Meal worm experiment puzzle with sample solutions
Some experimenters wanted to test the response of meal worms to light and moisture. To do this they set up four boxes, as shown in the sketch below. They used lamps for light sources and constantly watered pieces of paper in the boxes for moisture. In the center of each box they placed 20 meal worms. One day later they located and counted the number of meal worms at the different locations in the boxes. They found the meal worms had crawled to the different locations in the boxes and recorded the results as below:
The diagrams show that meal worms respond to (respond means move toward or away from):
- Light but not moisture
- Moisture but not light
- Both light and moisture
- Neither light nor moisture
Explain your choice.
Student sample answers: Names are fictitcious
“No definite pattern was followed by the meal worms.”
“Because even though the light was moved in different places, the meal worms didn't do the same things.
“They usually went to the end of the box with the light.”
“Because there are 17 worms by the light and there are only 3 by the moisture.”
“Because in all situations, the majority go where there’s light. Wetness doesn't seem to make a difference.”
“Boxes I and II show they prefer dry and light to wet and dark, Box IV eliminates dryness as a factor, so they do respond to light only. Box III shows that wetness cancels the effect of the light, so it seems they prefer dry. (It would be clearer if one of the boxes was wet-dry with no light).”
“ When the light was on the dry side they all crowded to the dry side. When it was on the wet side, an equal amount went to each side.”
“In experiment 3 the meal worms split half wet, half dry. So it’s safe to assume that light was not the only factor involved.”
“I, II, and IV show that meal worms seem to like the light, but in III they seem to be equally spaced. This leads one to believe that meal worms like the dryness and the reason in pictures III and IV they are by the light is because of the heat that the light produces which gives a dryness effect.”
“The Meal worms in all cases respond to light. However in box 3 the division is about 1:1. This shows that the worms are attracted to the light but not like the situations where the dry area was next to the light. When there is no choice between wet and dry such as in case IV the worms turn to the light.” They might also test a box like this wet/dry with no light to further verify the effect of moisture.
Or create a matrix:
|Most light||10 + 15 = 25||17 + 18 = 35||60|
|Less light||3 + 4 = 7||10 + 2 = 12||19|
Could also add a third to moisture. Wet, moist, dry (moist = 1/2 of what they set it to be) .