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Labs With Hypotheses

Example #1: Conducting a Biological Experiment

Purpose: to learn how to use the scientific method by conducting an experiment.

Introduction

You have learned so far that scientists use the "scientific method" in solving problems. Although there is no set order to the sequence, a scientific investigation may include some or all of the following activities.

literature search, stating the problem, writing a hypothesis, designing an experiment, collecting data/observation, verification, graphing data, interpreting data, and forming a conclusion.

Except for stating the problem and experimental design, you will carry out all of these steps in this investigation.

Your experiment will be carried out on yeast. a micro-organism, which is used in recipes for homemade bread. According to the recipe for bread, you dissolve a package of yeast in warm water, add flour, sugar, salt, and margarine and mix. The bread dough is kneaded several times and the bread dough is placed into a baking pan left to rise in a warm place for an hour before baking in a hot oven.

Stating the Problem

What does temperature have to do with making bread dough rise?

Literature Search

Use your textbook and any other resource to research what is known about yeast and baking.

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Writing a Hypothesis

Read the section "Experimental Design" that follows to determine what the independent and dependent variables are. Write a formalized hypothesis using the "If . . ., then . . ." form discussed in writing exercise on hypotheses. Include the dependentand independentvariables.

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Experimental Design: This is your procedure. Your team will set up three test tubes containing yeast, water and sugar stoppered with a gas delivery tube. By placing the end of the delivery tube under water, you can count the gas bubbles given off by the yeast. Each test tube of yeast will be in a water bath of different temperature. Tube A will be in water bath cooled by a few ice cubes, tube B will be in room temperature water, and tube C will be in a warm water bath.

phoex1.jpg

Assemble the apparatus and allow the set ups to sit for five minutes so differences in air pressure due to temperature differences equalize. After the five minute pause, place the open end of the delivery tube under water and begin to collect data on gas production. For the next ten minutes, keep count of the number of gas bubbles released from each set up and record in the table below.

Prepare a graph of the data using time along the x axis and the running total of gas bubbles released on the y axis. Plot three curves on the same graph and label each with the temperature you recorded for each test tube. Before handing in your report, validate your results by comparing your graph results with at least one other team.

Data/Observations

Carbon Dioxide Bubbles Released by Yeast
Time in
minutes
1 2 3 4 5 6 7 8 9 10
Tube A
___ oC.
                   
Tube B
___ oC.
                   
Tube C
___ oC.
                   

Interpretations and Conclusions

  1. Which set of conditions is most similar to the conditions for the bread dough in the recipe? And why were there two other conditions used in this experiment?

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  2. Why should you compare your results with other teams before writing your conclusion?

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  3. What was the independent variable in this experiment?_________________________________ What was the dependent variable in this experiment?
    ___________________________________________________________________

  4. Write a conclusion for this experiment. Describe how the independent and dependent variable are related. Tell how the data supports this hypothesis.
    ___________________________________________________________________

    ___________________________________________________________________

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  5. What does temperature have to do with making bread dough rise?
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Additional info for teachers


Example #2: Catalysts and the Control of Biochemical Reactions

Introduction

Catalysts are chemicals which promote chemical reactions in other chemicals but do not become a part of the product nor do they get used up. Catalysts can be simple as elements or complex compounds. Platinum and silver are two previous metals that act as catalysts in several inorganic reactions. Living cells use special catalysts that are complex proteins. These organic catalysts are called enzymes. Enzymes control cellular chemical reactions. Enzymes are "substrate specific" in that a given enzyme will work with the reactants of only one chemical reaction. In this investigation, you will experiment on both an enzyme and a simple inorganic catalyst.

First you will test the relationship between temperature and reaction rates of both an enzyme and an inorganic catalyst. The enzyme iscatalasewhich is naturally found in cells and is used to break down Hydrogen Peroxide which if too concentrated can be toxic to cells. The inorganic catalyst is Manganese Dioxide (MnO2). MnO2 also catalyzes the breakdown of Hydrogen Peroxide (H 2O2) into two harmless substances.

State the Problem:__________________________________________________________

The second experiment will involve just catalase. In this experiment you will test the relationship between reaction rate and quantity of enzyme.

State the Problem:__________________________________________________________

Read the experimental design and write a formalized hypotheses for each experiment. Remember to include both the dependent and independent variable.

