2 to Energy to Life From Chemistry - Pearson...using chemistry in new ways to help us understand life and biological processes on this planet. Chemistry is cen-tral to understanding

■ Explain the fundamentals of chemistry and apply them to real-world environmentalsituations

■ Describe the molecular building blocks of livingorganisms

■ Differentiate among the types of energy andrecite the basics of energy flow

From Chemistry to Energy to Life2

Upon successfully completing this chapter, you will be able to

Beautiful Pavilion Lake, BritishColumbia, hides scientificsecrets beneath its surface.

■ Distinguish photosynthesis, respiration, andchemosynthesis, and summarize their importanceto living things

■ Itemize and evaluate the major hypotheses forthe origin of life on Earth

■ Outline our knowledge regarding early life andgive supporting evidence for each major concept

02_with_ch02.qxd 2/13/09 11:27 PM Page 31

of calcium carbonate (a combination of calcium, car-bon, and oxygen) of organic derivation. The light-bluepatches visible within the lake in the photo are some ofthese structures. Microbialites that occur in freshwaterenvironments are less well known scientifically than themuch more common oceanic reefs, which are also com-posed of calcium carbonate.

Darlene Lim and her colleagues from the Universityof British Columbia and NASA’s Ames ResearchCenter are interested in learning about the biologicalorigins of the Pavilion Lake freshwater microbialites andthe geobiological conditions that control their morphol-ogy (that is, their physical form). The widely varyingmorphologies of the Pavilion Lake microbialites, whichrange from chimney-shaped to cone-, leaf-, and dome-shaped, vary with depth; the structures occur in waterdepths ranging from 5 cm to 60 m, and the pressureand light levels at these depths differ substantially.These differences in the physical environment must

This is a sample of a micro-bialite from Pavilion Lake.

CENTRAL CASE:THE UNUSUAL MICROBIALITES OF PAVILION LAKE

“Life exists in the universe only because the carbonatom possesses certain exceptional properties.”—SIR JAMES JEANS,ASTRONOMER, PHYSICIST,AND MATHEMATICIAN

“Science never gives up searching for truth, since itnever claims to have achieved it.”—JOHN CHARLES POLANYI, CHEMISTRY NOBEL PRIZE WINNER

Pavilion Lake (see photo) is a beautiful, clear blue-green lake that is protected as part of the MarbleCanyon Provincial Park system in the interior of BritishColumbia.The lake holds traditional spiritual significancefor the Ts’kw’aylaxw First Nation. In recent years, a groupof scientists from NASA’s Ames Research Center alsohas taken a particular interest in some of the uniquecharacteristics of the lake.The feature of greatest scien-tific interest is the presence in the lake of a variety ofmicrobialites—reeflike sedimentary structures composed


CHAPTER TWO FROM CHEMISTRY TO ENERGY TO LIFE 33

Chemistry and theEnvironmentExamine any environmental issue—whether it is a question of basic science or an application tohuman–environment interactions—and you will likelydiscover chemistry playing a central role. Chemistry iscrucial to understanding how gases, such as carbon diox-ide and methane, contribute to global climate change,and to understanding how the climate, atmosphere, andlife on Earth came to be as they now are. Scientists areusing chemistry in new ways to help us understand lifeand biological processes on this planet. Chemistry is cen-tral to understanding how pollutants, such as sulphurdioxide and nitric oxide, cause acid rain, and how pesti-cides and other artificial compounds we release into theenvironment affect the health of wildlife and people.Chemistry is also essential in understanding water pollu-tion and sewage treatment, atmospheric ozone deple-tion, hazardous waste and its disposal, and just about anyenergy issue.

Chemistry can help solve environmental problemsScientists use chemistry to develop new solutions toenvironmental problems. Bioremediation—the use ofnaturally occurring microbial organisms to accelerate thecleanup of chemicals at polluted sites—is one illustrationof this. Hydrocarbon-consuming bacteria and fungi areused to clean up the soil beneath leaky gasoline tanksthat threaten drinking water supplies. Other kinds ofmicrobes are used to degrade chemical pesticide residuesin soil.

When the Exxon Valdez oil tanker ran aground inAlaska’s Prince William Sound in 1989, it spilled 42 millionlitres of crude oil, coating 2100 km of Alaskan coastline.The largest oil spill in North American history, it killedthousands of seabirds, sea otters, and harbour seals andcountless fish, smothered intertidal plants and animals,and defiled the area’s relatively pristine environment.

The study of terrestrial carbonates, like the micro-bialites of Pavilion Lake, may help scientists answer ques-tions like these. In the process, they hope to develop adeeper understanding of early environments and life onEarth, as well.1

have influenced the biological processes through whichthe structures are formed.

Understanding how life-supporting environmentsoriginated on Earth depends to a great extent onunderstanding the formation of carbonate rocks.Carbonate rocks contain carbon dioxide and areextremely important long-term storage reservoirs forcarbon that would otherwise remain in the atmosphere.The formation of carbonates early in Earth’s history wasa crucial step in the chemical evolution of the terrestrialatmosphere and an integral part of the history of chem-ical interaction among the atmosphere, hydrosphere,biosphere, and lithosphere.

Scientific models predict that if Mars once had a thickCO2-rich atmosphere, like that of early Earth, thereshould be massive carbonates present at or nearthe surface of the planet, as there are on Earth.However, scientists have detected only trace levels ofcarbonate in Martian soil, and no massive carbonateoutcrops have been identified on the surface. Where,then, are the missing carbonates?

Geobiologist Darlene Lim collects a sediment sample from a core.


PART ONE FOUNDATIONS OF ENVIRONMENTAL SCIENCE34

Thousands of workers and volunteers launched acleanup effort of unprecedented scope. The cleanupcrews corralled the oil with booms, skimmed it from thewater, soaked it up with absorbent materials, and dis-persed it with chemicals. They pressure-washed thebeaches (FIGURE 2.1), removed contaminated sandwith backhoes, and even tried burning the oil. Scientistsused the opportunity to test a new bioremediation strat-egy in which they stimulated naturally occurring bacte-ria to biodegrade, or break down, the oil. About 5% ofthe single-celled microbes naturally present on Alaskanbeaches feed on hydrocarbons produced by the region’sconifer trees. Hydrocarbons from conifers are chemi-cally similar to those that make up crude oil, so scientistspredicted that the microbes might also be able todegrade oil.

Today many wildlife populations at the site of theExxon Valdez spill have recovered, but some have not, andpockets of oil remain. The results of the bioremediationexperiments were interpreted differently by differentresearchers. Some felt that the new approach hadincreased the rate of remediation fivefold; others felt thatthe benefits had been minimal. Part of the reason for theunpredictable behaviour of spilled oil and its responseto remediation efforts is the widely variable chemistry ofcrude oil. It is the chemistry of oil that causes it to gum upbirds’ feathers and mammals’ fur, impairing their insulat-ing abilities and causing hypothermia. It is the chemistryof oil that causes it to float on water, or clump togetherand sink to the bottom, accumulate on beaches, or bewashed away by the rain. It is the chemistry of oil—sochallenging to deal with when released into a naturalsetting—that provides the energy to power our remark-able civilization and modern way of life (Chapter 15).

Plants also have been pressed into service in environ-mental cleanups. Plants, such as wheat, tobacco, waterhyacinths, chrysanthemums, and cattails, have been usedto clean up toxic materials from soils, in an approachcalled phytoremediation. Some types of plants draw upheavy metals, such as lead and cadmium, through theirroots and stomata, thus removing the toxins from the soiland concentrating them in plant tissue, which can laterbe harvested and disposed of properly (see “The ScienceBehind the Story: Letting Plants Do the Dirty Work,”• p. 35).

Environmental chemists are excited about the count-less future applications of chemistry that may help usaddress environmental problems. To appreciate the com-plex chemistry involved in environmental science, andto understand how Earth’s system supports life, we mustbegin with a grasp of the fundamentals.

Atoms and elements are chemical building blocksAll material in the universe that has mass and occupiesspace is called matter. Matter can be transformed fromone form into another, but it cannot be created ordestroyed. This principle is referred to as the law of con-servation of matter. In environmental science, this prin-ciple helps us understand that the amount of matter staysconstant as it is recycled in nutrient cycles and ecosys-tems. It also makes clear that we cannot simply wish awaythe matter (such as waste and pollution) that we want toget rid of. Every drop of oil spilled in a pristine bay willend up somewhere, whether it sinks into the sediment,coats a bird’s feathers, or is consumed by bacteria

FIGURE 2.1Workers spray fertilizer on an oil-coated Alaskanbeach, in an effort to balance the chemistry of the siteand stimulate naturally occurring bacteria to consumeand biodegrade the spilled oil.



(FIGURE 2.2). Every piece of garbage or billow of smoke-stack pollution or canister of nuclear waste we dispose ofwill not simply disappear; instead, we will need to takeresponsible initiatives to mitigate its impacts.

The carbon, calcium, and oxygen of which thePavilion Lake microbialites are composed are elements.An element is a fundamental type of matter, a chemicalsubstance with a given set of properties, which cannot bebroken down into substances with other properties.Chemists currently recognize 92 elements occurring in

nature, as well as more than 20 others that have beenartificially created. Elements that are especially abundantin living organisms include carbon, nitrogen, hydrogen,and oxygen (Table 2.1). Each element has its ownabbreviation, or chemical symbol. The periodic table of theelements summarizes information on the elements in acomprehensive and elegant way. (Please see Appendix Con the Companion Website at www.pearsoned.ca/withgott.)

Elements are composed of atoms, the smallest com-ponents that maintain the chemical properties of the

The lemon-scented geranium has thepotential for use in phytoremediation.

When soil is contaminated with heavymetals from mining, manufacturing, oilextraction, or military facilities, the standardsolution is to dig up tons of soil and pile itinto a hazardous waste dump. Bulldozingso much dirt can release toxic chemicalsinto the air and costs up to $7.5 millionper hectare. As an alternative, scientistsare developing methods of phytoremedia-tion, using plants (phyto means “plant”) toremediate, or detoxify, contaminated soils.

For example, researchers at theUniversity of Guelph in Ontario haverecently shown that the lemon-scentedgeranium (Pelargonium, see photo) has anatural ability to absorb heavy metals, suchas copper, mercury, lead, and nickel, fromcontaminated soil.The plants absorb metalions through their roots and store them intheir leaves and shoots. Normally, heavymetals are not readily accessible to plants,because they are tied up in the soil in theform of compounds that do not dissolveeasily in water. But chemicals called chelat-ing agents can bind to the metals, makingthem more water-soluble, and thus moreaccessible to plant roots.

Dr. Praveen Saxena, a professor ofhorticulture at the University of Guelph,says his research team has found that thegeranium is a more powerful accumulatorof toxic metals than any plant that has yet

THE SCIENCE BEHIND THE STORY Letting Plants Do the Dirty Workbeen tested.The geraniums could be avail-able for commercial use in phytoremedia-tion within three to five years.

