Ch 4. Copyright C Pearson Education, Inc., publishing as Benjamin Cummings 1. This lecture will help you understand: From Chemistry to Energy to Life

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1 This lecture will help you understand: Ch 4 From Chemistry to Energy to Life Part 1: Foundations of Environmental Science PowerPoint Slides prepared by Jay Withgott and Heidi Marcum The fundamentals of environmental chemistry The molecular building blocks of organisms Energy and energy flow Photosynthesis, respiration, and chemosynthesis Major hypotheses for life s origins Our knowledge of early life Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Central Case: Bioremediation of the Exxon Valdez Oil Spill In 1989, 11 million gallons coated the Alaskan coastline - The largest spill in U.S. history Defiled the pristine environment Tourism plummeted and jobs were lost Bioremediation= pollution cleanup through enhanced natural biodegradation Chemistry is crucial for understanding: How gases contribute to global climate change How pollutants cause acid rain The effects on health of wildlife and people Water pollution Wastewater treatment Atmospheric ozone depletion Energy issues Chemical building blocks Matter = all material in the universe that has mass and occupies space - Can be transformed from one type of substance into others - But it cannot be destroyed or created which is - The law of conservation of matter - Helps us understand that the amount of matter stays constant - It is recycled in nutrient cycles and ecosystems Chemical building blocks Element = a fundamental type of matter, with a given set of properties - Atoms = the smallest components that maintain an element s chemical properties - The atom s nucleus has protons (positively charged particles) and neutrons (particles lacking electric charge) - Atomic number = the defined number of protons - Electrons = negatively charged particles surrounding the nucleus - Balances the positively charged protons publishing as Benjamin Cummings 1

2 Structure of the Atom Atoms have a specific arrangement nucleus small dense region in the center of an atom that contains protons and neutrons Electrons Surround the nucleus and are in constant motion The nucleus is a very small part of the atom If it were the size of a marble, the atom would fill a football stadium The Atomic Nucleus Protons and Neutrons are bound together to form the nucleus of the atom Electrons Electrons are in constant motion in space surrounding the nucleus Atoms are Neutral Atoms have equal numbers of protons and electrons and are neutral in charge Atomic Number Atomic number the number of protons in an atom of an element C 6 ex: Carbon s atomic number is 6 Each atom of carbon has 6 protons and consequently 6 electrons Atomic Mass (Atomic weight) Atomic mass the sum of the protons and neutrons in an atom C How many neutrons in this atom? 6 publishing as Benjamin Cummings 2

3 N 14 7 How many protons? 7 How many neutrons? 7 How many electrons? 7 P What is the atomic number? 15 How many protons? 15 How many neutrons? 16 Why are some atomic mass numbers shown as fractions? Some atomic mass numbers are shown as fractions because they are an average of all the isotope ratios of an element OK so what s an isotope? Isotope Isotopes atoms of the same element that differ in the number of neutrons they contain because they have the same number of electrons, all isotopes of an element have the same chemical properties Isotopes of Carbon Radioactive Isotopes C 6 12 C 6 13 C 6 14 Carbon 12 has 6_ protons and 6_ neutrons Carbon 13 has _ 6 protons and 7_ neutrons Carbon 14 has 6_ protons and 8_ neutrons Nuclei are unstable and break down at a constant rate over time Radiation given off by these isotopes can be dangerous publishing as Benjamin Cummings 3

4 Radioactive Isotopes Important scientific uses Finding the age of rocks and fossils Cancer radiation treatments Irradiation of food to kill bacteria Used as labels or tracers to follow the movement of substances in organisms Chemical building blocks Isotopes = atoms with differing numbers of neutrons - Mass number = the combined number of protons and neutrons - Isotopes of an element behave differently - Some isotopes are radioactive and decay until they become nonradioactive stable isotopes - Emit high-energy radiation Radioactive decay Molecules & Compounds Half-life = the amount of time it takes for one-half of the atoms to give off radiation and decay - Different radioscopes have different half-lives ranging from fractions of a second to billions of years - Uranium-235, used in commercial nuclear power, has a half-life of 700 million years Atoms may also gain or lose electrons to become ions, electrically charged atoms Molecules = Combinations of two or more atoms - Oxygen gas = O 2 Compounds = A molecule composed of atoms of two or more different elements - Water = two hydrogen atoms bonded to one oxygen atom: H Carbon dioxide = one carbon atom with two oxygen atoms: CO2 Bonds Chemical Bonds Electrons determine chemical properties of elements Chemical reactions involve sharing or exchanging electrons publishing as Benjamin Cummings 4

