Chapter 2 Essential Chemistry for Biology Power Point
Chapter 2 Essential Chemistry for Biology Power. Point® Lectures created by Edward J. Zalisko for Campbell Essential Biology, Sixth Edition, and Campbell Essential Biology with Physiology, Fifth Edition – Eric J. Simon, Jean L. Dickey, Kelly A. Hogan, and Jane B. Reece © 2016 Pearson Education, Inc.
Why Chemistry Matters Copper (essential element) Table salt Lemon juice
Chapter Thread: Radioactivity Figure 2. 0 -2 Radioactivity: pros and cons of radiation © 2016 Pearson Education, Inc.
Biology and Society: Radiation and Health • Radioactivity, the emission of high-energy particles, can • penetrate living tissues and • kill cells by damaging DNA. • Radiation is most dangerous when exposure is • uncontrolled and • covers most or all of the body, such as when a person is exposed to radioactive fallout from a nuclear detonation or accident. © 2016 Pearson Education, Inc.
Biology and Society: Radiation and Health • Radiation can also be medically beneficial, helping to treat cancer. • Controlled medical radiation therapy exposes only a small part of the body to a precise dosage of radiation. • This provides a large and deadly dose to cancerous cells but mostly spares surrounding healthy tissues. What makes something radioactive? • Many questions about life can be reduced to questions about chemicals and their interactions. • Knowledge of chemistry is therefore essential to understanding biology. © 2016 Pearson Education, Inc.
Some Basic Chemistry • Take any biological system apart, and you eventually end up at the chemical level. • Chemical reactions are always occurring in the human body. © 2016 Pearson Education, Inc.
Matter: Elements and Compounds • Matter is anything that occupies space and has mass. – found on Earth in three physical states: Solid, Liquid and Gas © 2013 Pearson Education, Inc.
Matter: Elements and Compounds • Matter is composed of chemical elements: • An element is a substance that cannot be broken down into other substances. • There are 92 naturally occurring elements on Earth • All of the elements are listed in the periodic table • Twenty-five are essential to life. • Four make up about 96% of the weight of the human body • CHON: Carbon (C), Hydrogen (H), Oxygen (O) and Nitrogen (N) • Each element has a symbol derived from its English, Latin, or German name.
Mercury (Hg) Copper (Cu) Lead (Pb) Figure 2. 1 -3 Abbreviated periodic table of the elements © 2016 Pearson Education, Inc.
Chemical composition of the human body by weight Carbon (C): 18. 5% Oxygen (O): 65. 0% Minor elements: around 4% Calcium (Ca): 1. 5% Phosphorus (P): 1. 0% Potassium (K): 0. 4% Sulfur (S): 0. 3% Sodium (Na): 0. 2% Chlorine (Cl): 0. 2% Hydrogen (H): 9. 5% Nitrogen (N): 3. 3% Magnesium (Mg): 0. 1% Trace elements: less than 0. 01% Boron (B) Chromium (Cr) Cobalt (Co) Copper (Cu) Fluorine (F) Iodine (I) Iron (Fe) Manganese (Mn) Molybdenum (Mo) Selenium (Se) Silicon (Si) Tin (Sn) Vanadium (V) Zinc (Zn) Figure 2. 2
Minor & Trace elements • Much of the remaining 4% is accounted for by 7 elements. These include the following. Calcium Minor elements Ca Phosphorus Iodine Trace elements Fluorine - building strong bones and teeth - found abundantly in milk & dairy products, sardines, green & leafy vegetables - component of DNA - found in eggs, beans and nuts Essential ingredient of thyroid hormone Found in dairy products Deficiency leads to goiter Needed for healthy bones and teeth
Matter: Elements and Compounds • Trace elements (less than 1%) • are required in only very small amounts and • are essential for life. • An iodine deficiency causes goiter. • Fluorine • is added to dental products and drinking water and • helps to maintain healthy bones and teeth. © 2013 Pearson Education, Inc.
Hyper functioning thyroid (goiter) Figure 2. 3 The relationship between diet and goiter
Matter: Elements, Atoms and Compounds • Each element consists of one kind of atom. • An atom is the smallest unit of matter that still retains the properties of an element. • Elements can combine to form compounds, which are substances that contain two or more elements in a fixed ratio. • Common compounds include • Na. Cl (table salt) and • H 2 O (water). © 2013 Pearson Education, Inc.
