Free response · Unit 8 Beta

Choice-chamber experiment: do mealworms avoid light?

Scientific Investigation · 4 points

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The question

Name: ______________________   Date: ____________   Choice-chamber experiment: do mealworms avoid light? (4 points)

Experimental setup

A choice chamber for mealworm larvae

Mealworms are the larvae of a beetle that lives in stored grain. A student notices that mealworms in a tray of bran gather under a piece of cardboard. To test whether they move away from light, the student builds a choice chamber: a clear plastic box divided into two equal halves with an open doorway between them, and a lamp above it. One half is covered with black paper. Ten mealworms are placed on the line between the halves, and the number in each half is recorded after 10 minutes.

Choice chamber with a light half and a dark halfA box seen from the side, divided into two equal halves with a doorway between them. A lamp shines down on the box. The left half is covered with black paper and is dark; the right half is uncovered and lit. Mealworms start on the dividing line in the middle.lampdark half(covered with black paper)light halfmealworms start on the center line; doorway at the bottom of the divider

  1. (a) Identify the independent variable and the dependent variable in this investigation. [1 point]

  2. (b) State the null hypothesis for this investigation. [1 point]

  3. (c) The black paper may also make the covered half warmer or cooler than the lit half. Describe how the student could change the design so that any preference can be attributed to light, and justify the change. [1 point]

  4. (d) Suppose 46 of 50 mealworms in five chambers end up in the dark half. The student wants to know whether the mealworms steer away from light (a taxis) or just move faster in light and slow down in the dark (a kinesis). Propose an additional observation or experiment that could distinguish these two explanations. [1 point]