As
a class, discuss gravity. Have students speculate about what
effect gravity has on plants. Introduce geotropism as the
effect of gravity on plants. Discuss phototropism or the effect
of light on plants. Pass out the handout and discuss plant
growth habits. Review the Growth Stages of a Soybean poster.
Ask students if radish seeds will mimic the general progression
of the soybean seedling.
Prepare a class demonstration on phototropism by cutting a
one-inch window on one end of a box. Place a potted radish
seedling about an inch tall into the box and close the lid,
opening it only to water the seedling. Make sure the window
faces a light source.
At the same time, soak radish seeds overnight in water. Line
a clear glass jar with a damp paper towel and place the seeds
between the towel and the jar, 1-inch from the lip. Keep the
towel wet and the jar in the dark until the seeds have germinated
and their stems extend an inch beyond the top of the jar.
Then place the jar on its side in the dark. Check the seedlings
in a day and discuss the change in direction of the growth
of roots and stems.
As
a class, discuss why roots grow down and stems grow up, even
if light is not present. After a week, have the class observe
and discuss why the plant in the first box grows toward the
light source. Discuss as a class or invite a local farmer
to your class to discuss how critical planting depth is in
growing good crops. Better yet, arrange to visit a farm or
farm equipment dealership to show students the sophisticated
machines and monitoring devices farmers use to ensure that
the seeds they plant are planted at just the right depth.
