TO: Members of Advanced Placement Biology Course: 2016 ... · PDF fileorgan systems, organisms, populations, ... Taxonomy is the branch of biology that names organ- ... Both groups

TO: Members of Advanced Placement Biology Course: 2016-2017 RE: Summer Assignment FROM: Mrs. Conkling

You are responsible for reading part of unit one, entitled The Chemistry of Life. This includes chapters 1-3 in your textbook. As you read each chapter you should take notes for yourself. In addition, for each chapter you will need to complete the corresponding study guide.

The 3 study guides will be electronically turned in following the procedure provided to all AP students by August 15, 2016. Failure to complete the assignment will result in your removal from the class before the academic year begins. Your performance will be numerically evaluated. Your responses to questions should be in sentence format. Many responses may require a paragraph or more. You must always include reasons to support any responses involving your opinion. Assignments will be reviewed carefully, as plagiarism will NOT be tolerated. All work on the assignment must be completed ON YOUR OWN! This refers to the desire to collaborate with your peers. Do not work together. Any and all questions regarding the assignment must be directed to me via e-mail. Should any two assignments appear to be copied (either from the textbook or another student's work); this will result in removal from the course, as well as further actions taken by the BHS Administration. This assignment is worth 20% of the first marking period grade.

Good luck with the assignment and enjoy your summer! If you have any questions you may email me at !conkling@ butlerboe.org

Sincerely,

Mrs. Conkling

CHAPTER 1

INTRODUCTION: THEMES IN THE STUDY OF LIFE

FRAMEWORK

This chapter outlines broad themes that unify the study of biology and describe the scientific construc-tion of biological knowledge. A course in biology is neither a vocabulary course nor a classification exer-cise for the diverse forms of life. Biology is a collection of facts and concepts structured within theories and organizing principles. Recognizing the common themes within biology will help you to structure your knowledge of this fascinating and challenging study of life.

CHAPTER REVIEW

Biology, the scientific study of life, is an extension of our innate interest in life in its diverse forms. The scope of biology is immense, spanning the submicro-scopic level to the complex web of ecosystems from the present back through nearly 4 billion years of evo-lutionary history. Recent advances in research meth-ods have aided the efforts of a large number of con-temporary biologists working throughout the marty subfields of biology to achieve an explosion of infor-mation. A beginning student can make sense of this expanding body of knowledge by focusing on a few enduring themes that unify the study of biology.

Life's Hierarchical Order

■ The living world is a hierarchy, with each level of biological structure building on the level below it (2-4)

The hierarchy of biological structure includes atoms, biological molecules, organelles, cells, tissues, organs,

organ systems, organisms, populations, communities, and ecosystems. The study of biology encompasses these various levels of structure and the interactions among them.

■ Each level of biological structure has emergent properties (4) Biology combines the pragmatic reductionist strategy, which breaks down complex Systems to simpler com-ponents, with the study of higher organizational lev-els of life. Interactions among componerits at each level of organization lead to the emergence of novel properties at the next level: The whole is greater than the sum of its parts.

The properties of life include order, reproduction, growth and development directed by heritable pro-grams, energy utilization, responsiveness to the envi-ronment, homeostasis, and evolutionary adaptation.

N Cells are an organism's basic units of structure and function (4-6)

The cell is thI simplest structural level capable of per-forming all the activities of life. Hooke first described and named cells in 1665 when he observed a slice of cork with a simple microscope. Leeuwenhoek, a con-temporary, developed lenses that permitted him to view the world of microscopic organisms. In 1839, Schleiden and Schwann concluded that all living things consist of cells. This cell theory now includes the idea that all cells come from other cells.

The electron microscope has revealed the complex structural organization of cells. Two major types of cells are recognized. The simpler prokaryotic cell, unique to bacteria/ lacks both ra nucleus to enclose its DNA and most cytoplasmic organelles. The eukaryot-ic cell, with its nucleus and numerous membrane-bound compartments, is typical of all other living organisms.

1

•

a

• The continuity of life is based on heritable information in the form of DNA (6-7)

The biological instructions for the development and functioning of organisms are coded in the arrange-ment of the four kinds of nucleotides in DNA mole-cules. A precise mechanism for replicating the DNA helix is essential for cell division and for the transmis-sion from parent to offspring of the units of inheri-tance called genes. All forms of life use essentially the same genetic code.

• Structure and function are correlated at all levels of biological organization (7-8)

The form of a biological structure gives information about its function, and a study of function provides insight into structural organization. The principle that form fits function is illustrated at all levels of biologi-cal organization.

111 Organisms are open systems that interact continuously with their environments (8)

Organisms affect and are affected by the physical and biological environments they interact with. Within an ecosystem, nutrients cycle between the abiotic and biotic components, and energy flows front sunlight to photosynthetic organisms (producers) to consumers and exits in the form of heat.

• Regulatory mechanisms ensure a dynamic balance in living systems (8-9)

Enzymes are organic catalysts produced by a cell that speed up its chemical reactions. Precise regulation of its enzymes allows a cell to respond to changing con-ditions or needs. Organisms maintain an internal bal-ance (homeostasis) through positive or negative feed-back systems that either speed up or slow down body processes.

