Page 268 - Microsoft Word - LessonPlan-Overview.doc
P. 268
from cell to cell, instructing the dominant over other stems that
organism to exhibit some behavior may grow along the sides of the
in response to what is going on in plant.
the outside world.
Plant Hormones
Ethylene is a plant hormone
involved in the ripening of fruit and
the dropping of leaves, fruits, and
flowers. When a piece of fruit is
ripe, or a flower has finished
blooming, ethylene is released to Figure 14 – Bonsai trees like this one are
make it fall. Unlike most unusually small because they have an
hormones, ethylene is a gas, so it unusually low amount of gibberellins.
can travel through the air from one
fruit to another, ripening all of the Conclusion
nearby fruit. (See the lab activity
“Two Bananas are Better than One” Plants are a tremendously diverse
for more on this.) group of organisms. Some, such
as the nonvascular plants have no
Gibberellins are growth hormones. tissues for carrying water or
They signal plants to grow taller, minerals, and must keep a small
and signal to a seed that it is time size. Others have such tissue, but
to stop being dormant and grow. no seeds. Still others have seeds
Gibberellins are sometimes given or flowers, and have developed
to decorative plants so they will ways to reproduce by spreading
grow taller. their seeds or attracting animals to
pollinate them. Plant reproduction
Cytokinins are hormones that consists of alternation of
increase cell division, and prevent generations, with the plants
the aging process. For this reason, alternating between gametophyte
florists sometimes add this and sporophyte. Hormones in the
hormone to cut flowers. Abscsisic plants cause changes based on the
acid closes the stomata and environment.
maintains dormancy. Finally,
auxins do many things, including
making the main stem of the plant
© 2011 Supercharged Science www.ScienceLearningSpace.com
670