The use of plants to remove haz-ardous materials from contaminated soilor groundwater is a relatively new tech-nology, which has been developed com-mercially only in the past 10 years or so.Before then, plants that were known toabsorb metals from the environment hadbeen used in prospecting for valuable ores.Samples of the plants were collected andanalyzed in the lab; if higher-than-normalconcentrations of the metal were found,a more detailed investigation would beundertaken to determine the ore-bearingpotential of the area. Yet despite thisnatural ability of plants to absorb contam-inants, research into their use for theremediation of contaminated soil is stillrelatively new, and very few plants haveyet demonstrated commercial success.

However, the lemon-scented gera-nium has many characteristics of a goodphytoremediation agent. It grows quickly,and its large volume—it is dense and bushy,and grows to a height of one metre—allows it to accumulate lots of metal ions.Unlike many plants, the geranium can alsotake up a wide variety of metals and cangrow in a variety of soils with relativelylow requirements for water and nutrients.Dr. Saxena says that lemon-scented gera-niums have survived as long as fourmonths in lab conditions that would kill aless hardy plant.

By using a process called embryoge-nesis, Saxena’s research team produceshundreds of geraniums from a small pieceof plant tissue. The researchers are alsotesting different genes that may beinserted into the embryos to enhance the

plants’ ability to absorb metals. Suchresults are beginning to be applied atcontaminated sites. Once the plants haveaccumulated metals from contaminatedsoil, they can be harvested and burned in a closed chamber, then put through asmelting procedure to recover the metals.Alternatively, the plants can be dried anddisposed of at a hazardous waste site.

The lemon-scented geranium has astrong natural fragrance, but this qualitydoes not contribute to the plant’s abilityto absorb toxins and is not affected by thetoxins taken up. After accumulating heavymetals from the soil, the lemon-scentedgeranium still smells nice. Because metalsand oils do not mix, the aromatic oil of thelemon-scented geranium, called citronella,can still be extracted and sold.2

Phytoremediation is a new pursuit,and it faces some hurdles. One is time;individual plants can take up only so muchof a substance, and 5 to 20 years ofrepeated plantings may be needed toreduce a soil’s metal content to an accept-able level. Metals also need to be in awater-soluble form. In addition, cleanup islimited to the depth of soil that plants’roots reach. Finally, plants that accumulatetoxins can potentially harm insects thateat the plants and, in turn, animals that eatthe insects.

Despite such obstacles, phytoremedi-ation is catching on. Many market analystspredict success for these new technolo-gies. The petroleum, mining, and smeltingindustries have many heavy metal-contaminated sites, and there should beno shortage of potential customers forthe lemon-scented geranium and other hard-working plants.



element (see FIGURE 2.3). Every atom has a nucleus con-sisting of protons (positively charged particles) and neu-trons (particles lacking any electric charge). The atoms ofeach element have a defined number of protons, referredto as the element’s atomic number. (Elemental carbon,for instance, has 6 protons in its nucleus; thus, its atomicnumber is 6.) An atom’s nucleus is surrounded by nega-tively charged particles known as electrons, which bal-ance the positive charge of the protons.

Isotopes Although all atoms of a given element con-tain the same number of protons, they do not necessarilycontain the same number of neutrons. Atoms of the sameelement with differing numbers of neutrons are referredto as isotopes (FIGURE 2.3A). Isotopes are denoted bytheir elemental symbol, preceded by the mass number, orcombined number of protons and neutrons in the atom.For example, 14C (carbon-14) is an isotope of carbon with8 neutrons (and 6 protons) in the nucleus rather than the

normal 6 neutrons and 6 protons of 12C (carbon-12). Theatomic number of carbon is 6, therefore all the isotopes ofcarbon have 6 protons (if not, they would not be carbonatoms), but different numbers of neutrons are possible,leading to different mass numbers for the various iso-topes of carbon.

Because they differ slightly in mass, isotopes of anelement differ slightly in their behaviour. This fact hasturned out to be very useful for researchers. Scientistshave been able to use isotopes to study a number ofphenomena that help illuminate the history of Earth’sphysical environment. Researchers also have used them tostudy the flow of nutrients within and among organisms,and the movement of organisms from one geographiclocation to another (see “The Science Behind the Story:How Isotopes Reveal Secrets of Earth and Life,”• pp. 38–39).

Some isotopes are radioactive and therefore “decay”spontaneously, changing their chemical identity as theyshed subatomic particles and emit high-energy radiation.Radioisotopes decay into lighter radioisotopes, until theybecome stable isotopes, which are not radioactive. Eachradioisotope decays at a rate determined by that isotope’shalf-life, the amount of time it takes for one-half theatoms to give off radiation and decay. Each radioisotopehas its own characteristic half-life, and the half-lives ofvarious radioisotopes range from fractions of a secondto billions of years. For example, the naturallyoccurring radioisotope uranium-235 (235U) is the princi-pal source of energy for commercial nuclear power. Itdecays into a series of daughter isotopes, eventually form-ing lead-207 (207Pb), and has a half-life of about 700 mil-lion years.

Ions Atoms can also gain or lose electrons, therebybecoming ions, electrically charged atoms or combina-tions of atoms (FIGURE 2.3B). Ions are denoted by theirelemental symbol followed by their ionic charge. For

FIGURE 2.2Matter can never just disappear or go away, as much as we mightsometimes wish it. In this case, oil that was spilled in a pristine bay whenthe Exxon Valdez ran aground in Alaska moved around and changed itsform, but all of it ended up somewhere—in the rocks and sediments atthe bottom of the bay, dispersed in the water, or clotting the feathers ofthousands of seabirds, as shown here.

Table 2.1 Earth’s Most Abundant Chemical Elements, by Mass

Earth’s crust Oceans Air Organisms

Oxygen (O), 49.5% Oxygen (O), 85.8% Nitrogen (N), 78.1% Oxygen (O), 65.0%

Silicon (Si), 25.7% Hydrogen (H), 10.8% Oxygen (O), 21.0% Carbon (C), 18.5%

Aluminum (Al), 7.4% Chlorine (Cl), 1.9% Argon (Ar), 0.9% Hydrogen (H), 9.5%

Iron (Fe), 4.7% Sodium (Na), 1.1% Other, < 0.1% Nitrogen (N), 3.3%

Calcium (Ca), 3.6% Other, 0.4% Calcium (Ca), 1.5%

Sodium (Na), 2.8% Phosphorus (P), 1.0%

Potassium (K), 2.6% Potassium (K), 0.4%

Magnesium (Mg), 2.1% Sulphur (S), 0.3%

Other, 1.6% Other, 0.5%



instance, a common ion used by mussels and clams toform shells is Ca2+, a calcium atom that has lost two elec-trons and so has a positive charge of 2. Ions that form asa result of the loss of electrons, and which therefore carrya positive charge, are called cations. Ions that form as aresult of gaining electrons, and which therefore carry anegative charge, are called anions.

Atoms bond to form moleculesand compoundsAtoms can bond together to form molecules, combina-tions of two or more atoms. Molecules can contain oneelement or several. Common molecules containing onlya single element include those of oxygen gas (O2) andnitrogen gas (N2), both of which are abundant in air. Amolecule composed of atoms of two or more differentelements is called a compound. Water is a compound; itis composed of two hydrogen atoms bonded to one oxy-gen atom, and denoted by the chemical formula H2O.Another compound is carbon dioxide, consisting of onecarbon atom bonded to two oxygen atoms; its chemicalformula is CO2.

Bonding Atoms bond or combine chemically becauseof an attraction for one another’s electrons. Because thestrength of this attraction varies among elements, atomsmay be held together in different ways, according to

whether and how they share or transfer electrons. Whenatoms in a molecule share electrons, they generate a cova-lent bond. For instance, two atoms of hydrogen bondto form hydrogen gas, H2, by sharing electrons equally.Atoms in a covalent bond can also share electronsunequally, with one atom exerting a greater pull. Such isthe case with water, in which oxygen attracts electronsmore strongly than hydrogen does, forming what aretermed polar covalent bonds. If the strength of attractionis sufficiently unequal, an electron may be transferredfrom one atom to another. Such a transfer creates oppo-sitely charged ions that are said to form ionic bonds. Theseassociations are called ionic compounds, or salts. Table salt(NaCl) contains ionic bonds between positively chargedsodium cations (Na+), each of which donated an electron,and negatively charged chloride anions (Cl–), each ofwhich received an electron.

Redox reactions The loss of an electron by a mole-cule, an atom, or an ion is an example of a process calledoxidation, whereas the addition of an electron is an exam-ple of reduction. The oxidation state or oxidation numberof an element is a measure of its charge in standard chem-ical conditions. The oxidation state of a free, uncombinedelement is zero. In reactions that involve oxidation andreduction (abbreviated redox), a change in oxidationstate occurs, typically (but not always) accompanied bya transfer of electrons. Substances that induce oxidationare called oxidizing agents; they are electron acceptors.Substances that induce reduction are called reducingagents; they are electron donors. Redox reactions are verycommon in the environment. Photosynthesis and respi-ration, discussed below, are both examples of redox re-actions; so is the combustion of wood, gasoline, or oil.Another common example is the formation of rust, inwhich iron oxidizes to Fe3+ and oxygen in the surround-ing air receives electrons.

Mixtures and solutions Elements, molecules, andcompounds can also come together in mixtures withoutchemically bonding or reacting. A physical mixture of twoor more substances is called a solution, a term most oftenapplied to liquids but also applicable to some gases andsolids. Air in the atmosphere is a solution formed of con-stituents, such as nitrogen, oxygen, water, carbon dioxide,methane (CH4), and ozone (O3). Human blood, oceanwater, mud, plant sap, and metal alloys, such as brass, areall solutions. Crude oil at high pressure may carry naturalgas in solution and often contains other substances dis-tributed unevenly. It is a heavy liquid mixture of manykinds of molecules consisting primarily of carbon andhydrogen atoms. Its physical properties vary with temper-ature, pressure, and composition.

Addition of1 neutron

(a) Hydrogen isotope, 2H Protons = 1 Neutrons = 1 Electrons = 1

Loss of1 electron

(b) Hydrogen ion, H+

Protons = 1 Electrons = 0

Hydrogen atom, HProtons = 1Electrons = 1

–

–

FIGURE 2.3The mass number of hydrogen is 1 (1 proton + 0 neutrons).Deuterium, an isotope of hydrogen (a), contains a neutron as well asa proton and thus it has greater mass than a typical hydrogen atom.Another isotope of hydrogen, called tritium (not shown here), has amass number of 3 (1 proton + 2 neutrons). Note that all these variantshave 1 proton—hence, they are all still “hydrogen,” chemically, but theyhave different mass numbers because of the different numbers ofneutrons in their nuclei. Shown in (b) is the hydrogen ion, H+. By losingits electron, it gains a positive charge.



