CHAPTER 2

• Hubbard Brook Experimental Forest

  • Compared the loss of water and nutrients from an uncut forest (control site) with one that had been stripped (experimental site)

  
• Stripped site


  • 30–40% more runoff
  • More dissolved nutrients
  • More soil erosion
• Science


  Discovering how nature works
• Tools of the scientist

  • Observations
  • Measurements
  • Experimentation
• Steps in the scientific method

  1. Identify a problem

  2. Gather relevant data

  3. Propose a hypothesis to explain the data

  4. Perform an experiment, collect data, and analyze data to test the hypothesis

  5. Modify the hypothesis as needed
• Model


  Physical or mathematical representation used to study complex systems like climate
• Scientific theory


  Well-tested and widely accepted hypothesis
• Scientific knowledge advances through

  • Scientists publish details of methods and results
  • Peer review provides scientific self-correction
  • New data and analysis can lead to revised hypotheses
• Critical thinking in science

  • Have a skeptical outlook
  • Evaluate evidence and hypotheses using inputs from a variety of reliable sources
  • Identify and evaluate personal assumptions, biases, and beliefs to distinguish facts and opinions before coming to a conclusion
• Scientific law or law of nature


  Well-tested, widely accepted description of what happens repeatedly and in the same way in nature
• Types of science


  • Reliable science
  • Unreliable science
  • Tentative science
• Limitations of science


  • Scientists cannot prove or disprove anything absolutely
  • Scientists are not free of bias about their own hypotheses and results
  • Systems in the natural world involve a many variables and complex interactions
  • Statistical tools are used to estimate large numbers
• Matter


  • Has mass and takes up space
  • Exists in three physical states: solid, liquid, or gas
  • Has two chemical forms: elements and compounds
• Elements


  • Have unique properties
  • Cannot be broken down chemically into other substances
• Compounds


  Combinations of two or more different elements
• Atomic number


  Same as number of protons in nucleus
• Mass number


  Number of protons plus neutrons in nucleus
• Isotope


  Form of an element with same atomic number but different mass number
• Atomic theory


  All elements are made of atoms
• Subatomic particles


  • Nucleus of the atom: Protons have positive charge, Neutrons have negative charge
  • Negatively charged electrons orbit the nucleus
• Molecule


  Combination of two or more atoms of same or different elements, held together by chemical bonds
• Ions


  Atom or group of atoms with net positive or negative electric charge, formed when electrons are gained or lost
• Acidity


  Measure of comparative amounts of hydrogen ions (H+) and hydroxide ions (OH–) in a volume of water solution, measured with pH
• Chemical formula


  Shows number of each type of atom or ion in a compound
• Ionic compounds


  Example: sodium chloride (NaCl), tend to dissolve in water and break into ions
• Covalent compounds


  Example: water (H2O)
• Organic compounds


  Contain at least two carbon atoms, types include hydrocarbons and simple carbohydrates
• Organic compounds


  • Contain at least two carbon atoms
  • Exception: methane (CH4)
• Types of organic compounds

  • Hydrocarbons
  • Simple carbohydrates
• Macromolecules


  • Complex organic molecules
  • Include complex carbohydrates, proteins, nucleic acids, and lipids
• Cells


  • Fundamental units of life
  • All organisms have one or more cells
• Genes


  • Sequences of nucleotides within DNA
  • Instructions called genetic information
  • Create inheritable traits
• Chromosomes


  Composed of many genes
• Physical change


  No change in chemical composition
• Chemical change


  Change in chemical composition
• We can change elements and compounds from one physical or chemical form to another, but we cannot create or destroy atoms
• Energy


  The capacity to do work or transfer heat
• Whenever energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed (first law of thermodynamics), and we end up with lower quality or less-usable energy than we started with (second law of thermodynamics)
• Kinetic energy


  • Energy of movement
  • Heat
  • Electromagnetic radiation
• Potential energy


  • Stored energy
  • Can be changed into kinetic energy