Mystery Worms A teacher collected some beetles from a rotting log and placed them in a container of dry oatmeal in her classroom. She kept the box covered with a light cloth so that the beetles could not escape. She also asked one of her students to add potato and apple pieces once a week to provide food and moisture for the beetles. After several weeks, the student reported that there were some strange-looking, wormlike organisms in the container.

Mystery Worms 1. Formulate a hypothesis that might explain the presence of the “worms” in the container. 2. How could you test your hypothesis? 3. Identify the variables in your proposed experiment. Identify the control in your proposed experiment.

1 – 2 How Scientists Work

The Steps of the Scientific Method Designing an Experiment State the Problem Analyze Results Form a Hypothesis Draw a Conclusion Set Up a Controlled Experiment Publish Results Record Results

How is Science Done? Scientists use the scientific method. When scientists have a question about something in the world they use this method to find an answer: State the Problem or Question Research State a hypothesis Design an experiment with a control group, constants and variables Analyze data/ results Conclusion or Summary

1. State the Problem or Question What have I observed? What do I want to know?

2. Research Has anyone asked this before? Did they discover an answer? How did they go about looking for an answer? What other things do I need to understand to answer my question?

3. Form a Hypothesis Based on the research you have done, write a possible answer or solution – your best educated guess – to your question.

4. Design an Experiment Control Group: Part of your experiment that is not varied in anyway. You can compare your test groups to this set standard group. Independent variable- The change/difference you make in the experiment (the thing you are testing). Also called manipulated variable Dependent variable- The differences that result from the experiment, the resulting effect. Also called responding variable. Constants- Things in the experiment that do not change, kept exactly the same for each test group so they do not affect the results.

5. Data/Results It is easier to understand the data if it is put into a table and/or graphed. Make sure all data is clearly labeled. Charts and graph should always include units and titles. When graphing the independent variable should be on the x axis and the dependent variable should be on the y axis. Dependent variable Independent variable

6. Analysis What happened? What was expected? What was unexpected? What trends did you notice in the data?

7. Conclusion or Summary Indicate whether or not the data supports the hypothesis and explain why or why not. Suggest possible improvements to the experiment. Suggest further avenues of research or uses for the information discovered.

Learning Checkpoint What are the steps of the scientific method? In which step would you find charts and graphs? What is the difference between an independent variable and a dependent variable? What is the purpose of a control group? What does it mean to have a controlled experiment?

An Example of Science at Work (1-2) Observed: sometimes organisms just “arose” from nonliving things: ex. maggots came from meat. The Question: How do new living things come into being? Hypothesis: In some cases, nonliving objects can spontaneously generate living organisms. 1st Experiment- 1668, Francesco Redi: Meat in covered and uncovered jars Proposed a new hypothesis: The maggots came from eggs left by flies on the meat that were too small to see. Concluded: Maggots came from flies.

Figure 1-8 Redi’s Experiment on Spontaneous Generation OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Science continues...New Ideas with new discoveries New discovery!- tiny microorganisms (discovered by Anton van Leeuwenhoek) 2nd Experiment- Mid 1700s, John Needham: Repeats Redi’s experiment. His hypothesis: Spontaneous generation can occur under the right conditions. Result: microorganisms appear in sealed flask of boiled gravy.

Science Experiments are always repeated: 3rd Experiment- Lazzaro Spallanzani: Thinks Needham did not boil gravy long enough to kill existing microorganisms. Results: When left exposed to air, microorganisms will appear in boiled gravy. He concluded that microorganisms could not come from gravy but appeared instead from microorganisms existing in the air.

Needham tried first but didn’t bring gravy to hot enough temperature. Figure 1-10 Spallanzani’s Experiment Section 1-2 Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. Needham tried first but didn’t bring gravy to hot enough temperature. Flask is sealed. Gravy is free of microorganisms. Gravy is boiled.

New Question: Is air the “life force”? 4th Experiment- 1864, Louis Pasteur: Set out to dismiss the notion that the “life force”, air was needed to generate life. Used curved neck on flask so air could get in but organisms would not. Concluded that all living things can only come from living things. This has been tested over and over and is now considered a theory called biogenesis.

Figure 1-11 Pasteur’s Experiment Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms.

Learning Checkpoint Did all 4 scientists use good scientific thinking and a controlled experiment? What is spontaneous generation? What was the point of the “swan neck” Pasteur added to his flask? What is biogenesis?

Example: Tomatoes Plant 20 seedlings = 50-60 tomatoes harvested Plant 20 seedlings w/ fertilizer = >100 tomatoes harvested What can you conclude? What other factors may affect the growth? weather better that year, different type of tomato seed, fewer pests than last year Hypothesis If I use fertilizer then the tomato crop will increases in production

Experiment Field 1 Brand A tomato seed Water three times a day for 15 minutes Similar type of soil Try to control pests Doesn’t receive fertilizer Field 2 Brand A tomato seed Water three times a day for 15 minutes Similar type of soil Try to control pests Receives fertilizer

Control Unfertilized tomato plants Independent variable Fertilizer Dependent variable # of tomatoes yielded Results Unfertilized = 55 Fertilized = 82 Conclusion The fertilizer caused an increase in the tomato crop