Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint ® Lecture Slides for Essential Biology, Second Edition & Essential Biology with Physiology Neil Campbell, Jane Reece, and Eric Simon Presentation prepared by Chris C. Romero CHAPTER 2 Essential Chemistry for Biology Figures 2.1 – 2.7

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Rain in the eastern United States can be more acidic than vinegar About 65% of your weight is oxygen atoms

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Because of surface tension, some insects can walk on water The iron in a multivitamin pill is the same element as the iron in a train or ship

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings There has been a sharp decline in tooth decay in the last few decades BIOLOGY AND SOCIETY: FLUORIDE IN THE WATER –Fluoride-containing chemicals have been added to drinking water and dental products The use of fluoride in drinking water illustrates the point that organisms are chemical systems

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Biology includes the study of life at many levels TRACING LIFE DOWN TO THE CHEMICAL LEVEL In order to understand life, we will start at the macroscopic level, the ecosystem, and work our way down to the microscopic level of cells Cells consist of enormous numbers of chemicals that give the cell the properties we recognize as life

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 2.1 Ecosystem African savanna Community All organisms in savanna Population Herd of zebras Organism Zebra Organ system Circulatory system Organ Heart Cell Heart muscle cell Tissue Heart muscle tissue Molecule DNA Atom Oxygen atom

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Take any biological system apart and you eventually end up at the chemical level SOME BASIC CHEMISTRY

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Matter is anything that occupies space and has mass Matter: Elements and Compounds Matter is found on the Earth in three physical states –Solid –Liquid –Gas

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Matter is composed of chemical elements –Elements are substances that cannot be broken down into other substances –There are 92 naturally occurring elements on Earth

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings All the elements are listed in the periodic table Atomic number Element symbol Mass number Figure 2.2

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Twenty-five elements are essential to life –Four of these make up about 96% of the weight of the human body –Trace elements occur in smaller amounts Figure 2.3

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Trace elements are essential for life –An iodine deficiency causes goiter Figure 2.4

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Elements can combine to form compounds –These are substances that contain two or more elements in a fixed ratio –Example: NaCl (salt)

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Each element consists of one kind of atom Atoms –An atom is the smallest unit of matter that still retains the properties of an element Nucleus Cloud of negative charge (2 electrons) (a) (b) 2Protons 2 Neutrons 2 Electrons Figure 2.5

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Atoms are composed of subatomic particles The Structure of Atoms –A proton is positively charged –An electron is negatively charged –A neutron is electrically neutral

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Most atoms have protons and neutrons packed tightly into the nucleus –The nucleus is the atom’s central core –The electrons orbit the nucleus

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Elements differ in the number of subatomic particles in their atoms –The number of protons, the atomic number, determines which element it is –An atom’s mass number is the sum of the number of protons and neutrons –Mass is a measure of the amount of matter in an object

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Isotopes are alternate mass forms of an element Isotopes –They have the same number of protons and electrons –But they have a different number of neutrons Table 2.1

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Radioactive isotopes –The nucleus decays, giving off particles and energy Radioactive isotopes have many uses in research and medicine –Example: PET scans

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 2.6 Hearing words Seeing words Speaking words Generating words (b) (a)

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA –Example: the 1999 Tokaimura nuclear accident

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Electrons determine how an atom behaves when it encounters other atoms Electron Arrangement and the Chemical Properties of Atoms Electrons orbit the nucleus of an atom in specific electron shells –The number of electrons in the outermost shell determines the chemical properties of an atom

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Atoms of the four elements most abundant in life Figure 2.7 Electron First electron shell (can hold 2 electrons) Outermost electron shell (can hold 8 electrons) Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Hydrogen (H) Atomic number = 1

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells Chemical Bonding and Molecules –These interactions usually result in atoms staying close together –The atoms are held together by chemical bonds

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings When an atom loses or gains electrons, it becomes electrically charged Ionic Bonds –Charged atoms are called ions –Ionic bonds are formed between oppositely charged ions Figure 2.8 Sodium atom (Na)Chlorine atom (Cl) Complete outer shells Sodium ion (Na  )Chloride ion (Cl  ) Sodium chloride (NaCl)