The chemical structure of thewater molecule facilitates lifeWater dominates Earth’s surface, covering more than 70%of the globe, and its abundance is a primary reason Earthis hospitable to life. Scientists think life originated inwater and stayed there for 3 billion years before movingonto land. Today every land-dwelling creature remainscritically tied to water for its existence.

The water molecule’s amazing capacity to support liferesults from its unique chemical properties. As just men-tioned, the oxygen atom attracts electrons more stronglythan do the two hydrogen atoms in a water molecule,resulting in a polar molecule in which the oxygen end hasa partial negative charge and the hydrogen end has a par-tial positive charge. Because of this configuration, watermolecules can adhere to one another in a special type ofinteraction called a hydrogen bond, in which the oxygenatom of one water molecule is weakly attracted to one or

two hydrogen atoms of another (FIGURE 2.4). The weakelectrical attraction of hydrogen bonding can also occurbetween hydrogen and certain other atoms, such as nitro-gen. In water, hydrogen bonds are most stable in ice,somewhat stable in liquid water, and broken in watervapour.

These loose connections among molecules give waterseveral properties important in supporting life and stabi-lizing Earth’s climate:

■ Water remains liquid over a wide range of tempera-tures. At Earth’s surface, water exists in liquid formfrom 0ºC all the way to 100ºC. This means thatwater-based biological processes can occur in a verywide range of environmental conditions.

■ Water exhibits strong cohesion. (Think of how waterholds together in drops, and how drops on a surfacejoin together when you touch them to one another.)This cohesion facilitates the transport of chemicals,

Dr. Keith Hobson works with EnvironmentCanada and the University of Saskatchewan.

Isotopes have become one of the mostpowerful instruments in the environmentalscientist’s toolkit.These alternative versionsof chemical elements enable scientists todate ancient materials, reconstruct pastclimates, and study the lifestyles ofprehistoric humans. They also allowresearchers to work out photosyntheticpathways, measure animals’ diets andhealth, and trace nutrient flows throughorganisms and ecosystems.

Researchers studying the past oftenuse radiocarbon dating. Carbon’s mostabundant isotope is 12C, but 13C and 14Calso occur in nature. Carbon-14 is radio-active and occurs in organisms at thesame low concentration that it occurs inthe atmosphere. Once an organism dies,no new 14C is incorporated into its struc-ture, and the radioactive decay process(• p. XX) gradually reduces its store of

THE SCIENCE BEHIND THE STORY How Isotopes Reveal Secrets of Earth and Life14C, converting these atoms to 14N (nitrogen-14).

The decay is slow and steady, actinglike a clock. Scientists can date ancientorganic materials by measuring the per-centage of carbon that is 14C and match-ing this value against the clock-likeprogression of decay. In this way, archeol-ogists and paleontologists have dated pre-historic human remains; charcoal, grain,and shells found at ancient campfires; andbones and frozen tissues of recentlyextinct animals, such as mammoths. Themost recent ice age has been dated from14C analysis of trees overrun by glacial icesheets.

Because the half-life of 14C is5730 years, radiocarbon dating is notuseful for items more than 50 000 yearsold; too little 14C would remain to permitaccurate analysis. For older items, scien-tists use other isotopes. Uranium-238(with a half-life of 4.5 billion years) hasbeen used to date very early fossils. Fordating geological formations, potassium–argon dating is useful (potassium-40decays to argon-40). Oxygen-18 has beenwidely used to measure changes in climateand sea level.

Researchers interested in present-day processes can use stable isotope

analysis. Unlike radioactive isotopes, stableisotopes occur in nature in constant ratios.For instance, nitrogen occurs as 99.63%nitrogen-14 and 0.37% nitrogen-15. Ratiosof isotopes are called isotopic signatures.The isotopic signatures of various environ-mental materials and processes are diag-nostic—almost like fingerprints. Forexample, organisms tend to retain 15N intheir tissues but readily excrete 14N. As aresult, animals higher in the food chainshow isotopic signatures biased toward15N, as do animals that are starving. KeithHobson—an ecologist with the Prairieand Northern Wildlife Research Centre,Canadian Wildlife Service of EnvironmentCanada, and the University ofSaskatchewan—used nitrogen signaturesto analyze the diets of seabirds andmarine mammals, to show that geese fastwhile nesting and to trace artificial con-taminants in food chains.

Hobson and other scientists have alsoused stable carbon isotopes for ecologicalstudies. Plants produce food through oneof three photosynthetic pathways, and theisotopic signature of carbon in plants variesamong these pathways. Grasses havehigher ratios of 13C to 12C than oak treesdo, for instance, whereas cacti have inter-mediate ratios. When animals eat plants,


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such as nutrients and waste, in plants and animalsand in the physical environment.

■ Water has a high heat capacity. Initial heating weakenshydrogen bonds between molecules but does notspeed molecular motion. As a result, water can absorba large amount of heat with only small changes in itstemperature. This quality helps stabilize systemsagainst change, whether those systems are organisms,ponds, lakes, or climate systems.

■ Water molecules in ice are farther apart than in liquidform (FIGURE 2.5A), so ice is less dense than liquidwater—the reverse pattern of most other com-pounds, which become denser as they freeze. This iswhy ice floats on liquid water. Floating ice has aninsulating effect that can prevent water bodies fromfreezing solid in winter.

■ Water molecules bond well with other polar mole-cules, because the positive end of one molecule bondsreadily to the negative end of another. As a result,

they incorporate the plants’ isotopic signa-tures into their own tissues, and this sig-nature passes up the food chain. As aresult, carbon isotope studies can tell ecol-ogists what an animal has been eating.Similarly, archeologists have used isotopicsignatures in human bone to determinewhen ancient people switched from ahunter–gatherer diet to an agriculturalone.

Isotopic data can even tell a scientistwhere an animal has been. For example,nectar-feeding bats have been shown tomove seasonally between communitiesdominated by cacti and communitiesdominated by trees. Such movementshave been inferred for migrating warblers,for elephants hunted for ivory, and for theoceanic movements of seals and salmon.

Recently, researchers used isotopesto track the movements of birds and otheranimals that migrate thousands of kilome-tres. This is possible because the isotopicsignature of hydrogen in rainfall variessystematically across large geographicregions.

This signature gets passed from rain-water to plants, and from plants to animals,leaving a fingerprint of geographic origin inan animal’s tissues. Hobson and colleaguesused a combination of isotopic data fromhydrogen and carbon to pinpoint the geo-graphic origins of monarch butterfliesthat had migrated to communal roosts inMexico, providing important informationfor their conservation (see map).

Stable isotope analysis is used tostudy many different environmental mate-rials and processes today. Other elementsshow patterns of natural variation that

have not yet been used or even discov-ered, researchers say, so there remainsmuch more we can learn from the use ofthese subtle chemical clues.

HighModerate LowLowest

Highest

High

Moderate

Low

Lowest

Hydrogen isotope ratios

United States

Canada

Mexico Overwinteringcolonies

Carbon isotope ratios

Plants in different geographic areas show different isotopic ratios for elements, such ascarbon and hydrogen. Caterpillars of monarch butterflies incorporate into their tissuescarbon and hydrogen in the isotopic ratios present in the plants they eat.When thesecaterpillars metamorphose into butterflies and migrate, they carry these isotopic signa-tures with them, providing scientists with clues to their origin. Shown is a map of isotopicratios across eastern North America produced from measurements of monarchs in thesummer.The four coloured bands show decreasing ratios of 13C to 12C from north tosouth.The five grey lines show increasing ratios of 2H (heavy hydrogen or deuterium) to1H from north to south. By measuring carbon and hydrogen isotope ratios in monarchswintering in Mexico, and matching the combination of these numbers against this map,researchers were able to pinpoint the geographic origin of many of the butterflies.

Source:Wassenaar, L. I., and K.A. Hobson. 1998. Proceedings of the National Academy of Sciencesof the USA 95:15436–15439.

Hydrogen atom

Oxygen atom

Hydrogen atom

(–)

(+)Hydrogen bond

Water molecule

(+)(–)

(–)(–)(+)

(+)

H

OH

FIGURE 2.4Water is a unique compound that has several properties crucial for life.Hydrogen bonds give water cohesion by enabling water molecules toadhere loosely to one another.



water can hold in solution, or dissolve, many othermolecules, including chemicals necessary for life(FIGURE 2.5B). It follows that most biologicallyimportant solutions involve water.

Hydrogen ions determine acidityIn any aqueous solution (a solution in which water is thesolvent), a small number of water molecules dissociateor split apart, each forming a hydrogen ion (H+) and ahydroxide ion (OH–). The product of hydrogen andhydroxide ion concentrations is always the same; as theconcentration of one increases, the concentration of theother decreases, and the product of their concentrationsremains constant. Pure water contains equal numbers ofthese ions, and we call this water neutral. Most aqueoussolutions, however, contain different concentrations ofthese two ions. Solutions in which the H+ concentrationis greater than the OH– concentration are acidic; thestronger the acid, the more readily dissociation occursand H+ ions are released. Solutions in which the OH–

concentration is greater than the H+ concentration arebasic.

Ice

Liquid water

(a) Why ice floats on water

FIGURE 2.5(a) Ice floats on water because solid ice is lessdense than liquid water.This is an unusualproperty of H2O—it is far more common forthe solid form of a material to be denser thanthe liquid form. In ice, each molecule isconnected to neighbouring molecules bystable hydrogen bonds, forming a spaciouscrystal lattice. In liquid water, hydrogen bondsfrequently break and reform, and themolecules are closer together and less wellorganized. (b) Water is often called the“universal solvent” because it can dissolve somany chemicals, especially polar and ioniccompounds. Seawater holds sodium andchloride ions, among others, in solution. (b) Water as a solvent; how water dissolves salt

Watermolecule

Sodium ion surroundedby negatively chargedregions of water molecules

Cl–

Na+

Chloride ion surroundedby positively chargedregions of water molecules

Salt(sodiumchloride, Na+Cl–)

Water has several special properties that make it accom-modating to life.Think about the process of a plant tak-ing up water through its root system; how might thechemical properties of water influence this process, orcause other materials to be taken up by the plant alongwith the water?

weighingthe issues

2–1WATER’S PROPERTIESFOR LIFE



The pH scale (FIGURE 2.6) quantifies the acidity orbasicity of solutions. The scale runs from 0 to 14; purewater has a hydrogen ion concentration of 10–7 and hasa pH of 7. Solutions with pH less than 7 are acidic,those with a pH greater than 7 are basic, and those witha pH of 7 are neutral. Because the pH scale is logarith-mic, each step on the scale represents a tenfold differ-ence in hydrogen ion concentration. Thus, a substancewith a pH of 6 contains 10 times as many hydrogen ionsas a substance with a pH of 7, and a substance with a pH of 5 contains 100 times as many hydrogen ions asone with a pH of 7. FIGURE 2.6 shows pH for a num-ber of common substances. Industrial air pollution hasintensified the acidity of precipitation, which isnaturally slightly acidic, such that the pH of rain inparts of the northeastern and midwestern United Statesand south–central Canada now frequently dips to 4or lower.

