Module 2. Bending

(Level of difficulty **)


Question: Can plants sense which direction light comes from?

Materials you will need:
•2 empty rinsed plastic yogurt containers or single-use cups (any size, preferably 3-10 oz)
•2 larger plastic or Styrofoam trays or bowls
•An awl
•Soil (dirt from outside should work)
•Seeds (bean, pea, cucumber, tomato, sunflower, corn, pumpkin or squash)
•Water (tap water is fine)
•Aluminum foil

•Poke small holes (1-3 per container) on the bottom of 2 containers or cups using an awl (have an adult help you with that!)
•Fill containers with soil and place them in a larger bowl/tray (to capture spills and leaks)
•Pour some water onto the soil to make it moist, but do not overwater (stop watering as soon as you see excess water coming out from the holes onto the tray)•Put the seeds in soil (it is OK to put multiple seeds into each container, but keep the number of seeds in both containers the same) and cover them with a little bit of soil (finger-thick layer or less)
•Wrap the two containers with foil (to block the light), leaving a small opening on the top versus on one side of the foil cover (so that the light will shine on the plant from either the top or from one side)(need picture)
•Put both containers next to the source of light (a windowsill).
•Wait for 3-14 days for the seeds to germinate
•Unwrap the pots and examine how it they look compared to each other

Helpful hints and suggestions:
•Don’t forget to label the containers (for example, “top” and “side”), so after your experiment is done you will not get confused which pot is which.
•Dependent on what kind of seeds you planted and how fresh they are, it may take a very different amount of time for the seeds to germinate and grow.
•Don’t forget to water your plants! The easiest way to water the plants is to add water to the dish/tray your pots are sitting in: the soil and the plant roots will take up the water through the hole that you drilled!

Expected results:
•Plants can sense the direction from where light come in and would typically stretch and bend towards the source of light (in this case, towards the hole in the foil).  In this experiment plants that had a side-hole in the foil should bend sideways, while the plants with a top-hole should grow straight up.

Follow-up questions:
•Why do you think plants grow towards light?
•If you were to repeat the experiment, would you get the same results?
•What would happen with the bended plant if you drilled a second hole on the opposite side of the foil cap or removed foil altogether (and allow light to come in from all sides)
•What do you think happens with the roots of these plants: in which direction do they grow? How can you check that?
•What would happen if you used another kind of seeds?