Biol 1440, Principles of Biology I

THE SCIENTIFIC METHOD
What is an experiment?

Principle

 Hypotheses are tested by experiments designed using the Scientific Method.

Objectives
  • Improve observational skills.
  • Learn how to apply the Scientific Method.
  • Learn the essential components of a hypothesis
  • Learn the use of a spectrophotometer.

Research Questions
  • How do we observe Nature?
  • What is a researchable question?
  • What is a hypothesis?

Readings

Scientific Method
Introduction to the Scientific Method
Steps to designing an experiment
 Introduction to Spectrophotometry
        

Students need

 1. Lab Notebook
2. calculator
3. metric ruler
4. marking pen
In your Lab Notebook Before Lab
1. Researchable Question
2. Hypothesis
3. Dilution Table for ethanol treatments
4. A Data Collection Table (DCT) with both A520 and Concentration of Anthocyanin columns

End of Lab
1. Completed your DCT
2. Graph Results
3. What is the overall trend?
4. What are the key results?
5. Conclusion: Do you support or reject your hypothesis? What results best justify your decision?

The Scientific Method

 

 
1. Making Observations
2. Constructing a Hypothesis
3. Designing an Experiment
4. Interpreting Results
5. Formulating Conclusions
Improving Lab Skills

Determining the concentration of anthocyanin
How to determine the amount of anthocyanin leaking from a red cabbage cell using the Lambert-Beer law.

Quiz Question
If the A520 = 0.37, what is the concentration of anthocyanin in µM?
Making Observations Student groups will be designing an experiment to test a hypothesis on cell membranes using a plant pigment, anthocyanin, which is found in many vegetables, such as red or purple cabbage and apples.  This pigment is stored in a large central vacuole, which also is surrounded by a membrane. 

What conditions weaken a plant's membranes to allow anthocyanin to leak for the cell?  This will lead you to a greater understanding of cell membranes, but more importantly, it will introduce you to how the process of science works through the Scientific Method.

Observe red cabbage in cross section and red cabbage cells containing anthocyanin.

Quiz Questions
Where is anthocyanin found in red cabbage cells?

What cell structures are affected by alcohol to cause anthocyanin to leak out?
Asking a researchable question

Formulate a Researchable Question based on your observations about red cabbage cells exposed to ethyl alcohol.

  • What do you know about alcohol?  What types of alcohol are there?  Is alcohol harmful?
  • Discuss these questions and others in your groups then as a class.

Alcohol
Excessive alcohol consumption can have many effects on humans.  The range of effects can be from mild physical impairment of motor functions to liver damage and in some cases death.  We know that alcohol can pass through the blood/brain membrane barrier.

Alcohol effects in animals occur at concentrations far lower than what you observed in previous labs.

How much is too much?  Science article on alcohol and the brain

  • What types of observations and data would you need to investigate the effects of alcohol on a cell?

  • How could you tell if the membranes in a red cabbage cell were altered by alcohol?  What simple observation could you make?

Formulating a hypothesis

 

 

 

 

 

 

Your group will formulate a hypothesis and then design an experiment to test your hypothesis based on how alcohol concentration might affect the cell membranes in beets.  In order for anthocyanin to be released from a red cabbage cell, both the membrane of the central vacuole and the plasma membrane must be damaged.  Thus, the presence of any anthocyanin in solution has to be the result of damaged cell membranes.

  • What can you conclude about an experiment, if the anthocyanin concentration increases, as measured by increased Absorbance?

  • Would you expect to see a gradual or sudden increase in anthocyanin concentration? 

  • How would you interpret the effect on the membrane?
How to design an experiment

Once your group has formulated a hypothesis, design an experiment to test it. 

  • What will be the dependent and independent variables?

  • What treatments will you use?  What dilutions of ethyl alcohol (EtOH) are needed? STOCK EtOH = 80%

Quiz Question
What is the fewest number of replications that an experiment should have?

Suggested 5 treatments ranging from 0 to 60% EtOH