Matter is composed of organicand inorganic compoundsBeyond their need for water, living things also depend onorganic compounds, which they create and of which theyare created. Organic compounds consist of carbon atoms(and generally hydrogen atoms) joined by covalent bonds,often with other elements, such as nitrogen, oxygen,sulphur, and phosphorus. Carbon’s unusual ability tobuild elaborate molecules has resulted in millions ofdifferent organic compounds, many of which are highlycomplex.

Chemists differentiate organic compounds frominorganic compounds, which also are importantin the support of life. Some inorganic compoundscontain carbon as a constituent, but they lack thecarbon–carbon bonds that are characteristic of organiccompounds. It is important to remember that in scien-tific terminology organic does not mean “natural” or

“environmentally friendly” or “pesticide free,” as wehave come to use the word in everyday language. Theterm organic does not even imply that a compound is orwas once alive—it simply refers to the presence in thechemical compound of carbon-based molecules withcarbon–carbon bonding.

Most biological materials, including crude oil andpetroleum products, are made up of organic compoundscalled hydrocarbons. Hydrocarbons consist primarily ofatoms of carbon and hydrogen (although other elementsmay enter the compounds, typically as impurities). Thesimplest hydrocarbon is methane (CH4), the key compo-nent of natural gas; it has one carbon atom bonded tofour hydrogen atoms (FIGURE 2.7A). Adding anothercarbon atom and two more hydrogen atoms gives us

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Ammonia

NaOH (sodiumhydroxide)

Soft soap

Seawater

Pure water

Normal rainwater

Acid rain

Lemon juiceExtreme acid rainCar battery acid

Stomach acid

Basic

Acidic

NeutralpH

FIGURE 2.6The pH scale measures how acidic or basic a solution is.The pH ofpure water is 7, the midpoint of the scale.Acidic solutions have higherhydrogen ion concentrations and lower pH, whereas basic solutionshave lower hydrogen ion concentrations and higher pH.

C

H

H H

H

C

H

H H

H

H

H

C

C

C

C

CH

H H

H

C

C

C

C

C

C

H

H

H

H

(a) Methane, CH4 (b) Ethane, C2H6 (c) Naphthalene, C10H8 (a polycyclic aromatic hydrocarbon)

FIGURE 2.7Hydrocarbons are a major class of organic compound, and mixtures of them make up fossil fuels, such as crude oil.The simplest hydrocarbon ismethane (a). Many hydrocarbons consist of linear chains of carbon atoms with hydrogen atoms attached; the shortest of these is ethane (b).Volatilehydrocarbons with multiple rings, such as naphthalene (c), are called polycyclic aromatic hydrocarbons (PAHs).



ethane (C2H6), the next-simplest hydrocarbon(FIGURE 2.7B). The smallest (and therefore lightest-weight) hydrocarbons (those consisting of four or fewercarbon atoms) exist in a gaseous state at normal temper-atures and pressures. Larger (and therefore heavier)hydrocarbons are liquids, and those consisting of morethan 20 carbon atoms are normally solids.

Some hydrocarbons from petroleum pose healthhazards to wildlife and people, as you will see in Chapters 11,13, 15, and 19. For example, polycyclic aromatic hydrocar-bons, or PAHs (FIGURE 2.7C), which are volatile mole-cules with a structure of multiple carbon rings, canevaporate from spilled oil and gasoline and can mix withwater. The eggs and young of fish and other aquatic crea-tures are often most at risk. PAHs also occur in particulateform in various combustion products, including cigarettesmoke, wood smoke, and charred meat.

Macromolecules are buildingblocks of lifeJust as the carbon atoms in hydrocarbons may be strungtogether in chains, other organic compounds some-times combine to form long chains of repeated mole-cules. Some of these chains, called polymers, play keyroles as the building blocks of life. Three types of poly-mers are essential to life: proteins, nucleic acids, andcarbohydrates. Lipids are not considered polymers butare also fundamental to life. These four types of mole-cules are referred to as macromolecules because of theirlarge size.

Proteins Proteins consist of long chains of organicmolecules called amino acids. Amino acids are organicmolecules in which a central carbon atom is linked to a

hydrogen atom, an acidic carboxyl group (—COOH), abasic amine group (—NH2), and an organic side chainunique to each type of amino acid (FIGURE 2.8A).Organisms combine up to 20 different types of aminoacids into long chains to build proteins (FIGURE 2.8B). Aprotein’s identity is determined by its particular sequenceof amino acids and by the shape the protein moleculeassumes as it folds. Protein molecules typically havehighly convoluted shapes, with certain parts of thechain exposed and others hidden inside the folds(FIGURE 2.8C). A protein’s folding pattern affects itsfunction, because the position of each chemical grouphelps determine how it interacts with cell surfaces andwith other molecules.

Proteins serve many functions. Some help producetissues and provide structural support for the organism.For example, animals use proteins to generate skin, hair,muscles, and tendons. Some proteins help store energy,and others transport substances. Some function as com-ponents of the immune system, defending the organismagainst foreign attackers. Still others act as hormones,molecules that serve as chemical messengers within anorganism. Finally, proteins can serve as enzymes, mole-cules that catalyze, or promote, certain chemical reac-tions. For example, bacteria used for bioremediation usespecialized enzymes to break down hydrocarbons, just aswe use enzymes to digest our food.

Nucleic acids Protein production is directed bynucleic acids. The two nucleic acids—deoxyribonucleicacid (DNA) and ribonucleic acid (RNA)—carry thehereditary information for organisms and are responsiblefor passing traits from parents to offspring. Nucleic acidsare composed of series of nucleotides, each of whichcontains a sugar molecule, a phosphate group, and anitrogenous base (FIGURE 2.9A). The double strands of

C CN

H

R

O

OH

H

H

Hydrogen

Aminoacid

Sidegroup

Carboxylgroup

Aminogroup

(a) General structure of an amino acid (b) Chain of amino acids (c) Protein

FIGURE 2.8Proteins are polymers that are vital for life.They are made up of long chains of amino acids (a, b) and fold up into complex convoluted shapes (c) thathelp determine their functions.



DNA can be pictured like a ladder twisted into a spiral,giving the entire molecule a shape called a double helix(FIGURE 2.9B). RNA is similar, but it is generally single-stranded and uses ribose (instead of deoxyribose) as itssugar group.

Hereditary information encoded in the nucleotidesequence of DNA is rewritten to a molecule of RNA. RNAthen directs the order in which amino acids assemble tobuild proteins, which go on to influence the structure,growth, and maintenance of the organism. Genetic infor-mation from DNA is passed from one generation toanother as the strands replicate during cell division andegg or sperm formation. Regions of DNA coding forparticular proteins that perform particular functions arecalled genes. In most organisms, the genome—the set ofall an organism’s genes—is divided among specializedareas called chromosomes, which act as the carriers ofgenetic information. Different types of organisms havedifferent numbers of genes and chromosomes. Most bac-teria have a single circular chromosome, for instance,whereas humans have 46 linear ones.

Carbohydrates A third type of biologically vitalpolymer, carbohydrates consist of atoms of carbon,hydrogen, and oxygen. Simple carbohydrates, called sug-ars or monosaccharides, have structures that are three toseven carbon atoms long, and formulas that are somemultiple of CH2O. Glucose (C6H12O6) is one of the mostcommon and important sugars, providing energy thatfuels plant and animal cells (FIGURE 2.10A). Glucosealso serves as a building block for complex carbohy-drates, or polysaccharides. Plants use starch, a glucose-based polysaccharide, to store energy, and animals eatplants to acquire starch (FIGURE 2.10B). In addition,both plants and animals use complex carbohydrates to

Phosphategroup

Sugar Nitrogenousbase

Nitrogenousbase

Sugar-phosphatebackbone

(a) DNA nucleotide

(b) DNA double helix

GC

T

A

A

T

FIGURE 2.9Nucleic acids encode genetic information in the sequence of nucleotides(a), small molecules that pair together like rungs of a ladder. DNAincludes four types of nucleotides, each with a different nitrogenousbase: adenine (A), guanine (G), cytosine (C), and thymine (T).Adeninepairs with thymine, and cytosine pairs with guanine. In RNA, thymine isreplaced by uracil (U). DNA twists in the shape of a double helix (b).

FIGURE 2.10The monosaccharide glucose (a) is the simplest and mostabundant carbohydrate and is a vital energy source for organisms.Linked glucose molecules form starch (b), an importantpolysaccharide. Cellulose (c) is an insoluble, fibrous polysaccharidethat gives strength to the stems, trunks, and cell walls of plants. (c) Cellulose, a fibrous polysaccharide

Cellulose fibres

Microfibril

Microfibril

Chains of cellulosemolecules

(a) Glucose, a simple carbohydrate

(b) Starch, a polysaccharide

O

H

OH

OH

C

H

HH

OH

C

H

HO

H

C

H

C

OH

C

C


VJonePa

Sticky Note

2.10c to be replaced. image to come


build structure. Insects and crustaceans form hard shellsfrom the carbohydrate chitin. Cellulose, the most abun-dant organic compound on Earth, is a complex carbohy-drate found in the cell walls of leaves, bark, stems, androots. Like starch, it is composed of glucose molecules,but bound together in a different way (FIGURE 2.10C).Cellulose is an insoluble, indigestible fibrous materialthat gives strength to plant structures and is used in themanufacture of many products that incorporate fibres,such as papers and textiles.

Lipids A fourth type of macromolecule includes achemically diverse group of compounds called lipids,which are classified together because they do not dissolvein water. These include the following:

■ Fats and oils, which are convenient forms of energystorage, especially for mobile animals. Their hydro-carbon structures somewhat resemble gasoline, asimilarity echoed in their function: to effectively storeenergy and release it when burned.

■ Phospholipids, which are similar to fats but consist ofone water-repellent (or hydrophobic) side and onewater-attracting (or hydrophilic) side. This character-istic allows them, when arranged in a double layer,to make up the primary component of animal cellmembranes.

■ Waxes, which are lipids that are digestible by somebut not all organisms. They can play structural roles(for instance, beeswax in beehives).

■ Steroids, which are used in animal cell membranesand in the production of hormones, including the sexhormones estrogen and androgen, which are vital tosexual maturation.

We create synthetic polymersThe polymers in nature that are so vital to our survivalhave inspired chemists. These scientists have taken thepolymer concept and run with it, creating innumerabletypes of synthetic (human-made) polymers, which wecall plastics. Polyethylene, polypropylene, polyurethane,and polystyrene are just a few of the many synthetic poly-mers in our manufactured products today (we oftenknow them by their brand names, such as Nylon, Teflon,and Kevlar). Plastics, many of them derived from hydro-carbons in petroleum, are all around us in our everydaylives, from furniture to food containers to fibre optics tofleece jackets.

