Bio1110 Chapter 2 Science Literacy and the Process of Science
  1. Sunlight contains harmful ultraviolet radiation that can be blocked by an ozone layer in the stratosphere.
    • Ultraviolet (UV) radiation from the sun can cause damage to living tissue if it penetrates the earth's atmosphere.

      • UV-A is the least damaging; 50% reaches the earth's surface.

      • UV-B is higher energy, but most is blocked by ozone (O3) and only 10% reaches the earth's surface.

      • UV-C is the most damaging, but virtually all is absorbed by oxygen gas O2.

    • • An ozone (O3) molecule absorbs UV-B rays in a reversible reaction to form a oxygen gas (O2) molecule and an oxygen atom.

      The oxygen gas (O2) in turn can absorb UV-C to form ozone (O3).

      Under normal conditions in the stratosphere, almost all of UV-C is absorbed by O2, and 90% of UV-B is absorbed by O3.

  2. An ozone hole over the Antarctic provided evidence that CFC chemicals may have been depleting the ozone layer.
    • CFCs (chlorofluorocarbons) are chemicals that accumulate in the atmosphere as a by-product of refrigerants, aerosol propellants, and foaming agents.

      UV-B radiation breaks down the CFC molecules in the stratosphere, releasing free chlorine ions, which destroy ozone (O3) molecules by converting them to oxygen gas (O2).

    • Ozone depletion

      Starting in the late 1970's, an ozone hole was discovered over Antarctica.

      These observations provided a correlation with the prediction from the hypothesis that CFC in the atmosphere can deplete the ozone layer.

      Other hypotheses may also explain the depletion of the ozone layer:

      • the ozone in the stratosphere was mixing with ozone in lower layers.
      • transient solar activities (sunspots)

      These other hypotheses can be ruled out by measurements of CFC concentrations in the atmosphere and also concentrations of chlorine that is a product of the breakdown of CFC.

  3. Scientific investigations involve using observations to formulate hypotheses in a series of steps called the process.
    • Scientific method

      • Make detailed observations that generate questions.

      • Form potential explanations - hypotheses.

      • Make falsifiable predictions based on the hypotheses.

      • Conduct experiments or observational studies to collect data.

      • Draw conclusions from data.

      • Reject or modify hypotheses that fail the test.
      Publishing conclusions in peer-reviewed journals to share results with other scientists.

    • Controlled experiment

      Experiments to test a hypothesis should consist of at least two parts.

      • A test where one variable is changed.

      • A control where that variable is unchanged.

      All other factors that may affect the experiment should be kept the same.

      In our hypothesis of exposure to UV-B, a test group may be exposed to high levels of UV-B, while a control group suffers no such exposure.

      All other factors, such as age, sex and diet, should be kept the same.

    • • An observational study involves collecting data in the field.

      Such studies may provide correlations that support a hypothesis, but there may be other factors that explain the collected data.

  4. Hypotheses that hold up to testing over time may be called theories.
    • A hypothesis that holds up to repeated testing over time and is accepted by the scientific community becomes a theory that can explain many observations.

      Note that a hypothesis can be easily falsified (disproved), but is difficult to prove with absolute certainty.