Plant roots always seem to know which way is down, and plant shoots always seem to know which way is up. If germinating seeds are placed in the dark for different amounts of time each day, does it change their ability to sense which way is up or down? Design an experiment to test this.
How does rotating the seeds for different amounts of time affect root-tip growth? Make several “sandwiches” containing germinated seeds. Keep one vertical for the length of the experiment, but rotate the others (so that the root tips are pointing up or sideways) for different periods of time each day. After the “upside-down” or rotated period each day, rotate the germinated seeds so the roots are pointed down. The direction of gravity the plant senses will be changed. Does the rotation change anything about how the roots grow? What other variables can you think to test?