We value synthetic polymers because they resistchemical breakdown. Although plastics make our liveseasier, the waste and pollution they create when we discardthem is long-lasting as well. In later chapters we will see

how pollutants that resist breakdown can cause problemsfor wildlife and human health, for water quality, formarine animals, and for waste management. Fortunately,chemists, policy makers, and citizens are finding moreways to design and use less-polluting substances and torecycle materials effectively.

Organisms use cells to compartmentalize macromoleculesNatural polymers and macromolecules help to buildcells, the most basic unit of life’s organization. All livingthings are composed of cells, and organisms range in theircomplexity from single-celled bacteria to plants and ani-mals that contain millions of cells. Cells vary greatly insize, shape, and function.

Biologists classify organisms into two groups basedon the structure of their cells. Eukaryotes include plants,animals, fungi, and protists. The cells of eukaryotes(FIGURE 2.11A) consist of an outer membrane of lipidsand an inner fluid-filled chamber containing organelles,internal structures that perform specific functions. Theseinternal structures include (among others) ribosomes,which are organelles that synthesize proteins, and mito-chondria, where the last step in the extraction of energyfrom sugars and fats occurs. Eukaryotes also have withineach of their cells a membrane-enclosed nucleus thathouses DNA. Eukaryotic organisms generally have manycells.

Prokaryotic organisms are much simpler and proba-bly existed on Earth for many millions of years beforethe emergence of the more complicated eukaryotic cells.Prokaryotes are generally single-celled, and theircells lack membrane-bound organelles and a nucleus(FIGURE 2.11B). All bacteria are prokaryotes, as are thelesser-known microorganisms called archaea. Bacteria arediverse and are ubiquitous in the environment, and, ofcourse, they do far more than attack oil spills. Many typesof bacteria perform functions vital to human life—forinstance, aiding in digestion and preventing the buildupof harmful wastes.

In eukaryotes, cells specialize in different roles and areorganized into collections of cells performing the samefunction, called tissues. Tissues make up organs, andorganisms are composed of organ systems. We have nowcompleted a (very quick!) review of the hierarchy inwhich matter is organized in living things on Earth(FIGURE 2.12). Over the next three chapters, we willexplore the levels of this hierarchy above the organismallevel, as we study the science of ecology. But first we willexamine energy, something that underlies every processin environmental science.



Energy FundamentalsCreating and maintaining organized complexity, whetherof a cell or an organism or an ecological system, requiresenergy. Energy is needed to power the geological forcesthat shape our planet; to organize matter into complexforms, such as biological polymers; to build and maintaincellular structure; and to power the interactions that takeplace among species. Indeed, energy is somehow involvedin nearly every biological, chemical, and physical event.A sparrow in flight expends energy to propel its bodythrough the air. When the sparrow lays an egg, its body usesenergy to create the calcium-based eggshell and colour itwith pigment. The sparrow sitting on its nest transfersenergy from its body in heating the developing chicks insideits eggs. Some of the most dramatic releases of energy innature do not involve living things; think of volcanoeserupting or tornadoes sweeping across the plains.

But what, exactly, is energy? Although intangible,energy can change the position, physical composition, ortemperature of matter. Scientists differentiate between

two types of energy: potential energy, energy of position;and kinetic energy, energy of motion. Consider riverwater held behind a dam. By preventing water from mov-ing downstream, the dam causes the water to accumulatepotential energy. When the dam gates are opened,the potential energy is converted to kinetic energy, in theform of water’s motion as it rushes downstream.

Such energy transfers take place at the atomic levelevery time a chemical bond is broken or formed.Chemical energy is potential energy held in the bondsbetween atoms. Bonds differ in their amounts of chemicalenergy, depending on the atoms they hold together.Converting a molecule with high-energy bonds (such asthe carbon–carbon bonds of petroleum products) intomolecules with lower-energy bonds (such as the bondsin water or carbon dioxide) releases energy by changingpotential energy into kinetic energy and produces motion,action, or heat. Just as our automobile engines split thehydrocarbons of gasoline to release chemical energy andgenerate movement, our bodies split glucose molecules inour food for the same purpose (FIGURE 2.13).

Plasmamembrane

Ribosome

Nucleus

Animal cell Plant cell

Nucleus Ribosome MitochondrionEndoplasmicreticulum

Cytoplasm

Mitochondrion

Centralvacuole

Plasmamembrane

Cell wallChloroplast

(a) Eukaryotic cell

Golgiapparatus

Ribosome Nucleoidregion (DNA)

Capsule

Cell wall Plasma membrane

(b) Prokaryotic cell

FIGURE 2.11Cells are the smallest unit of life that can function independently. Eukaryotic cells (a) contain organelles, such as mitochondria and chloroplasts, as wellas a membrane-enclosed nucleus that contains DNA. Plant cells (right) have rigid cell walls of cellulose, whereas animal cells (left) have more flexiblecell membranes. Prokaryotic cells (b) are simpler, lacking membrane-bound organelles and an enclosed nucleus.



In addition to occurring in the form of chemicalenergy, potential energy can occur as nuclear energy, theenergy that holds atomic nuclei together and is releasedwhen an atom is split. It can also occur as stored mechan-ical energy, such as the energy in a compressed spring ora tree that bends in the wind. Kinetic energy also cantake a variety of forms, though all are typically expressedthrough movement of electrons, atoms, molecules, orobjects. In addition to movement, such as wind or run-ning water, these include radiant or electromagneticenergy, which travels in photons of light; electricalenergy, the movement of electrons, of which lightning isa natural example; thermal energy, or heat, expressed inthe vibrational movement of atoms and molecules; andsound, which results when something causes an object tovibrate.

Energy is always conserved . . .Although energy can change from one form to another,it cannot be created or destroyed. The total energy inthe universe remains constant and thus is said to beconserved. Scientists have dubbed this principle the firstlaw of thermodynamics. The potential energy of thewater behind a dam will equal the kinetic energy of itseventual movement down the riverbed. Similarly, burn-ing converts the potential energy in a log of firewood toan equal amount of energy produced as heat and light.We obtain energy from the food we eat, which weexpend in exercise, put toward the body’s maintenance,or store as fat. We do not somehow create additionalenergy or end up with less than the food gives us. Anyindividual system can temporarily increase or decreasein energy, but the total amount in the universe remainsconstant.

. . . but energy can changein form and qualityAlthough the first law of thermodynamics requires thatthe overall amount of energy be conserved in any processof energy transfer, the second law of thermodynamicsstates that the nature of energy will change from a more-ordered state to a less-ordered state, if no force counter-acts this tendency. That is, systems tend to move towardincreasing disorder, or entropy. For instance, after deathevery organism undergoes decomposition and loses itsstructure. A log of firewood—the highly organized andstructurally complex product of many years of slow treegrowth—transforms in the campfire to a residue ofcarbon ash, smoke, and gases, such as carbon dioxide and

Hierarchy of Matter Within Organisms

A structure in anorganism composed ofseveral types of tissuesand specialized forsome particular function

An integrated system oforgans whose action iscoordinated for aparticular function

A group of cells withcommon structure andfunction

The smallest unit of livingmatter able to functionindependently, enclosed in a semi-permeablemembrane

A combination of two ormore atoms chemicallybonded together

The smallest componentof an element thatmaintains the element’schemical properties

An individual living thingOrganism

Organ

Organsystem

A structure inside aeukaryotic cell thatperforms a particularfunction

Organelle

Tissue

Cell

Molecule

Atom

A large organic molecule(includes proteins,nucleic acids,carbohydrates, and lipids)

Macro-molecule

–

FIGURE 2.12Within an organism, matter is organized in a hierarchy of levels, fromatoms through cells through organ systems.



water vapour, as well as the light and the heat of the flame.With the help of oxygen, the complex biological polymersthat make up the wood are converted into a disorganizedassortment of rudimentary molecules and heat and lightenergy.

The nature of any given energy source helps deter-mine how easily humans can harness it. Such sources aspetroleum products and high-voltage electricity containconcentrated energy that is easily released. It is relativelyeasy for us to gain large amounts of energy efficientlyfrom these high-quality sources. In contrast, sunlightand the heat stored in ocean water are considered low-quality energy sources. Each and every day the world’soceans absorb heat energy from the Sun equivalent tothat of 250 billion barrels (roughly 40 trillion litres) ofoil—more than 3000 times as much as our global soci-ety uses in a year. But because this energy is spreadout across such vast spaces, it is diffuse and difficult toharness.

In every transfer of energy, some portion usable to usis lost. The inefficiency of some of the most commonenergy conversions that power our society can be surpris-ing. When we burn gasoline in an automobile engine,only about 16% of the energy released is used to powerthe automobile’s movement. The rest of the energy is con-verted to heat. Incandescent light bulbs are worse; only5% of their energy is converted to the light that we usethem for, while the rest escapes as heat. Viewed in thiscontext, the 15% efficiency of much current solar tech-nology looks pretty good.

Although the second law of thermodynamics specifiesthat systems tend to move toward disorder, the order ofan object or a system can be increased through the inputof additional energy from outside the system. This isprecisely what living organisms do. Organisms maintaintheir structure and function by consuming energy. Theyrepresent a constant struggle to maintain order and com-bat the natural tendency toward disorder.

Light energy from the Sun powers most living systemsThe energy that powers Earth’s ecological systems comesprimarily from the Sun. The Sun releases radiation fromlarge portions of the electromagnetic spectrum, althoughour atmosphere filters much of this out, and we can seeonly some of this radiation as visible light (FIGURE 2.14).

Foodmolecules

CO2O2

(a) Potential energy (b) Kinetic energy

Glucose

+ + +C6H12O6

Oxygen Carbon dioxide Water

H2O

Heat

FIGURE 2.13Energy is released when potential energy is converted to kinetic energy. Potential energy stored in sugars, such as glucose, in the food we eat (a),combined with oxygen, becomes kinetic energy when we exercise (b), releasing carbon dioxide and water as by-products.

Contrast the ease of harnessing concentrated energy,such as that of petroleum, with the ease of harnessinghighly diffuse energy, such as that of heat from theoceans. How do you think these differences haveaffected our society’s energy policy and energy sourcesthrough the years?

weighingthe issues

2–2ENERGY AVAILABILITYAND ENERGY POLICY



Most of the Sun’s energy is reflected, or elseabsorbed and reemitted, by the atmosphere, land, orwater (see Chapter 14). Solar energy drives our weather

and climate patterns, including winds and oceancurrents. A small amount (less than 1% of the total)powers plant growth, and a still smaller amount flowsfrom plants into the organisms that eat them and theorganisms that decompose dead organic matter. Aminuscule amount of energy, relatively speaking, iseventually deposited below ground in the form of thechemical bonds in fossil fuels.

