The Scientific Investigation as a Model of the Natural World
Combined variables – While we try to control all variables but one in the classic experimental design, natural environments are complex combinations of numerous variables. The behavior of living things may change depending on the way that different environmental conditions combine.
Children who do investigations where all but one variable is controlled need to have time to think about and discuss how the introduction of additional variables found in the animals habitat might change the behavior of the animal from what was observed in the investigation.Here are some discussion points that came from student investigations in my classroom and sample questions to ask students to encourage them to compare and contrast their scientific models with the natural systems that they represent. These comparisons often give students ideas for future investigations or research.
Priority of preferences
Isopods– a preference for light or dark– In a complex environment, a living thing may have to forgo a preference for one thing in order to survive. (leaving shade to find food)Question: In nature, what are some situations where an isopod might leave a dark place and go into the light?
A continuum of choices
Worms-preference for wet or dry -How much moisture? - Students set up experiment with very wet soil and very dry soil. Most of the worms moved to the dry soil. Question: When worms are in their natural environments do you think they only has a choice of being in either very dry soil or very wet soil? How could you test for different amounts of moisture?
Hidden variables
Slugs -Do slugs prefer soft or hard food?- cooked carrots and rotting carrots – both are soft but are they the same?Slugs ate more cooked soft carrots than fresh hard carrots. But in nature, food is often softer when it is decomposing. Question: How would a carrot get soft if it were in a garden? Do you think that slugs would still prefer soft carrots if they were soft because they were rotting?
Behavior in new environment
Crayfish -When an animal is put in the new environment of the experimental design, its behavior may be different than it would be if it were in its native habitat. That male crayfish walked around the outer edges of the basin for instance, may be occurring because the crayfish is in a place it has not been before and may not reflect usual behavior in familiar surroundings.Question: Do you think that being taken out of one environment and being placed in another might change the way a crayfish first behaves? What further investigation could you do that would give you evidence that the crayfish would be have the same way in the environment that it is familiar with?
At the end of the investigation: Question:How is the environment that you set up for your organism in this investigation like the organism's natural environment and how is it different?