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Slide 1

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Sensitivity in
plants…read more

Slide 2

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Phototropism The movement of plants in
response to light.
If exposed to unilateral light:
the shoot will bend towards it.
the roots will grow away from it.
Shoots = positively Roots = negatively
phototropic phototropic
This tropic response helps to
ensure that shoots receive as
much all-round light as possible,
allowing the maximum amount of
photosynthesis to take place.…read more

Slide 3

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Experiment A
Once the tip is removed, upward growth stops.
When the tip is replaced, growth begins again.
Conclusion: The tip of a shoot exerts an influence on
the region of growing cells behind it.…read more

Slide 4

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Experiment B
Shoot bends
(Just behind the tip)
The shoot stops growing on the side that the
blade is inserted.
The shoot bends over.
Conclusion: The signal from the tip is blocked by the
razor blade; likely to be chemical.…read more

Slide 5

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Experiment C
(Left for several Shoot bends
Decapitated shoot doesn't grow.
Normal growth resumes when agar is places on
decapitated shoot.
Conclusion: A chemical message is produced in the tip,
which diffuses down into the agar and then diffuses into the
rest of the shoot, stimulating normal growth.…read more

Slide 6

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Experiment D
The side with the agar block grows more than
the other side.
The shoot bends away from the stimulated side.
The Went Bioassay ­ The amount of
chemical messenger in the agar
block can be used to measure the
biological activity of the messenger
chemical.…read more

Slide 7

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Slide 8

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