Download Tropism PPT

Growth Control in
Plants
Learning Objectives
• Explain tropisms—phototropism,
geotropism/gravitropism and
thigmotropism.
What is a Hormone?
What do hormones do?
Can you think of any
examples?
Chemical
Messengers
Oestrogen
Glucagon
ADH
Coordinate systems
What is a Hormone?
What do hormones do?
Insulin
Can you think of any
examples?
Testosterone
Travel in the blood,
secreted by glands
HGH
Causes a change in how
the body works
Control Growth, blood sugar, sex
development, mood, metabolism.
Hormones in Plants
What do hormones control
in plants?
Anything Relating to Growth!
Roots and Shoots
Seed Germination
Leaf Fall
Disease Resistance
Fruit Formation and Ripening
Flowering Time
Bud formation
Tropisms
 “Directional growth response”
 Plants grow in a certain direction in
response to a stimulus
Let’s Explore Tropisms!
Use your observations from the
following to complete the table
Tropism
1. Phototropism
2. Geotropism/
Gravitropism
3. Chemotropism
4. Thigmotropism
5. Hydrotropism
Stimulus
Response
• Look at the picture.
• What is happening?
• The seedlings are
bending toward the
light!
• An example of phototropism
• Since they bend TOWARD the light,
it is POSITIVE tropism.
• What is happening
here?
• The seedling has been knocked over and
its shoot is shown to have changed its
direction of growth.
• This is an example of geotropism/
gravitropism. The stimulus is gravity.
The shoot part of the plant grow AWAY
from gravity, so it is NEGATIVE
tropism.
• What is happening
here?
• The top picture shows a
Venus flytrap capturing
a fly. The stimulus is
touch.
• This shows thigmotropism.
• Since it closes TOWARD
the touch, it is POSITIVE.
• The bottom picture also
shows POSITIVE tropism
as the vine touches a
surface and winds around
it.
Tropism
Stimulus
Response
1. Phototropism
Light
Plant grows toward
light
2. Geotropism/
Gravitropism
Gravity
Shoots grow away
from gravity; roots
grow toward gravity
3. Thigmotropism
Touch
Plant part either
moves toward or
away from what
touched it
What Causes Tropisms?
• Hormone  Auxin
• Auxin promotes growth
Don’t need to
know for unit test –
just thought it was
fascinating!!
What Causes Tropisms?
• Shoots of plants contain Auxin
A) When light shines directly above tip, growth
is equal towards light source
What Causes Tropisms?
B)When light shines from an angle:
• Sunlight breaks down Auxin
• So the side of the tip that has the most direct
sunlight will have the least amount of Auxin
• Area of the plant that is more shaded will have
more Auxin
• More growth on shaded side
• Lop sided growth & plant bends towards light
Tropisms Montage!
Match the correct scenario to the
tropism.
Roots Growing Downwards
into Dark Soil
Positive
Phototropism
Shoots Growing Upwards
towards light.
Negative
Geotropism
Shoots Growing
Upwards
Negative
Phototropism
Roots Growing
Downwards.
Positive
Geotropism
Weed killers
Selective weed killers kill some plants but not
others.
This can be useful for getting rid of
dandelions in a lawn without killing the grass,
or getting rid of thistles in a field without
killing the wheat plants.
The selective weed killer contains growth
hormone that causes the weeds to grow too
quickly.
The weed killer is absorbed in larger quantities
by the weeds than the beneficial plants
Agent Orange
Rooting Powders
• Powder contains auxins
• Cuttings are dipped in powder
• Promotes root growth
Fruit Ripening
• Ethene – promotes fruit ripening
• Naturally given off by ripe fruit
• Converts starch into sugar
Plenary
Using Plant Hormones
Auxiins cause
Match the sentences
upwards
Hormone rooting powder
from cell to cell in solution
Cuttings can produce
clones of the parent plant
Hormone weed killers
cell growth
Shoots grow
downwards
Flowering can be induced
a source of light
Plant hormones can be used
Roots grow
Auxins can diffuse
Plants grow towards
to ripen fruit
causes roots to grow
by the use of plant hormones
are not usually harmful to animals
Using Plant Hormones
Hormone rooting powder causes roots to grow
Auxiins cause cell growth
Cuttings can produce clones of the parent plant
Hormone weed killers are not usually harmful to animals
Shoots grow upwards
Flowering can be induced by the use of plant hormones
Plant hormones can be used to ripen fruit
Roots grow downwards
Auxins can diffuse from cell to cell in solution
Plants grow towards a source of light