As this is a science class, it would be beneficial to start out with a discussion on just what is "science." Science is a methodical process which seeks to determine the secrets of the natural world by using the scientific method.
The Scientific Method The scientific method is a process scientists must follow in determining the workings of the universe. There are five basic components to the scientific method:
All valid scientific hypotheses must be testable.
It is impossible to prove something to be true (this dips deeply into philosophy, but Truth is an ever-elusive principle.) One can create a theory with an overwhelming amount of support, but one valid piece of contrary evidence can strike it down. As such, science and scientific theories are an ever-evolving as new ideas and technologies allow us to create and test hypotheses in new and exciting ways.
An example of the scientific method in action:
Have you ever noticed that many houseplants grow toward the window? Charles Darwin, the father of modern evolutionary thought, along with his son Francis, asked these same questions and went on to propose a hypothesis.
First of all, they observed that many of their houseplants grew toward the window. They speculated that what the plants were really doing was growing toward the sunlight. If they rotated the plant, the direction of growth would also rotate toward the new orientation of the sunlight. Based on these and other observations, they hypothesized that some mechanism in the tip of the growing stem somehow sensed the light and grew toward it. They then created an experiment to test this hypothesis. They removed the tips of grass seedlings and placed them, along with some unaltered grass seedlings, on a window sill. The unaltered seedlings curved normally toward the light, but the tipless plants grew straight upward.
This experiment provided evidence to support their hypothesis, but it was not enough. What are some problems that you can think of which might have affected the experiment? A big one would be what if the lack of bending was a wound response to having the tip of the grass cut off and not due to the loss of a light-sensing mechanism.
In another experiment, the Darwins covered the tips of the seedlings with tinfoil and grew them on a window sill along with normal grass seedlings. Again, the plants with the covered tips grew straight while the uncovered plants grew toward the sun. These results were consistent with the hypothesis that it was the tip of the stem that detected the light. Yet, the Darwins observed that the actual bending response of the seedling occurred some distance below the tip. They concluded that the tip of the seedling sensed the direction of light and then sent a signal down to a receptive region which caused the curvature.
You will note that this second hypotheses asks many questions: What is the nature of this alleged signal? How does this actually cause the seedling to curve? A scientific hypothesis often not only explains one phenomena but, by its very explanation, leads to more questions.
You will note that the Darwins always included normal plants with their experimentally modified plants. The normal plants were known as controls. Without controls, one cannot draw conclusions from the experiment. Controls enable scientists to test the effects of a single variable. If the controls bend toward the light and the experimentals do not, it is likely (but not always certain) that the difference in behavior is due to the way that we have modified the experimentals. For example, we cannot attribute the lack of bending of the seedlings with the tips removed to an overcast day because it was overcast for the control seedlings and they still bent toward the light.