1

• Relate the structure of an atom to the identity of elements.

Section Objectives:

• Relate the formation of covalent and ionic chemical bonds to the stability of atoms.

Section Objectives:

• Distinguish mixtures and solutions.

• Define acids and bases and relate their importance to biological systems.

• An element is a substance that can’t be broken down into simpler chemical substances.

ElementsElements

• Everything – whether it is a rock, frog, or flower – is made of substances called elements. • Of the naturally occurring elements on Earth,

only about 25 are essential to living organisms.

• Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body.

Natural elements in living thingsNatural elements in living things

Trace elementsTrace elements

• Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms.

• Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat.

Table 6.1 Some Elements That Make Up the Human Body

Element SymbolPercent By Mass in Human Body

Element SymbolPercent By Mass in Human Body

Molybdenum

Oxygen

Carbon

Hydrogen

Nitrogen

Calcium

Phosphorus

Potassium

Sulfur

Sodium

Chlorine

Magnesium

Selenium

Iron

Zinc

Copper

Iodine

Manganese

Boron

Chromium

Cobalt

Fluorine

O

C

H

N

Ca

P

K

S

Na

Cl

Mg

65.0

18.5

9.5

3.3

1.5

1.0

0.4

0.3

0.2

0.2

0.1

Fe

Zn

Cu

I

Mn

B

Cr

Mo

Co

Se

F

trace

trace

trace

trace

trace

trace

trace

trace

trace

trace

trace

2

• An atom is the smallest particle of an element that has the characteristics of that element.

Atoms: The Building Blocks of ElementsAtoms: The Building Blocks of Elements

• Atoms are the basic building blocks of all matter.

• All nuclei contain positively charged particles called protons (p+).

• The center of an atom is called the nucleus (NEW klee us).

The structure of an atom

• Most contain particles that have no charge, called neutrons (n0).

The Structure of an atom

Nucleus

Electron energy levels

• The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e-)

• This region of space is referred to as an electron cloud.

The Structure of an atom

• Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus.

Electron energy levels

• Electrons exist around the nucleus in regions known as energy levels.

• The first energy level can hold only two electrons. The second level can hold a maximum of eight electrons. The third level can hold up to 18 electrons.

Nucleus8 protons (p+)8 neutrons (n0)

Oxygen atom

Electron energy levels

• Atoms contain equal numbers of electrons and protons; therefore, they have no net charge.

3

• Atoms of the same element always have the same number of protons but may contain different numbers of neutrons.

Isotopes of an ElementIsotopes of an Element

• Atoms of the same element that have different numbers of neutrons are called isotopes (I suh tophs) of that element.

• A compound is a substance that is composed of atoms of two or more different elements that are chemically combined.

Compounds and BondingCompounds and Bonding

• Table salt (NaCl) is a compound composed of the elements sodium and chlorine.

• Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms.

How covalent bonds formHow covalent bonds form

• For many elements, an atom becomes stable when its outermost energy level is full.

• Sharing electrons with other atoms is one way for elements to become stable.

• Two hydrogen atoms can combine with each other by sharing their electrons.

How covalent bonds formHow covalent bonds form

• Each atom becomes stable by sharing its electron with the other atom.

Hydrogen molecule

How covalent bonds formHow covalent bonds form

Click image to view movie.

How covalent bonds formHow covalent bonds form

• The attraction of the positively charged nuclei for the shared, negatively charged electrons holds the atoms together.

Hydrogen molecule

4

• A covalent bondholds the two hydrogen atoms together.

How covalent bonds formHow covalent bonds form

• A molecule is a group of atoms held together by covalent bonds. It has no overall charge.

Water molecule

• An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion. An ion is a charged particle made of atoms.

How ionic bonds formHow ionic bonds form

• The attractive force between two ions of opposite charge is known as an ionic bond.

• Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances.

Chemical ReactionsChemical Reactions

• All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism.

Chemical ReactionsChemical Reactions

• In a chemical reaction, substances that undergo chemical reactions, are called reactants.

Writing chemical equationsWriting chemical equations

• Substances formed by chemical reactions, are called products.

• A molecule of table sugar can be represented by the formula: C12H22O11.

Writing chemical equationsWriting chemical equations

• The easiest way to understand chemical equations is to know that atoms are neither created nor destroyed in chemical reactions. They are simply rearranged.

5

• A mixture is a combination of substances in which the individual components retain their own properties.

Mixtures and SolutionsMixtures and Solutions

• Neither component of the mixture changes.

• A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent).

Mixtures and SolutionsMixtures and Solutions

• Sugar molecules in a powdered drink mix dissolve easily in water to form a solution.

• Chemical reactions can occur only when conditions are right.