Evolvtion, Unity, and Diversity

N Diversity and unity are the dual faces of life on Earth (9-12)

About 1.5 million species, out of an estimated total of -5 to 100 million, have been identified and named. Taxonomy is the branch of biology that names organ-isms and classifies species into hierarchical groups. - Traditionally, life forms have been organized into

five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia. Molecular evidence has led to support for

three domains into which a varying number of king-doms are grouped. The prokaryotes are split into the domains Archaea (Archaebacteria) and Bacteria (Eubacteria), and the eukaryotes are placed in the domain Eukarya. Within the Eukarya, the traditional kingdom Protista contains mostly unicellular or sim-ple multicellular forms. The other three kingdoms contain multicellular organisms characterized to a large extent by their mode of nutrition. Plants are photosynthetic, fungi absorb their nutrients from decomposing organic material, and animals ingest other organisms.

Within this diversity, living forms share a universal genetic code and similarities in cell structure.

E Evolution is the core theme of biology (12-13)

Evolution connects all of life by common ancestry. The history of living forms extends back over 3 billion years to the ancient prokaryotes.

In The Origin of Species, published in 1859, Charles Darwin presented his case for evolution, or "descent with modification," that present forms evolved from a succession of ancestral forms. Darwin synthesized the theory of natural selection as the mechanism of evolu-tion by drawing an inference from two observations: Individuals vary in many heritable traits, and individ-uals with traits best suited for an environment leave a larger proportion of offspring than do less fit individ-uals. This differential reproductive success within a population results in the gradual accumulation of favorable adaptations to the challenges of an environ-ment.

According to Darwin, new species originate when isolated populations diversify over time in response to different environmental selective pressures. Evolution makes sense of boila the unity and diversity of life.

science as a Process F. .■

Science, which is a way of knowing, involves asking questions about nature and believing that those ques-tions are answerable.

El Testable hypotheses are the hallmarks of the scientific process (13-18)

11.:11 rf-of The sdengioprocess is based on hypothetico-deduc-tive thinking. A hypothesis is a tentative explanation for an observation or question. Deductive reasoning pioaletts"ailirthe general to the specific, from a gen-eraff-Fpoliggili to specific predictions of results if the

general premise is true. A hypothesis is usually tested by performing experiments or making observations to see whether predicted results occur.

There are five important aspects of hypotheses: hypotheses are possible causes or explanations; hypotheses reflect past experience with similar situa-tions; having multiple hypotheses is good science; hypotheses must be testable using the hypothetico-deductive method; and hypotheses can be rejected but not proven.

The scientific process makes use of controlled experiments in which subjects are divided into an experimental group and a control group. Both groups are treated alike except for the one variable that the experiment is trying to test. Adequate sample size and control of other variables are important components of an experiment.

The experiments of Reznick and Endler illustrate the hypothetico-deductive approach. By maintaining control populations and following generations of guppies transplanted from sites with pike-cichlids to sites with killifish for n years, they were able to con-clude that natural selection due to differential preda-tion was the most likely explanation for differences in life history characteristics between guppy popula-tions.

Science is characterized as progressive and self-cor-recting. Scientists build on the work done by others, refining or refuting their ideas, both cooperating and competing with each other.

Facts, in the form of observations and experimental results, are prerequisites of science, but it is the new ways of organizing and relating those facts that advance science. A theory is broader in scope than a hypothesis and is supported by a large body of evi-dence.

■ Science and technology are functions of society (18-19)

Science and technology are interwoven as the infor-mation generated by science is used in the develop-

ment of goods and services, and as technological advances are used to extend scientific knowledge. The fields of molecular biology and genetic engineering illustrate this relationship. Technology contributes to our standard of living and has made it possible for the human population to expand rapidly but at a price of severe environmental consequences. Solutions to environmental problems and future uses of scientific knowledge and technologies will involve politics, eco-nomics, and cultural values as well as science and technology.

■ Biology is a multidisciplinary adventure (19)

Biology is a demanding science—partly because liv-ing systems are so complex and partly because biolo-gy incorporates concepts from chemistry, physics, and math. This book presents a wealth of information. The basic themes of biology will help you understand, appreciate, and structure your growing knowledge of biology.

STRUCTURE YOUR KNOWLEDGE

1. This chapter presents unifying themes of biology. Briefly describe each of these in your own words: a. hierarchy of organization b. emergent properties c. cellular basis of life d. heritable information e. correlation of structure and function f. interaction of organisms with their environ-

ment • g. regulatory mechanisms h. unity and diversity i. evolution j. science as a process k. sdente and technology 1. biology is multidisciplinary

THE CHEMICAL CONTEXT OF LIFE

• FRAMEWORK

This chapter considers the basic principles of chem-istry that explain the behavior of atoms and molecules and that form the basis for our modem understand-ing of biology. Emergent properties are associated with each new level of structural organization as the subatomic particles—protons, neutrons, and electrons—are organized into atoms and atoms are combined by covalent or ionic bonds into molecules.

CHAPTER REVIEW

Chemical Elements and Compounds

■ Matter consists of chemical elements in pure form and in combinations called compounds (22-23)

Matter is anything that takes up space and has mass. The basic forms of matter are elements, substances that cannot be chemically broken down to other types of matter. A compound is made up of two or more ele-ments combined in a fixed ratio. A compound usually has characteristics quite different from its constituent elements, an example of the emergence of novel prop-erties in higher levels of organization.

■ INTERACTIVE QUESTION 2.1

On.Earth, mass and weight may be considered syn-onymous.

a. Define mass.

b. Define weight.