Experimental Design

Procedure A

Use three test tubes. Add one "measure" of MnO2 to first test tube. To the second and third tubes add a small piece of potato and liver respectively. Place these three test tubes in a boiling water bath for eight minutes. Remove the tubes and add 10 ml of H2O2 (DO NOT BOIL THE H202!) and observe and record the reaction.

pho1ex2.jpg

Add a fresh piece of liver, potato, new MnO2 to three clean tube and add the H2O2 without boiling anything. Again observe and record the reaction. These observations will serve as a control.

Hypothesis:

Procedure B

Use two test tubes. Grind up a piece of potato and a piece of liver and place each into a test tube. Add H2O2 and observe and record the reaction.

Hypothesis:_______________________________________________________

Data

Condition Proc. A: whole Proc. A: boiled Proc. B: ground
Contents of tube MnO 2 Liver Potato MnO 2 Liver Potato Liver Potato
Describe
the
reaction
rate.
               

phot2ex2.jpg

Analysis

  1. Assuming that the breakdown of H2O2 results two substances, it is obvious that one of these is a gas. Determine by testing what the gas is and give your evidence. ___________________________________________________________________

  2. The second breakdown product is a harmless liquid. Complete the chemical equation below. H2O2 ------(catalyst)------> ___________ + ___________

  3. How do you think grinding affects the amount of enzyme present?

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  4. How can you be sure that sand is not a catalyst and is causing the reaction?

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  5. How could you be sure that MnO2 was not used up or chan ged by the reaction?

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  6. How did the reaction of the boiled materials differ from each other?

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Conclusions

  1. What can you conclude about catalytic reactions and temperature?

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  2. What can you conclude about the reaction rate and the amount of enzyme used?

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  3. What does conclusion #1 imply about why people die when infection causes extreme fever?

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Example #3: Factors Affecting Photosynthesis

Introduction

Photosynthesis is the process of changing light energy into chemical energy (food or fuel). Organisms that can do this are called "autotrophic." These organisms generally appear green in color and include most true plants and some protists. Other organisms get their food by eating other organisms. Is there a relationship between color and the ability to make food? Furthermore, what evidence do we have that light is actually used in making food?

After stating the two problems below, read the experimental design, identify the variables, and write a hypothesis for each problem.


State the Problem:

  1. ___________________________________________________________________

  2. ___________________________________________________________________

Experimental Design #1:

Using just a single normal uncovered leaf of Coleus or some other variegated leaf plant, you can determine the relationship between photosynthesis and chlorophyll. Since the leaves are variegated, only some of the leaf is green while other parts are pink or have no color at all. Testing for the distribution of starch in the leaf will indicate photosynthesis. If starch tests out positive, we can see where food making has taken place.

What is the independent variable?__________________________________

What is the dependent variable?____________________________________

Hypothesis #1: ________________________________________________

___________________________________________________________________

___________________________________________________________________

Experimental Design #2:

Cover a leaf from a potted plant with aluminum foil to cut off its sunlight. Place the plant in the greenhouse or under a grow light. After four days, remove the covered leaf and a normal leaf from the plant. Place both leaves in boiling water to destroy their cell membranes (heat denatures the protein). Boil the leaves in alcohol to remove their pigments. Finally, test the leaves for starch using Iodine. Presence of starch indicates food making while lack of starch would indicate that food has been used up by cellular respiration. What is the independent variable? _________________________________

What is the dependent variable?____________________________________

Hypothesis #2: ________________________________________________

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Assumptions

The above procedure should provide us with observations we need to confirm or deny our hypotheses provided that the following assumptions are true:

  1. Starch is an indicator of glucose which implies that photosynthesis is going on. It is a known fact that starch is a polymer of glucose.
  1. Since the leaf wrap in foil can not make food in darkness, then it is reasonable to think that the leaf tissues must be using stored food therefore the starch stored previously will be reduced or eliminated entirely.

  2. It is also assumed that boiling the leaf will not remove starch from the leaves.

Observations / Data

Sketch the leaves as they appeared before removing their pigments and as they appeared after the Iodine was added. Use colored pencils for accuracy.

pho2ex3.jpg

Analysis

  1. Which leaf contained the most starch?____________________________

  2. In what part of the leaves did starch appear?____________________

Conclusions

  1. Write a conclusion about the relationship between chlorophyll and photosynthesis? Describe the relationship. Tell what data supports your conclusion. ___________________________________________________________________

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  2. Write a conclusion about the relationship between light and photosynthesis? Describe the relationship. Tell what data supports your conclusion? ___________________________________________________________________

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