Living in a Carbon World

Part C: Building Carbon Compounds

In the carbon cycle, carbon atoms are constantly on the move, cycling into and out of different components of the biosphere and geosphere. Carbon atoms do not cycle as single atoms but instead move as part of carbon compounds, some small and simple and others large and highly complex. The carbon cycle is tightly coupled with other biogeochemical cyclescycles of other chemical elements such as nitrogen, phosphorus, sulfur and iron that move into and out different components of the geosphere and biosphere. . For example, many carbon compounds produced by living organisms contain nitrogen and phosphorus atoms.

Consider the image of the global carbon cycle pictured on the right, (click to enlarge the image). Each arrow represents a pathway that carbon atoms take as they move throughout the Geosphere and Biosphere. Some of these carbon compounds move quickly from one part of the carbon cycle to another whereas others are stored for millions and millions of years. As carbon compounds move throughout the Geosphere and Biosphere, they undergo many different chemical changes. These chemical changes (transformations) require the breaking and building of chemical bonds between the atoms. Some of these chemical changes seem quite minor but may have major influences on the carbon cycle, climate, and the environment. For example, when plants convert inorganic CO2 into organic sugars (C6H12C6), they provide food for food for animals and other heterotrophs organisms that cannot manufacture their own food and instead obtain their food and energy by taking in organic substances, usually plant or animal matter; animals, protozoans, fungi, and most bacteria are heterotrophs. When soil bacteria break down carbon compounds in the soil, they release carbon dioxide (CO2) or methane (CO4). Both these gases are greenhouse gases and have been linked to climate change.

Scientists predict that more than ten million different carbon compounds are in existence on Earth today. In this section, you will carry out four short investigations to explore how carbon atoms can join with other types of atoms to form the millions of different types of carbon compounds that can be found in the Geosphere and Biosphere. To get you started thinking about carbon's ability to form so many different types of carbon compounds, watch this short NPR video clip, It's All About Carbon: Episode 1.

NOTE: If the video does not load, you can watch the video here: Episode 1: Global Warming, It's All About Carbon - YouTube You can also follow this link where you can watch other episodes of this NPR series.

Laboratory Investigation 1: Evidence for a Chemical Change

In the video you just watched, you learned that carbon atoms bond easily and strongly with other atoms to form many different types of carbon compounds. In this investigation, you will look for evidence of a new carbon compound being formed when two carbon compounds are brought together: the CO2 from your own breath and a solution of calcium hydroxide Ca(OH)2.

  1. (Class demo) Chalk is made of calcium carbonate (CaCO3). When vinegar is added to chalk, fizzing occurs indicating that chalk is made of calcium carbonate. You will use the vinegar test to indicate the presence of calcium carbonate.
  2. Examine the limewater and describe its appearance. Limewater is the common name for saturated calcium hydroxide solution, Ca(OH)2 (aq).
  3. Place one of the drinking straws into the lime water and blow gently into the liquid. DO NOT INHALE OR BLOW TOO HARD. Continue exhaling through the straw until a white precipitate (solid) forms. The solution should look very milky with small particles.
  4. Place the coffee filter over the empty cup. Carefully pour the lime water into the cup through the filter to separate the precipitate from the liquid.
  5. Put the filter with white precipitate aside and allow it to dry and solidify.
  6. Place a drinking straw into a cup of regular water (instead of limewater) and blow gently. Observe what happens. This serves as your experimental control.

  7. Checking In

    Describe how limewater and regular water react differently when carbon dioxide gas is added to each.

  8. To prove that the substance you filtered out of the lime water is indeed calcium carbonate, use the eyedropper to add a small amount of white vinegar to the precipitate.


  • What evidence did you observe that a new kind of carbon compound was formed in this investigation.
  • Describe what happens to the carbon atoms in carbon dioxide (CO2) when you blow CO2 into the limewater?
  • Why does this investigation serve as a model for understanding chemical change as a key component of the carbon cycle.

Carbon Dioxide and Water Molecules Carbon dioxide and water molecules.

Laboratory Investigation 2: Modeling Photosynthesis and Cell Respiration

In this investigation, you will use a "ball and stick" molecular model kit to investigate how the two key biosphere processes of photosynthesis and cell respiration create new carbon compounds. Gather your materials and follow the instructions for modeling photosynthesis and cell respiration below:

Use the six carbon dioxide and six water molecules to model photosynthesis. Here is the chemical equation for photosynthesis.

6CO2 + 6H2O ==> C6H12O6 + 6O2

1. Begin by taking the carbon dioxide and water molecules apart.

2. Build your glucose molecule using the image of a glucose molecule pictured on the right to guide you. If you click to enlarge the image, you will easily see how the carbon, hydrogen and oxygen atoms are bonded to each other. NOTE: Do not take apart the glucose molecule until you start Investigation 3:

3. Use the remaining oxygen atoms and bonds to build six O2 molecules (O=O). These oxygen gas molecules are released to the air and provide some of the necessary oxygen for life on earth.