Periodic table of the elements Atomic number (number of protons) 6 C Element symbol Mass number (number of protons plus neutrons) 12 H He Li Be B Na Mg Al Si P C N O F Ne S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Figure 2. 1 a
Periodic table of the elements
The Structure of Atoms • Atoms are composed of three subatomic particles • A proton is positively charged, • - An element is defined by its number of protons • A neutron is electrically neutral • - Neutrons can vary between isotopes • An electron is negatively charged • When an atom has an equal number of protons and electrons, • its net electrical charge is zero and • the atom is neutral. © 2013 Pearson Education, Inc.
Two simplified models of a Helium atom 2 Nucleus Protons 2 Neutrons 2 Electrons Nucleus 2 e– Electron cloud containing two electrons
The Structure of Atoms • Most atoms have protons and neutrons packed tightly into the nucleus. • The nucleus is the atom’s central core. • Electrons orbit the nucleus. Electron shell or Electron energy level © 2013 Pearson Education, Inc.
Structure of an atom Protons • Positive charge • Determine element Neutrons • No charge • Determine isotope © 2016 Pearson Education, Inc. Atom Electrons • Negative charge • Participate in chemical reactions • Outer-shell electrons determine chemical behavior Nucleus • Consists of neutrons and protons
Atomic and mass number • All atoms of a particular element have the same unique number of protons. • This number is the element’s atomic number. - Thus, an atom of helium, with 2 protons, has an atomic number of 2, and No other element has 2 protons. • The periodic table lists elements in order of atomic number (also the number of electrons) • An atom’s mass number is the sum of the number of protons and neutrons in its nucleus. - for an atom of helium, with 2 protons, and 2 electrons its mass number is 4 © 2016 Pearson Education, Inc.
Isotopes • Isotopes are alternate mass forms of an element. – Isotopes have the same number of protons and electrons, – but they have a different number of neutrons.
Radioactive Isotope • A radioactive isotope is one in which the nucleus decays spontaneously. • Radiation from decaying isotopes can • damage cellular molecules and • pose serious health risks. • Natural sources of radiation can also pose a threat. • The 1986 Chernobyl nuclear accident released large amounts of radioactive isotopes. • Radon, a radioactive gas, is a carcinogen that can cause lung cancer. • Radon testing is a standard procedure before a house is bought or sold.
Practice 1. Ordinary oxygen has an atomic mass of 16 and an atomic number of 8. How many neutrons does this type of oxygen have? 2. Phosphorous has an atomic number of 15 and an atomic weight of 30. 974. How many neutrons does this type of oxygen have? 3. Silicon has an atomic number of 14 and a mass number of 28. How many neutrons are found in silicon?
Electron Arrangement and the Chemical Properties of Atoms • Of the three subatomic particles, only electrons are directly involved in the chemical activity of an atom. • Electrons orbit the nucleus of an atom in specific electron shells. • The farther an electron is from the nucleus, the greater its energy. • The number of electrons in the outermost shell (valance) determines the chemical properties of an atom. • Valance electrons determine how an atom • behaves when it encounter other atoms
Atoms of the four elements most abundant in living matter Electron First electron shell (can hold 2 electrons) Hydrogen (H) Atomic number 1 How many electrons can each orbital hold? Outer electron shell (can hold 8 electrons) Carbon (C) Atomic number 6 Nitrogen (N) Atomic number 7 Oxygen (O) Atomic number 8 Figure 2. 6 The rule really is to fill one level before you move to the next level
Practice 1. By definition all atoms of carbon have exactly six _______ , but the number of _______ varies from one isotope to another. 2. As two atoms approach each other, which subatomic particles will first come into contacts?
Chemical Bonding and Molecules • In chemical reactivity, atoms tend to - complete a partially filled valence or empty a partially filled valence • Chemical reactions enable atoms to give up or acquire electrons, in order to complete their outer shells. • Chemical reactions usually result in atoms staying close together and being held together by attractions called chemical bonds. • EIGHT is GREAT. Will steal or share electrons to get eight valance electrons © 2013 Pearson Education, Inc.
