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Biochemical Compound Classification

There are four major categories of biologically important molecules.

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What Am I Made of?

What Am I Made of?

Credit: Bernhard Ungerer
Source: http://commons.wikimedia.org/wiki/File:3D_Male_Skeleton_Anatomy.png
License: CC BY-NC 3.0

Did you ever wonder what you’re made of? You probably already know that your body contains millions of cells, but what elements are you made of? If you came with an ingredients list, like a package of food, what contents would it list?

The Back Story

  • You feel like you’re made of solid matter, but you’re actually about 60 to 70 percent water. All that water, or H2O, is why the elements oxygen (O) and hydrogen (H) are the first and third elements, respectively, in the human body.
  • Can you guess which element is second in the human body? Watch this video to find out. The video reviews the top ten elements in the human body.


Show What You Know

Learn more about the elements in your body at the links below. Then answer the questions that follow.

  1. Water contains twice as many atoms of hydrogen as oxygen. Why isn’t hydrogen listed as the most common element in the human body, rather than oxygen?
  2. List the top six elements (by mass) in the human body, from 1 to 6. Which of these six elements are nonmetals?
  3. Fill in the blanks in the following paragraph with the correct elements. Choose from the six elements you listed in your answer to question 2, and use each element just once.
    • The element that makes up 18 percent of your body’s mass is (a) _____. The proteins in your body require the element (b) _____. Your nucleic acids, such as DNA, require the element (c) _____. Almost all of the (d) _____ in your body is found in your bones and teeth. The element that contributes 65 percent to your body’s mass is (e) _____. The remaining element of the top six is found in all the liquids and tissues of your body. This element is (f) _____.
  4. Most matter in your body that isn’t water is made of organic compounds. What is an organic compound?
  5. List the four major classes of organic compounds that make up your body and also the cells and tissues of other living things.

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Image Attributions

  1. [1]^ Credit: Bernhard Ungerer; Source: http://commons.wikimedia.org/wiki/File:3D_Male_Skeleton_Anatomy.png; License: CC BY-NC 3.0

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