64 Lesson 1

ExaminE any EnvironmEntal issuE, and you will likely find chemistry at its core. Chemistry is crucial to understanding how pollutants cause acid rain; how gases such as carbon dioxide and methane contribute to global climate change; how pesticides and other manufac-tured chemicals affect our health and the health of wildlife and the envi-ronment; and how matter is cycled through the environment. Chemistry is central, too, in understanding water pollution and wastewater treat-ment, hazardous waste and its cleanup and disposal, the atmospheric “ozone hole,” and most energy issues.

Chemistry is also central to many solutions to environmental prob-lems. For example, some organisms can help clean up certain kinds of pollution. Bacteria and fungi that consume the harmful substances in gasoline can be used to clean up soil beneath leaky gasoline tanks that threaten drinking water supplies. Other microorganisms can be used to break down pesticide residue in soil. Plants as different as wheat, tobacco, water hyacinth, and cattails have helped clean up toxic waste sites, often by absorbing toxic metals into their roots. These are all instances of bioremediation, the reduction of chemical pollution using organisms that consume or neutralize the polluting substances. Using bioremediation requires both knowledge of the chemical makeup of the pollution and of the biological and chemical makeup of the organisms used. There is no escape from chemistry.

Building Blocks of Chemistry Atoms and elements are the building blocks of chemistry.

To appreciate the chemistry involved in environmental science, we must begin with a basic fact. All material in the universe that has mass and occupies space is called matter.

Atoms and Elements Atoms are the basic units of matter. An element is a chemical substance with a given set of properties that cannot be broken down into substances with other properties.

Reading Strategy Before you read, create an outline using the dark blue, green, and light blue headings in this lesson. As you read, fill in key phrases or sentences about each heading.

vocabulary matter, atom, element, nucleus, molecule, compound, hydrocarbon, solution, macromolecule, protein, nucleic acid, carbohydrate, lipid, pH

• Differentiate among an atom, an element, a molecule, and a compound.

• Discuss how various macromolecules are essential to life.

• Identify some unusual properties of water.

Guiding Question: What properties of matter are most important to environmental systems?

Matter and the EnvironmentLE

SSO

N 1

FOCUS Show students a glass of water. Ask them to describe ways that water is important to living things. Then, ask students to identify other types of matter in the environ-ment that living things rely on. Have students watch for information in the lesson about properties that make these types of matter impor-tant to environmental systems.

GUIDING QUESTION

3.1 LESSON PLAN PREVIEWDifferentiated Instruction Struggling students fill in a two-column table of section vocabulary as they read.Real World Students explore macromolecules as “the build-ing blocks of life.”Inquiry Students learn about the cohesion of water through a hands-on activity.

3.1 RESOURCESLesson 3.1 Worksheets • Lesson 3.1 Assessment • Chapter 3 Overview Presentation

Transferof electron

Sodium atom (Na) Chlorine atom (Cl)

Sodium ion (Na) Chloride ion (Cl)

(b) Ionic BondingSalt (NaCl)

Proton

Neutron

Electron

Nucleus

– –

– –

– –

– –

–

–

H H

O

Water molecule (H2O)(a) Covalent Bonding

Earth’s Environmental Systems 65

Every atom has a nucleus, or central core, containing par-ticles called protons and neutrons. Protons are positively charged; neutrons have no electric charge. The atoms of each element have a defined number of protons, called the atomic number. Carbon, for example, has six protons in its nucleus; so its atomic number is 6. An atom’s nucleus is surrounded by negatively charged particles known as electrons, which usually balance the positive charge of the protons (Figure 1).

Chemists currently recognize 92 elements occurring naturally, as well as about 20 others that scientists have made. Each element is assigned a chemical symbol. The periodic table of the elements in Appendix D summarizes information on the elements. Carbon, nitrogen, hydrogen, and oxygen are elements especially abundant in living things.

Bonding When atoms combine, it is called bonding. Atoms bond because of an attraction that involves sharing or transfer of their electrons. Because the strength of this attraction var-ies among elements, atoms bond in different ways, according to whether and how they share or transfer electrons. When atoms share electrons, they generate a covalent bond and form a mol-ecule. For example, two atoms of hydrogen (H) bond to form hydrogen gas, H2, by sharing electrons equally. Atoms in a covalent bond can also share electrons unequally, with one atom exerting a greater pull. Such is the case with water, in which oxygen attracts electrons more strongly than hydrogen, forming what are termed polar covalent bonds (Figure 2a). These polar bonds are respon-sible for some of the unusual properties of water that you’ll learn about later. If the strength of attraction is unequal enough, an elec-tron may be transferred from one atom to another. Such a transfer creates oppositely charged atoms, or ions, that form ionic bonds. Table salt (NaCl) contains ionic bonds (Figure 2b).

