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Life and ChemistryHave you ever modeled a volcanic eruption by mixing

vinegar and baking soda? When baking soda—also called sodium bicarbonate (NaHCO3)—combines with the acetic acid (CH3COOH) in vinegar, a chemical reaction occurs. A chemical reaction is the process that occurs when compounds, called reactants, form one or more new substances, called products.

During a chemical reaction, bonds are broken and new bonds are formed. When sodium bicarbonate and acetic acid react, water (H2O), carbon dioxide (CO2), and sodium acetate (NaCH3COO) form. You will see bubbles form when vinegar and baking soda mix. The bubbles are caused by the CO2 gas and the water that are released as the products of this chemical reaction.

Chemical reactions are everywhere. Moldy bread and green pennies are the results of chemical reactions. Chemical reactions also occur in your body. These chemical reactions take place in your body’s cells. They are essential for human life.

What do you think? Read the three statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.

Before Statement After

1. Elements can be broken down into smaller parts.

2. Organic compounds are foods grown without pesticides.

3. Organ systems work together.

Key Concepts • What are the functions of

inorganic substances in the human body?

• What are the functions of organic substances in the human body?

• How does the body’s organization enable it to function?

Reading Check1. Name a common result of a chemical reaction.

Building Vocabulary As you read, circle all the words you do not understand. Highlight the part of the text that helps you understand these words. Review the marked words and their definitions after you finish reading the lesson.

Interactions of Human Body SystemsThe Human Body

Reading Essentials Interactions of Human Body Systems 383

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Elements and CompoundsElements are the basic units that make up chemicals.

Elements cannot be broken down or changed into another element during a chemical reaction. Elements have different physical properties. Of the almost 100 elements found in nature, six elements make up 99 percent of your body’s mass. These elements are carbon, oxygen, hydrogen, nitrogen, calcium, and phosphorus.

Compounds are substances made of two or more elements. Unlike elements, compounds can be broken down into simpler substances. Acetic acid is a compound. It is formed when the elements carbon, hydrogen, and oxygen combine.

Compounds form when elements bind together in one of two different ways. Compounds have either ionic bonds or covalent bonds. Ionic bonds are formed when electrons travel from one element to another. One element has a positive charge, and the other has a negative charge. The opposite charges attract. Table salt, or sodium chloride (NaCl), is an example of a compound with an ionic bond.

Covalent bonds are formed when the electrons in each element are shared. Many gases, such as oxygen (O2) and nitrogen (N2), form by covalent bonds.

Inorganic SubstancesInorganic compounds are everywhere on Earth. Inorganic

compounds are substances that do not contain carbon-hydrogen bonds. Substances such as ammonia (NH3) and NaCl are inorganic compounds. Many inorganic compounds, such as water and oxygen gas, are essential for human life.

Ionic Compounds As you have read, NaCl is an inorganic compound that forms by ionic bonding. Ionic bonds are formed when a positive ion is attracted to a negative ion. When a substance gives up or gains an electron, the substance is called an ion. In the compound NaCl, Na+ is a positively charged ion, and Cl– is a negatively charged ion. Many ions are important for human survival. For example, calcium (Ca2+) helps nerves and muscle cells function. Calcium also makes up bone. These compounds rely on water to move through the body.

Water You might know that water is called the universal solvent. A solvent is a substance that dissolves other substances. Ionic compounds dissolve well in water. That makes it possible for ions such as Na+, Cl–, and Ca2+ to travel through the body dissolved in water.

Reading Check2. Name the elements that make up most of the body’s mass.

Make a layered book to record your notes on human body chemistry.

Reading Check3. Explain what an ion is.

Organic SubstancesIonic CompoundsWater

Essential to Life

384 Interactions of Human Body Systems Reading Essentials


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Reading Check6. Identify Which element must an organic compound contain?

Wa ter is able to dissolve many substances because of its polarity. Water molecules are formed by covalent bonds that link the hydrogen (H) to the oxygen (O).

As shown in the figure above, water is able to easily dissolve ionic substances. This is because the positive ions (Na+) in the compound NaCl are attracted to the oxygen end of the water molecules and the negative ions (Cl–) are attracted to the hydrogen end of the water molecules.

Look again at the water molecule above. The molecule has a bent shape with the large oxygen atom at one end of the molecule. This bent shape results in the oxygen end of the molecule having a negative charge. The hydrogen end has a positive charge.