Acids and basesAcids and bases

• A reaction may depend on:

- energy availability

- temperature

- concentration of a substance

- pH of the surrounding environment

• The pH is a measure of how acidic or basic a solution is.

Acids and basesAcids and bases

• A scale with values ranging from below 0 to above 14 is used to measure pH.

More acidic Neutral More basic

• Substances with a pH below 7 are acidic. An acid is any substance that forms hydrogen ions (H+) in water.

Acids and basesAcids and bases

• A solution is neutral if its pH equals seven.

More acidic Neutral More basic

• Substances with a pH above 7 are basic. A base is any substance that forms hydroxide ions (OH-) in water.

Acids and basesAcids and bases

pH 11

6

Question 1

Which of the following is an element?

D. water

C. sodium chloride

B. carbon

A. chlorophyll

The answer is B. An element can't be broken down into simpler chemical substances. Chemical elements combine in different ways to form a variety of substances useful to living things.

Table 6.1 Some Elements That Make Up the Human Body

Element SymbolPercent By Mass in Human Body

Element SymbolPercent By Mass in Human Body

Molybdenum

Oxygen

Carbon

Hydrogen

Nitrogen

Calcium

Phosphorus

Potassium

Sulfur

Sodium

Chlorine

Magnesium

Selenium

Iron

Zinc

Copper

Iodine

Manganese

Boron

Chromium

Cobalt

Fluorine

O

C

H

N

Ca

P

K

S

Na

Cl

Mg

65.0

18.5

9.5

3.3

1.5

1.0

0.4

0.3

0.2

0.2

0.1

Fe

Zn

Cu

I

Mn

B

Cr

Mo

Co

Se

F

trace

trace

trace

trace

trace

trace

trace

trace

trace

trace

trace

The smallest particle of an element that has the characteristics of that element is a(n) __________.

Question 2

D. atom

C. nucleus

B. electron

A. proton

The answer is D. Atoms are the basic building blocks of all matter and have the same general structure, including a nucleus and electrons. Elements found in both living and nonliving things are made of atoms.

Nucleus

Electron energy levels

An atom has a nucleus and electrons in energy levels.

Which of the following can contain two types of particles?

D. electrons

Question 3

B. protons

C. neutrons

A. nucleus

7

The answer is A. The nucleus is the center of the atom and may contain both positively charged particles and particles that have no charge.

Nucleus

8 protons (p+)

8 neutrons (n0)

Oxygen atom

Question 4

B. Sodium and chlorine atoms have no overall electrical charge.

A. Sodium and chlorine are sharing electrons in their outer energy levels.

Sodium and chlorine combine to form table salt. What do you know to be true?

Question 4

D. Sodium and chlorine atoms in table salt have full outer energy levels.

C. Sodium and chlorine are less stable in the compound sodium chloride.

Sodium and chlorine combine to form table salt. What do you know to be true?

The answer is D. Sodium and chlorine atoms combine because the resulting compound, table salt, is more stable than the individual atoms. Sodium loses an electron in its outer energy level, chlorine gains that electron in its outer energy level, and an ionic bond is formed.

Section Objectives

• Identify how the process of diffusion occurs and why it is important to cells.

• Relate water’s unique features to polarity.• Water is perhaps the

most important compound in living organisms.

Water and Its ImportanceWater and Its Importance

• Water makes up 70 to 95 percent of most organisms.

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Water is Polar

• Sometimes, when atoms form covalent bonds they do not share the electrons equally. This is called a polar bond.

Water is Polar

• A polar molecule is a molecule with an unequal distribution of charge; that is, each molecule has a positive end and a negative end.

• Water is an example of a polar molecule.

• Water can dissolve many ionic compounds, such as salt, and many other polar molecules, such as sugar.

Water is Polar

• Water molecules also attract other water molecules.

• Weak hydrogen bonds are formed between positively charged hydrogen atoms and negatively charged oxygen atoms.

Hydrogen atom

Hydrogen atom

Oxygen atom

• Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids.

Water resists temperature changes

Water expands when it freezes

• Water is one of the few substances that expands when it freezes.

• Ice is less dense than liquid water so it floats as it forms in a body of water.

Early observations: Bownian motion

• In 1827, Scottish scientist Robert Brown used a microscope to observe pollen grains suspended in water. He noticed that the grains moved constantly in little jerks, as if being struck by invisible objects.

• This motion is now called Brownian motion.

• Today we know that Brown was observing evidence of the random motion of atoms and molecules.

9

The process of diffusion

• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

• Diffusion results because of the random movement of particles (Brownian motion).

• Three key factors—concentration, temperature, and pressure—affect the rate of diffusion.

The results of diffusion

• When a cell is in dynamic equilibrium with its environment, materials move into and out of the cell at equal rates. As a result, there is no net change in concentration inside or outside the cell.

