Scientific Method Ch 1-3

Steps of The Scientific Method 1. State the problem/ Ask a Question 2. Make observations/gather information (data) 3. Form a Hypothesis 4. Set up a controlled experiment (test the hypothesis) 5. Analyze data collected from experiment 6. Draw a conclusion (this accepts or rejects the hypothesis and is a logical answer to the question/problem.)

Asking a Question In 1976, a deadly and contagious human disease appeared in several villages in the central African nation of the Democratic Republic of Congo. Think of at least 3 questions that a scientist sent to investigate an outbreak of disease would have. (Discuss with partner, be ready to share one with the class) You can write them under this slide if you wish.

Collecting Data For our disease example, one way scientists collected data was through sampling. They took samples of the people’s blood (from both infected and non-infected). They found and photographed a virus! Sampling is when scientists collect a sample or small part of a population to represent the whole population. To ensure accurate representation a sample must be random, and large- include as many subjects (members of the population) as possible.

Read Forming a Hypothesis pg 17 The scientists Hypothesis? After a problem has been stated or a question is asked, and we’ve gathered information about the subject we must form a Hypothesis! Hypothesis= A testable scientific explanation for a set of observations. Often written as an “If, Then” statement. Read Forming a Hypothesis pg 17 The scientists Hypothesis? “If the virus were the true disease-causing agent, then introducing the virus into healthy tissue would cause cell death like that found in victims of the disease.” Another Ex: If animal metabolism is related to temperature, then increasing ambient temperature will increase animal metabolism . We can test this b/c we know we will be increasing temperature and looking to see what happens to animal metabolism.

Experiment An experiment is done to collect data which will provide us with evidence that will either support the hypothesis or tell us that we need to make a new hypothesis. Experiments should be designed so that they can be repeated by other scientists. Experiments are repeated many times to ensure that results are valid. Sometimes unexpected discoveries are made, even if something goes wrong during the experiment! Variables: factors in an experiment that can change

A Controlled Experiment A hypothesis should be tested by an experiment in which one variable is changed at a time. All other variables should be kept unchanged or controlled This type of experiment is called a controlled experiment.

Types of Variables Manipulated Variable or Independent Variable: The factor that is deliberately changed Answers the question: “What do I change?” Responding Variable or Dependent Variable: The factor that is observed and changes on response to the manipulated or independent variable. Answers the question: “ What do I observe?” Controlled Variables (The Controls): The variables that are kept constant to prevent their influence on the effect of the independent variable on the dependent. Answers the questions: “What do I keep the same?”

Two Groups Control Group and Experimental Group These groups are designed exactly the same except the experimental group has something changed (the independent variable) Example: Testing how well fertilizer helps plants grow. What would be the control variables? What would make the control group different from the experimental?

Experiment Examples: What are the different variables? OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Several days pass Maggots appear Controlled Variables: jars, type of meat, location, temperature, time Manipulated/Independent Variables: gauze covering that keeps flies away from meat Responding/ Dependent Variable No maggots appear whether maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Spallanzani’s Experiment Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. sealed. Gravy is free of microorganisms. Controlled Variables? Boiling the gravy, same type of gravy, same flasks, same amount of time Manipulated or Independent Variable? Flask sealed or unsealed Responding or Dependent Variable? Whether or not there were microorganisms (bacteria) in the gravy.

Drawing a conclusion Following the experiment data collected during the experiment must be analyzed to determine if hypothesis is supported or not. The hypothesis isn’t wrong or right- rather it is supported or is refuted (not supported- and a new hypothesis is made for the original question asked.)

Developing a Theory In science the word theory applies to a well- tested explanation that unifies a broad range of observations. Broad and comprehensive statement of what is thought to be true. Sometimes more than one theory is needed to explain a particular circumstance.

Star Questions 2. 1. A prediction was made that the best conditions for earthworm growth occur when there are fewer than five earthworms per cubic meter of soil. This prediction is called a A law. B theory. C hypothesis. D conclusion.

3. 4.