The Sun’s light energy is used directly by some organ-isms to produce their own food. Such organisms, calledautotrophs or primary producers, include green plants,algae, and cyanobacteria (a type of bacteria namedfor their characteristic blue-green, or cyan, colour.)Autotrophs turn light energy from the Sun into chemicalenergy via a process called photosynthesis (FIGURE 2.15).In photosynthesis, sunlight powers a series of chemicalreactions that convert carbon dioxide and water into sug-ars, transforming low-quality energy from the Sun intohigh-quality energy the organism can use. This is calledprimary production.

Photosynthesis produces foodfor plants and animalsPhotosynthesis occurs within cell organelles calledchloroplasts, where the light-absorbing pigmentchlorophyll (which is what makes plants green) uses solarenergy to initiate a series of light-dependent chemicalreactions. During these reactions, water molecules aresplit, and they react to form hydrogen ions (H+) andmolecular oxygen (O2), thus creating the oxygen that webreathe. The light-dependent reactions also producesmall, high-energy molecules that are used to fuel reactionsin the Calvin cycle. In these reactions, carbon atoms fromcarbon dioxide are linked together to manufacture sugars.

Visible light

High energy,shorterwavelength

Gammarays X-rays Ultra-

violet Infrared

Wavelength (metres)

Radiowaves

Low energy,longerwavelength

Mic

row

aves

10–14 10–12 10–10 10–8 10–6 10–4 10–2 1

Sun

FIGURE 2.14The Sun emits radiation from many portions of the electromagnetic spectrum.Visible light makes up only a small portion of this energy. Some radiationthat reaches our planet is reflected back; some is absorbed by air, land, and water ; and a small amount powers photosynthesis.

Sunlight

Light reactions

Chloroplast

Calvin cycle

H2O

CO2

O2

Sugars

ATP ADP

NADP+

Inorganicphosphate

NADPH

FIGURE 2.15In photosynthesis, autotrophs, such as plants, algae, and cyanobacteria,use sunlight to convert carbon dioxide and water into sugars and oxy-gen.This schematic diagram summarizes the complex sets of chemicalreactions that take place within chloroplasts. In the light reactions,water is converted to oxygen in the presence of sunlight, creating high-energy molecules (ATP and NADPH) that help drive reactions in theCalvin cycle, in which carbon dioxide is used to produce sugars.Molecules of ADP, NADP+, and inorganic phosphate created in theCalvin cycle in turn help power the light reactions, creating an endlessloop.



Photosynthesis is a complex process, but the overall reac-tion can be summarized with the following equation:

→

The numbers preceding each molecular formula indi-cate how many molecules of each type are involved in thereaction. Note that the sums of the numbers on each sideof the equation for each element are equal; that is, thereare 6 C, 24 H, and 24 O on each side. This illustrates howchemical equations are balanced, with each atom recycledand matter conserved. No atoms are lost; they are simplyrearranged among molecules. Note also that waterappears on both sides of the equation. The reason is thatfor every 12 water molecules that are input and dissociatedin the process, 6 water molecules are newly created. Wecan streamline the photosynthesis equation by showingonly the net loss of 6 water molecules:

→

Thus, in photosynthesis, water, carbon dioxide, andlight energy from the Sun are transformed to producesugar (glucose) and oxygen. Thus, photosynthesis is aredox reaction: carbon dioxide is reduced in the forma-tion of sugar, and water is oxidized in the formation ofmolecular oxygen. To accomplish this, green plants drawup water from the ground through their roots, absorbcarbon dioxide from the air through their leaves, andharness sunlight. With these ingredients, they createsugars for their growth and maintenance, and they releaseoxygen as a by-product. Animals, in turn, depend on thesugars and oxygen from photosynthesis. Animals surviveby being consumers or heterotrophs, organisms that gaintheir energy by feeding on other organisms. The energygenerated by consumers is called secondary production.They eat plants (thus becoming primary consumers), oranimals that have eaten plants (thus becoming secondaryconsumers), and they take in oxygen. In fact, it is thoughtthat animals appeared on Earth’s surface only after theplanet’s atmosphere had been supplied with oxygen bycyanobacteria, the earliest autotrophs.

Cellular respiration releaseschemical energyOrganisms make use of the chemical energy created byphotosynthesis in a process called cellular respiration. Torelease the chemical energy of glucose, cells use the reac-tivity of oxygen to convert glucose back into its originalstarting materials; in other words, respiration oxidizes

C6H12O6 (SUGAR) � 6O2

6CO2 � 6H2O �ENERGY FROM THE SUN

C6H12O6 (SUGAR) �6O2 � 6H2O

6CO2 � 12H2O �ENERGY FROM THE SUN

glucose to produce carbon dioxide and water. The energyreleased during this process is used to form chemicalbonds or to perform other tasks within cells. The netequation for cellular respiration is thus the opposite ofthat for photosynthesis:

C6H12O6 (SUGAR) � 6O2 → 6CO2 � 6H2O � ENERGY

However, the energy gained per glucose molecule inrespiration is only two-thirds of the energy input per glu-cose molecule in photosynthesis—a prime example of thesecond law of thermodynamics in action. Respirationoccurs in autotrophs that create glucose and also in het-erotrophs. Most animals are heterotrophs, including thefungi and microbes that decompose organic matter. Inmost ecological systems, plants, algae, or cyanobacteriaform the base of a food chain through which energypasses to heterotrophs.

Geothermal energy also powersEarth’s systemsAlthough the Sun is Earth’s primary power source, it is notthe only one. A minor additional source is the gravita-tional pull of the Moon, which causes ocean tides. A moresignificant additional energy source is heat emanatingfrom inside Earth, powered primarily by radioactivity.When we think of radioactivity, nuclear power plants andatomic weapons may come to mind, but radioactivity isa natural phenomenon.

As discussed earlier, radioactivity is the release ofhigh-energy rays or particles by radioisotopes as theirnuclei spontaneously decay. Radiation from naturallyoccurring radioisotopes deep inside Earth heats theinside of the planet, and this heat gradually makes itsway to the surface. This internal heat energy drives platetectonics, heats magma that erupts from volcanoes, andwarms groundwater (FIGURE 2.16). Called geothermalenergy, this heat from deep within the planet is nowbeing harnessed for commercial power in some loca-tions where it is particularly concentrated at thesurface.

Long before humans came along, geothermal energywas powering other biological communities. On thefloor of the ocean, jets of geothermally heated water—essentially underwater geysers—gush into the icy-colddepths. One of the amazing scientific discoveries ofrecent decades was the realization that these hydrother-mal vents can host entire communities of organisms thatthrive in the extreme high-temperature, high-pressureconditions. Gigantic clams, immense tubeworms, andodd mussels, shrimps, crabs, and fish all flourish in theseemingly hostile environment near scalding water that



shoots out of tall chimneys of encrusted minerals(FIGURE 2.17).

These locations are so deep underwater that theycompletely lack sunlight, so their communities cannot fuelthemselves through photosynthesis. Instead, bacteria indeep-sea vents use the chemical-bond energy of hydrogensulphide (H2S) to transform inorganic carbon intoorganic carbon compounds in a process calledchemosynthesis:

→

There are many different types of chemosynthesis, butnote how this particular reaction for chemosynthesisclosely resembles the photosynthesis reaction. These twoprocesses use different energy sources, but each useswater and carbon dioxide to produce sugar and a by-product, and each produces potential energy that is laterreleased during respiration. Energy from chemosynthesispasses through the deep-sea-vent animal community, asheterotrophs, such as clams, mussels, and shrimp, gainnutrition from chemoautotrophic bacteria. Hydrothermalvent communities excited scientists not only because theywere novel and unexpected, but also because someresearchers believe they may help us understand how lifeitself originated.

The Origin of LifeHow and where life originated is one of the most centrallyimportant—and intensely debated—questions in modernscience. In searching for the answer, scientists have

C6H12O6 (SUGAR) + 3 H2SO46CO2 + 6H2O + 3H2S

learned a great deal about the history of life on Earth andabout what early Earth was like. That scientific interest hasextended to other planets, such as Mars, which may proveto have once harboured life. We study the geological andchemical environments of both planets to learn moreabout what this part of the solar system was like billionsof years ago, when life first took hold on this planet.

Early Earth was a very different placeEarth formed about 4.5 billion years ago in the same wayas the other planets of our solar system: dispersed bitsof material whirling through space around our Sun weredrawn by gravity into one another, coalescing into a seriesof spheres. For several hundred million years after theplanets formed, there remained enough stray material inthe solar system that Earth and the other young planetswere regularly bombarded by large chunks of debris inthe form of asteroids, meteorites, and comets. The largestimpacts were probably so explosive that they vaporizedthe newly formed oceans. Add to this the severe volcanicand tectonic activity and the intense ultraviolet radiation,and it is clear that early Earth was a pretty hostile place(FIGURE 2.18). Any life that emerged during this “bom-bardment stage” might easily have been killed off. Onlyafter most debris was cleared from the solar system waslife able to gain a foothold.

Earth’s early atmosphere was very different from ouratmosphere today. It was chemically reducing, and free(uncombined) oxygen was largely lacking until

FIGURE 2.16These thermal pools at Rabbitkettle Hot Springs in Nahanni NationalPark Reserve, Northwest Territories, are heated year-round bygeothermal energy from deep below ground.The bright colours of therocks are from colonies of bacteria that thrive in the hot mineral-ladenwater.The calcium carbonate deposits that form the edges of the poolswere made primarily by inorganic precipitation processes; contrast thiswith the calcium carbonate microbialite structures from Pavilion Lake,B.C., discussed in the Central Case.

(a) Hydrothermal vent

(b) Giant tubeworms

FIGURE 2.17Hydrothermal vents on the ocean floor (a) send spouts of hot mineral-rich water into the cold blackness of the deep sea.Amazingly, specializedbiological communities thrive in these unusual conditions. Odd creatures,such as these giant tubeworms (b), survive thanks to bacteria thatproduce food from hydrogen sulphide by the process of chemosynthesis.



photosynthesizing microbes started producing it.Whereas today’s atmosphere is dominated by nitrogenand oxygen (see Table 2.1), Earth’s early atmosphere isthought to have contained large amounts of hydrogen,ammonia (NH3), methane, carbon dioxide, carbonmonoxide (CO), and water vapour. Figuring out howEarth’s atmosphere evolved into its current state is aninteresting and challenging area of research. We knowwhere some of the constituents that were so abundantearly in Earth’s history have gone; for example, much of thecarbon dioxide from the early atmosphere is now boundup in thick sequences of carbonate rocks—limestones.This is a good thing; if the carbon dioxide were releasedfrom carbonate rocks, we would have an atmosphere of95% carbon dioxide, similar to that of Venus, and thatwould definitely not be conducive to life as we know it.

Several hypotheses have beenproposed to explain life’s originMost scientists interested in life’s origin think that lifemust have begun when inorganic chemicals linked them-selves into small molecules and formed organic com-pounds. Some of these compounds gained the ability toreplicate, or reproduce themselves, whereas others foundways to group together into proto-cells. There is muchdebate and ongoing research, however, on the details ofthis process, especially concerning the location of the firstchemical reactions and the energy source(s) that poweredthem.