FIGURE 1 Atom In an atom, protons and neutrons are held in the nucleus, and electrons move around the nucleus. Each chemical element has a different total of protons, neutrons, and electrons. The carbon atom above has six of each. Electrons actually move around the nucleus in more complex ways than is implied in the diagrams on this page.

FIGURE 2 Bonding In a water molecule (a), each hydrogen atom shares two electrons with the oxygen atom, forming a covalent bond. In table salt (b), the sodium atom loses an electron to the chlorine atom, forming an ionic bond.

66 Lesson 1

Molecules and Compounds Atoms joined by covalent bonds are called molecules. A molecule is a combination of two or more atoms of the same type or of different types joined by covalent bonds. Common molecules include those of oxygen (O2) and nitrogen (N2). A substance composed of atoms of two or more different elements is called a compound. Water is a compound made up of two hydrogen atoms bonded to one oxygen atom, so it is represented by the chemical formula H2O. Another compound is carbon dioxide, consisting of one carbon atom bonded to two oxygen atoms; its chemical formula is CO2.

▶ Organic and Inorganic Compounds Living things are made of organic compounds, and they produce organic compounds. Organic compounds consist of carbon atoms (and usually hydrogen atoms) joined by covalent bonds. Other elements may also be present. Carbon’s unusual ability to build elaborate molecules has resulted in millions of different organic compounds. Because of the diversity of organic compounds and their importance in living organisms, chemists differentiate organic com-pounds from inorganic compounds, which lack carbon-to-carbon bonds.

▶ Hydrocarbons Crude oil and petroleum products are made up primar-ily of hydrocarbons. Hydrocarbons are organic compounds containing only hydrogen and carbon. Some hydrocarbons, and products of their burning, are hazardous, so hydrocarbons are common topics in environ-mental science. For example, polycyclic aromatic hydrocarbons, or PAHs, can evaporate from spilled or incompletely burned oil and gasoline and can mix with water. They can be toxic to aquatic animals such as fish. PAH particles can also result from burning and may be present in wood smoke, charred parts of meat, and cigarette smoke (Figure 3a). Some PAH parti-cles have been shown to cause cancer in people. Other hydrocarbons, such as those emitted in automobile exhaust, can cause smog when exposed to sunlight (Figure 3b).

ReadingCheckpoint

How do organic and inorganic compounds differ?

FIGURE 3 Hydrocarbons (a) Cigarette smoke contains harmful polycyclic aromatic hydrocarbons. (b) Other hydrocarbons include those from auto emissions that cause smog.

(a) Cigarette smoke

(b) Traffic and smog in Beijing

ANSWERS

Reading Checkpoint Unlike organic compounds, inorganic compounds lack carbon-to-carbon bonds.

Cartilage

Muscle

Tendon

Bone

Ligament

Earth’s Environmental Systems 67

Solutions Elements, molecules, and compounds can also come together in mixtures without bonding chemically. A mixture in which all the ingredients are evenly distributed is called a solution. Solutions can be liquids, gases, or solids. Air, for example, is a solution formed mostly of nitrogen, oxygen, water, carbon dioxide, methane (CH4), and ozone (O3). Human blood, ocean water, plant sap, and metal alloys such as brass are also solutions.

Macromolecules Proteins, nucleic acids, carbohydrates, and lipids are the build-

ing blocks of life.

Organic compounds sometimes combine to form long chains of repeated molecules. Some of these chains, called polymers, play key roles as build-ing blocks of life. Three types of polymers are essential to life: proteins, nucleic acids, and carbohydrates. Lipids are not polymers but are also essential to life. Proteins, nucleic acids, carbohydrates, and lipids are called macromolecules because of their large size.

Proteins Proteins are polymers that serve many functions in organ-isms. They are organic compounds made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Some help produce tissues and provide support. For example, the production of bones, skin, hair, muscles, and some other body tissues relies on proteins (Figure 4). Other proteins store energy, transport substances, or work within the immune system. Still others act as hormones, molecules that serve as chemical messengers within an organism. Proteins can also serve as enzymes, molecules that promote certain chemical reactions.