5 Electron Energy Levels Nucleus K (first energy level) 4 Types of Chemical Bonds Ionic Covalent Van der Waals Hydrogen M (third energy level) Ionic Bonds Sodium and Chlorine become + _ Na Cl Sodium atom (Na) Chlorine atom (Cl) Bond formed when one or more electrons are transferred from one atom to another Sodium ion (Na + ) Chloride ion (Cl - ) Sodium chloride (NaCl) Covalent Bonds Form when electrons are shared between atoms in such a way that each atom has a completed outer shell of electrons Two electrons shared = single bond Four electrons shared = double bond H H Two Molecules of Hydrogen Each has one electron in its energy level publishing as Benjamin Cummings 5

6 H H Covalent Bonding Two molecules of Hydrogen Share electrons to form a single covalent bond Atoms are held together with bonds O O Molecule of Oxygen Double covalent bond Covalent bond = atoms in a molecule share electrons - For example, the atoms that bond to form H 2 0 Polar covalent bonds = Atoms share electrons unequally, with one atom exerting a greater pull - The oxygen in a water molecule attracts electrons Ionic bonds = an electron is transferred from one atom to another - Are not molecules, but are salts, such as table salt, NaCl Solutions = no chemical bonding, but is a mixture of substances (i.e., blood, oil) Water Molecule Polarity With 8 protons in its nucleus, oxygen has stronger attraction for electrons than hydrogen, with only one proton in its nucleus Water Molecule Polarity At any given time, there is a greater probability of finding shared electrons near the oxygen atom than near the hydrogen atom publishing as Benjamin Cummings 6

7 The Water Molecule The Water Molecule Another depiction Hydrogen Bonds Polarity causes the hydrogen atoms in one molecule to be attracted to the oxygen atoms in other polar molecules Attractive force creates a weak bond called a hydrogen bond Not as strong as covalent or ionic bonds, but strongest of bonds that form between molecules Hydrogen Bonds Cohesion A single water molecule may be involved in as many as four hydrogen bonds at the same time Cohesion Attraction between molecules of the same substance (like water) Allows insects to walk on water and water to bead up publishing as Benjamin Cummings 7

8 Adhesion An attraction between molecules of substances Water sticks to other things Responsible for capillary action Solutions & Suspensions A mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined Two types of mixtures with water Solution A mixture of two or more substances in which the molecules of the substances are evenly distributed Example: Salt in water Suspensions Mixture of water and nondissolved materials Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out Movement of water molecules keeps the small particles suspended Water: the main reason life can exist Additional properties of water Hydrogen bond = oxygen from one water molecule attracts hydrogen atoms of another Water s strong cohesion allows nutrients and waste to be transported Water absorbs heat with only small changes in its temperature, which stabilizes systems Less dense ice floats on liquid water Water dissolves other molecules publishing as Benjamin Cummings 8

9 ph ph is the measurement of the concentration of H + ions in a solution Ranges from 0-14 A substance with ph of 6 contains 10 times as many hydrogen ions as a substance with ph of 7 ph Acids - compounds which break into hydrogen (H + ) ions and another compound when placed in an aqueous solution ph of less than 7.0 Example: HCl, lemon juice, rain ph Bases - compounds which break up into Hydroxyl (OH - ) ions and another compound when placed in an aqueous (liquid) solution. ph of more than 7.0. Example: Sodium Hydroxide (NaOH), bleach, ammonia, soap ph Pure water has an equal number of hydrogen ions (H + ) and hydroxyl ions (OH -). The ph of pure water is 7.0. Buffers Weak acids and bases that can react with strong acids or bases to prevent sudden, sharp changes in ph Most acidic Lots of H + Neutral (Distilled water) Most basic Lots of OH - ph scale Hydrogen ions determine acidity The ph scale ranges from 0 to 14 and quantifies the acidity of solutions - Acidic solutions have a ph less than 7 - Basic solutions have a ph greater than 7 - Neutral solutions have a ph of 7 A substance with ph of 6 contains 10 times as many hydrogen ions as a substance with ph of 7 publishing as Benjamin Cummings 9