Primordial soup:The heterotrophic hypothesisThe hypothesis traditionally favoured is that life evolvedfrom a “primordial soup” of simple inorganic chemicals—

carbon dioxide, oxygen, and nitrogen—dissolved in theocean’s surface waters or tidal shallows. Scientists sincethe 1930s have suggested how simple amino acids mighthave formed under these conditions and how more com-plex organic compounds could have followed, includingsimple ribonucleic acids that could replicate themselves.This hypothesis is termed heterotrophic because it pro-poses that the first life forms used organic compoundsfrom their environment as an energy source.

Lab experiments have provided evidence that such aprocess can work. In 1953, biochemists Stanley Miller andHarold Urey passed electricity through a mixture of watervapour, hydrogen, ammonia, and methane, which wasbelieved at that time to represent the early atmosphere.They were able to produce many organic compounds,including amino acids. Subsequent experiments confirmedthese findings, but scientists since then have modifiedtheir ideas about early atmospheric conditions, so theseexperiments seem less likely to represent what actuallyhappened.

“Seeds” from space:The panspermia hypothesisAnother hypothesis proposes that microbes from else-where in the solar system travelled on meteorites thatcrashed to Earth, seeding our planet with life. Scientistshad long rejected this idea, believing that even if aminoacids or bacteria were to exist in space, the searing tem-peratures that comets and meteors attain as they enterour atmosphere should destroy them before they reachthe surface.

However, the Murchison meteorite, which fell inAustralia in 1969, was found to contain many aminoacids, suggesting that amino acids within rock can surviveimpact. Since then, experiments simulating impact con-ditions have shown that organic compounds and somebacteria can withstand a surprising amount of abuse.Furthermore, planetary scientists have shown that largeasteroid impacts on one planet, such as Mars, can throw upso much material that some eventually may make its wayto other planets, such as Earth. And recent astrobiologyresearch suggests that comets have brought large amountsof water, and possibly organic compounds, to Earththroughout its history. As a result of such findings, long-distance travel of microbes through space and into ouratmosphere now seems more plausible than previouslythought.

Life from the depths: The chemoautotrophichypothesis In the 1970s and 1980s, several scientistsproposed that life originated at deep-sea hydrothermalvents, like those in FIGURE 2.17, where sulphur wasabundant. In this scenario, the first organisms werechemoautotrophs, creating their own food from hydrogen

FIGURE 2.18The young Earth on which life originated was a very different placefrom our planet today. Microbial life first evolved amid sulphur-spewingvolcanoes, intense ultraviolet radiation, frequent extraterrestrial impacts,and an atmosphere containing ammonia.



sulphide. A related hypothesis suggests that life originatedin the hot, moist environment of thermal pools and hotsprings, like those in FIGURE 2.16—an environment thatis presently favoured by specifically adapted types of bac-teria. Current research on extremophiles—organisms thatare adjusted to conditions of extreme heat, cold, pressure,acidity, or salinity—by scientists like Darlene Lim and hercolleagues is helping to further our understanding of theearliest life forms on Earth and the environmental condi-tions in which they survived.

Genetic analysis of the relationships of present-dayorganisms suggests that some of the most ancientancestors of today’s life forms lived in extremely hot,wet environments. The extreme heat of hydrothermalvents could act to speed up chemical reactions thatlink atoms together into long molecules, a necessaryearly step in life’s formation. Scientists have shownexperimentally that it is possible to form amino acidsand begin a chain of steps that might potentially leadto the formation of life under high-temperature, high-pressure conditions similar to those of hydrothermalvents.

such as dinosaurs. Scientists also learn about thebiological processes that formed these ancient struc-tures by studying similar processes in operation today,in places like Pavilion Lake. FIGURE 2.19 comparesmodern-day structures built by algae with the ancientremains of similar structures built by algae hundreds ofmillions of years ago.

Ancient life forms are preserved in the rock record bythe process of fossilization. As organisms die, some areburied by sediment. Under the right conditions, the hardparts of their bodies—such as bones, shells, and teeth—may be preserved as the sediments are compressed intorock. Minerals replace the organic material, leavingbehind a fossil, a remnant or an imprint, preserved in

Which lines of evidence in the debate over the origin oflife strike you as the most convincing, and why? Whichstrike you as the least convincing, and why? Can youthink of any further scientific research that could bedone to address the question of how life originated?

weighingthe issues

2–3HYPOTHESES ON LIFE’S ORIGIN

The fossil record has taught us much about life’s historyWhether the first life arose in deep-sea vents, tidal pools,or comet craters, we know that life diversified into count-less forms over Earth’s long history. The earliest evidenceof life on Earth comes from rocks about 3.5 billion yearsold. Although these earliest traces are controversial, thereis ample evidence that simple forms of life, such as single-celled bacteria, were present on Earth well over 3 billionyears ago. Remains of these microscopic life forms (andtheir chemical by-products, in the form of the isotopicsignatures of biological processes) have been preserved inthe rock record, just as have later, much larger creatures,

(a)

FIGURE 2.19These modern-day algal structures (a), called stromatolites, shown herein a protected salt-water environment in Australia, are probably verysimilar to the structures built by the first bacterial life forms on Earth.Compare the modern stromatolites to the ancient remnants of algalstructures from 400 million to 500 million years ago (b) preservednear the Champlain Bridge, Ottawa River, and to the freshwatermicrobialite structures currently forming at Pavilion Lake in BritishColumbia.

Modern-day stromatolites, Australia

(b) Remains of ancient stromatolites, Ottawa River



stone, of the dead organism (FIGURE 2.20). Geologicalprocesses over millions of years have buried sedimentaryrock layers and later brought them to the surface, reveal-ing assemblages of fossils representing plants and animalsfrom different time periods. The cumulative body of fos-sils worldwide is known as the fossil record.Paleontologists study the fossil record to infer the historyof past life on Earth. The rocks in which these fossils werepreserved are also scientifically significant; they give usabundant information about the environments in whichthe organisms lived, including the chemistry, topography,other organisms, and even climate.

The fossil record clearly shows that:

■ The species living today are but a tiny fraction of allthe species that ever lived; the vast majority of Earth’sspecies are long extinct.

■ Earlier types of organisms changed, or evolved, intolater ones.

■ The number of species existing at any one time hasincreased through history.

■ There have been several episodes of mass extinction,or simultaneous loss of great numbers of species inEarth’s history.

The fossil record also tells us that for most of life’shistory, microbes, like the bacteria that consume hydro-carbons or the cyanobacteria that produce oxygen, werethe only life on Earth. It was not until about 600 millionyears ago that large and complex organisms, such as ani-mals, land plants, and fungi, appeared.

The crude oil with which we power modern soci-ety is itself a kind of fossil. Plant and animal mattercan be preserved as it sinks to the seafloor and isburied in the absence of oxygen; eventually itbecomes compressed and turns into the amorphousmixes of hydrocarbons we call fossil fuels. Coal, oil,and natural gas are the fossil fuels we use to power ourcivilization. When we drive a car, ignite a stove, orflick on a light switch, we are using energy from lifethat died and was buried millions of years ago andpreserved in the rock record.

Present day organisms and their genes also help us decipher life’s historyBesides fossils, biologists also use present-day organismsto infer how evolution proceeded in the past. By compar-ing the genes, the external characteristics of organisms, orboth, scientists can create branching trees, similar to fam-ily genealogies, which show the relationships amongorganisms and thus their history of divergence throughtime. As you follow such a tree from its trunk to the tipsof its branches, you proceed forward through time, trac-ing the history of life.

A major advance was made in recent years as scien-tists discovered an entire new domain of life, thearchaea, single-celled prokaryotes that are geneticallyvery different from bacteria. Today most biologists viewthe tree of life as a three-pronged edifice consisting ofthe bacteria, the archaea, and the eukaryotes(FIGURE 2.21).

We will examine the flowering of the diversity of lifeon our planet in Chapter 3 and further in Chapter 9. Therelationships among organisms, and those betweenorganisms and their environments, form the basis forecology, a discipline of primary importance to environ-mental science.

FIGURE 2.20The fossil record has helped reveal the history of life on Earth.Thenumerous fossils of trilobites suggest that these animals, now extinct,were abundant in the oceans from roughly 540 million to 250 millionyears ago.



ConclusionLife has flourished on Earth for more than 3 billion years,stemming from an origin that scientists are eagerlyattempting to understand. Deciphering how life origi-nated depends on understanding energy, energy flow, andchemistry. Knowledge in these areas also enhances ourunderstanding of how present-day organisms interactwith one another, how they relate to their nonliving envi-ronment, and how environmental systems function.

Energy and chemistry are in some way tied to nearly everysignificant process involved in environmental science.

Chemistry can also be a tool for finding solutions toenvironmental problems. Cleaning up chemical pollutionthrough bioremediation with microbes or plants is justone example. Knowledge of chemistry can be a powerfulally, whether you are interested in analyzing agriculturalpractices, managing water resources, reforming energypolicy, conducting toxicological studies, or finding waysto mitigate global climate change.

First humans0

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Oldest prokaryotic fossils

Oldest chemical evidence of life

Origin of life

Earth’s crust cools and solidifies

Origin of Earth

Bacteria Archaea

Eukaryotes

Protists Plants Fungi Animals

FIGURE 2.21The fossil record and the analysis of present-day organisms and their genes allow scientists to reconstruct evolutionary relationships among organismsand to build a “tree of life.”As you progress upward from the trunk of the tree to the tips of its branches, you are moving forward in time. Each forkdenotes the divergence of major groups of organisms, each group of which in this greatly simplified diagram includes many thousands of species.Thetree of life as understood by scientists today consists of three main groups: the bacteria, the recently discovered archaea, and the diverse eukaryotes.Protists and ancestral eukaryotes are poorly known, and their future study may well produce discoveries that further revise our understanding of life’s history.



Praveen Saxena studies traditional plants,including breadfruit, in his lab at theUniversity of Guelph.

CANADIANENVIRONMENTAL PERSPECTIVES

Praveen Saxena

■ Professor of physiology and devel-opmental biology

■ Horticulturalist and herbal medi-cine expert

■ Researcher, Plant Cell TechnologyLaboratory, University of Guelph

■ Conservationist of rare andendangered plants

Praveen Saxena is interested inplants—mainly, he is interested in plantsthat have been used as herbal remediesfor many generations. As he points out,plants naturally produce thousands of

chemicals. Some of these are potentiallyuseful in the treatment of human ailments,but others may be seriously harmful. Inaddition to their natural chemical con-stituents, many plants bioconcentratechemicals—some of them potentiallyharmful, such as heavy metals—from thesurrounding environment. (This is thebasis for their potential usefulness for phy-toremediation; see “The Science Behindthe Story: Letting Plants Do the DirtyWork,”).

