Example

Dress Rehearsal

Everyone’s heard about the “greenhouse effect,” yet few can explain exactly what it is other than it might be accountable for rising climatic temperatures. Your astronomy textbook does a credible job providing an explanation, and you learn that the photons of visible light from the sun are absorbed by the materials on which they shine. This causes those objects to absorb the heat, and they become warm.

For example, when the sun shines on your car seats through closed windows, heat is generated. Your car seats become hot. You sit down and jump up immediately! This heat generates more photons, but they have less energy than those produced by the sun. These give off infrared radiation rather than the visible radiation coming from the sun. They are not strong enough to pass through glass, and they become trapped inside the car. The air then becomes hot and produces more infrared photons in a never-ending cycle of heat.

Similarly, carbon dioxide and other gases in the earth’s atmosphere also absorb photons. Carbon dioxide, produced by the burning of fossil fuels and coal, remains in the air. The heat absorbed by all this carbon dioxide might result in the warming of the earth’s climate. This, dear friend, is where uncertainty comes in. The effects of this trapped carbon dioxide are not entirely known. Scientists differ: some say it has little effect while others predict outcomes so catastrophic it probably keeps them awake at night.

Your textbook does not delve into this disagreement, so you might seek further information from another source in order to learn more about this unsolved issue. It is hard to predict the consequences due to the uncertainty of “future emissions and the concentration of greenhouse gases, the net warming effect in the atmosphere, and the response of the climate system,” but many scientists predict that the temperature of the earth will continue to increase, land areas will be warmer than oceans, different parts of the world will be warmer than others, and winters will warm more than summer. Hmm, interesting perspective.

As a reader and researcher, it’s your job to continue investigating this issue. Look for credible sources and reliable evidence for both sides. Because this is such a hotly contested issue, be sure to consider the authors’ purpose as you analyze the texts. Why do they include this particular set of information? What information might be missing? Are there any possible biases or political agendas that may be affecting the author’s purpose? A good researcher must consider all of these possibilities when trying to find credible sources and truly understand a concept.

Source:

“Future Temperature Changes.” Climate Change- Science. 14 April 2011. United States Environmental Protection Agency. 5 May 2012. http://www.epa.gov/climatechange/science/futuretc.html.

Drill

Read the following experiment and answer the questions that follow:

Background/Purpose
Apples and other fruit will turn brown when they are cut and the enzyme contained in the fruit (tyrosinase) and other substances (iron-containing phenols) are exposed to oxygen in the air. 

The purpose of this chemistry laboratory exercise is to observe the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen. 

A possible hypothesis for this experiment would be: 

Acidity (pH) of a surface treatment does not affect the rate of the enzymatic browning reaction of cut apples.

Materials

The following materials are needed for this exercise:

• Five slices of apple (or pear, banana, potato, or peach) 
• Five plastic cups or other clear containers 
• Vinegar (or dilute acetic acid) 
• Lemon juice 
• Solution of baking soda (sodium bicarbonate) and water (you want to dissolve the baking soda. Make the solution by adding water to your baking soda until it dissolves.) 
• Solution of milk of magnesia and water (ratio isn't particularly important - you could make a mixture of one part water one part milk of magnesia. You just want the milk of magnesia to flow more readily.) 
• Water 
• Graduated cylinder or measuring cups

Procedure

Day One

1. Label the cups:
Vinegar
Lemon Juice
Baking Soda Solution
Milk of Magnesia Solution
Water 

2. Add a slice of apple to each cup. 

3. Pour 50 ml or 1/4 cup of a substance over the apple in its labeled cup. You may want to swirl the liquid around the cup to make sure the apple slice is completely coated. 

4. Make note of the appearance of the apple slices immediately following treatment. 

5. Set aside the apple slices for a day.

Day Two

1. Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the apples in the other column. Record whatever you observe, such as extent of browning (e.g., white, lightly brown, very brown, pink), texture of the apple (dry? slimy?), and any other characteristics (smooth, wrinkled, odor, etc.) 

2. If you can, you may want to take a photograph of your apple slices to support your observations and for future reference. 

3. You may dispose of your apples and cups once you have recorded the data.

Results
What does your data mean? Do all of your apple slices look the same? Are some different from others? If the slices look the same, this would indicate that the acidity of the treatment had no effect on the enzymatic browning reaction in the apples. On the other hand, if the apple slices look different from each other, this would indicate something in the coatings affected the reaction. First, determine whether or not the chemicals in the coatings were capable of affecting the browning reaction. 

Even if the reaction was affected, this does not necessarily mean the acidity of the coatings influenced the reaction. For example, if the lemon juice-treated apple was white and the vinegar-treated apple was brown (both treatments are acids), this would be a clue that something more than acidity affected browning. However, if the acid-treated apples (vinegar, lemon juice) were more/less brown than the neutral apple (water) and/or the base-treated apples (baking soda, milk of magnesia), then your results may indicate acidity affected the browning reaction.

Source:
Helmenstine, Anne Marie, PhD. “Effect of Acids and Bases on the Browning of Apples - Chemistry Experiments.” About.com Chemistry. 2012. About.com. 8 May 2012. http://chemistry.about.com/od/demonstrationsexperiments/ss/appleenzyme.htm.

QUESTIONS:

1. What is the author’s purpose of the experiment?
2. What is the purpose of the “Results” section of the experiment procedure?
3. What is the purpose of testing an apple in water?
4. What is the purpose of creating a hypothesis that claims there will be no effect rather than a hypothesis that attempts to guess what the effect might be?

ANSWERS:

1. The purpose was to observe and explain the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen.

2. The purpose is to point out that just because we were testing to see if acid influences browning of apples, does not mean that any changes we see are necessarily the result of acid. The author wants to be sure the reader looks at the results closely and considers all possibilities before jumping to any conclusions.

3. The other substances tested were acids and bases, so to have a complete picture of how each might affect the apples, a neutral substance is needed for comparison.

4. According to Helmenstine, you want your hypothesis to be a null hypothesis or no-difference hypothesis because it is easier to test whether or not a treatment has an effect than it is to try to assess what that effect is. In short, an effective hypothesis is based on a yes/no question because a science experiment can clearly provide a yes or no answer. It is much more difficult to design an experiment that reliably provides a more complex answer, such as how or why this effect occurs. Scientists reach those conclusions by performing many experiments that answer yes/no questions, gradually building toward a more complex understanding through many reliable tests.