Material moving out of cell equals material moving into cell

Diffusion in living systems

• The difference in concentration of a substance across space is called a concentration gradient.

• Ions and molecules diffuse from an area of higher concentration to an area of lower concentration, moving with the gradient.

• Dynamic equilibrium occurs when there is no longer a concentration gradient.

Explain why water is important to living organisms.

Question 1

Living organisms must have water for life processes, because critical molecules and ions must be free to move and collide, which only happens when they are dissolved in water. Water also transports materials in living organisms, such as in blood or sap.

Answer

How does water's chemical structure impact its role in living organisms?

Question 2 Positively charged end

Negatively charged end

+

+

―

Because water is polar, it can dissolve many ionic compounds and polar molecules. Water has the property of capillary action that enables plants to get water from the ground. Water also resists temperature changes, which allows cells to maintain homeostasis.

10

Which of the following best describes diffusion?

Question 3

B. net movement of particles from area of low concentration to area of high concentration

A. slow process resulting from random movement of particles

D. net movement of particles from high to low concentrations that accelerates when pressure decreases

C. rapid process that is unaffected by increases in temperature

Which of the following best describes diffusion?

Question 3

The answer is A. Diffusion is a slow process resulting from the random movement of particles, and is the net movement of particles from areas of high concentration to areas of lower concentration.

• Classify the variety of organic compounds.

Section Objectives:

• Describe how polymers are formed and broken down in organisms.

• Compare the chemical structures of carbohydrates, lipids, proteins, and nucleic acids, and relate their importance to living things.

• Identify the effects of enzymes.

• A carbon atom has four electrons available for bonding in its outer energy level. In order to become stable, a carbon atom forms four covalent bonds that fill its outer energy level.

The Role of Carbon in Organisms The Role of Carbon in Organisms

• Two carbon atoms can form various types of covalent bonds—single, double or triple.

Single Bond Double Bond Triple Bond

11

• Carbon compounds vary greatly in size.

Molecular chains

• When carbon atoms bond to each other, they can form straight chains, branched chains, or rings.

Molecular chains

• Small molecules bond together to form chains called polymers. A polymer is a large molecule formed when many smaller molecules bond together.

• A carbohydrate is a biomolecule composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom.

The structure of carbohydrates

• The largest carbohydrate molecules are polysaccharides, polymers composed of many monosaccharide subunits. (ie. potatoes, liver)

The structure of carbohydrates

• The simplest type of carbohydrate is a simple sugar called a monosaccharide (mah noh SA kuh ride). (ie. glucose, fructose)

• Lipids are large biomolecules that are made mostly of carbon and hydrogen with a small amount of oxygen. (ie. fats, oils, waxes)

The structure of lipids

• They are insoluble in water because their molecules are nonpolar and are not attracted by water molecules.

• A protein is a large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

The structure of proteins

12

The structure of proteins

• The basic building blocks of proteins are called amino acids.

• There are about 20 common amino acids that can make literally thousands of proteins.

• Peptide bonds are covalent bonds formed between amino acids.

The structure of proteins

• Proteins are the building blocks of many structural components of organisms.

The structure of proteins The structure of proteins

• Enzymes are important proteins found in living things. An enzyme is a protein that changes the rate of a chemical reaction.

• They speed the reactions in digestion of food.

• A nucleic (noo KLAY ihk) acid is a complex biomolecule that stores cellular information in the form of a code.

The structure of nucleic acids

• Nucleic acids are polymers made of smaller subunits called nucleotides.

The structure of nucleic acids

• Nucleotides are arranged in three groups—a nitrogenous base, a simple sugar, and a phosphate group.

Phosphate

Sugar

Nitrogenous base

13

• DNA, which stands for deoxyribonucleic acid is a nucleic acid.

The structure of nucleic acids

Phosphate

Sugar

Nitrogenous base

The structure of nucleic acids

• The information coded in DNA contains the instructions used to form all of an organism’s enzymes and structural proteins.

• Another important nucleic acid is RNA, which stands for ribonucleic acid. RNA is a nucleic acid that forms a copy of DNA for use in making proteins.

How many covalent bonds does a carbon atom need to form in order to become stable?

Question 1

D. 4

C. 3

B. 2

A. 1

The answer is D. A carbon atom has four electrons available for bonding in its outer energy level and needs to form four covalent bonds in order to become stable.

A __________ is a biomolecule composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom.

Question 2

D. fatty acid

C. protein

B. lipid

A. carbohydrate

The answer is A. Lipids are made mostly of carbon and hydrogen, and proteins contain nitrogen in addition to carbon, hydrogen and oxygen.

14

In which type of molecule will you find peptide bonds?

Question 3

D. fatty acid

C. protein

B. lipid

A. carbohydrate

The answer is C. Amino acids are the basic building blocks of proteins and are linked together by peptide bonds.