III Life requires about 25 chemical elements (23-24)

Carbon (C),coxygen (0), hydrogen (H), and nitrogen ( N) make 1115 96% of living matter. The remaining 4% is composed of the seven elements listed on the fol-lowing page. Some elements, like iron (Fe) and iodine (I), may be required in very minute quantifies and are called trace elements. '

Atoms and Molecules

II Atomic structure determines the behavior of an element (24-28)

An atom is the smallest unit of an element retaining the physical and chemical properties of that element. Each element has its own unique type of atom.

5

T tl a

•

•

rt

F a

'amin Add

Ai IN LLK.A.4.1.1VZ

Fill in the names beside the symbols of the following elements commonly found in living matter.

Symbol i Element

• Ca P K . S •

Na CI Mg

Subatomic Particles Three stable subatomic parti-cles are important to our understanding of atoms. Uncharged neutrons and poSitively charged protons are packed tightly together to form the nucleus of an atom. Negatively charged electrons orbit rapidly about the nucleus.

Protons and neutrons have' a .similar mass of about 1.7 x 10-24 g or 1 dalton each. A dalton is the measure-ment unit for atomic mass. Electrons have negligible mass.

Atomic Number and Atomic Weight Each element has a characteristic atomic number, or number of pro-tons in the nucleus of its atom. Unless otherwise indi-cated, the number of protons in an atom is equal to the number of electrons, and the atom has a neutral electrical charge. A subscript to the left of the symbol for an element indicates its atomic number; a super-script indicates mass number. The mass number is equal to the number of protons and neutrons in the nucleus and approximates the mass of an atom of that element in daltons. The term atomic weight is often used to refer to the mass of an atom.

E INTERACTIVE QUESTION 2.3

The difference between the mass number and the atomic number of an atom is equal to. the number of

An atom of phosphorus, P, contains

isotopes are unstable, or radioactive; their nucl spontaneously decay, giving off particles and energy.

Radioactive isotopes are important tools in biologi-cal research and medicine because they can be intro-duced into organisms and detected in minute quanti-ties. Techniques using scintillation counters or autora-diography can determine the quantity and location of radioactively labeled molecules within a cell or tissue. Too great an exposure to radiation from decaying iso-topes poses a significant hazard to life.

The Energy Levels of Electrons Energy is defined as the ability to do work. Potential energy is energy stored in matter as a consequence of the relative posi-tion of masses. Matter naturally tends to move toward a more stable lower level of potential energy and requires the input of energy to return to a higher potential energy.

The potential energy of electrons increases as their distance from the positively charged nucleus increas-es. Electrons can orbit in several different potential energy states, called energy levels or electron shells, surrounding the nucleus.

NI INTERACTIVE QUESTION 2.4

To move ttra.'7sliell.::fa0.her from the nucleus, an elec-tron must;-(abT8/01.e'rgase) energy; energy is (absorb6dire1et4d) 'when an electron moves to a closer shell.:(CifdetgreCf-teims.)

woItzemiAT*.WitM-1:74

4 i4e(911.143:40:,ti Lt 1->̀ '-

Electroll . 0:1 itigcelgh :11-1Fee-dimensional space or volume -SAiitilin i.hiaiTanelectron is found 90% of the

protons, electrons, Ind neutrons. The ova atomic weight of phosphorus is

' :C.

• t

Isotopes Although the number of protons is icontt stant, the number of neutrons can vary among the

-;-1-Elect

ter.

vv . rbital."No more than two electrons

ame rbital.- The first electron shell m a single spherical orbital,

e second electron shell can electrons in its four orbitals,

11;Ytiand three dumbbell-A...., - along the x, y, and z axes.

R 4 F,•,•

i • Viand 'Chemical Properties

,atom is a function of its ''ircTparticular, the number of outermost electron shell, or

enc&S'hell of eight electrons is mrtreactive or inert atom.

alence shells are chemicall paired electrons. The pen-

s-wanged in order of the ecerbris to orbitals.

I ATOMS

have subatomic particles

determine located in combine

to get located in •

constant for each

ic

may • er in various

f.

outer shell called

Chapter 2: The Chemical Context of Life 7

• ■ INTERACTIVE QUESTION 2.5

Draw the electron configuration for these atoms. a. 7N C. 12Mg .

b.80 d. 17C1

■ INTERACTIVE QUESTION 2.6

Fill in the blanks in the following concept map to help you review the atomic structure of atoms.

such as 02, indicates only the kinds and numbers of atoms in a molecule. In an oxygen molecule, two pairs of valence electrons are shared between oxygen atoms, forming a double covalent bond.

The valence, or bonding capacity, of an atom equals the number of unpaired electrons in its valence shell.

II INTERACTIVE QUESTION 2.7

What are the valences of the four most common ele-ments of living matter?

a. hydrogen ̂ b. oxygen c. nitrogen ^ d. carbon

Electronegativity is the attraction of an atom for shared electrons. If the atoms in a molecule have simi-lar electronegativities, the electrons remain equally shared between the two nuclei, and the covalent bond is said to be nonpolar. If one element is more elec-tronegative, it pulls the shared electrons closer to itself, creating a polar covalent bond. This unequal sharing of electrons results in a slight negative charge associated with the more electronegative atom and a slight positive charge associated with the atom from which the electrons are pulled.