When we use plants as herbal reme-dies, we risk ingesting these harmfulchemicals.Yet herbal remedies are poorlycontrolled in comparison with syntheticpharmaceuticals. There are wide varia-tions in the chemical compositions of theplants used in various herbal mixtures,and gaps in the scientific understanding ofhow plants concentrate certain elements.One of the projects in Dr. Saxena’s labinvolves technologies for growing plantsin vitro (that is, in test tubes), so theirchemical characteristics can be moreclosely monitored and controlled, andtheir use as medicines rendered safer.

Dr. Saxena is also a plant conserva-tionist. He is particularly interested in theconservation of unique, rare, and endan-gered medicinal, ornamental, and foodcrop plants. One of his main interests is inbreadfruit, a nutritious food crop that isimportant in traditional agro-forestry sys-tems in many parts of the world. A num-

ber of breadfruit cultivars (• p. XXX) arebecoming rare and endangered as a resultof cultural and environmental changes.Dr. Saxena and his colleagues have devel-oped techniques for the in vitro conser-vation and multiplication of breadfruitcultivars.This technology has the potentialto promote sustainable agriculture andfood security in the tropics, where bread-fruit is a multipurpose life-supportingcrop. The scientists hope to extend theirwork on breadfruit to other importantfood and medicinal crops.3

“Plants have been used since ancienttimes to heal and cure disease, yet onlynow are they being grown in controlledconditions and measured for how muchmedicine they actually contain.” —Praveen Saxena

Thinking AboutEnvironmental PerspectivesWe tend to think of herbal medicines asbeing “natural,” or inherently safe. However,as Dr. Saxena points out, this is not alwaysthe case. Herbal remedies are much lessactively studied, screened, regulated, andmonitored than conventional pharma-ceuticals. Do you think herbal remediesshould be more tightly regulated? Howmight scientific research such as that ofDr. Saxena and his colleagues contributeto the safety of herbal medicines?

REVIEWING OBJECTIVES

You should now be able to:

Explain the fundamentals of chemistry and apply themto real-world environmental situations

■ Understanding chemistry provides a powerful toolfor developing solutions to many environmentalproblems.

■ Atoms form molecules, and changes at the atomiclevel can result in alternative forms of elements, suchas ions and isotopes.

■ Characteristics of the water molecule help facilitatelife.

■ Living things depend on organic compounds, whichare carbon based.

Describe the molecular building blocks of livingorganisms

■ Proteins, nucleic acids, carbohydrates, and lipids arekey building blocks of life.

■ Organisms use cells to compartmentalize their com-ponent parts.

Differentiate among the types of energy and recite thebasics of energy flow

■ Energy can be either potential (stored energy, orenergy of position) or kinetic (energy of motion).Chemical energy is an example of potential energystored in the bonds between atoms.


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■ The total amount of energy in the universe is con-served; energy cannot be created or destroyed.

■ Systems tend to increase in entropy, or disorder,unless energy is added to build or maintain order andcomplexity.

■ Earth’s systems are powered mainly by radiationfrom the Sun, as well as by geothermal heating fromthe planet’s core, and by tidal interactions amongEarth, the Sun, and the Moon.

Distinguish photosynthesis, respiration, and chemosyn-thesis, and summarize their importance to living things

■ In photosynthesis, autotrophs use carbon dioxide,water, and solar energy to produce the sugars theyneed, as well as oxygen.

■ In respiration, organisms extract energy from sugarsby converting them in the presence of oxygen intocarbon dioxide and water.

■ In chemosynthesis, specialized autotrophs use carbondioxide, water, and chemical energy from minerals toproduce the sugars they need.

Itemize and evaluate the major hypotheses for the originof life on Earth

■ The heterotrophic hypothesis proposes that life arosefrom chemical reactions in surface or shallow watersof the ocean.

■ The panspermia hypothesis proposes that substancesneeded for life’s origin on Earth arrived from space.

■ The chemoautotrophic hypothesis proposes thatlife arose from chemical reactions near deep-seahydrothermal vents.

Outline our knowledge regarding early life and givesupporting evidence for each major concept

■ The fossil record has revealed many patterns in thehistory of life, including that species evolve, mostspecies are extinct, and species numbers on Earthhave increased.

■ By comparing modern-day organisms scientists caninfer genetic relationships among them and under-stand their evolutionary history.

TESTING YOUR COMPREHENSION

1. What are the basic building blocks of matter? Provideexamples by using chemicals common in livingorganisms.

2. Name four ways in which the chemical nature of thewater molecule facilitates life.

3. What is a redox reaction? Give an example of a redoxreaction that occurs in nature.

4. What are the three classes of biological polymers, andwhat are their functions?

5. Describe the two major forms of energy, and giveexamples of each.

6. State the first law of thermodynamics, and describesome of its implications.

7. What are the three major sources of energy thatpower Earth’s environmental systems?

8. What substances are produced by photosynthesis?By cellular respiration? By chemosynthesis?

9. Compare and contrast three competing hypothesesfor the origin of life.

10. Name three things scientists have learned from thefossil record.

SEEKING SOLUTIONS

1. Under what types of conditions might bioremediationbe a successful strategy, and when might it not be?

2. Can you think of an example of an environmentalproblem not mentioned in this chapter that a goodknowledge of chemistry could help us solve?

3. Describe an example of energy transformation fromone form to another that is not mentioned in thischapter.

4. Give three examples of ways in which the input ofenergy can impede the tendency toward disorder thatthe second law of thermodynamics describes.

5. Referring to the chemical reactions for photosynthe-sis and respiration, provide an argument for whyincreasing amounts of carbon dioxide in the atmos-phere because of global climate change might poten-tially increase amounts of oxygen in the atmosphere.Give an argument for why it might potentiallydecrease amounts of atmospheric oxygen. Whatwould you need to know to determine which of thesetwo outcomes might occur?

6. THINK IT THROUGH The ministry of the environ-ment has put you in charge of cleaning up an old



industrial site so that it meets safety standards anddoes not contaminate drinking water supplies. Yourstaff ’s initial inspection of surface soil at the siteshows that it is contaminated with oil and with lead,a toxic heavy metal. Your job allows you to engageexperts in bioremediation and phytoremediation atlocal universities, as well as environmental engineers

in the private sector. You have a budget of several mil-lion dollars and five years to get the job done. Whatsteps will you take to get the site cleaned up? Describescientific research you would commission, economicquestions you would ask, and engineering optionsyou might consider.

INTERPRETING GRAPHS AND DATA

In phytoremediation, plants are used to clean up soil orwater contaminated by heavy metals, such as lead (Pb),arsenic (As), zinc (Zn), and cadmium (Cd). For plants toabsorb these metals from soil, the metals must be dissolvedin soil water. For any given instance, all metal can beaccounted for as either remaining bound to soil particles,being dissolved in soil water, or being stored in the plant.

In a study on the effectiveness of alpine penny-cress(Thlaspi caerulescens) for phytoremediation, Enzo Lombiand his colleagues grew crops of this small perennial plantfor approximately one year in pots of soil from contami-nated sites. They then measured the amount of zinc andcadmium in the soil and in the plants when they wereharvested.

1. What were the zinc and cadmium concentrations inthe soil prior to phytoremediation? What were thezinc and cadmium concentrations in the soil afterone year of phytoremediation?

2. How much zinc and cadmium were removed fromthe soil? If the plants continued to remove zinc andcadmium from the soil at the rates shown above,approximately how long would it take to remove allthe zinc and cadmium?

3. Alpine penny-cress is one of many plants that pro-duce natural chelating agents (see “The Science

Behind the Story: Letting Plants Do the DirtyWork,” that increase the solubility of metals in soilwater. If these dissolved metals were not subse-quently taken up by the plants, what might be anunintended consequence of having increased theirsolubility?

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0Zinc Cadmium

Removal of zinc and cadmium from contaminated soil by alpine penny-cress, Thlaspi caerulescens. Data from Lombi, E., et al. 2001.Phytoremediation of heavy metal-contaminated soils: naturalhyperaccumulation versus chemically enhanced phytoextraction.Journal of Environmental Quality 30:1919–1926.

CALCULATING FOOTPRINTS

In ecological systems, a rough rule of thumb is that whenenergy is transferred from plants to plant-eaters or fromprey to predator, the efficiency is only about 10%. Muchof this inefficiency is a consequence of the second law ofthermodynamics. Another way to think of this is that eat-ing 10 calories of plant material is the ecological equiva-lent of eating one calorie of material from an animal.

Humans are considered omnivores because we caneat both plants and animals. The choices we make aboutwhat to eat have significant ecological impacts. With this

in mind, calculate the ecological energy requirements forfour different diets, each of which provides a total of 2000dietary calories per day.

1. How many ecologically equivalent calories would ittake to support you for a year on each of the fourdiets listed?

2. What is the relative ecological impact of including aslittle as 10% of your calories from animal sources(e.g., milk, dairy products, eggs, and meat)? What is



the ecological impact of a strictly carnivorous dietcompared with a strict vegetarian diet?

3. What percentages of the calories in your own diet doyou think come from plant versus animal sources?Estimate the ecological impact of your diet, relativeto a strictly vegetarian one.

4. Describe some challenges of providing food for thegrowing human population, especially as people inmany poorer nations develop a taste for anAmerican-style diet rich in animal protein and fat.

Number of Calories Ecologically Total Ecologically Source of Consumed Equivalent Equivalent

Diet Calories By Source Calories By Source Calories Per Day

100% plant Plant 0.00

0% animal Animal

90% plant Plant 1800 1800 3800

10% animal Animal 200 2000

50% plant Plant

50% animal Animal

0% plant Plant

100% animal Animal

TAKE IT FURTHER

Go to www.pearsoned.ca/withgott where you willfind

■ Suggested answers to end-of-chapter questions■ Quizzes, animations, and flashcards to help you study■ Research NavigatorTM database of credible and reli-

able sources to assist you with your research projects■ Tutorials to help you master how to interpret graphs■ Current news articles that link the topics that you

study to case studies from your region and aroundthe world

■ ECO Occupational Profiles: If you found this chap-ter especially interesting, you might want to learnmore about the following jobs by visiting theOccupational Profiles website of the EnvironmentalCareers Organization. Go to www.eco.ca and checkout the following careers:■ Analytical chemist■ Biochemist■ Chemical technician■ Environmental chemist■ Microbiologist

CHAPTER ENDNOTES

1. Pavilion Lake Research Project: Relevance toAstrobiology and Space Exploration, www.pavilionlake.com.

2. Based on Fragrant Geraniums Clean Pollutants fromSoil, www.carleton.ca/jmc/cnews/30031998/story1.html

3. University of Guelph, Department of Plant Agriculture,www.plant.uoguelph.ca/faculty/psaxena/, and PlantCell Technology Laboratory, www.plant.uoguelph.ca/research/cellculture/index.html, among othersources.


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