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings A covalent bond forms when two atoms share one or more pairs of outer-shell electrons Covalent Bonds Figure 2.9

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones Chemical Reactions –Such changes in the chemical composition of matter are called chemical reactions Unnumbered Figure 2.1 Hydrogen gasOxygen gasWater Reactants Products

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Chemical reactions can be symbolized with equations –On the left side of the equation are the reactants, the starting materials –On the right side of the equation are the products, the end materials

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Chemical reactions cannot create or destroy matter –They only rearrange it

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Life on Earth began in water and evolved there for 3 billion years WATER AND LIFE –Modern life still remains tied to water –Your cells are composed of 70%–95% water

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The abundance of water is a major reason Earth is habitable Figure 2.10

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Studied in isolation, the water molecule is deceptively simple The Structure of Water –Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds Unnumbered Figure 2.2 H O H

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen –This unequal sharing makes water a polar molecule ()()()() ()()()() Figure 2.11a

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The polarity of water results in weak electrical attractions between neighboring water molecules –These interactions are called hydrogen bonds (b) ()() Hydrogen bond ()() ()() ()() ()() ()() ()() ()() Figure 2.11b

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The polarity of water molecules and the hydrogen bonding that results explain most of water’s life- supporting properties Water’s Life-Supporting Properties –Water’s cohesive nature –Water’s ability to moderate temperature –Floating ice –Versatility of water as a solvent

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Water molecules stick together as a result of hydrogen bonding The Cohesion of Water –This is called cohesion –Cohesion is vital for water transport in plants Figure 2.12 Microscopic tubes

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid –Hydrogen bonds give water an unusually high surface tension Figure 2.13

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Because of hydrogen bonding, water has a strong resistance to temperature change How Water Moderates Temperature

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Heat and temperature are related, but different –Heat is the amount of energy associated with the movement of the atoms and molecules in a body of matter –Temperature measures the intensity of heat Water can absorb and store large amounts of heat while only changing a few degrees in temperature

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Water can moderate temperatures –Earth’s giant water supply causes temperatures to stay within limits that permit life –Evaporative cooling removes heat from the Earth and from organisms Figure 2.14

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings When water molecules get cold, they move apart, forming ice The Biological Significance of Ice Floating –A chunk of ice has fewer molecules than an equal volume of liquid water

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The density of ice is lower than liquid water –This is why ice floats Figure 2.15 Hydrogen bond Liquid water Hydrogen bonds constantly break and re-form Ice Stable hydrogen bonds

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Since ice floats, ponds, lakes, and even the oceans do not freeze solid –Marine life could not survive if bodies of water froze solid

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings A solution is a liquid consisting of two or more substances evenly mixed Water as the Solvent of Life –The dissolving agent is called the solvent –The dissolved substance is called the solute Figure 2.16 Ion in solution Salt crystal

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings When water is the solvent, the result is called an aqueous solution

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Acid Acids, Bases, and pH –A chemical compound that donates H + ions to solutions Base –A compound that accepts H + ions and removes them from solution

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Basic solution Neutral solution Acidic solution Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Human blood Pure water Urine Tomato juice Grapefruit juice Lemon juice; gastric juice pH scale To describe the acidity of a solution, we use the pH scale Figure 2.17

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Buffers are substances that resist pH change –They accept H + ions when they are in excess –They donate H + ions when they are depleted Buffering is not foolproof –Example: acid precipitation Figure 2.18

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Atoms SUMMARY OF KEY CONCEPTS Visual Summary 2.1 Proton  Positive charge  Determines element Neutron  No charge  Determines isotope Electron  Negative charge Participates in chemical reactions Outer-shell electrons determine chemical behavior Nucleus Consists of neutrons and protons

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The Structure of Water Visual Summary 2.2 Hydrogen bond ()() ()() ()() ()() ()() ()() ()() ()()

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Acids, Bases, and pH Visual Summary 2.3 Basic Neutral [H  ] = [OH  ] Acidic Lower H  concentration Greater H  concentration