Review of the Scientific Method "The scientific method is nothing but the normal working of the human mind." Thomas Huxley

What is the Scientific Method? The scientific method is a planned, logical, approach taken to solving a problem It consists of asking a question, developing a possible solution, testing the possible solution, recording data, and analyzing results

Steps of the Scientific Method The basic scientific method consists of five broad steps: Identifying the problem or question Developing a possible solution, or hypothesis Designing and executing a test Collection and analysis of data The formulation of a conclusion

Identifying the Problem or Question Identify a problem to be solved or a questioned to be answered. To be scientifically valid, questions or problems must be falsifiable. Usually scientists collect information about a problem or question, before positing a possible solution. The possible solution to a scientific problem or question is known as a hypothesis

The Hypothesis A hypothesis is a possible solution to a scientific problem or question. To be valid a hypothesis must be testable Ex. Which of the following are valid hypotheses? The sky is blue due to the reflection of sunlight off the Earth’s oceans. The sky is blue due to the scattering of blue light by oxygen in the atmosphere. The sky is blue because a higher being made it that way.

Procedure: What is an Experiment? An experiment is a test designed to prove or disprove a hypothesis Experimental Design involves: Establishing controlled and uncontrolled variables Establishing the independent and dependent variables. Experiments generate data which scientists record in tables, etc.

Collecting and Analyzing Data Data collection occurs as an experiment proceeds. Usually data is numerical in form However, during an experiment observations may be made that can include temperature changes, the formation of gas bubbles, changes in color, etc.

Analysis of Data Numerical Data is usually analyzed by determining the mean, median, and mode. Numerical data is often graphed as a means of visually determining relationships between variables.

Conclusions After the data is analyzed a determination must be made as to whether the data supports or refutes the hypothesis. If the data supports the hypothesis… If the data refutes the hypothesis… If the data is indeterminate…

An Example of Experimental Design Francesco Redi Tests the Theory of Spontaneous Generation

Background – Spontaneous Generation Until the seventeenth century experimentation was treated as an art rather than science. Many strange, and now discredited, ideas about how living organisms are propagated flourished. The theory of spontaneous generation was a very popular, ancient theory used to explain the seeming production of many animals from non-living materials.

Example One Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. Conclusion: It was perfectly obvious to ancient peoples that the muddy soil gave rise to the frogs.

Example Two: Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs. As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around. Conclusion: It was obvious to them that the mice came from the moldy grain.

Example Three Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them. Many times they would have to remove maggots from the putrefying meat. Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the maggots and flies

Redi’s Experiment Francesco Redi (1626-1697), an Italian scientist, thought that the Theory of spontaneous Generation was incorrect. In 1668 he designed what is thought to be the first experiment explicitly designed via the scientific method. The experiment tested the idea that maggots, and therefore flies, are generated spontaneously from rotting meat.

Redi’s Problem and Hypothesis Observation: There are flies around meat carcasses at the butcher shop. Question: Where do the flies come from? Does rotting meat turn into, or generate, the flies? Hypothesis: Rotten meat does not turn into flies. Only flies can make more flies. Prediction: If meat cannot turn into flies, rotting meat in a sealed (fly-proof) container should not produce flies or maggots.

Redi’s Test and Observations No Cover Cheesecloth Cover Impervious Cover Data: Presence or absence of flies and maggots observed in each jar was recorded. In the control group of jars, flies were seen entering the jars. Later, maggots, then more flies were seen on the meat. In the gauze-covered jars, no flies were seen in the jars, but were observed around and on the gauze, and later a few maggots were seen on the meat. In the sealed jars, no maggots or flies were ever seen on the meat.

Redi’s Conclusions Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. Maggots appeared on the gauze. In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms.

Controlled Versus Uncontrolled Variables A controlled variable is any factor in an experiment that is kept the same in all trials of the experiment. Controlled variables are more commonly known as Constants. Uncontrolled variables are those factors in an experiment that are allowed, or chosen, to change during the experiment. There are two types of uncontrolled variables: Independent and Dependent

Independent versus Dependent Variables The independent variable (aka: manipulated variable) is the factor in an experiment that is chosen, or manipulated by the experimenter. What was the independent variable in Redi’s experiment? The dependent variable (aka: responding or measured variable) in an experiment is the factor that changes or responds to changes in the independent variable. What was the dependent variable in Redi’s experiment?

Control Group versus Experimental Group The control group in an experiment is the set of tests in which nothing was manipulated by the experimenter. The control group is the standard by which all changes in the manipulated tests are measured. What was the control group in Redi’s experiment? The experimental group in an experiment is the set of tests in which the experimenter manipulates the independent variable. What was the experimental group in Redi’s Experiment?

Identifying Controls and Variables Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group a task (in this case they’re supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given anything. After one hour Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.

Identifying Controls and Variables What was Smithers’ …… Control Group? Independent Variable? Dependent Variable? What should Smithers’ conclusion be? How could Smithers’ improve his experiment?

Assignment: Work in pairs to complete “The Simpsons Identifying Controls and Variables” worksheet. If you do not finish the assignment in class complete it as home work.

Yesterday’s Classwork/Homework Identifying Experimental Variables and Controls