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# 1.9: Significance of Carbon

Difficulty Level: At Grade Created by: CK-12
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Carbon. Element number six. Right in the middle of the first row of the Periodic Table. So what?

Carbon is the most important element to life. Without this element, life as we know it would not exist. As you will see, carbon is the central element in compounds necessary for life.

### The Significance of Carbon

A compound found mainly in living things is known as an organic compound. Organic compounds make up the cells and other structures of organisms and carry out life processes. Carbon is the main element in organic compounds, so carbon is essential to life on Earth. Without carbon, life as we know it could not exist.

#### Compounds

A compound is a substance that consists of two or more elements. A compound has a unique composition that is always the same. The smallest particle of a compound is called a molecule. Consider water as an example. A molecule of water always contains one atom of oxygen and two atoms of hydrogen. The composition of water is expressed by the chemical formula H2O. A model of a water molecule is shown in Figure below. Water is not an organic compound.

A water molecule always has this composition, one atom of oxygen and two atoms of hydrogen.

What causes the atoms of a water molecule to “stick” together? The answer is chemical bonds. A chemical bond is a force that holds molecules together. Chemical bonds form when substances react with one another. A chemical reaction is a process that changes some chemical substances into others. A chemical reaction is needed to form a compound. Another chemical reaction is needed to separate the substances in a compound.

#### Carbon

Why is carbon so basic to life? The reason is carbon’s ability to form stable bonds with many elements, including itself. This property allows carbon to form a huge variety of very large and complex molecules. In fact, there are nearly 10 million carbon-based compounds in living things! However, the millions of organic compounds can be grouped into just four major types: carbohydrates, lipids, proteins, and nucleic acids. You can compare the four types in Table below. Each type is also described below.

Type of Compound Examples Elements Functions
Carbohydrates sugars, starches carbon, hydrogen, oxygen provides energy to cells, stores energy, forms body structures
Lipids fats, oils carbon, hydrogen, oxygen stores energy, forms cell membranes, carries messages
Proteins enzymes, antibodies carbon, hydrogen, oxygen, nitrogen, sulfur helps cells keep their shape, makes up muscles, speeds up chemical reactions, carries messages and materials
Nucleic Acids DNA, RNA carbon, hydrogen, oxygen, nitrogen, phosphorus contains instructions for proteins, passes instructions from parents to offspring, helps make proteins

The Miracle of Life: Carbohydrates, Proteins, Lipids & Nucleic Acids video can be viewed at http://www.youtube.com/watch?v=nMevuu0Hxuc (3:28).

#### Energy From Carbon?

It may look like waste, but to some people it's green power. Find out how California dairy farms and white tablecloth restaurants are taking their leftover waste and transforming it into clean energy. See From Waste To Watts: Biofuel Bonanza at http://www.kqed.org/quest/television/from-waste-to-watts-biofuel-bonanza for further information.

### Summary

• Carbon is the main element in organic compounds. Carbon can form stable bonds with many elements, including itself.
• There are four major types of organic compounds: carbohydrates, lipids, proteins, and nucleic acids.

### Practice

Use this resource to answer the questions that follow.

• http://www.hippocampus.org/Biology \begin{align*}\rightarrow\end{align*} Biology for AP* \begin{align*}\rightarrow\end{align*} Search: Organic Molecules: Overview
1. What is an organic compound? Roughly how many organic compounds exist?
2. Describe the element carbon.
3. What is the chemical composition of aspirin? Is it a natural or synthetic compound?
4. Describe organic reactions.

### Review

1. Explain why carbon is essential to all known life on Earth.

2. Which type(s) of organic compounds provide energy?

3. Which organic compound stores genetic information?

4. Examples of proteins include ____________.

### Vocabulary Language: English Spanish

chemical bond

chemical bond

A force that holds atoms together.
chemical reaction

chemical reaction

Process that changes some chemical substances into others.
compound

compound

Substance with a unique, fixed composition that consists of two or more elements.
lipid

lipid

Organic compound such as fat or oil.
organic compound

organic compound

Compound found in living things that contains mainly carbon.
protein

protein

Organic compound made up of amino acids.

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