FIGURE 4 Proteins Proteins are needed for the development of the bones, muscles, tendons, ligaments, and cartilage (left), as well as the skin and hair (above), that make up a knee.

Nitrogenousbase

Sugar-phosphatebackbone

68 Lesson 1

FIGURE 5 DNA The nucleic acid DNA plays an important role in heredity. DNA is one of two nucleic acids. In the diagram (a), you can see its unique double-helix shape. The computer model (b) shows what DNA actually looks like (colors have been added).

Nucleic Acids Nucleic acids are macromolecules that direct protein production. Deoxyribonucleic acid (DNA) carries hereditary information and is responsible for passing traits from parents to offspring. Ribonucleic acid (RNA) are copies of DNA segments that are involved in making proteins. Nucleic acids are composed of long chains of nucleotides, each of which contains a sugar molecule, a phosphate group, and a nitrogenous base. The double strands of DNA can be pictured as rungs of a ladder twisted into a spiral, giving the molecule a shape called a double helix (Figure 5). RNA is similar, but it is generally single-stranded and contains a different sugar than DNA does.

Very generally, heredity works this way: The parts of DNA that “order” the production of certain proteins are called genes. Information that has been inherited is encoded in DNA and rewritten to a molecule of RNA. RNA then directs the order in which amino acids assemble to build proteins. Genetic information in DNA is passed from one generation to another during cell division and egg or sperm formation. In most organ-isms, the set of all of an individual’s genes is divided into chromosomes.

Carbohydrates Carbohydrates are polymers that consist of atoms of carbon, hydrogen, and oxygen. A simple carbohydrate, or sugar, has three to seven carbon atoms and a formula that is some multiple of CH2O. Glucose, for example, is C6H12O6. Glucose is one of the most common and important sugars because it provides the energy that fuels plant and animal cells. Glucose also serves as a building block for complex carbo-hydrates, such as starch. Plants use starch to store energy, and animals acquire starch when they eat plants.

In addition, the structures that support the bodies of most plants and animals contain complex carbohydrates. Insects and crustaceans form hard outer coverings from the carbohydrate chitin. Cellulose is a complex carbohydrate found in the cell walls of plants.

(a)

(b)

ANSWERS

Reading Checkpoint Deoxyribo-nucleic acid (DNA) and ribonucleic acid (RNA)

Lipids

Fats and oils

Phospholipids

Waxes

Steroids and steroid hormones

Store energy, which is released when they burn; hydrocarbons with chemical structures similar to gasoline

Primary component of cell membranes; similar to fats

Make up biological structures such as honeycombs in beehives; eaten by some organisms

Cell membrane component (steroids); produce bodily changes, such as sexual development (steroid hormones)

Animal fats, vegetable oils, petroleum

Primary component of lecithin

Beeswax

Cholesterol (steroid); androgen, estrogen, testosterone (steroid hormones)

Characteristics ExamplesLipid type

Hydrogen atom

Oxygen atom

Hydrogen atom

()

()Hydrogen bond

Water molecule

()()

()()()

()

H

OH

Earth’s Environmental Systems 69

ReadingCheckpoint

Name two nucleic acids.

Lipids Lipids are a chemically diverse group of macromolecules that are classified together because they do not dissolve in water. Lipids are made up of carbon, hydrogen, oxygen, and sometimes phosphorus. Fats, oils, phospholipids, waxes, and steroids are common lipids. You can learn more about lipids, including their roles in living things, in Figure 6.

Water Water is a unique compound with several

unusual properties that make it essential to life.

Water covers more than 70 percent of Earth’s surface. Water’s abundance is a primary reason there is life on Earth. Scientific evidence demonstrates that life origi-nated in water and stayed there for 3 billion years before moving onto land. Every organism, even if it lives only on land, relies on water for its survival.

Properties of Water Water is our most familiar com-pound. The water molecule’s amazing capacity to support life results from its unique chemical properties. A water molecule’s single oxygen atom attracts electrons more strongly than its two hydrogen atoms, resulting in a polar molecule with a partial negative charge at the oxygen end and a partial positive charge at the hydrogen end. Because of this configuration, water molecules adhere to one another in a special type of attraction called a hydrogen bond, in which the oxygen atom of one water molecule is weakly attracted to one or two hydrogen atoms of another (Figure 7). These loose connections among molecules give water several properties important in supporting life and stabilizing Earth’s climate.