10 Organic Compounds Break Organic Compounds = carbon atoms joined by covalent bonds and may include other elements - Such as nitrogen, oxygen, sulfur, and phosphorus Hydrocarbons = contain only carbon and hydrogen - The simplest hydrocarbon is methane - Hydrocarbons can be a gas, liquid or solid Macromolecules Polymers = long chains of repeated molecules - The building blocks of life Macromolecules = large-size molecules - Three types of polymers are essential to life - Proteins - Nucleic acids - Carbohydrates - Lipids (are not polymers, but are also essential) Proteins Produce tissues, provide structural support, store and others transport energy - Animals use proteins to generate skin, hair, muscles, and tendons - Some function as components of the immune system - They can serve as enzymes, molecules that promote certain chemical reactions A special process involving proteins Deoxyribonucleic acid (DNA) and Ribonucleic Acid (RNA) carry the hereditary information of organisms - Long chains of nucleotides that contain - Sugar, phosphate, and a nitrogen base Information in DNA is rewritten to RNA RNA directs amino acid assembly into proteins Genes = regions of DNA that code for proteins that perform certain functions Genome = an organism s genes - Divided into chromosomes Carbohydrates and lipids Carbohydrates = consist of atoms of carbon, hydrogen, and oxygen - Sugars = simple carbohydrates - Glucose = provides energy for cells - Complex carbohydrates build structures and store energy - Starch = a complex carbohydrate Lipids = a chemically diverse group of compounds grouped together because they don t dissolve in water - For energy, cell membranes, structural support, and steroids publishing as Benjamin Cummings 10

11 We create synthetic polymers Plastics = synthetic (human-made) polymers - Best known by their brand names (Nylon, Teflon, Kevlar) - Many are derived from petroleum hydrocarbons - Valuable because they resist chemical breakdown - Problematic because they cause long-lasting waste and pollution - Wildlife and health problems, water quality issues, harmful to marine animals - We must design less-polluting alternatives and increase recycling Organization of matter in living things Cell = the basic unit of life s organization Eukaryotes = multi-celled organisms containing internal structures (organelles) - Plants, animals, fungi, protists - Ribosomes synthesize proteins - Mitrochondria extract energy from sugars and fats - Nucleus houses DNA Prokaryotes = single-celled organisms lacking organelles and a nucleus Hierarchy of matter in organisms Matter is organized in a hierarchy of levels, from atoms through cells through organ systems Energy fundamentals Energy = that which can change the position, physical composition or temperature of matter - Potential energy = energy of position - Kinetic energy = energy of motion - Chemical energy = potential energy held in the bonds between atoms Kinetic energy is changed into potential energy to produce motion, action, and heat Energy is conserved...but changes in quality First law of thermodynamics = energy can change forms, but cannot be created or destroyed Second law of thermodynamics = the nature of energy changes from a more-ordered to a less-ordered state - Entropy = an increasing state of disorder ENERGY LAWS: TWO RULES WE CANNOT BREAK The first law of thermodynamics: we cannot create or destroy energy. We can change energy from one form to another. The second law of thermodynamics: energy quality always decreases. When energy changes from one form to another, it is always degraded to a more dispersed form. Energy efficiency is a measure of how much useful work is accomplished before it changes to its next form. publishing as Benjamin Cummings 11

12 People harness energy Solar energy Waste Heat Chemical energy (photosynthesis) Waste Heat Chemical energy (food) Waste Heat Mechanical energy (moving, thinking, living) Waste Heat An energy source s nature determines how easily energy can be harnessed - Petroleum provide large amounts of efficient energy - Sunlight provides low-quality energy, because it is spread out and difficult to harness Energy conversion efficiency = the ratio of useful energy output to the amount needing to be input - An engine burns petroleum to power a car, but most energy is lost as heat Organisms maintain life by consuming energy The sun s energy powers life The sun releases radiation from the electromagnetic spectrum - Some is visible light Solar energy drives weather and climate, and powers plant growth Photosynthesis Autotrophs (primary producers) = organisms such as green plants, algae and cyanobacteria produce their own food from the sun s energy Photosynthesis = the process of turning light energy from the sun into chemical energy - Carbon dioxide + water + sun s energy is converted into sugars and high-quality energy Photosynthesis produces food Cellular respiration releases chemical energy Chloroplasts = organelles where photosynthesis occurs - Contain chlorophyll = a light-absorbing pigment - Light reaction = splits water by using solar energy - Calvin cycle = links carbon atoms from carbon dioxide into sugar (glucose) 6CO 2 + 6H the sun s energy C 6 H 12 O 6 + 6O 2 C 6 H 12 O 6 + 6O 2 Organisms use chemical energy from photosynthesis Oxygen is used to convert glucose into water + carbon dioxide + energy Heterotrophs = organisms that gain energy by feeding on others - Animals, fungi, microbes 6CO 2 + 6H energy publishing as Benjamin Cummings 12