X INTERACTIVE QUESTION 2.8

Explain whether the following molecules contain non-polar or polar covalent bonds. (Hint: N and 0 both have high electronegativities.)

a. nitrogen molecule N N

H e I -

b. methane t H—C—H

III Atoms combine by chemical bonding to form molecules (28-31)

Atoms with incomplete valence shells can either share electrons with or completely transfer electrons to or from other atoms such that each atom is able to com-plete its valence shell. These interactions usually result in attractions, called chemical bonds, that hold the atoms together.

Covalent Bonds When two atoms share a pair of valence electrons, a covalent bond is formed. A mole-cule consists of two or more atoms held together by covalent bonds. A structural formula, such as H-H, indicates both the number and type of atoms and also the bonding within a molecule. A molecular formula,

N c. ammonia H i I H

H

H d. formaldehyde C = 0

H"

8 Unit One: The Chemistry of Life

Ionic Bonds If two atoms are very different in their attraction- for the shared electrons, the more elec-tronegative atom may completely transfer an electron from another atom, forming an ionic bond in which atoms are held together because of the attraction of their opposite charges. This transfer of an electron results in the formation of charged atoms or mole-cules called ions. The atom that lost the electron is a positively charged cation. The negatively charged atom that gained the electron is called an anion. Ionic compounds, called salts, often exist as three-dimen-sional crystalline lattice arrangements held together by electrical attraction. The number of ions present in a salt crystal is not fixed, but the atoms are present in specific ratios. Salts have strong ionic bonds when dry, but the crystal dissolves in water.

Ion also refers to entire covalent molecules that are electrically charged. Ammonium (NH4 )1- is a cation; this covalently bonded molecule is missing one elec-tron.

II INTERACTIVE QUESTION 2.9

Calcium (20Ca) and chlorine (17C1) can combine to form the salt calcium chloride. Based on the number of electrons in their valence shells and their bonding capacities, what would the molecular formula for this salt be? a. Which atom becomes the cation? b.

■ Weak chemical bonds play important roles in the chemistry of life (31-32)

Weak bonds, such as ionic bonds in water, form tem-porary interactions between molecules and are involved in many biological signals and processes. Weak bonds within large molecules such as proteins help to create the three-dimensional shape and result-ing activity of these molecules.

Hydrogen Bonds When a hydrogen atom is cova-lently bonded with an electronegative atom and thus has a partial positive charge, it can be attracted to another electronegative atom and form a hydrogen bond.

Van der Waals Interactions All atoms and mole-cules are attracted to each other when in close contact by van der Waals interactions. Momentary uneven electron distributions produce changing positive and

-- negative regions that create these weak attractions.

N INTERACTIVE QUESTION 2.10

Sketch a water molecule, showing its shape and AP electron shells with the covalently shared electrons. Indicate the areas with slight negative and positive charges that enable a water molecule to form hydro-gen bonds.

• A molecule's biological function is related to its shape (32-33)

A molecule's characteristic size and shape affects how it interacts with other molecules. When atoms form covalent bonds, their s and three p orbitals hybridize to form four teardrop-shaped orbitals in a tetrahedral arrangement. These hybrid orbitals dictate the specific shapes of different molecules. •

■ Chemical reactions make and break chemical bonds (33-35)

Chemical reactions involve the making or breaking of chemical bonds in the transformation of matter into different forms. Matter is conserved in chemical reac-tions; the same number and kinds of atoms are pres-ent in both reactants and products, although the rearrangement of electrons and atoms causes the properties of these molecules to be different.

•

■ INTERACTIVE QUESTION 2.11

Fill in the missing coefficients for respiration, the con-version of glucose and oxygen to carbon dioxide and water, so that all atoms are conserved in the chemical reaction.

C6H1206 + 02 --> COz + H2O

Most reactions'are reversible—the products of the for-ward reaction •can become reactants in the revers reaction. Increasing the concentrations of react

• •

•

Chapter 2: The Chemical Context of Life 9

• speeds up the rate of a reaction. Chemical equilibri-um may be reached when the forward and reverse reactions proceed at the same rate, and the relative concentrations of reactants and products no longer change.

STRUCTURE YOUR KNOWLEDGE

Take the time to write out or discuss your answers to the following questions. Then refer to the suggested answers at the end of the book.

1. Fill in the following chart for the major subatomic particles of an atom.

Particle Charge Mass Location

2. Atoms can have various numbers associated with them. a. Define the following and show where each of

them is placed relative to the symbol of an ele-ment such as C: atomic number, mass number, atomic weight.

b. Define valence. c. Which of these four numbers is most related to

the chemical behavior of an atom? Explain.

3. Explain what is meant by saying that the sharing of electrons between atoms falls on a continuum from covalent bonds to ionic bonds.

TEST YOUR KNOWLEDGE

MULTIPLE CHOICE: Choose the one best answer.

1. Each element has its own characteristic atom in which a. the atomic weight is constant. b. the atomic number is constant. c. the mass number is constant. d. two of the above are correct. e. all of the above are correct.

2. Radioactive isotopes can be used in studies of metabolic pathways because a. their half-life allows a researcher to time an

experiment. b. they are more reactive. c. the cell does not recognize the extra protons in

the nucleus, so isotopes are readily used in metabolism.

d. their location or quantity can be experimental-ly determined because of their radioactivity

e. their extra neutrons produce different colors that can be traced through the body.