FIGURE 6 Lipids Lipids include fats, oils, phospholipids, waxes, steroids, and steroid hormones.

FIGURE 7 Water Molecule Water molecules have a negative charge at the oxygen end and a positive charge at the hydrogen end, which causes them to adhere to one another in hydrogen bonds. These bonds give water several properties essential to life.

70 Lesson 1

▶ Cohesion Water sticks to itself. (Think of how water droplets on a surface join when you touch them to one another.) This property, called cohesion, allows the transport of materials, such as nutrients and waste, in plants and animals. Cohesion between water molecules is so strong that certain animals, such as the raft spider in Figure 8, can actually walk on water!

▶ Resistance to Temperature Change Heating weakens the hydrogen bonds in water, but it does not initially increase the molecular motion, which is what causes temperature to rise. As a result, water can absorb a large amount of energy with only small changes in its temperature. This resistance to temperature change helps stabilize aquatic environmental systems and the climates in which they exist. It also explains why people like to live and vaca-tion on the coast. Because it takes bodies of water longer to heat up and cool down, coastal areas are cooler in hot weather and warmer in cold weather.

▶ Ice Density Water molecules in ice are farther apart than in liquid water (Figure 9), so ice is less dense than liquid water—the reverse pattern of most other compounds, which become denser as they freeze. This is why ice floats on liquid water. Floating ice insulates bodies of water, preventing them from freezing solid in winter, allowing animals and plants to survive in the water at the bottom.

▶ Universal Solvent Water molecules bond well with other polar molecules, because the positive end of one molecule bonds easily to the negative end of another. As a result, water can hold in solution, or dissolve, many other molecules, including chemi-cals vital for life. Because of this property, water is often called “the universal solvent.”

FIGURE 9 Density of Ice Icebergs float on top of bodies of water because ice is less dense than liquid water.

FIGURE 8 Cohesion of Water Because cohesion between water molecules is so strong, insects such as this raft spider can actually walk across it.

How do the nonliving parts of Earth’s systems provide the basic materials to support life?Explanation Point out the key concept: Water is a unique compound with several unusual properties that make it essential to life. Have students write a short paragraph justifying the use of the adjectives unique and essential to describe water.

BIG QUESTION

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Ammonia

NaOH (sodiumhydroxide)

Soap

Seawater

Pure water

Normal rainwater

Acid rain

Lemon juice

Car battery acidStomach acid

Basic

Acidic

NeutralpH

Earth’s Environmental Systems 71

11. Classify Is table salt (NaCl) a compound? How can

you tell?2. Review List the four types of macromolecules.

What is one role played in the body by each?3. Apply Concepts How would each of the four

properties of water referred to in this lesson help a fish living in a pond?

4. What would you say to a classmate who said that he wanted to fulfill his science requirement by taking environmental sci-ence so he could avoid chemistry?

Acids, Bases, and pH In any water solution, a small number of water molecules separate into ions, or charged atoms. Each separation results in a hydrogen ion (H+) and a hydroxide ion (OH–). Pure water contains equal numbers of these ions, so we say that it has a neutral pH. Most water solutions, however, contain different concentrations of the two ions. Solutions in which the H+ concentration is greater than the OH– con-centration are acidic, whereas solutions in which the OH– concentration exceeds the H+ concentration are basic, or alkaline.

The acidity or alkalinity of a solution is described by pH. The pH scale runs from 0 to 14. A pH of 7 is perfectly neutral—pure water has a pH of 7. Solutions with a pH less than 7 are acidic, and those with a pH greater than 7 are basic. Each point on the scale represents a tenfold difference in hydrogen ion concentration. Thus, a substance with a pH of 6 is 10 times as acidic as a substance with a pH of 7, and a substance with a pH of 8 is one-tenth as acidic as one with a pH of 7. Figure 10 shows the a pH of several common substances.

FIGURE 10 pH The pH scale describes how acidic or basic a substance is. Lemon juice is rather acidic and soap is rather basic.

ANSWERS

Lesson 1 Assessment For answers to the Lesson 1 Assessment, see page A–3 at the back of the book.