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Designing Experiments About the Carbon Cycle

Eric Johns & Frank Ferrara

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Synopsis:
This part of the Carbon Cycle depicts the effects of carbon levels on photosynthesis and cellular respiration.  The experiments found below are designed to reinforce the concept of the carbon cycle.  Although the experiments have materials and procedures listed below they are meant to be used as scientific inquiry for students and teachers.
 

 

A. Background Information
    Carbon is the basis for all life on earth due to its versatile bonding configurations.  Carbon can bond to itself, can form single bonds (alkanes), double bonds ( alkenes), triple bonds (alkynes), rings, and chains.  Carbon is the first element in group IV.  It is a nonmetal with an atomic number of six and an atomic mass of approximately 12.  Carbon has four electrons in its outer shell and forms covalent bonds.  Carbon is quite inert at ordinary temperatures, but it combines with oxygen at moderate temperatures making it an important reducing agent for metallic oxides.
 

    Carbon exists as a free mineral in graphite and diamond.  The formation of coal involves an enrichment in carbon by the loss of volatile substances.  Dry plant matter--dry peat--lignite--  bituminous--anthracite/soft coal/hard coal  (Carbon amounts contain 44%C, 50%C, 57%C, 78%C, and 81%C.)
    Petroleum and natural gas are also fossil fuels called hydrocarbons which contain carbon .  Hydrocarbons and their derivatives form the basis of organic chemistry.  The element carbon is also found in carbonate rock.  The most important carbonate rock is limestone (CaCO3, or calcium carbonate).  Carbon is found in the atmosphere as carbon dioxide where it plays an important role in maintaining the earth's radiant equilibrium.   An increase in CO2 concentration increases the atmosphere's ability to retain heat.  As a result, the earth's atmosphere reaches radiant equilibrium at a higher temperature.  This is why  carbon dioxide is one of the major greenhouse gases.   The largest storage of carbon occurs in the oceans, while the atmosphere stores the least amount of carbon.   Carbon dioxide as a solid is dry ice.  Solid carbon dioxide undergoes sublimation ( when a solid turns into a vapor while skipping the liquid phase) to form the gas CO2.
      The oceans are the major sinks for carbon dioxide.   Many organisms living in the ocean utilize carbon dioxide to make calcium carbonate shells (CaCO3).  Over millions of years of time these shells have decomposed into chalk.  Chalk is mined and utilized to make chalk sticks for writing on the blackboard.
        To comprehend the carbon cycle,  it might be useful to show students a transparency that gives an overview of the major cycles in the biosphere.  The pupils should each have their own facsimile of the diagram and trace the cycles as they are explained.  To assess for comprehension, the labels can be concealed by the transparency and the students can be asked to name the cycle.  Since there are many  ways to depict the carbon cycle, it is a good idea to expose students to several of them.  Pupils should be able to quantify data on total production (sources) and total loss (sinks) as well as the net increase and decrease of carbon.
 

 
 
 

Designing Experiments: Science as Inquiry

Constructing and testing hypotheses; collecting and analyzing data; drawing conclusions:

    Laboratory experience can do more than illustrate a concept or principle; they can reinforce an understanding of examples of interesting problems that can be presented to students to introduce them to concepts such as formulation and testing of hypotheses, control versus experimental groups, the need for accurate data collection, and graphing techniques.
 

Testing for Carbon Dioxide: Plants, like animals, have respiration.  Their respiration wastes include carbon dioxide.

Question:

Will a plant like (Lemna) give off more CO2 during the day or night?

    Plants produce carbon dioxide and water vapor during cellular respiration.

Materials:

Method:

    1. Place the plant inside the large jar.
    2. Fill the small container with lime water and place it inside the jar.
    3. Close the jar and store it in a dark place overnight.  Notice how the lime water turns cloudy.

Testing the Gases Plants Emit

Question:

Will plants emit more Oxygen during the day or night?

    During the process of respiration, plants in the dark emit carbon dioxide.   Plants in the light emit oxygen as a by-product of photosynthesis.  Oxygen is a key component of fire, while carbon dioxide puts out fires.
 

