Chapter 3 Summary
3-1 The Nature of Science
Many scientific methods exist in the world of science. Scientists collect scientific data by conducting experiments, which
involve making observations and measurements. They try to come up with scientific hypotheses to explain what they have
seen or measured. Scientists can test a hypothesis by using a model. They arrive at conclusions by use of deductive
reasoning and inductive reasoning.
Scientific laws and scientific theories are the foundation of sound science or consensus science. News reports often focus
on more controversial frontier science or on junk science, which lacks reliability and peer review.
3-2 Models and Behavior of Systems
The environment consists of interacting systems that have inputs, flows or throughputs, and outputs. Systems undergo
changes as a result of feedback loops. These can be either positive feedback loops or negative feedback loops. Systems
often show time delays between input of a stimulus and the response to it. Complex systems also may be affected by
synergistic interactions or synergy.
3-3 Matter
Matter is found in two chemical forms, elements and compounds. The building blocks of matter are atoms, ions, and
molecules. An atom is made up of a cloud of electrons that surrounds a nucleus containing protons and (in most cases)
neutrons.
Each element has a specific atomic number. Different isotopes of an element have different mass numbers. Atoms of
some elements can form ions. The pH of a solution is a measure of its concentration of hydrogen ions (H+).
Organic compounds and inorganic compounds can be written as chemical formulas.
Genes carry the genetic codes that create individual traits. Chromosomes are bundles of genes that make up a single DNA
molecule.
The most abundant form of matter in the universe is plasma. On earth, most matter is found as a solid, liquid, or gas.
Matter quality is a measure of how useful a form of matter is as a resource. High–quality matter is easier to extract and
disperse than low–quality matter. Material efficiency or resource productivity limits the use of materials.
3-4 Energy
Heat can be transferred by convection, conduction, or radiation. Temperature reflects the average speed of motion of
atoms, ions, and molecules in a given sample of matter.
Energy quality is a measure of the ability of a source of energy to do useful work. High–quality energy is much more
concentrated and efficient than low–quality energy. Two major types of energy are potential energy and kinetic energy.
One form of energy can be changed to another. Ionizing radiation and nonionizing radiation are forms of electromagnetic
radiation.
3-5 The Law of Conservation of Matter: A Rule We Cannot Break
Matter can undergo a physical change or a chemical change (chemical reaction). The law of conservation of matter means
that there is no "away" in “to throw away."
Pollutants can be classified into three categories: degradable (nonpersistent) pollutants, biodegradable pollutant, slowly
degradable pollutants, and nondegradable pollutants.
3-6 Nuclear Changes
Matter can undergo a nuclear change. The rate of natural radioactive decay of radioisotopes can be expressed in terms of
half–life. As radioisotopes decay they emit one or more forms of ionizing radiation such as gamma rays, alpha particles,
and beta particles.
A nuclear power plant carries out nuclear fission in a controlled chain reaction. Enough fissionable material must be
present in order to reach critical mass. Scientists are still investigating ways to develop controlled nuclear fusion as a
source of energy.
3-7 Energy Laws: Two Rules We Cannot Break
The law of conservation of energy, also known as the first law of thermodynamics, means that we cannot get something
for nothing in terms of energy quality. The second law of thermodynamics tells us that in any energy conversion we always
end up with less usable energy than we started with.
Energy efficiency, or energy productivity, is the cheapest and most efficient way to get more energy.
3-8 Matter and Energy Laws and Environmental Problems
Most advanced industrialized countries have high–throughput economies that are unsustainable. Changing to a matter–
recycling andreuse economy would buy some time, but the ultimate solution is a shift to a low–throughput (low–waste)
economy.