Scientific method Why is it used? When is it used? What is it?

Why is the scientific method important? to distinguish between valid research and propaganda

The main steps of the scientific method Feedback falsifiable Observation Question Hypothesi s Prediction Tes t: Experiment or additional observation Test does not support hypothesis; revise hypothesis or pose new one Test supports hypothesis; make additional predictions and test them

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 2.10x

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Biosphere Ecosystem - abiotic factors - all organisms Community Population Organism ECOSYSTEM LEVEL Eucalyptus forest COMMUNITY LEVEL All organisms in eucalyptus forest POPULATION LEVEL Group of flying foxes ORGANISM LEVEL Flying fox ORGAN SYSTEM LEVEL Nervous system ORGAN LEVEL Brain Brain Spinal cord Nerve TISSUE LEVEL Nervous tissue CELLULAR LEVEL Nerve cell MOLECULAR LEVEL Molecule of DNA Figure 1.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Organisms are made up of: –organ systems –organs –tissues –cells –molecules ECOSYSTEM LEVEL Eucalyptus forest COMMUNITY LEVEL All organisms in eucalyptus forest POPULATION LEVEL Group of flying foxes ORGANISM LEVEL Flying fox ORGAN SYSTEM LEVEL Nervous system ORGAN LEVEL Brain Brain Spinal cord Nerve TISSUE LEVEL Nervous tissue CELLULAR LEVEL Nerve cell MOLECULAR LEVEL Molecule of DNA Figure 1.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Each level of organization builds on the one below it –At each level, new properties emerge biological function starts at the chemical level ATOMS AND MOLECULES

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Atom is smallest particle of an element; each element has unique number of protons Electrical charges of particles Atoms consist of protons, neutrons, and electrons Figure 2.4A A. Helium atom Protons Neutrons Electrons Nucleus

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An element is a substance that cannot be broken down to other substances by ordinary chemical means Molecules are combinations of atoms of the same or different elements Life requires about 25 chemical elements

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings O, C, H, N, and Ca Table 2.2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Isotopes have a different number of neutrons Table 2.4 –Some isotopes are radioactive

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Radioactive isotopes can be useful tracers for medical diagnosis Figure 2.5BFigure 2.5A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Electrons are arranged in shells –The outermost shell determines the chemical properties of an atom Figure 2.6 HYDROGEN (H) Atomic number = 1 CARBON (C) Atomic number = 6 NITROGEN (N) Atomic number = 7 OXYGEN (O) Atomic number = 8 Electron Outermost electron shell (can hold 8 electrons) First electron shell (can hold 2 electrons)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Atoms can join with other atoms Ionic bonds Covalent bond: polar and nonpolar Hydrogen bonds

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ions = atoms that gained or lost electrons –An electrical attraction between ions = ionic bond Figure 2.7A Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) NaClNaCl + –

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sodium and chloride ions bond to form sodium chloride, common table salt Figure 2.7B Na + Cl –

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings atoms share outer shell electrons with other atoms and form molecules Nonpolar - electrons are shared equally by the atoms Polar - electrons are unequally shared Covalent bonds

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Free radicals - reversed fountain of youth Unpaired electron, very reactive damages DNA in mitochondria, causes artery damage, cancer, speeds aging process Source: metabolism, sunlight, alcohol, smoking Neutralized by Vit E, carotenoids, Vit C Eat your fruits and veggies

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen Figure 2.9 (–) O (+) HH Water: What does it have to do with life?

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The slightly negative O is attracted to the positive H, creating a hydrogen bond Water’s polarity leads to hydrogen bonding and other unusual properties Figure 2.10A Hydrogen bond

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings surface tension created by cohesive water molecules Hydrogen bonds make liquid water cohesive Figure 2.11

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Trees move water because of H-bonds Figure 2.11x

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings It takes a lot of energy to disrupt hydrogen bonds –Water absorbs a lot of heat energy with only a small increase in temperature –As water cools, a slight drop in temperature releases a large amount of heat Water’s hydrogen bonds moderate temperature

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –A water molecule takes a large amount of energy with it when it evaporates –evaporative cooling Figure 2.12

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Molecules in ice are farther apart than those in liquid water Ice is less dense than liquid water Figure 2.13 Hydrogen bond ICE Hydrogen bonds are stable LIQUID WATER Hydrogen bonds constantly break and re-form

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Frozen water floats (left) and frozen benzene sinks (right) Figure 2.13x2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings - Lower water is protected by the surface layer of ice. –Life can survive in cold water underneath ice. –Spring thaw pushes nutrient-rich bottom water to surface

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many solutes will stick to polar water molecules and dissolve in water Water is a versatile solvent Figure 2.14 Ions in solution Salt crystal Cl – Na + Cl – – –– – – Na

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Like no other common substance, water exists in nature in all three physical states: Figure 2.10B –solid –liquid –gas

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Which element did this damage? Figure 2.16B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A compound that releases H + ions in solution is an acid, and one that accepts H + ions in solution is a base. The chemistry of life is sensitive to acidic and basic conditions AcidAcid - + H + Base - + H + Base

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Acidity is measured on the pH scale: –0-7 is acidic –8-14 is basic –neutral, pH of 7 Figure 2.15 pH scale Acidic solution Neutral solution Basic solution Increasingly ACIDIC (Higher concentration of H + ) Increasingly BASIC (Lower concentration of H + ) NEUTRAL [H + ] = [OH – ] Lemon juice; gastric juice Grapefruit juice Tomato juice Urine PURE WATER Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner Human blood H+H+ OH –

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Acid rain is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids Connection: Acid rain threatens the environment Figure 2.16A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Acid precipitation damage to trees Figure 2.16x1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 2.10Bx