5. Or maybe you’re just a tired
student who is sick of hearing
about plants and just wants a
stinking answer?!?!
I swear, if she makes
me take notes on plants
again, I will throw this
book at the wall and run
for the hills!
6. So here are the facts…
• Plant tropisms
– Plants respond to an
environmental stimulus by
growing in a particular direction
– Growth in response to a
stimulus is called a tropism
7. • Like a 7th-grader’s attitude, a tropism
can be positive or negative
I better hurry up
and get this
report
finished..then I’ll
have more time
for math Forget that book
problems! report, I’m going
to IM my friends
all night!
POSITIVE NEGATIVE
8. • Light Tropism
– When you place a houseplant so
that it gets light from only one
direction, such as a window,
what happens?
– You may have noticed that the
plant will start bending towards
the light
11. • Gravity Tropism
– Plant growth also changes in
response to the direction of gravity
– This change is called gravitropism
– If a plant is placed on its side or
turned upside down, the shoot tips
have a negative gravitropism (away
from the center of the Earth) and
the roots have a positive
gravitropism (towards center of
Earth).
12. This plant is on its side, and the shoots still
grow upward!
13. Seasonal Changes
• Plants living in regions with cold winters
can detect changes in seasons because
the days get shorter and nights get
longer
• The opposite happens when spring and
summer approach
• Plants respond to the change in the
length of day
14. Length of Day
– short-day plants flower when night length is
long
– long-day plants flower when night length is
short
15. Seasons and Leaf Loss
– Evergreen trees
shed some of their
leave year-round so
that some leaves are
always on the tree
• leaves are often
covered with a
thick cuticle to
protect leaves
from cold and dry
weather
16. – Deciduous trees
lose all of their
leaves around the
same time each
year (either cold or
dry season)
• loss of leaves
helps plants
survive low
temperatures or
long periods
without rain
17. Seasons and Leaf Color
– leaves of deciduous
trees may change color
before they are lost
– as fall approaches,
green chlorophyll
breaks down and
orange and yellow
pigments are revealed
– they’re usually hidden
by the green
chlorophyll, but they are
always present