13 Geothermal energy powers Earth s systems Hydrothermal vents = host entire communities that thrive in high temperature and pressure - Lack of sun prevents photosynthesis - Chemosynthesis = uses energy in hydrogen sulfide to produce sugar Early Earth was a very different place 4.5 billion years ago, Earth was a hostile place - Severe volcanic and tectonic activity - Intense ultraviolet energy from the sun - No oxygen existed in the atmosphere, until photosynthesis developed in microbes - No life existed 6CO 2 + 6H H 2 S C 6 H 12 O 6 + 3H 2 SO 4 Several hypotheses explain life s origin Primordial soup (the heterotrophic hypothesis) = life originated from a primordial soup of simple inorganic chemicals in the oceans - First life forms used organic compounds for energy Seeds from space (the panspermia hypothesis) = microbes from space traveled on meteorites to Earth Life from the depths (the chemoautotrophic hypothesis) = life originated in deep-sea hydrothermal vents, with abundant sulfur - First organisms were chemoautrotrophs The fossil record teaches about life s history Single-celled bacteria occurred on Earth 3 billion years ago Fossil = an imprint in stone of a dead organism Fossil record = gives information about the history of past life The fossil record shows that Earlier organisms evolved into later ones The vast majority of species are extinct Numbers of species increase over time Earlier organisms were smaller and simpler Several mass extinctions have occurred Large, complex organisms occurred 600 million years ago - Plants, animals, fungi Present-day organisms help decipher history Biologists use present-day organisms to get information about evolution Archea = single-celled prokaryotes very different from bacteria The tree of life now consists of 3 prongs: bacteria, archaea, eukaryotes publishing as Benjamin Cummings 13

14 Conclusion Life on Earth has flourished for over 3 billion years Deciphering life s origins depends on understanding - Energy - Energy flow - Chemistry Chemistry can also help find solutions to environmental problems QUESTION: Review Which of the following part of an atom has a negative charge? a) Proton b) Neutron c) Electron d) Hydrogen QUESTION: Review Ionic bonds are bonds that a) Share electrons b) Occur when an electron is transferred from one atom to another c) Share electrons unequally d) Lose an electron QUESTION: Review Which of the following is NOT a reason water is essential for life? a) Water can absorb large amounts of heat without changing temperature b) Waste and nutrients can be transported in water c) Ice floats on liquid water, so fish survive cold winters d) Water usually cannot dissolve other molecules QUESTION: Review Of the following macromolecules, which one is NOT a polymer? a) Lipids b) Proteins c) Carbohydrates d) Nucleic acids QUESTION: Review Sugars, starches, and glucose are all: a) Lipids b) Proteins c) Carbohydrates d) Nucleic acids publishing as Benjamin Cummings 14

15 QUESTION: Review According to the second law of thermodynamics? a) Energy cannot be created or destroyed b) Things tend to move toward a more disorderly state c) Matter can be created, but not energy d) Kinetic energy is the most efficient source of energy QUESTION: Review Which of the following organisms is an autotroph? a) Deep-sea tubeworm b) Horse c) Pine tree d) None of these QUESTION: Weighing the Issues Which hypothesis do you believe best explains the origin of life on Earth? a) The heterotrophic hypothesis (primordial soup) b) The panspermia hypothesis ( seeds from space) c) The chemoautotrophic hypothesis (life from the ocean depths) d) None of these; life did not evolve QUESTION: Interpreting Graphs and Data A molecule of the hydrocarbon ethane contains? a) 10 carbon atoms and 8 hydrogen atoms b) 8 carbon molecules and 10 hydrogen enzymes c) Carbon and hydrogen DNA d) Two different ions QUESTION: Interpreting Graphs and Data Which is the most acidic material? a) Soft soap b) Rainwater c) Acid rain d) Lemon juice publishing as Benjamin Cummings 15