mystery worms

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?

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