Bio1100 Chapter 1 Scientific Thinking   Chap 2
  1. Scientific investigations involve using observations   to formulate hypotheses  , in a series of steps called the scientific   method.
    • Scientific method

      1. Make observations that generate questions about the world.

      2. Form potential explanations - hypotheses.

      3. Devise testable and falsifiable predictions based on the hypotheses.

      4. Conduct critical experiments, with good of control of variables, to test hypotheses and their predictions.

      5. Draw conclusions and make revisions.
      Good hypotheses lead to new observations and hypotheses; science progresses in a spiral of knowledge.


    • Make observations

      If you observe that some individuals take echinacea when they suffer from a common cold.

      They claim the extract helps reduce the symptoms of the cold.

      A logical question from this observation is whether one causes the other.

    • Form potential explanations - hypotheses

      A useful hypothesis should

      • establish mutually exclusive alternative explanations.

      • generate testable and falsifiable predictions.

      It may be easier to disprove (falsify) predictions based on a negative statement (null hypothesis):

      Echinacea has no effect on the symptoms of the common cold.


    • Devise predictions

      Use "if ... then" logic to produce testable and falsifiable predictions based on the hypotheses.


    • Conduct a critical experiment to test a prediction.

      Hypothesis: Echinacea reduces cold symptoms.

      Experiment: subjects are divided into evenly distributed groups given different treatments:

      • One group (experimental group) of subjects receives the echinacea treatment.

      • Other groups (control groups) receive either no treatment at all or take a placebo: a tablet that does not contain echinacea.

    • An experiment should control its variables (conditions that are subject to change): only one variable should be changed at a time.

      In this experiment the variable is receiving echinacea or not.

      A properly controlled experiment allows us to draw conclusions from the experiment.

      Note that sometimes patients will respond favorably to the placebo; this "placebo effect" may have explanations other than the treatment.

      • Experimental group: a group of individuals who are exposed to a particular treatment

      • Control group: a group identical to the experimental group with one exception: they are not exposed to the treatment (or is treated with placebo)

      A properly controlled experiment allows us to compare results between groups that differ by only one variable.

      This experiment of placing a balloon with cold or warm fluid in the stomach shows no real difference in relief from ulcers.

      The relief some experienced may be due to the placebo effect.


    • Draw conclusions, make revisions

      Note that positive experimental results usually only support the hypothesis.

      It is difficult to prove a hypothesis with only a few tests; it is much easier to falsify a hypothesis.

      Reject or modify hypothesis if necessary.

  2. Hypotheses that hold up to testing over time may be combined into statements called theories   .
    • Theory formation

      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.


  3. Statistics may help to avoid associating correlation   with causation   .
    • Drawing conclusions from an experiment based on limited (anecdotal) evidence is risky.

      Larger sample sizes will generally help us draw more accurate conclusions with the use of statistics.

      Be careful not to associate correlation with causation.

    • Statistics can help to identify relationships between variables, and graphs can show these relationships visually.

      A positive correlation exists when one variable increases, so does the other.

      In this case one variable is access to textbooks and the other is exam scores.

      However, correlation may not imply causation, especially if there are inherent biases in the samples.

      • What are some possible sample biases in this hypothetical study?
        • sample size too small
        • income levels

  4. Biology is the study of living   things, which share six basic properties.
    • Basic properties of life

      • A complex, ordered organization consisting of one or more cells

      • The use and transformation of energy to perform work

      • Sensitivity and responsiveness to the external environment

      • Regulation and homeostasis

      • Growth, development, and reproduction

      • Evolution: species change over time


    • Cell theory

      1. All living organisms are made up of one or more cells.

      2. All cells arise from pre-existing cells.

    • All living things need energy by converting potential energy from another source to kinetic energy to keep them alive.

    • Living things respond to stimuli in the environment.

      • What is the stimulus for eating ice cream, even when you are not hungry?
        • Sweet and fatty foods that taste good.

    • Living organisms are able to maintain homeostasis: relatively stable state and constant internal conditions.
      For example, our energy intake (potential energy) and consumption (kinetic energy) must be kept in relative balance.

    • All humans started life as a single zygote, or fertilized egg.

      The zygote undergoes many rounds of cell division called mitosis to produce the trillions of cells of the adult.

      Specialized cells in the adults undergo meiosis to form sex cells (eggs and sperm), which can fuse (fertilization) to form the next generation zygote.

    • All living things are related to each other through step-wise evolution from common ancestors.

      Related organisms inherit their traits through a hierarchy of common ancestors.

      For example, salamanders, tigers, gorillas, and humans all inherited 4 limbs from a distant ancestor.

      But only the latter 3 inherited milk from a more recent ancestor.