Download science-10-gravitropism-and-phototropism

Phototropism and
Gravitropism!
Main Understandings
Explain phototropism and gravitropism as
examples of control systems in plants
Explain how our understanding of
phototropism and gravitropism has
changed over time.
Cool Killer Parasitic Fungi
How do plants respond to different stimuli?
Tropism: a growth in response to a stimuli
Positive tropism: the plant grows TOWARDS the stimuli
Negative tropism: the plant grows AWAY from the stimuli
What is phototropism?
When light is the stimulus that the plant responds to
The plant has a hormone called auxin. This hormone is found
in both the roots and the top of the plant (the shoot)
and causes plant growth.
A high concentration of auxin results in the elongation/
growth of that part of the plant!
How does it work? Auxin
The auxin molecules
moves away from the
light and result in
cell elongation
wherever they move.
Light overhead: auxin
moves down the stem
causing the stem to
grow
Light to the side: the auxin moves away from the light
causing that side to grow and the plant to bend towards the
light.
Darwin’s famous experiment
Cut off the tip it did not
grow
Covering the tip, it did
not bend.
Covering the base it bent.
● Another scientist Boysen-Jensen studies plants after
Darwin.
● Inserted a disk on each side of the plant. Found when it
was on the shady side- phototropism was affected.
● Found when it was in the sunny side it did not affect
bending.
Let’s see it in action!
gravitropism
Roots also have auxins that move based on the root’s position
Root horizontal- the auxin moves down and the BOTTOM SIDE GROWS
LESS (this is opposite of auxin in the shoot).
Therefore, the top side grows more and it bends down.
Questions?!
We will now explore tropism through an interactive virtual
lab!
MAX groups of two- but must work through the questions
together and not split up the work.
Once you have shown us your completed sheet- you can work on
your science pitch.