What biomolecule is represented in this diagram?

Question 4

D. lipid

C. protein

B. nucleotide

A. carbohydrate

Phosphate

SugarNitrogenous

base

The answer is B. Nucleotides are the smaller subunits that make up nucleic acids. Nucleotides are composed of three groups: a nitrogenous base, a simple sugar, and a phosphate group.

Phosphate

SugarNitrogenous

base

Describe an enzyme and its function.

Question 5 An enzyme is a protein that enables other molecules to undergo chemical changes to form new products. Enzymes increase the speed of reactions that would otherwise proceed too slowly.

Substrate

Active site

15

• Atoms are the basic building block of all matter.

Atoms and Their Interactions

• Atoms consist of a nucleus containing protons and usually neutrons. The positively charged nucleus is surrounded by rapidly moving, negatively charged electrons.

• Atoms become stable by bonding to other atoms through covalent or ionic bonds.

• Components of mixtures retain their properties.

Atoms and Their Interactions

• Solutions are mixtures in which the components are evenly distributed.

• Acids are substances that from hydrogen ions in water. Bases are substances that form hydroxide ions in water.

• Water is the most abundant compound in living things.

Water and Diffusion

• Water is an excellent solvent due to the polar property of its molecules.

• Particles of matter are in constant motion.

• Diffusion occurs from areas of higher concentration to areas of lower concentration.

• All organic compounds contain carbon atoms.

Life Substances

• There are four principal types of organic compounds, or biomolecules, that make up living things: carbohydrates, lipids, proteins, and nucleic acid.

• The structure of a biomolecule will help determine its properties and functions.

Question 1

What is the difference between a compound and an element?

Answer

A compound is a substance that is composed of atoms of two or more different elements that are chemically combined. An element is a substance that can't be broken down into simpler chemical substances.

Question 2

What is it called when atoms share electrons?

D. diffusion

C. hydrogen bonding

B. ionic bonding

Water molecule

A. covalent bonding

16

The answer is A.Covalent bonds differ from ionic bonds in that the shared electrons move about the nuclei of both atoms of the covalent compound.

Water molecule

Question 3

Which of the following combinations will produce a solution?

D. oil and vinegar

C. powdered drink mix and water

B. sand and sugar crystals

A. chocolate chips and cookie dough

The answer is C. All of the combinations are mixtures because the individual components retain their own properties. A solution is a mixture in which one or more substances is dissolved in another and will not settle out of solution.

Water molecules

Sugar molecules

Sugar crystal

Question 4

What type of substance forms hydrogen ions in water?

D. polar

C. base

B. acid

A. enzyme

The answer is B. Any substance that forms hydrogen ions (H+) in water is an acid. The pH of a substance is a measure of how acidic or basic a solution is.

Question 5

Which of the following best describes a molecule with an unequal distribution of charge?

D. diffuse

C. basic

B. acidic

A. polar

17

The answer is A. Each polar molecule has a positive end and a negative end. Polar water molecules attract ions and other polar molecules, and can dissolve many ionic compounds.

Question 6

Name the chemical reaction illustrated in the diagram.

B. condensationGlucose

Fructose

Sucrose

CH2OH

O

OH

CH2OH

HO

OH

OH

OH

OH

HO

OHOCH2

CH2OH

+ H2O

O

OHHO

OH

OHOCH2

OH

HO

O +

CH2OH

D. glycolysis

C. Protein synthesis

A. hydrolysis

The answer is B. In condensation reactions, small molecules bond together to produce a polymer and water.

Glucose

Fructose

Sucrose

CH2OH

O

OH

CH2OH

HO

OH

OH

OH

OH

HO

OHOCH2

CH2OH

+ H2O

O

OHHO

OH

OHOCH2

OH

HO

O +

CH2OH

Question 7

An oxygen atom has 8 protons and 8 neutrons. How many electrons does it have?

D. 0

C. 32

B. 18

A. 8

The answer is A. Atoms contain equal numbers of electrons and protons and have no net charge.

Nucleus

8 protons (p+)

8 neutrons (n0)

Oxygen atom

Question 8

Based on your knowledge of biomolecules, which of the following substances would be most effective at breaking down this polymer?

B. lipase

CH2OH

O

OHHO

OH

OHOCH2

OH

HO

O

CH2OH

D. water

C. pepsin

A. nuclease

18

The answer is D. This is a sucrose molecule, formed from glucose and fructose in a condensation reaction. The products of this reaction are the sucrose molecule and water. If water is added to sucrose, hydrolysis occurs and breaks the covalent bonds between the subunits.

Photo CreditsPhoto Credits

• Aaron Haupt

• Corbis

• Digital Stock

• Elaine Shay

• Mark Thayer

• PhotoDisc

• Alton Biggs

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