3. In a reaction in chemical equilibrium, a. the forward and reverse reactions are occurring

at the same rate. b. the reactants and products are in equal concen-

tration. c. the forward reaction has gone further than the

reverse reaction. d. there are equal numbers of atoms on both sides

of the equation. e. a, b, and d are correct.

4. Oxygen has eight electrons. You would expect the arrangement of these electrons to be: a. eight in the second energy shell, creating an

inert element. b. two in the first energy shell and six in the sec-

ond, creating a valence of six. c. two in the Is orbital and two each in the three

2p orbitals, creating a valence of zero. d. two in the is orbital, one each in the 2s and

three 2p orbitals, and two in the 3s orbital, cre-ating a valence of two.

e. two in the 15 orbital, two in both the 2s and 2px orbitals, and one each in the 2py and 2pz orbitals, creating a valence of two.

5. A covalent bond between two atoms is likely to be polar if a. one c4., the atoms is much more electronegative

than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped mol-

ecule. e. one atom is an anion.

6. A triple covalent bond would a. be very polar. b. involve the bonding of three atoms. c. involve the bonding of six atoms. d. produce a triangularly shaped molecule. e. involve the sharing of six electrons.

10 Unit One: The Chemistry of Life

7. A cation a. has gained an electron. b. can easily form hydrogen bonds. c. is more likely to form from an atom with six or

seven electrons, in its valence shell. d. has a positive charge. e. Both c and d are correct.

8. What types of bonds are identified in the follow-ing illustration of a water molecule interacting with an ammonia molecule?

a. Bonds 1 are polar covalent bonds, bond 2 is a hydrogen bond, and bonds 3 are nonpolar covalent bonds.

b. Bonds 1 and 3 are polar covalent bonds and bond 2 is a hydrogen bond.

c. Bonds 1 and 3 are polar covalent bonds and bond 2 is an ionic bond.

d. Bonds 1 and 3 are nonpolar covalent bonds and bond 2 is a hydrogen bond.

e. Bonds 1 and 3 are polar covalent bonds and bond 2 is a nonpolar covalent bond.

9. Which of the following weak bonds may form between any closely aligned molecules?

a. nonpolar covalent b. polar covalent c. ionic d. hydrogen e. van der Waals interactions

10. The ability of morphine to mimic the effects of the body's endorphins is due to a. a chemical equilibrium developing between

morphine and endorphins. b. the one-way conversion of morphine into

endorphin. c. molecular shape similarities that allow mor-

phine to bind to endorphin receptors. d. the similarities between morphine and heroin. e. hydrogen bonding and other weak bonds

forming between morphine and endorphins.

The six elements most common in living organisms are:

14xi- 32 c 31 an 7N 16 151-

Use this information to answer questions 11 through 16.

11. How many electrons does phosphorus have in its valence shell? a. 5 b. 7 c. 8 d. 15 e. 16

12. What is the atomic weight of phosphorus? a. 15 b. 16 c. 31. d. 46 e. 62

13. A radioactive isotope of carbon has the mass number 14. How many neutrons does this isotope have? a. 6 b. 7 c. 8 d. 12 e. 14

14. How many covalent bonds is a sulfur atom most likely to form? • a. 1 b. 2 c. 3 d. 4 e. 5

15. Basecli::on electron configuration, which of these elem;ents would have chemical behavior most like that oloxyge-ii? a. C b. H c. N. d. P e. .S

16. How, many of these elements are found next to each other (side by side) on the periodic table? a t one group of two b.'-tiViigiolips of two c.- `one- group of two and one group of three

`3d:'"ongr'giotip of three e. all of them

16'- 16 r,„ 1174

13`-' "

•

Chapter 2: The Chemical Context of Life 11

• 17. Taking into account the bonding capacities or valences of carbon (C) and oxygen (0), how many hydrogen (H) must be added to complete the structural diagram of this molecule?

0 C— C—C—C C— C—C

0

a. 9 b. 10 c. 11 d. 12 e. 13

18. A sodium ion (Na)+ contains 10 electrons, 11 pro-tons, and 12 neutrons. What is the atomic number of sodium? a. 10 b. 11 c. 12 d. 23 e. 33

19. What type of bond would you expect potassium (34K)to form? a. ionic; it would donate one electron and carry a

positive charge b. ionic; it would donate one electron and carry a

negative charge c. covalent; it would share one electron and make

one covalent bond d. covalent; it would share two electrons and

form two bonds e. none; potassium is an inert element

20. What is the molecular shape of methane (CHO? a. planar or flat, with the H arranged at four cor-

ners around the C b. pentagonal, or a flat five-sided arrangement c. tetrahedral, due to the hybridization of the s

and three p orbits of the C d. circular, with the four H attached in a ring

around the C e. linear, since all the bonds are nonpolar covalent

•

,. .

•

• .

•

WATER AND THE FITNESS OF THE ENVIRONMENT

FRAMEWORK

Water makes up 70% to 95% of the cell content of liv-ing organisms and covers 75% of the Earth's surface. Its unique properties make the external environment fit for living organisms and the internal environment of organisms fit for the chemical and physical process- es of life. .

Hydrogen bonding between polar water molecules tates a cohesive liquid with a high specific heat and t h heat of vaporization, both of which help to regu-e environmental temperature. The polarity of water

makes it a versatile solvent. An organism's pH may be regulated by buffers. Acid precipitation poses a seri-ous environmental threat.