4. Examine the equation for cell respiration pictured on the right. The chemical equation for cell respiration is:

C6H12O6 + 6O2==> 6CO2 + 6H2O + energy for cell functions

Then, answer the Checking In questions below:

Checking In

  1. In the glucose molecule, carbon atoms form bonds with_______: Check all that apply and then click the the Check Answers button at the end of the list.
  2. In the glucose molecule in both photosynthesis and respiration, the carbon atoms originally came from the_____: Check all that apply and then click the the Check Answers button at the end of the list.

Laboratory Investigation 3: Biosynthesizing New Biomolecules From Glucose

  1. Take your glucose molecule and join with at least one other team.
  2. Take apart the glucose molecules. NOTE: You do not have to disconnect all of the bonds from the atoms.
  3. Use the atoms and bonds from both teams to build a new biomolecules organic carbon compounds produced in living things; examples include carbohydrates, lipids(fat, soils, waxes), and DNA. . Your biomolecule can take any shape you like. The one rule you must follow is that no "electron bond prong" is left unconnected to another atom. It is possible to have a few atoms and bonds leftover when you build your biomolecule. NOTE: Your teacher may decide to produce you with nitrogen atoms. Using these atoms will allow you to build protein molecules.
  4. When you are finished building your new biomolecules, compare them with other biomolecules made by other teams.


Look at the the other biomolecules the class has made from the original glucose biomolecules.

  • How are they similar? How are they different?
  • If you had a thousand glucose biomolecules, how many different types of biomolecules do you think you could make? Why?
  • Imagine that carbon could only form one electron bond as opposed to four. What effect might this have on the size and diversity of molecules you have been able to build so far?

Laboratory Investigation 4: Biosynthesis of Large Complex Biomolecules using CHNOPS acronym for carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur atoms; 97% of organisms are made of just these six elements

The biomass of all organisms is comprised mostly of proteins, carbohydrates, nucleic acids (DNA, RNA), and lipids (fats oils and waxes). Glucose and other carbohydrates contain carbon, hydrogen and oxygen atoms. However, organisms in the biosphere build millions of different biomolecules that contain nitrogen, phosphorus and sulfur. As a matter of fact, 97% of a living organism is made of only six elements; carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur or CHNOPS for short. Other elements such as magnesium and iron are also important but in very small quantities. Lack of any of these soil nutrientsnutrients in soil that are essential for plant growth; the most important soil nutrients include nitrogen, phosphorus, magnesium and sulfur. will limit plant growth and carbon storage. In this investigation, you will examine several Jmol images of biomolecules and identify the types of elements(atoms) in each.

  1. Make a three column chart in your Lab notebook or on a separate piece of paper. Give your chart the following headings:
  • Column A = Name of biomolecule (ex. DNA, fructose etc.);
  • Column B = Type of biomolecule (ex. carbohydrate, protein etc.);
  • Column C = Types of atoms (elements). Use first letters (C H N O P S Mg I);
  • Click to enlarge and closely examine each Jmol biomolecule image pictured below. Identify each different type of element(atom) in each Jmol biomolecule.
  • Fill-in the required information in your 3-column chart for each Jmol image.

  • Checking In

    1. What element forms the structural backbone of all the biomolecules you have analyzed? Click the Check Answers button at the bottom of the list.
    2. What elements are in ALL of the plant biomolecules you have examined so far? Check all that apply and then click the Check Answers button at the bottom of the list.
    3. What types of biomolecules cannot be biosynthesized without nitrogen atoms? Check all that apply and then click the Check Answers button at the bottom of the list.
    4. In Lab 1B, you calculated the amount of carbon in a local tree. If the soil surrounding your local tree was deficient in nitrogen, phosphorus, sulfur, magnesium and/or iron, you might expect to observe the following: Check all that apply and then click the Check Answers button at the bottom of the list.

    Stop and Think:

    1: Explain why the carbon atoms in carbon compounds such as proteins and DNA originally came from CO2 molecules in the atmosphere.

    2: Explain why a lack of soil nutrients (ex. nitrogen, phosphorus, sulfur and magnesium) limits a tree's ability to grow and store carbon.

    3: Explain how trees and all other organisms in the biosphere are able to make millions of different configurations of carbon compounds.

    Optional Extensions

    Want to learn more about carbon compounds, biomolecules, CHNOPS, soil nutrients and more? Check out these resources.

    • Research the latest research! New research on the carbon cycle, climate and the environment is on-going. You can use ScienceDaily and to research recent research on the relationship between the carbon cycle and other biochemical cycles by using combinations of the following tags: carbon cycle, carbon storage/sequestration, CO2 fertilization, trees, forests, soil nutrients. Here is an example: Soil nutrients limit ability of plants to slow climate change
    • Use MolView to explore Jmol biomolecules made by many different types of organisms.