Organic SubstancesYou may have heard the term organic used to describe

certain fruits and vegetables. However, when the term organic is used in science, it describes certain compounds. Those compounds contain carbon and other elements, such as hydrogen, oxygen, phosphorus, nitrogen, or sulfur, held together by covalent bonds.

Visual Check4. Identify Which ion is attracted to the oxygen end of the water molecule?

Key Concept Check5. Describe How does water help the body obtain ionic substances?

Structure of a Water Molecule

+

Salt dissolvedin water

Water molecule

+

+

+

-

-

-

-

-

- -

-

--

-

--

+

+

+

++

+

+

+ +

+

+ ++

+

+

-

++

+

+

+

++

+

+

-

+

Cl

Na

Na



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Organic compounds carry out many different functions. Substances that form from joining many small molecules together are called macromolecules. The four macromolecules in the body are carbohydrates, lipids, proteins, and nucleic acids. They are shown in the figure above.

Carbohydrates Sugars, starches, and cellulose are carbohydrates. Carbohydrates are formed when simple sugars, called monosaccharides (mah nuh SA kuh ridez), are joined together. Carbohydrates are the body’s major source of energy.

Lipids Triglycerides and cholesterol are lipids (LIH pihdz). Like carbohydrates, they are made from carbon hydrogen, and oxygen. Lipids help insulate your body and are a major part of cell membranes.

Proteins The adult human body is made up of 10–20 percent protein. Proteins form when amino (uh MEE noh) acids, the building blocks of protein, join together. Some proteins give cells structure, some help cells communicate, and some are enzymes.

Nucleic Acids Much as computer chips store information, nucleic acids are macromolecules that store information. This information is used by the body to perform different functions. Nucleic acids are formed when nucleotides (NEW klee uh tidez), molecules made of a nitrogen base, a sugar, and a phosphate group, join together. The body contains two types of nucleic acids, DNA and RNA.

Reading Check8. State Amino acids join together to form . (Circle the correct answer.)a. carbohydratesb. lipidsc. proteins

Visual Check7. Identify Circle the macromolecule that is made of nucleotide polymers.

Key Concept Check9. Describe What are the functions of organic compounds in the human body?

Macromolecules

During digestion,

humans break down

carbohydrates

into glucose, a

monosaccharide, and

store it as glycogen.

Lipids, also called fats,

contain fewer oxygen atoms

than carbohydrates and

do not dissolve in water.

All amino acids

consist of carbon, oxygen,

hydrogen, and nitrogen.

Some also contain sulfur.

DNA is made of two

strands of nucleotide

polymers. RNA is made

of a single strand.

Carbohydrate

Lipid Protein Nucleic acid



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The Body’s OrganizationTo function and survive, macromolecules in the human

body must be organized in different compartments. For example, most DNA is stored in the nuclei of cells. Cholesterol and other types of lipids are used to form cell membranes. Organizing macromolecules in specific locations helps cells carry out specific functions.

Cells Recall that cells are the building blocks of all living organisms. Cells have different shapes depending on their function. Neurons are long and slender so they can carry information over long distances. Red blood cells are flexible disks that can move easily through blood vessels.

Tissues Cells that work together and perform a function make up tissues. Cardiac muscle cells form a tissue that helps the heart pump blood throughout the body.

Organs A group of tissues that work together and perform a function is an organ. The liver, spleen, and lungs are organs.

Organ Systems As shown in the figure to the right, an organ system is a group of organs that works together and performs a specific task. Organ systems work together and help the body communicate, defend itself, process energy, transport substances, and move.

Reading Check10. Summarize Where is most DNA stored?

Key Concept Check 12. Explain How does the body’s organization enable it to function?

Visual Check11. Identify What is bone tissue made of?

Organ System

Bone cell

Bone tissue

Skeletal system

Bone

(organ)



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Mini Glossary

Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?

What do you think

END OF LESSON

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

ConnectED

amino (uh MEE noh) acid: a building block of protein

macromolecule: a substance that is formed from joining

many small molecules together

monosaccharide (mah nuh SA kuh ride): a simple sugar

nucleotide (NEW klee uh tide): a molecule made of a

nitrogen base, a sugar, and a phosphate group

1. Review the terms and their definitions in the Mini Glossary. Write a sentence that describes the importance of amino acids.

2. Use what you have learned about macromolecules to complete the table. The third item has been completed for you.

Macromolecules How They Are Formed Examples

Carbohydrates

Lipids

Proteins when amino acids join together enzymes

Nucleic acids

3. Compare and contrast elements and compounds.



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