Chemical bonding between atoms Ionic bonds are attractions between ions of opposite charge – steal electrons from other = Unequal attraction Covalent bonds are formed when atoms share electrons – Non polar covalent bonds = Equal attraction; ie: H 2 – Polar covalent bonds = Assymetric attraction; ie: HO 2 Hydrogen bonds form between a positively charged hydrogen atom and any other negatively charged atom van der Waals interactions form between negatively charged and positively charged regions in molecules.
Ionic Bonds When an atom loses or gains electrons, it becomes electrically charged. • Ions are atoms or molecules that are electrically charged as a result of gaining or losing electrons • Ionic bonds are formed between oppositely charged ions. • steal electrons from other = Unequal attraction • Table salt = ionic compounds are held together by ionic bonds Outer shell has 1 electron The outer electron is stripped from sodium and completes the chlorine atom’s outer shell Outer shell has 7 electrons Na Sodium atom Cl Chlorine atom Figure 2. 7 Electron transfer and ionic bonding Complete outer shells Na Sodium ion Cl Chlorine ion Sodium chloride (Na. Cl) The attraction between the ions—an ionic bond—holds them together
Animation: Ionic Bonds © 2016 Pearson Education, Inc.
Calcium chloride molecule is an ionic compound formed by an ionic bond between calcium ion and two chloride ions.
Covalent Bonds • A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. – Non polar covalent bonds = Equal attraction (H 2) – Polar covalent bonds = Asymmetric attraction (HO 2 • Covalent bonds are the strongest of the various bonds. • Covalent bonds hold atoms together in a molecule. • The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell. © 2013 Pearson Education, Inc.
Animation: Covalent Bonds © 2016 Pearson Education, Inc.
Common ways to represent molecules Electron configuration Structural formula Space-filling model Ball-and-stick model H H Hydrogen gas (H 2) O O Oxygen gas (O 2) Double bounds H H C H H Methane (CH 4) Overlapping of orbitals/No + or – charges Figure 2. 8
Electron configuration Structural formula O O Double bond C C H H Single bond Space-filling model H H Name (molecular formula) : Formaldehyde (CH 2 O) © 2016 Pearson Education, Inc. Ball-and-stick model
Hydrogen Bonds • A molecule of water (H 2 O) consists of two hydrogen atoms joined to one oxygen atom by single covalent bonds, • Water is a compound in which the electrons in its covalent bonds are shared unequally - This causes water to be a polar molecule (uneven distribution of charge), one with opposite charges on opposite ends (+ poles versus - poles) - Oxygen has stronger “attraction” for the electrons than hydrogen and therefore “higher electronegativity” slightly H H O slightly –
Animation: Water Structure © 2016 Pearson Education, Inc.
Hydrogen Bonds • The polarity of water results in weak electrical attractions between neighboring water molecules. - These interactions are called hydrogen bonds. Hydrogen bond Figure 2. 8 Hydrogen bonding in water
Practice What happens when the outermost electron shell of an element such as neon contains the maximum number of eight electrons? a. It becomes extremely unstable and reactive b. It becomes stable and inert c. It forms covalent bonds in an aqueous solution An atom with an unfilled outer shell is a. b. c. d. extremely unreactive likely to bond with another atom unable to bond with another atom polar
Practice The number of protons of an atom of an element determines its a. weight b. isotopic status c. mass number d. tendency to form ionic bonds e. atomic number Fluorine’s atomic number is 9 and its mass number is 19. which of the following is true of fluorine? a. It contains 9 protons and 10 neutrons b. It contains 19 protons and 9 neutrons c. It has no net charge when it has 19 electrons d. It contains 9 protons and 19 neutrons e. It is lighter than helium
Chemical Reactions • Chemical reactions occurs when: ü One substance combine with another ü One substance is broken down into another ü Chemical bonds are broken and other bonds form • Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones. ü Such changes in the chemical composition of matter are called chemical reactions. ü Reaction between oxygen gas & hydrogen gas that forms water. • Chemical reactions include ü reactants, the starting materials, and ü products, the end materials. • Chemical reactions ü can rearrange matter ü but cannot create or destroy matter.
Water: The Molecule That Supports All of Life • Water is the biological medium on Earth - Life on Earth began in water and evolved there for 3 billion years before spreading onto land • The abundance of water is the main reason Earth is habitable • All living organisms require water more than any other substance • Most cells are surrounded by water, and cells themselves are about 70– 95% water • Water is the only common substance in the natural environment that exists in all three physical states of matter: solid, liquid, and gas. • Water is a reactant in many of the chemical reactions of life.
