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Chapter 2 Opening Question Why is the search for water important in the search for life? What are the six elements that living things are primarily composed of? • Carbon – C • Oxygen – O • Nitrogen – N • Hydrogen – H • Phosphorous – P • Sulfur - S Carbon • Role: Major Structural atom in all organic molecules • Abiotic Source: The atmosphere (CO2) • Biotic Processes: Photosynthesis and Cellular Respiration and Decomposition Oxygen • Role: Major component of all organic molecules; aerobic respiration • Abiotic Source: The atmosphere (O2) • Biotic Processes: Used in cellular respiration. Released in photosynthesis Nitrogen • Role: Major component of proteins and nucleic acids (DNA, RNA) • Abiotic Source: Atmosphere (N2) • Biotic Processes: bacteria convert N2 in air into usable form for plants; Released to environment by decomposition Phosphorous • Role: Major component of nucleic acids and phospholipids (cell membrane); also used for energy storage and release (ATP) • Abiotic Source: Rocks (lithosphere); Released in weathering • Biotic Processes: Absorbed by plants in soil; Released by decomposition Sulfur • Role: Major component of proteins (amino acid side chain) • Abiotic Source: Rocks - Lithosphere • Biotic Processes: Absorbed by plants from the soil; Released by decomposition Hydrogen • Role: Major component of all biological molecules; Does not exist freely in nature • Abiotic Source: Rocks – Hydrosphere (H2O • Biotic Processes: Incorporated into food chains along with water, Released through decomposition/water release What is the term used to describe other elements that are found in much smaller amounts in organisms? • TRACE ELEMENTS • Potassium, Sodium, Iron, Zinc, Calcium, Magnesium, Fluoride • Essential for proper functioning of body systems Figure 2.2 The Periodic Table (Part 2) He from periodic table here Which identifies an element as being a particular element? Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Atomic structure • The element magnesium has an atomic number of 12 and a mass number of 24. 1. How many protons and neutrons are in the nucleus? How many electrons are in this atom? 2. Is the magnesium atom likely to bond with other atoms? Why or why not? Figure 2.1 OCTET RULE Chapter 2, Question 2 • Which of the atoms in the following figures can form the most covalent bonds? a. Li b. C c. N d. O Chapter 2, Question 3 • Lithium (metal) and fluorine (nonmetal) are most likely to form which kind of bond? a. Hydrogen b. Ionic c. Covalent What is the difference between ionic and covalent bonding? • Covalent bonding involves the sharing of electrons – much stronger bond • Ionic bonding involves the transfer of electrons Distinguish between nonpolar and polar covalent bonding. • A polar covalent bond results when electrons are unequally shared by atoms because one atom has a stronger attraction for them (ex: H2O, HCl) Figure 2.8 Water’s Covalent Bonds Are Polar How is a hydrogen bond different from a colvalent or ionic bond? • Hydrogen bonds: attractive force BETWEEN molecules due to the slightly + and -; weak force, but strong in large numbers Which inorganic molecule comprises over 70% of all organisms? • WATER!! Which two characteristics of water account for its special properties? Polarity (H is + and O is -) Ability to form Hydrogen Bonds Review: What is the structure of a biological molecule important? What are the special characteristics of water? • High Heat Capacity • Cohesion • Surface Tension • Adhesion • Universal Solvent (“like dissolves like” • Less Dense in Solid Form than in Water Video liquid form • Temperature Buffer Figure 2.14 Hydrogen Bonding and the Properties of Water Concept 2.2 Atoms Interact and Form Molecules Water molecules form multiple hydrogen bonds with each other—this contributes to high heat capacity. Concept 2.2 Atoms Interact and Form Molecules A lot of heat is required to raise the temperature of water—the heat energy breaks the hydrogen bonds. In organisms, presence of water shields them from fluctuations in environmental temperature. Concept 2.2 Atoms Interact and Form Molecules Water has a high heat of vaporization—a lot of heat is required to change water from liquid to gaseous state. Thus, evaporation has a cooling effect on the environment. Sweating cools the body—as sweat evaporates from the skin, it transforms some of the adjacent body heat. 2.4 What Makes Water So Important for Life? • Cohesion: water molecules resist coming apart from one another. • • Helps water move through plants • • Results in surface tension Figure 2.15 Surface Tension Surface Tension Cohesion and Adhesion What is the difference between a solvent and a solute? • A solution is a substance (solute) dissolved in a liquid (solvent). • Many important biochemical reactions occur in aqueous solutions. Figure 2.10 Water Molecules Surround Ions What is the difference between substances that are hydrophilic and hydrophobic? 2.2 How Do Atoms Bond to Form Molecules? Polar molecules that form hydrogen bonds with water are hydrophilic (“water-loving”). Nonpolar molecules such as hydrocarbons (fatty acids, oils) that that do not react with water, are hydrophobic (“water-hating”). SNAP – Symmetrical Nonpolar, Asymmetrical Polar Chapter 2, Question 4 • Which of the following characteristics does not apply to water? a. All three atoms in water readily form hydrogen bonds with other molecules. b. The covalent bonds in water are polarized. c. The water molecule readily forms hydrophobic interactions. d. The water molecule is asymmetric. Water Dissociates! 2.4 What Makes Water So Important for Life? • A water molecule can be pulled apart into a proton and a hydroxide ion by other water molecules • This happens approx. once for every 10,000,000 (10^7) water molecules 2.4 What Makes Water So Important for Life? In pure water, the concentrations of H+ (H3O+) and OH- are each 10^-7 (one in ten million) The pH of pure water = _________ Physiological pH = ___________ Figure 2.14_3 Acidic solution Neutral solution Basic solution How do we identify substances as being acidic or basic? • A compound that increases the [H+] of a solution is an acid. This results in a decrease in the [OH-] in solution. • A compound that increases the [OH-] in a solution is a base. This decreases the [H+] in solution. What is pH? How do you calculate the pH of a solution? MATH!! • A measurement of the concentration of H+ ions in a solution • pH = - log [H+] • IMPORTANT: [H+] x [OH-] = 10^-14 IMPORTANT: The concentrations of H+ and OHare INVERSELY proportional; As one ion increases, the other decreases!! Example: • If a solution has a [H+] of 10^-4, what is the pH of the solution? • If a solution has a [OH-] of 10^-5, what is the pH of the solution? • If a solution has a pH of 10, what is the [H+] of the solution? pH Sale pH is a logarithmic scale: • Each whole number on the pH scale represents a power of 10 • A solution with a pH of 5 has a [H+] that is _____ times more acidic than a solution with a pH of 7. Chapter 2, Question 5 • Cola has a pH of 2 and black coffee has a pH of 5. How many times more concentrated are the hydrogen ions (H+) in cola than in black coffee? a. 10 b. 100 c. 20 d. 1000 Blood pH Question: • Living organisms maintain constant internal conditions (homeostasis). • Buffers help maintain constant pH because it can act as BOTH Figure 2.17 Buffers Minimize Changes in pH