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.
Transcript
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
Designing an Experiment
State the Problem
Form a Hypothesis
Set Up a Controlled Experiment
Record Results
Analyze Results
Draw a Conclusion
Publish Results
The Scientific MethodThe Steps of the Scientific Method
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.
Independent variable
Dependent 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.
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.PROCEDURE
Controlled Variables:jars, type of meat,location, temperature,time
Manipulated Variables:gauze covering thatkeeps flies away from meat
Uncovered jars Covered jars
Several days pass
Maggots appear No maggots appearResponding Variable: whether maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.
Figure 1-8 Redi’s Experiment on Spontaneous Generation
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.
Gravy is boiled. Flask isopen.
Gravy is teeming with microorganisms.
Gravy is boiled. Flask issealed.
Gravy is free of microorganisms.
Section 1-2
Figure 1-10 Spallanzani’s Experiment
Needham tried first but didn’t bring gravy to hot enough
temperature.
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.
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Curved neckis removed.
Broth is teeming with microorganisms.
Figure 1-11 Pasteur’s Experiment
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?
