The Scientific Process, The Cell Theory
January 12 and 14, 2004

Readings: Starr pps. 12-16, CD: 1.5-1.6

"Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house". --Jules-Henri Poincaré

"If we knew what we were doing, it wouldn't be called research, would it?" --Albert Einstein

I. How is Biology studied?

Biology is an ongoing record of discoveries that arise from people asking questions about the natural world. Is is based on the idea that natural phenomena have natural causes that can be discovered by testing.

Questions, and the search for their answers, form the basis of all sciences, and science is limited to questions that can be tested.

Explanations are sought using a process known as Scientific Method. This approach requires evidence to answer questions. Note: The scientific method is not a rigid set of rules that must all be done; but makes up the 'common threads' of most successful experiments. The Scientific Method is based on a number of set of skills collectively known as Science Process Skills:

1. Observing: Observe some aspect of nature.
2. Questioning: "Why do...?" "What happens if I...?" "How does...?"
3. Inferring: Develop a hypothesis (a possible explanation that may answer the question)

Make a prediction of what the outcome would be if the hypothesis were true
This is called deductive, or "if-then", reasoning

4. Measuring: Test the prediction by experiments, observations, or models.

Usually, a literature search is done before doing the test to avoid "reinventing the wheel".
If the tests do not confirm the prediction, determine whether the hypothesis may need to be modified
If the tests do confirm the prediction, repeat the tests for consistency

5. Communicating: Explain the results and Report the conclusions via papers in scientific journals (peer-reviewed.)

(A final Science Process Skill: Classifying - grouping objects or organisms into categories based on shared properties.)

II. Experimentation: The Key to the Scientific Method

A key ingredient of the scientific process: the controlled experiment.

Control group: the group in which all factors are held constant
Controls are essential for comparison with the experimental group.
Setting up the right controls is crucial for good experimental design.

Experimental group: the group in which one factor or treatment is varied


Experiment: Why are we sleepy in N100?

Worksheet: Scientific Method

The "Science Cycle":


III. About the words "hypothesis", "theory", and "law":

1. For a hypothesis to be valid, it must be able to be tested.

A hypothesis is always a tentative explanation - and must be falsifiable.
A hypothesis can be disproved, but never proved with absolute certainty!

2. A theory is a broad explanation that synthesizes many different once-unrelated facts observations, hypotheses, and findings to explain natural processes or phenomena. Theories are very well-supported by available evidence and very widely accepted by the scientific community (ie: the Cell Theory, Evolutionary Theory)

The scientific community accepts a theory that stands up to continual testing and best explains the available evidence, and discards a theory that is inconsistent with current information.

Theories provide a framework to explain the known information of the time, but are are subject to constant evaluation and updating. Because biology and science is an "ongoing record", new information is always being reported - and theories can, and do change over time as more knowledge becomes available. There is always the possibility that new evidence will conflict with a current theory.

This is a strength of science, not a weakness! Old ideas must sometimes be given up in light of new evidence that better explains the theory or hypothesis.

Some examples of theories that have been rejected because they are now better explained by current knowledge:

Some examples of theories or phenomena that were initially rejected because they fell outside of the accepted knowledge of the time, but are well-accepted today due to increased knowledge and data include:

*Nobel Prize Winners

Note: The popular usage of the word theory differs fron the scientific use of the word theory! In everyday speech, "theory" often means a hypothesis, speculation, or opinion. When people say "I have a theory about why the Supreme Court refused to allow further recounts in Florida..." they generally do not mean that they have gathered a large body of facts and findings about this matter. Really, they may have an idea, opinion, or a hypothesis about this matter.

3. Laws (ie: Newton's Law of Gravity) are principles or generalizations about actions or phenomena. A law is not an explanation. Laws don’t rely on complex external proofs; they are accepted as is, based upon the fact that they have always been observed to be true. A theory would attempt to explain why the Law of Gravity operates as it does, but currently, there are many options for a 'Theory of Gravity'! Some possible theories include String Theory (itself currently being re-evaluated as the Theory of Everything!), Einstein's Theory of General Relativity, etc.

Note: Hypothesis do not 'become' theories and theories do not 'become' laws (like, for example, a bill becomes a law in congress.) Each one is a different feature of the scientific method.

IV. A Big Theory of Biology: The Cell Theory

The discovery of the cell was made possible by the invention of the microscope

Robert Hooke, 1662: cork appeared as a "a great many little boxes" (or "celles", meaning 'small rooms')

Anton van Leewenhook, 1673: Observations of pond water: "Little eels, or worms, lying all huddled up together and wriggily, and the whole water seemed to be alive with these animalcules and cells fill'd with juices."

By the early 1800s, cells were found to be the basic building block of all life studied at that time.

Matthias Schleiden and Theodor Schwann, in 1839, brought 200 years of scattered observations together into a simple, testable Cell Theory:

1. The cell is the fundamental unit of life.
2. All organisms are composed of one or more cells.

At this time, there was a widely held Theory of Spontaneous Generation - that meat spontaneously generated maggots, broth or milk spontaneously generated bacteria, etc.

Louis Pasteur's work provided evidence contrary to this theory by covering meat to prevent flies from laying their eggs on the surface, sealing flasks from the air to prevent contamination by microbes, and concluded that "There is no circumstance known in which it can be affirmed that microscopic beings come into the world without...parents similar to themselves".

This, as well as findings from other scientists of that time studying animal and plant reproduction and embryo development, reproduction of bacteria and algae, provided evidence for the third part of the cell theory:

3. All cells come from preexisting cells.

Each one of these three tenets of the Cell Theory:

Objectives, 01 /15/ 03

1. Know the 'steps' of the scientific method and the science process skills
2. Explain the need for a control group whenever experiments are performed
3. Explain the use of the word 'theory' in the scientific process
4. Explain the 3 tenets of the Cell Theory, and the names of the scientists involved.

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