Materials:

  Methods:

    1. Place a sprig of Elodea into each of two test tubes full of water.   Be certain that the two sprigs are of equal length.  Place a couple
            of inches of water in each.
    2. Place your finger over one test tube so that you do not lose any water, invert it, and place inside one jar.
    3. Repeat with the other test tube.  Now you have two identical setups.
    4. Place one in a dark closet, the other in the sun or under a grow lamp.
    5. After a couple of days,  some gas should have collected at the upper end of the test tubes.  Carefully invert each of the test tubes
            keeping them closed with your finger.
    6. Holding a burning match or candle near each test tube, let the gas escape.  The gas from one test tube will glow brightly, while the gas
            from the other might extinguish the flame.
 

The Greenhouse Effect

Hypothesis:

The amount of CO2 in a closed environment will cause the temperature to rise in that environment.

    The atmosphere is a thin layer of gases that surround the earth.  Among these gases are nitrogen, oxygen, ozone, and carbon dioxide.  Since the Industrial Revolution,  the amount of carbon dioxide in the atmosphere has been steadily increasing.  Infrared rays,  the heat energy of the sun, pass easily through the atmosphere.  The earth reflects most of the heat back to the sky, but the carbon dioxide in the atmosphere acts as a lid to reflect back and trap some of the heat energy.  This has perhaps magnified the greenhouse effect to produce global warming.   Most nations are starting to address this common problem by trying to reduce their carbon dioxide output.  In this activity, you will compare plant growth in a normal environment with plant growth in a closed environment.
 

Materials:

Methods:

    1. Fill the seed trays with soil, and plant several kinds of flower seeds in them.
    2. Be certain that the soil is moist.
    3. Place a thermometer in each tray.
    4. Cover one tray with plastic wrap, securing it by placing the large rubber band around tray.
    5. Place both trays in an outside location. Shelter them from rain but expose them to the sun.
    6. As the seedlings grow taller,  insert the ice-cream sticks in the corners of the wrapped tray to keep the plastic from the touching the
            plants, them replace the plastic wrap.
    7. Weekly, observe and record the temperatures of both trays.  You will notice that the closed environment is warmer than the other tray.
 

Stomata In Plants

Hypothesis:

When the stomata of plants are closed for an extended period of time the plant will die.

   Plants have tiny openings called the stomata on the underside of their leaves.  The function of the stomata is to let out excessive gases, such as oxygen, and to take in carbon dioxide.  If the stomata are blocked, the leaf is unable to take in carbon dioxide and dies.
 

Materials:

Methods:

    1. Keep the plant in the dark for several days.  Then select two leaves and coat their upper surfaces heavily with petroleum jelly.
    2. Select two more leaves and heavily coat their under surface with petroleum jelly.
    3. Place the plant in a sunny window for a week and observe.  The leaves coated on the underside will appear to die as time goes on.
 

Transpiration - Plant Water Loss

Hypothesis:

Transpiration occurs in leaves after being separated from the tree.

   Plants absorb water from the earth.  Water moves up from the roots, through vessels and tracheids, to reach the leaves.   Most of the water in the leaves, about 90%, is lost through the stomata.   This water loss through the stomata is called transpiration.  Since large trees lose as much as 6800 kg (14, 900 lb.)  of water in half a day, this transpiration can affect the local weather (micro weather) in terms of humidity and temperature.  A plant that runs out of water in the soil will transpire itself to death.
 

Materials:

Methods:

    1. Place the sandwich bag over one leaf of the plant.  Utilize tape to seal the bag tightly around the stem.
    2. Place the plant in the sun for several hours.  Observe the interior of the bag for cloudiness as water collects on its inner surface.
    3. After several hours in the sun, the bag will show water condensation and will be slightly cloudy.
 

Plants Produce Water (Vapor)

Hypothesis:

Plants will transpire water from their leaves in the dark.
 

Materials:

Methods:

    1. Place the plant and a strip of cobalt chloride in the jar.  Cover the jar and set it in a dark place overnight.  The paper will turn from
            cobalt blue to pink.  The pink indicates the presence of water.
    2. You can test the cobalt chloride paper by blowing on it.  Water vapor in your breath will turn the cobalt chloride pink.


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