essentials of biology sylvia s. mader chapter 2 lecture outline prepared by: dr. stephen ebbs...
TRANSCRIPT
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Essentials of BiologySylvia S. Mader
Chapter 2Lecture Outline
Prepared by: Dr. Stephen EbbsSouthern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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2.1 The Nature of Matter
• Matter refers to anything that takes up space and has mass.
• Matter is composed of elements, substances that cannot be broken down into another substance.– There are 92 natural elements.– Living organisms are made primarily of six
elements.
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2.1 The Nature of Matter (cont.)
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Atomic Structure
• The atomic theory states that elements are made of tiny particles called atoms.
• The name of an atom is represented by the atomic symbol.– Hydrogen = H– Sodium = Na– Chloride = Cl
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Atomic Structure (cont.)
• Atoms are composed of three smaller particles.– Neutrons, which have no electrical charge.
– Protons, which have a positive charge.
– Electrons, which have a negative charge.
• Atoms have a mass number determined by the weight of the neutrons and protons.
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Atomic Structure (cont.)
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Atomic Structure (cont.)
• All atoms of an element have the same number of protons, the atomic number.
• The atomic number and mass number are often included with the chemical symbol.
12
6CMass number
Atomic numberChemical symbol
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The Periodic Table
• The elements are organized to form the periodic table.– The columns in the table are groups.– The rows in the table are periods.
• Elements in groups have similar chemical and physical characteristics.
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The Periodic Table
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Isotopes
• The atomic number indicates the number of protons in an atom.
• The atomic mass is the sum of the number of protons and neutrons.
• If an atom has the same number of protons but a different number of neutrons it is an isotope.
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Isotopes (cont.)
• The nucleus of an isotope can be unstable and may disintegrate, or decay.
• Decaying isotopes emit radiation.
• Radiation can be detected with instruments such as a Geiger counter.
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Uses of Radioactive Isotopes
• Radioactive isotopes can be used as tracers to follow the movement of that element.
• Radioactive isotopes can be used to sterilize medical and dental instruments.
• Radioactive isotopes can also be used to kill cancer cells.
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Uses of Radioactive Isotopes (cont.)
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Uses of Radioactive Isotopes (cont.)
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Arrangements of Electrons in an Atom
• Electrons encircle the nucleus of an atom at discrete energy levels called electron shells.
• In atoms with two or more shells, the outer shell follows the octet rule (8 electrons)
• The electrons in the outer valence shell determine the chemical reactivity of atoms.
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Arrangements of Electrons in an Atom (cont.)
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Types of Chemical Bonds
• A group of atoms bonded to one another form a molecule.
• If the molecule has more than one type of element present it is a compound.
• Different types of bonds hold molecules and compounds together.
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Types of Chemical Bonds (cont.)
• Charged atoms, or ions, can form when atoms lose or gain electrons.
• Positive and negative ions are attracted to one another and bond together in ionic bonds.
• A salt is a dry solid composed of atoms connected by ionic bonds.
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Types of Chemical Bonds (cont.)
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Types of Chemical Bonds (cont.)
• A covalent bond results when two atoms share electrons, thereby completing their valence shells.
• When molecules contain covalent bonds, the structure of the molecule can be drawn with a formula or model.
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Types of Chemical Bonds (cont.)
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Chemical Reactions
• When molecules or compounds are chemically changed it is called a chemical reaction.
• Photosynthesis is an example of a chemical reaction.
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Chemical Reactions (cont.)
• Molecules that participate in a reaction are reactants.
• Molecules formed by a reaction are products.
6 CO2 + 6 H2O C6H12O6 + 6 O2
carbondioxide
water oxygenglucose
The chemical reaction for photosynthesis
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2.2 Water’s Importance to Life
• Water is the single most important molecule of earth.
• All organisms are 70-90% water.
• Water has unique properties that make it a life-supporting substance.
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The Structure of Water
• Atoms differ in their electronegativity, or their affinity for electrons in a covalent bond.
• The unequal sharing of electrons in a molecule such as water makes the molecule polar.
• Polar water molecules are attracted to one another and can form hydrogen bonds.
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The Structure of Water (cont.)
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Properties of Water
• Water is a solvent that can dissolve many substances.– Molecules that attract water are hydrophilic.– Molecules that cannot attract water are
hydrophobic.
• Water dissolves polar nonionic substances, ions, and some nonpolar gases.
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Properties of Water (cont.)
• Water shows cohesion and adhesion.
• When water molecules cling together with hydrogen bonds it is called cohesion.
• When water molecules adhere to polar surfaces it is called adhesion.
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Properties of Water (cont.)
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Properties of Water (cont.)
• Water also has a high surface tension.
• The stronger the force between molecules in a liquid, the stronger the surface tension.
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Properties of Water (cont.)
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Properties of Water (cont.)
• Water has a high heat capacity, protecting organisms from temperature changes.
• Water has a high heat of vaporization.
• These properties of water keep temperatures compatible with those of living organisms.
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Properties of Water (cont.)
• Frozen water (ice) is less dense than liquid water, so ice floats.
• Unlike other substances, water expands as it freezes.
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Properties of Water (cont.)
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Acids and Bases
• When water dissociates, it releases an equal number of ions.– Hydrogen ions (H+)– Hydroxide ions (OH-)
H – O – H H+ + OH-
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Acids and Bases (cont.)
• Acidic solutions have a high H+ concentration.
• An acid is a substance that releases H+ when dissolved in water.
HCl H+ + Cl-
Hydrochloric acid
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Acids and Bases (cont.)
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Acids and Bases (cont.)
• Basic solutions have a low H+ concentration.
• A base is a substance that releases OH- when dissolved in water.
NaOH Na+ + OH-
Sodium hydroxide
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Acids and Bases (cont.)
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pH and the pH scale
• The pH is a mathematical way of indicating the number of H+ ions in a solution.
• The pH scale is used to express acidity or basicity (alkalinity).
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Buffers and pH
• Within the body, the pH is kept in a narrow range to maintain health.
• A buffer is a chemical or combination of chemicals that keeps a pH within a given range.
• Buffers resist changes in pH by taking up extra H+ or OH- from solution.
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Buffers and pH (cont.)