Purpose
To determine the response of oat seedlings to
light.
| Procedure |
| 1. |
Fill
the flowerpot with potting soil to within
2 inches (5 cm) from the top. |
| 2. |
Sprinkle
the oat seeds over the surface of the soil. |
| 3. |
Cover
the seeds with about 1 inch (2.5 cm) of
soil. |
| 4. |
Moisten
the soil with water and keep it moist, but
not dripping wet. |
| 5. |
Place
the pot on a table near a window. |
| 6. |
Allow
the pot to remain undisturbed for 14 days. |
| 7. |
Make
daily observations and record the growth
of the oat seeds above the surface of the
soil. |
Results
The first signs of growth generally appear in
four to six days. Straight,
closed tube- like structures break through the
soil and grow toward the
light. After several more days, leaves break
through the ends of these tubes. The tubes and
leaves bend toward the light.
Why?
As the seeds germinate, each primary leaf is
protected by a hollow,
cylindrical structure, the coleoptile, which
surrounds it. After the
coleoptile has grown above the surface of the
soil, it stops growing and the primary leaf
breaks through. The coloeptile shoot and the
leaf bend toward the light as a result of the
buildup of the growth hormone auxin. The auxin
migration theory for this phototropism (growth
toward the light) state that light-sensitive
auxin moves from the light side of the dark
side of unevenly lighted growing tips. The cells
on the shaded side contain a higher concentration
of auxin which promotes cell elongation. Thus,
the cells on the shaded side are longer than
on the lighted side. As a result, the plant
bends toward the light.
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