U INTERACTIVE QUESTION 3.1

Draw the four water molecules that can hydrogen-bond to this water molecule. Indicate the slight nega-tive and positive charges that account for the forma-tion of hydrogen bonds.

CHAPTER REVIEW

Water's Polarity and its Effects

RI The polarity of water molecules results in hydrogen bonding (37-38)

A water molecule consists of two hydrogen atoms each covalently bonded to a more electronegative oxy-gen atom. This polar molecule has an L shape with a slight positive charge on each hydrogen atom and a slight negative charge associated with the oxygen. ilvdrogen bonds form between the hydrogen atoms of one water molecule and the oxygen atoms of two

'icr molecules, creating a higher level of structural aniziltion and leading to the emergent properties

: water. I

NE Organisms depend on the cohesion of water molecules (38-39}

Liquid water is unusually cohesive due to the con-stant forming and re-forming of hydrogen bonds that hold the molecules together. This cohesion creates a more structurally organized liquid and enables water to move against' gravity in plants. The adhesion of water molecules to the walls of plant vessels also con-tributes to water transport. Hydrogen bonding between water molecules produces a high surface ten-sion at the interface between water and air.

as when as when

when

hydrogen bonds break

results in a high

results in

temperature regulation

because

thus water has a high

d.

organisms and

environment

hydrogen bonds form

• moist air moving

poleward

condenses into

h.

floats and insulates

1 bodies of

water

e.

thus when

water evaporates

leads to seas absorb

moderates

temperature changes

a.

Chapter 3: Water and the Fitness of the Environmeni

r

pi Water moderates temperatures on Earth (00-00)

Heat and Temperature In a body of matter, heat is a measure of the total quantity of kinetic energy, the energy associated with the movement of atoms and molecules. Temperature measures the average kinetic energy of the molecules in a substance.

Temperature is measured using a Celsius scale. Water at sea level freezes at 0°C and boils at 100°C. Heat is measured by the calorie (cal). A calorie is the amount of heat energy it takes to raise 1 g of water 1°C. A kilocalorie (kcal) is 1000 calories, the amount of heat required to raise 1 kg of water 1°C. A joule (J) equals 0.239 cal; a calorie is 4.184 J.

Water's High Specific Heat Specific heat is the amount of heat absorbed or lost when 1 g of a sub-stance changes its temperature by 1°C. Water's specif-ic heat of 1 cal/g/°C is unusually high compared with that of other common substances; water must absorb or release a relatively large quantity of heat in order for its temperature to change. Heat must be absorbed to break hydrogen bonds before water mole-cules can move faster and the temperature can rise, and conversely, heat is released when hydrogen bonds form as the temperature of water drops. The ability of large bodies of water to stabilize air temper-ature is due to the high specific heat of water. The high proportion of water in the environment and within organisms keeps temperature fluctuations within limits that permit life.

Evaporative Cooling The transformation from a liq-uid to a gas is called vaporization or evaporation and happens when molecules with sufficient kinetic ener-gy overcome their attraction to other molecules and escape into the air as gas. The heat of vaporization is the quantity of heat that must be absorbed for 1 g of a liquid to be converted to a gas. Water has a high heat of vaporization (580 cal/g) because a, large amount of heat is needed to break the hydrogen bonds holding water molecules together. This property of water helps moderate the climate on Earth as solar heat is dissipated from tropical seas during evaporation and heat is released when moist tropical air condenses to form rain.

As a substance vaporizes, the liquid left behind loses the kinetic energy of the escaping molecules and cools down. Evaporative cooling helps to protect ter-restrial organisms from overheating and contributes to the stability of temperatures in lakes and ponds.

vs Oceans and lakes don't freeze solid because ice floats (40-41)

As water cools below 4°C, it expands. By 0°C, each water molecule becomes hydrogen-bonded to four

other molecules, creating a crystalline lattice that spaces the molecules apart. Ice is less dense than liq-uid water, and therefore, it floats. The floating ice insulates the liquid water below.

gt INTERACTIVE QUESTION 3.2

The following concept map is one way to show how the breaking and forming of hydrogen bonds is relat-ed to temperature regulation. Fill in the blanks and compare your choice of concepts to those given in the

- — answer sectiorr-Or, better still, create your own map-to help you understand how water stabilizes tempera-ture.

HYDROGEN BONDING

between

II Water is the solvent of life (41-43)

A solution is a liquid homogeneous mixture of two or more substances; the dissolving agent is called the solvent and the substance that is dissolved is the solute. An aqueous solution is one in which water is

•

14 Unit One: The Chemistry of Life

the solvent. The positive and negative regions of ( '.er molecules are attracted to oppositely charged

or partially charged regions of polar molecules. , solute molecules become surrounded by water

molecules and dissolve into solution.

