Transcript Plant Adaptations and Tropisms

Plant Adaptations
and Tropisms
Adapt or Die!
 Plants dominate the surface of the Earth.
There are not many areas where you
can’t find at least a few plants. Given that
the Earth has a vast array of different
environments, each with its own
characteristics and challenges, it would
make sense that plants either adapt to
the areas they live in or die trying.
 Remember, unlike the animals, once a
plant is in place, it is not going anywhere!
Desert Plants
 To save water…
 Leaves are small – needles – so to minimize
water loss. Thick cuticle to keep water inside.
 Stems are modified to store water.
 Roots are extensive to maximize water
absorption.
 Seeds germinate quickly in short rainy
season.
Wet Plants
 Plants that live in swamps or wetlands
must:
 Float leaves and stems to surface for gas
exchange. Oxygen is needed for cellular
respiration (making ATP).
 Hollow stems can move oxygen downward
for use in parts below the water-line.
 Plants also limit water intake in various ways
so cells do not swell and rupture the cell
walls.
Fire! Fire! Fire!
 Fires happen and they kill some plants in
the forest. But, fires can also be a good
thing…
 It removes old and dead trees that take up
room that new growth would like to use.
 The ashes enrich the soil and can make
acidic soils a little less acidic.
 Some seeds, while in the ground, require a
lot of heat to germinate. When they final
punch through the surface, the competition
for soil and nutrients is gone!
Cold Plants
 Cold areas have tough temperatures, tough
soils and they tend to have short growing
seasons.
 To overcome this a plant may…
 Lose the leaves – too much energy needed to keep
them and they will only weigh you down in the snow.
 Rely on needles – less surface area to gather ice
and they minimize water loss.
 Undergo a very short reproductive and growing
season.
TROPISMS
Tropisms
 A tropism is a plant growth response to
an external/environmental stimulus.
(Basically, a change in plant growth
because of something around it.)
 There are positive tropisms in which
the plant grows toward a stimulus and
negative tropisms in which the plant
grows away from the stimulus.
Phototropism
 A phototropism is a plants
bending and growth of its
stem toward the sunlight.
(Photo = Light)
 Photosynthesis is needed
so get your leaves up and
at the sun.
 Roots show a negative
response to light.
 Auxins help the plant bend
toward or away from the
sun.
Gravitropism
 A gravitropism is a
plants growth response
to gravity.
 Stems show a negative
response while roots
show a positive
response to gravity.
 Helps in seed
orientation when
planted.
 Also known as
geotropism.
Thigmotropism
 Thigmotropisms are
plant growth responses
to touch.
 Leaner plants will often
use the stronger plants
around it to gain height
without growing the
thick stem/trunk.
Chemotropism & Hydrotropism
 Chemotropisms are
plant growth patterns
directed by chemicals in
the environment.
 Think of what fertilizers
do to plants – they
fluorish.
 Acids or toxins added to
soil by industry can alter
plant growth
dramatically.
 A hydrotropism is a
plants growth toward
water.
 This is a great
example of a positive
tropism.
That’s All I Got…