almost always formed after the information related to the problem has been carefully studied. But sometimes a hypothesis is the result of creative thinking that often involves bold, original guesses about the problem. In this regard, forming a hypothesis is like good detective work, which involves not only logic, but hunches, intuition, and the taking of chances. To the problem, “What invisible trail does a rattler follow in tracking down its prey?” the scientists suggested a hypothesis. The scientists suggested that after the snake sounds its victim, the snake follows the smell of its own venom to locate the animal. 2 1. What is the second step of the scientific method? 2. What is a hypothesis? 3. What hypothesis did the scientists form for our example experiment? 3) Perform Experiments The scientists next had to test their hypothesis by performing certain activities and recording the results. These activities are called experiments. Whenever scientists test a hypothesis using an experiment, they must make sure that the results of the experiment clearly support or do not support the hypothesis. That is, they must make sure that one, and only one, factor affects the results of the experiment. The factor being tested in an experiment is called the variable. In any experiment, only one variable is tested at a time. Otherwise it would not be clear which variable had caused the results of the experiment. In the rattlesnake experiments, the scientists tested whether the snake’s venom formed an invisible trail that the snake followed. The venom was the variable, or single factor, that the scientists wanted to test. The scientists performed the experiment to test this variable. First, the scientists dragged a dead mouse that had been struck and poisoned by a rattlesnake along a curving path on the bottom of the snakes empty cage. When the snake was placed in its cage, its tongue flicked rapidly, its head moved slowly from side to side, and it followed the exact trail the scientists had laid out. The results seemed clear, but the scientists had one more experiment to perform. To be sure it was the scent of the venom and no other odor that the snake followed, the scientists ran a control experiment. A control experiment is run in exactly the same way as the experiment with the variable, but the variable is left out. So the scientists dragged an unbitten dead mouse along a path in the cage. The experiment was exactly the same, except this mouse had not been poisoned. This time the snake seemed disinterested. Its tongue flicked very slowly and it did not follow the path. 1. What is the third step of the scientific method? 2. What is a variable? 3. What is a control experiment? 4. Why is it important to perform a control experiment? 3 4) Recording and Analyzing Data The rattlesnake experiments were repeated many times, and the scientists carefully recorded the data from the experiments. Data include observations such as measurements. The scientists analyzed the recorded data. 1. What is the fourth step of the scientific method? 2. What is data? 3. What data do you think the scientists could have measured in the experiments discussed in the paragraph above? 5) Stating a Conclusion After analyzing the recorded data, the scientists came to a conclusion. A conclusion is a reasoned deduction or inference. They concluded that the scent of venom was the only factor that could cause a rattlesnake to follow its bitten victim. Rattlesnake venom is made up of many different substances. Exactly which ones are responsible for the snake’s behavior are as yet unknown. As is often the case in science, a solution to one mystery bring to light another mystery. Using scientific methods similar to those described here, scientists hope to follow a path that leads to the solution to this new mystery. 1. What is the last step of the scientific method? 2. What is a conclusion? 3. Describe an experiment that could test the new venom problem stated above. Imagine that you have a way to separate each substance in the venom. How will you design your experiment? Be specific. 4