Module 3. Gravity

(Level of difficulty **)

Question: In which direction do plants grow, or do plants know what is “up” and what is “down” for a plant?

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)

•Using an awl (have an adult help you with it), poke small holes (1-3 per container) on the bottom of one and on the side of another container or cup
•Fill both cups 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 cups the same) and cover them with a little bit of soil (finger-thick layer or less)
•Carefully rotate one of the two cups and put it on its side, holes down.
•Place both containers next to the source of light (a windowsill).
•Wait for 3-14 days for the seeds to germinate
•Observe the direction of plant growth.

Helpful hints and suggestions:
•Don’t forget to label the containers (for example “up” 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:
•Seedlings in both pots should grow towards their respective “up”, i.e. away from Earth’s gravity. If you now place the pot that was positioned sideways right side up, the plant will look like it’s been growing sideways.

Follow-up questions:
•What would happen with the plants after they have germinated if you switched orientation of the pots (i.e. placed the side-grown pot up and the vertically-grown pot to the side)?
•If you were to repeat the experiment, would you get the same results?
•What would happen if you did exactly the same experiment in the dark?
•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?
•What would happen if you did this experiment in space far away from the Earth (link to NASA “”)