A watery world Figure 2. 10
Figure 2. UN 03 2 Hydrogen gas + O 2 2 H 2 O Oxygen gas Water Reactants Products
Structure/Function: Water • The polarity of water molecules and the hydrogen bonding that results explain most of water’s life-supporting properties. • We will explore four of those properties: a) the cohesive nature of water, b) the ability of water to moderate temperature (strong resistance to change in temperature. ), c) the biological significance of ice floating (Frozen water floats), and d) the versatility of water as a solvent. © 2016 Pearsn Education, Inc.
The Cohesion of Water • Because of small size, bent shape and polarity, Water molecules stick together as a result of hydrogen bonding Evaporation from the leaves • This tendency of molecules of the same kind to stick together is called Cohesion Microscopic waterconducting tubes fw Colorized SEM Flo wo • Cohesion is vital for the transport of water from the roots to the leaves of plants. ater Cohesion due to hydrogen bonds between water molecules
Animation: Water Transport © 2016 Pearson Education, Inc.
The Cohesion of Water • Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid. – Hydrogen bonds give water unusually high surface tension and make water behave as though it were coated with an invisible film. Figure 2. 12 © 2013 Pearson Education, Inc.
2. How Water Moderates Temperature • Because of hydrogen bonds water has a strong resistance to temperature change than most other substances. • 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. • When water is heated, the heat energy i. first disrupts hydrogen bonds and ii. then makes water molecules jostle around faster. • Because heat is first used to break hydrogen bonds rather than raise the temperature, water absorbs and stores a large amount of heat while warming up only a few degrees. • Conversely, when water cools, hydrogen bonds form, a process that releases heat.
2. How Water Moderates Temperature • Water can moderate temperatures. • Earth’s giant water supply causes temperatures to stay within limits that permit life by ü storing a huge amount of heat from the sun during warm periods and ü giving off heat that warms the air during cold periods. • Evaporative cooling occurs when a substance evaporates and the surface of the liquid remaining behind cools down • removes heat from Earth and from organisms
Evaporative cooling • When a substance evaporates by changing the physical state from a liquid to gas , the surface of the liquid remaining behind cools down. • The molecules with the greatest energy (hottest one) tend to vaporize first • Evaporative cooling removes heat from the Earth and from organisms. Figure 2. 12 Sweating as a mechanism of evaporative cooling
3. The Biological Significance of Ice Floating • When water molecules get cold enough, they move apart (the movement of its molecules slows), forming ice. - A chunk of ice has fewer molecules than an equal volume of liquid water. • Ice floats because it is less dense than the liquid water around it. - the water molecules are spaced out more than in liquid water • Oceans & lakes don’t freeze solid b/c surface insulates water below allowing life to survive the winter • If ice sank, ponds, lakes, & even oceans would freeze solid • Life in water could not survive if bodies of water froze solid.
Figure 2. 13 -1 Hydrogen bond Liquid water Hydrogen bonds constantly break and re-form. Ice Stable hydrogen bonds hold molecules apart, making ice less dense than water. Figure 2. 13 Why ice floats © 2016 Pearson Education, Inc.
4. Water as the Solvent of Life • A solution is a liquid consisting of a homogeneous mixture of two or more substances. ü The dissolving agent is the solvent (medium of for chemical reaction). ü The dissolved substance is the solute (table salt ). • When water is the solvent, the result is an aqueous solution • Water dissolve an enormous variety of solutes necessary for life. ü Hydrophilic substance dissolves in water, have attraction to water (polar molecules) ü Hydrophobic substance that don’t have an attraction to water (nonpolar molecules, oil and butter) • Water is the solvent inside all cells, in blood, and in plant sap. • When water dissolves salt ions, each ion becomes surrounded by oppositely charged regions of water molecules.
Polarity makes H 2 O a good solvent polar H 2 O molecules surround + & - ions Sodium ion in solution Chloride ion in solution Cl Na – Cl – Na Salt crystal Figure 2. 15
Practice Surface tension and capillary action occur in water because it a. has hydrogen bonds b. has ionic bonds c. is dense d. is nonpolar e. is wet In the reaction glucose + fructose sucrose + water, _____ is a reactant and _____ is a product.