Hydrophilic and Hydrophobic Substances Ionic and polar substances are hydrophilic; they have an affini-ty for water due to electrical attractions and hydrogen bonding. Nonpolar and non-ionic compounds are hydrophobic; they will not mix with or dissolve in water.

al INTERACTIVE QUESTION 3.3

Indicate whether the following are hydrophilic or hydrophobic. Do these substances contain ionic, polar, or nonpolar bonds?

a. olive oil

b. sugar

c. salt

d. candle wax

skte Concentration in Aqueous Solutions Most of emical reactions of life take place in water. A

mole (mol) is the amount of a substance that has a mass in grains numerically equivalent to its molecu-lar weight (sum of the weight of all atoms in the mol-ecule) in daltons. A mole of any substance has exactly the same number of molecules-6.02 x 1023, called Avogadro's number. The molarity of a solution (abbreviated M) refers to the number of moles of a solute dissolved in 1 liter of solution.

g INTERACTIVE QUESTION 3.4

a. How many grams of lactic acid (C3H603) are in a 0.5 M solution of lactic acid? (12C, 11-I, 160)

b. How many grams of salt (NaC1) must be dis-solved in water to make 2 liters of a 2 M salt solution? (23Na, 34CI)

Dissociation of Water Molecules

(which molecule can dissociate into a hydrogen ion,

(which binds to another water molecule to form a hydronium ion, H30

4), and a hydroxide ion, OH-.

Although reversible and statistically rare, this dissoci-ation into the highly reactive hydrogen and hydroxide ions has important biological consequences.

El Organisms are sensitive to changes in pH (43-45)

Acids and Bases In pure water, the concentrations of Fr and OH- ions are the same; both are equal to 10-7 M. When acids or bases dissolve in water, the H4 and OH- balance shifts. An acid adds H4 to a solution, whereas a base reduces H* in a solution by accepting hydrogen- ions or by adding hydroxide ions (which then combine with H4 and thus remove hydrogen ions). A strong acid or strong base dissociates com-pletely when mixed with water. A weak acid Or base reversibly dissociates, releasing or binding H4. A solu-tion with a higher concentration of H4 than of OH- is considered acidic. A basic solution has a higher con-centration of OH- than of H.'.

The pH Scale In any solution, the product of the [H+] and [OW] is constant at 10-14 M. Brackets, [ indicate molar concentration. If the [1-14] is higher, then the [OH-] is loWer, due to the tendency of excess hydrogen ions to combine with the hydroxide ions in solution and form water. Likewise, an increase in [OH-] causes an equivalent decrease in [H4). If [OH-] is equal to 10-10 M, then [Hi will equal 10-4 M.

The logarithmic pH scale compresses the range of hydrogen and hydroxide ion concentrations, which can vary in different solutions by many orders of magnitude. The pH of a solution is defined as the negative log .(base 10) of the [H4): pH = -log [H4]. For a neutral solution, [H4] is 10-7 M, and the pH equals 7. As the [H*] increases in an acidic solution, the pH value decreases. The difference between each unit of the pH scale represents a tenfold difference in the con-centration of [H4] and [OH"].

BF INTERACTIVE QUESTION 3.5

Complete the following table to review your under-standing of pH

[H4] [OH-] pH Acidic, Basic, or Neutral?

10-11 ' 3 acidic

10-8

10-7

1 .

L.

Chapter 3: Water snd the Fitness of thr Ent ,ironme .1' 3

Buffers Most cells have an internal pH close to 7. Buffers within the cell maintain a constant pH by accepting excess H+ ions or donating H.' ions when

concentration decreases. Weak acid-base pairs that reversibly bind hydrogen ions are typical of most buffering systems.

by plants. In lakes and ponds, a lowered pH and the accumulation of minerals leached from the i acid rain harm many species of fishes, amphibians, and aquatic invertebrates.

STRUCTURE YOUR KNOWLEDGE -

II INTERACTIVE QUESTION 3.6

The carbonic acid/bicarbonate system is an important biological buffer. Label the molecules and ions in this equation and indicate which is the H+ donor and

acceptor. 2.

In which direction will this reaction proceed (a) when the pH of a solution begins to fall?

(b) when the pH rises above normal level?

' H2CO3 .<=t HCO3 H+

S Acid precipitation threatens the fitness of the environment (45-46)

Acid precipitation, with a pH lower than normal pH 5.6, is due to the reaction of water in the atmosphere with the sulfur oxides and nitrogen oxides released by the combustion of fossil fuels. Lowering the pH of the soil solution affects the solubility of minerals needed

1. Fill in the table below that summarizes the prop-erties of water that contribute to the fitness of the environment for life.

To become proficient in the use of the concepts-relating to pH, develop a concept map to organize your understanding of the following terms: pH, [H+3, (OH-1, acidic, basic, neutral, buffer, 1-14, acid-base pair. Remember to label connecting lines and add additional concepts as you need them. A suggested concept map is given in the answer section, but remember that your concept map should represent your own understanding. The value of this exercise is in organizing these concepts for yourself.

TEST YOUR KNOWLEDGE

MULTIPLE CHOICE: Choose the one best answer.

1. Each water molecule is capable of forming a. one hydrogen bond. b. three hydrogen bonds. c. four hydrogen bonds. d. one covalent bond and two hydrogen bonds. e. one covalent bond and three hydrogen bonds.

Property EX. planation of Property Example of Benefit to Life

a. Hydrogen bonds hold molecules together and adhere them to hydrophilic surfaces.

b.

High specific heat c.

- .

Temperature changes in environment and org-anisms are moderated.

d. Hydrogen bonds must be broken for water to evaporate.

e.

f. Water molecules with high kinetic energy evap- orate; remaining molecules are cooler.

g.

