1. Scientific Method Analysis A Few Experiments to Consider Biology: Mr. Elder: CAHS

2. Experiment #1: Plants Producing Water Vapor Experiment: Forty bean plants, growing in pots, were covered one afternoon by individual glass containers and left in the laboratory overnight. Next morning, the inside of the lid of each container was found to be covered in droplets of a fluid which proved to be water. Conclusion: Plants generally give off water vapor.

3. Critiques… 1. Lack of controls. The water could have come from the plants, the soil, the pots, or the air in the jar. Control experiments should have been set up to test for these possibilities. 2. The conclusion contains some points that are not valid. (a) The experiment was done overnight and so can tell us nothing about the behavior of the plants at other times of day; the word 'generally' is not justified. (b) It was carried out with an adequate number of bean plants but can tell us nothing about other kinds of plants; the word 'plants' should be qualified.

4. Example #2: The Dog Who Understands French Mr. Smith of Morningside has taught his dog Rover to understand French. Mr. Smith noticed that every evening, after dinner, when he went to the door with his coat on and said "Walkies", Rover immediately understood and came running. Mr. Smith was going to France for the summer and, as an experiment in international understanding, decided to teach Rover French. He started to say "Allons" instead of "Walkies". To his delight, Rover very quickly understood and came running. Mr. Smith concluded that he his dog, Rover was becoming bilingual.

5. Critiques… Is this the only explanation? No. The dog may respond to a total situation (after dinner, going to the door, coat on, call) of which what is actually called is only a small part. A change in the call may not matter much to the dog.

6. How Could We Find Out FOR SURE? (a) Call "Allons" to the dog in a different situation: for example, in the morning when he does not usually go for a walk. (b) Go to the door, in the normal way (coat on, after dinner) without calling anything. (c) Do likewise and call something silly like "Rhubarb

7. Example #3: Salt is bad for grass. Jon noticed this spring that his grass would not grow near his driveway. It was a particularly bad winter and he used a lot of salt to melt the ice. Jon filled 20 cups with soil and placed one teaspoon of grass seed in each. He watered all 20 with 50 ml of water. In another 20 cups he also added a half teaspoon of rock salt left over from winter. All of the cups were placed on the window sill for 2 weeks. After 2 weeks the cups without the salt had tufts of grass growing; the salty ones did not. He determined that it WAS the salt that caused the problem.

8. Critique… It’s a good experiment!!! It has a clear PROBLEM. It has some helpful background INFORMATION It has a reasonable HYPOTHESIS It has an EXPERIMENT with only ONE variable and is appropriately CONTROLED. It has clear OBSERVATIONS and a CONCLUSION that verifies the HYPOTHESIS.