Practice Why does ice float on water? a. Ice has a higher p. H than water b. Molecules of water are spaced father apart than molecules of ice c. Ice has a lower p. H than water d. Molecules of ice are spaced father apart than molecules of water Cocoa is mixed with hot water to make hot chocolate. The cocoa is the ______, the hot water is the _____, and the hot chocolate is the _____. a. b. c. d. e. solute ……. . . solvent ……… solution solvent ……. . … solution ……. . solute solution………. . . solvent ………. . . solute solvent ……. . … solute……… solution solute……. . . solution …. …. . solvent
Practice The hydrogen bond between two molecules arises because water is a. b. c. d. polar hydrophobic a liquid nonpolar Which of the following is not a property of water? a. b. c. d. e. polarity a good solvent cohesion nonpolarity store heat well
Practice Which of the following p. H values indicates a slightly acidic solution? a. b. c. d. e. 9 7 3 11 6. 5 H 2 SO 4 can ionize to yield two H+ ions and one H 2 SO 4 is a. b. c. d. e. molar an acid a base a solution a buffer ion.
Practice A basic solution contains a. b. c. d. more OH- ions than H+ ions the same number of OH- ions as H+ ions no OH- ions more H+ ions than OH- ions Which of the following has concentration of hydrogen ions? a. b. c. d. baking soda at p. H 9 Household ammoniac at p. H 11 human blood at p. H 7 black coffee at p. H 5 the greatest
Practice Which of these refers to atoms with the same atomic number but different atomic masses? a. b. c. d. e. these atoms are different elements these atoms have different numbers of elements these atoms are isomers these atoms are isotopes these atoms have different numbers of protons An ionic bond involves______. a. b. c. d. e. the sharing of a single pair of electrons an attraction between ions of opposite charge no atoms other than sodium and chlorine the unequal sharing of an electron pair water avoidance
Practice Which of these refers to atoms with the same atomic number but different atomic masses? a. b. c. d. e. these atoms are different elements these atoms have different numbers of elements these atoms are isomers these atoms are isotopes these atoms have different numbers of protons An ionic bond involves______. a. b. c. d. e. the sharing of a single pair of electrons an attraction between ions of opposite charge no atoms other than sodium and chlorine the unequal sharing of an electron pair water avoidance
Practice What determines the types of chemical reactions that an atom participates in ? a. b. c. d. e. its atomic mass the number of electrons in the innermost electron shell the number of electrons in the outermost electron shell the number of protons it contains its atomic number An unchanged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?
Practice The unequal sharing of electrons within a water molecule makes the water molecule _____. In a neutral solution the concentration of _____. a. hydrogen ions is equal to the concentration of hydroxide ions b. water molecules is less than the concentration of hydrogen ions c. hydrogen ions is less than the concentration of hydroxide ions d. water molecules is less than the concentration of hydroxide ions e. hydrogen ions is greater than the concentration of hydroxide ions
Practice Which of the following substance is a substance that resists changes in p. H? a. b. c. d. e. acid buffer base Solvent solution What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?
Acids, Bases, and p. H • To describe the acidity of a solution, chemists use the p. H scale, a measure of the hydrogen ion (H+) concentration in a solution. • The scale ranges from 0 (most acidic) to 14 (most basic) • Each p. H unit represents a tenfold change in the concentration of H+. OH− − OH−OH − OH H OH− H Basic solution 13 Lower H concentration • A compound that accepts H+ and removes them from solution is a base. Oven cleaner 12 Household bleach Household ammonia 11 Milk of magnesia 10 9 Seawater 8 OH− H H OH− − OH H − OH H Neutral solution H H OH− H H − OH H H Acidic solution Human blood [H ] [OH−] 7 Pure water 6 Urine Greater H concentration • A chemical compound that releases H+ to a solution is an acid. 14 5 4 Black coffee Tomato juice 3 Grapefruit juice, soft drink 2 Lemon juice, stomach acid Battery acid 1 0 p. H scale Figure 2. 17
Figure 2. 15 -1 OH OH H Basic solution © 2016 Pearson Education, Inc. OH H OH H H OH H H Neutral solution Acidic solution OH H H
Acids, Bases, and p. H • Biological fluids contain buffers which are substances that minimize changes in p. H (that resist p. H change). Buffers ü accept H+ when they are in excess and ü donate H+ when they are depleted. Buffers & Cellular regulation - p. H of cells must be kept at ~ 7 p. H affects shape of molecules affect function therefore p. H affects cellular function © 2013 Pearson Education, Inc.