Ice floats h. i.

k. Most chemical reactions in life involve solutes dissolved in water. •

"16 Unit One: The Chemistry of Life

2. The polarity of water molecules -, .. promotes the formation of hydrogen bonds.

helps water to dissolve nonpolar solutes. . lowers the heat of vaporization and leads to

evaporative cooling. d. creates a crystalline structure in liquid water. e. does all of the above.

3. What accounts for the movement of water up xylem vessels in a plant? a. cohesion b. hydrogen bonding c. adhesion d. hydrophilic vessel walls_ e. all of the above

4. Climates tend to be moderate by large bodies of water because a. a large amount of solar heat is absorbed by the

gradual rise in temperature of the water. b. the gradual cooling of the water releases heat

to the environment. c. the high specific heat of water helps to regulate

air temperatures. d. a great deal of heat is absorbed and released by

the breaking and forming of hydrogen bonds. e. of all of the above.

- Temperature is a measure of specific heat.

. average kinetic energy of molecules. • c. total kinetic energy of molecules. d. Celsius degrees. e. joules.

6. Evaporative cooling is a result of a. a low heat of vaporization. b. a high heat of melting. c. a high specific heat. d. a reduction in the average kinetic energy of the

liquid remaining after molecules enter the gaseous state.

e. release of heat caused by the breaking of hydrogen bonds when water molecules escape.

7. Ice floats because a. air is trapped in the crystalline lattice. b. the formation of hydrogen bonds releases heat;

warmer objects float. c. it has a smaller surface area than liquid water. d. it insulates bodies of water so they do not

freeze from.the bottom up. e. hydrogen bonding spaces the molecules farther

apart, creating a less dense structure.

The molarity of a solution is equal to Avogadro's number of molecules in 1 liter of solvent.

b. the number of moles of a solute in 1 liter of solution.

c. the molecular weight of a solute in 1 liter of solution.

d. the number of solute particles in 1 liter of sol-vent.

e. 342 g if the solute is sucrose.

9. Some archaebacteria are able to live in lakes with pH values of 11. How does pH 11 compare with the pH 7 typical of your body cells? a. It is four times more acidic than pH 7. b. It is four times more basic than pH 7. c. It is a thousand times more acidic than pH 7. d. It is a thousand times more basic than pH 7. e._ It_is ten thousand_ times more basic tharLpH_Z___

10. A buffer a: changes pH by a magnitude of 10. b. absorbs excess OW. c. releases excess H. d. is often a weak acid—base pair. e. maintains pH at a value of 7.

11. Which of the following is least soluble in water? a. polar molecules b. nonpolar compounds c. ionic compounds d. hydrophilic molecules e. anions

12. Which would be the best method for reducing acid precipitation? a. Raise the height of smoke stacks so that

exhaust enters the upper atmosphere. b. Add buffers and bases to bodies of water

whose pH has dropped. c. Use coal burning generators rather than

nuclear power to produce electricity. d. Increase emission control standards for facto-

ries and automobiles. e. Reduce the concentration of heavy metals in

industrial exhaust.

13. What bonds must be broken for water to vapor-ize? a. polar covalent bonds b. nonpolar covalent bonds c. hydrogen bonds d. ionic bonds e. polar covalent and hydrogen bonds

14. How would you make a 0.1 M solution of glucose (C6111206)? The mass numbers for these elements are C = 12, 0 = 16, H = 1. a. Mix 6 g C, 12 g H, and 6 g 0 in 1 liter of water. b. Mix 72 g C, 12 g H, and 96 g 0 in 1 liter of

water. c. Mix 18 g of glucose with enough water to make

1 liter of solution.

T •

d. Mix 29 g of glucose with enough water to yield

1 liter of solution.

e. Mix 180 g of glucose with enough water to yield 1 liter of solution.

15. How many molecules of glucose would be in the

solution in question 14?

a. 0.1 c. 60 e. 6 x 1022

b. 6 d. 6 x 1023

16. Why is water such an excellent solvent?

a. As a polar molecule, it can surround and dis-

solve ionic and other polar molecules.

b. It forms ionic bonds with ions, hydrogen bonds

with polar molecules, and hydrophobic inter-

actions with nonpolar molecules.

c. It forms hydrogen bonds with itself.

d. It has a high specific heat and high heat - of

vaporization.

e. It is wet and has a great deal of surface tension.

17. Adding a base to a solution would

a. raise the pH.

b. lower the pH.

c. decrease 11-11.

d. do both a and c.

e. do both b and c.

Chapter 3: Water and the Fitness of the EllitiT071711C7li

18. The following are pH values: cola-2; orange

juice-3; beer-4; coffee-5; human blood-7.4. Which

of these liquids has the highest molar concentra -

tion of OF?

a. cola

b, orange juice

c. beer

d. coffee

e. human blood

19. Comparing the [H÷] of orange juice and coffee,

a. the [1-11 of coffee is two times higher.

b. the (H+) of coffee is 100 times higher.

c. the [1-11 of orange juice is_10 times higher.-- -

d. the 11-11 of orange juice is 100 times higher.

e. the (1-1+) of orange juice is 1000 times higher.

20. The ability of water molecules to form hydrogen

bonds accounts for water 's

a. high specific heat.

b. evaporative cooling.

c. high heat of vaporization.

d. cohesiveness andsurface tension.

e. All of the above result from water 's hydro-

gen-bonding capacity.

•

to