• Increases in global CO 2 concentrations may lead to the acidification of the oceans and ecological disasters • When CO 2 dissolves in seawater, it reacts with water to form an carbonic acid, which ü lowers ocean p. H and ü can greatly change marine environments. CO 2 Carbon dioxide Figure 2. 16 Ocean acidification by atmospheric CO 2 © 2016 Pearson Education, Inc. CO 2 Carbon dioxide H 2 O H 2 CO 2 Water Carbonic acid
Evolution Connection: Radioactivity as an Evolutionary Clock • The natural process of radioactive decay can be used to obtain important data about the evolutionary history of life on Earth. • Fossils are reliable chronological records of life because we can determine their ages through radiometric dating, which is based on the decay of radioactive isotopes. • Carbon-14 üis present in trace amounts in the environment and üis a radioactive isotope with a half-life of 5, 700 years. © 2016 Pearson Education, Inc.
Evolution Connection: Radioactivity as an Evolutionary Clock • A living organism assimilates the different isotopes of an element in proportions that reflect their relative abundances in the environment. • A fossil’s age can be estimated by measuring the ratio of the two isotopes to learn how many half-life reductions have occurred since it died. • Using such techniques, scientists can üestimate the ages of fossils from around the world and üplace them in an ordered sequence called the fossil record. © 2016 Pearson Education, Inc.
100 Carbon-14 radioactivity (as % of living organism’s C-14 to C-12 ratio) Carbon-14 75 50 25 0 0 5. 7 11. 4 17. 1 22. 8 28. 5 34. 2 39. 9 45. 6 51. 3 Time (thousands of years) Figure 2. 17 Radiometric dating © 2016 Pearson Education, Inc. 100 75 50 25 0 0 5. 7 11. 4 17. 1 22. 8 28. 5 34. 2 39. 9 45. 6 51. 3 Time (thousands of years)
Figure 2. UN 05 Attraction between oppositely charged ions holds the ions in an ionic bond. Li F Lithium ion Fluoride ion Lithium fluoride (ionic compound) © 2016 Pearson Education, Inc.
Figure 2. UN 06 Electron sharing H O H Atoms joined into a molecule via covalent bonds © 2016 Pearson Education, Inc.
Figure 2. UN 07 ( ) Hydrogen bond ( ) H ( ) O H ( ) ( ) © 2016 Pearson Education, Inc. ( )
Figure 2. UN 11 F K Fluorine atom Potassium atom © 2016 Pearson Education, Inc.
The Process of Science: Can Radioactive Tracers Identify Brain Diseases? • Cells use radioactive isotopes the same way they use nonradioactive isotopes of the same element. • Once the cell takes up a radioactive isotope, the location and concentration of the isotope can be detected because of the radiation it emits. • This makes radioactive isotopes useful as tracers for monitoring living organisms. • A medical diagnostic tool called a PET scan works by detecting small amounts of radiation emitted by radioactive materials that were purposefully introduced into the body. • In 2012, researchers from a U. S. pharmaceutical company announced the results of a study that used PET scans to investigate Alzheimer’s disease.
The Process of Science: Can Radioactive Tracers Identify Brain Diseases? • Observation: brains of people with Alzheimer’s are often filled with clumps of a protein called amyloid • Question: Can these clumps be detected by a PET scan? • Hypothesis: PET scan would detect a molecule called florbetapir, which contains the radioactive isotope fluorine 18, after it binds to amyloid deposits in living patients • Prediction: using florbetapir during PET scans could help with diagnosis and thereby improve disease management.
The Process of Science: Can Radioactive Tracers Identify Brain Diseases? • Experiment involved using the radioactive isotope and PET scans to test 229 patients who had been diagnosed with mental decline. • Results indicated that 113 patients showed amyloid deposits in their PET scans. As a result, • doctors changed the diagnosis in 55% of the patients and • the PET scan data led to changes in treatment (such as different drugs) in 87% of cases.
Figure 2. 5 © 2016 Pearson Education, Inc.
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