Download Plant Hormones

Pop-Quiz
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What two gases must be regulated in
the body?
List the five areas that hormones are
responsible for in plants?
List the main groups of hormones
Answer
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Oxygen and Carbon dioxide must be
regulated in the body
Hormones in plants are responsible for
phototropism, geotropism, apical
dominance, ripening of fruit, abscission.
The main groups of hormones are
Auxins, gibberellins, cytokinins, abscisic
acid and Ethylene
So what and how do plants
respond?
Plants have a number of stimuli to deal
with in their environment:
 Light is needed to photosynthesis
 Plants need to know when it is the best
time of year to flower
 Seeds need to know which way is down
so as to send roots and shoots in the
right direction
Plant Tropisms
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1. Tropism: the way a plant grows in response to
stimuli in the environment.
Phototropism: growth response to light
-Plants bend towards light
Geotropism: growth response to gravity
-plant roots grow down with gravity, shoots (stems)
grow up against gravity and out of the soil.
Thigmotropism: growth response to touch
-vines grow up around trees, venus flytrap closes
when leaves are touched
What type of tropism is shown in these pictures?
light
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Phototropism in
growing shoots is a
response to blue light.
Other responses are
stimulated by different
light Reponses.
Positive phototropism is
the growth towards the
light source.
Photoperiod and flowering
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Some plants require
long nights to flower
others require short
nights.
Photoperiod is the
length of time to
which an organism
is exposed to light
Gravity
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Geotropism is the
response of plants
to gravity.
Roots are positively
geotropic they grow
towards the pull of
gravity
Touch
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Thigmotropism is
growth changes in
response to contact
with a surface
Movement response are
produced by changes in
the internal fluid
pressure of particular
groups of cells.
Tropism
Stimulus
Effect
Response
Phototropism
Light
Cell elongation
stimulated on the
shade side of the
plant
The growing
shoot bends
towards the light
Gravitropism or
Geotropism
Gravity
Cell elongation is
stimulated on upper
portion of root
The growing root
bends towards
the centre of
gravity
Hydrotropism
Water
availability
Root tips closest to a Growth of the root
water source &
towards a water
soluble minerals grow source
faster than those
further away
Thigmotropism
Touch
Plant runners change
direction when they
come in contact with
any object.
Plant runners (eg
Vines) wrap
around branches
or trellis etc
Temperature
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Some plants enter a
dormant stage before
winter; bud dormancy is
broken by a period of
winter cold. Seeds enter
a dormant stage and
remain so until
conditions are right for
successful germination.
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Some plants require
exposure to
cold(vernalisation)
as seeds, others
require vernalisation
after their first year
of growth, in order
to complete their life
cycle.
Summary:Water and nutrients
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Most land plants
obtain water and
nutrients from soil.
Most nutrients are
taken up selectively
by active transport
into roots; Water
moves into roots
passively.
Summary:Transport of
substances
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Most water and
nutrients pass
through the root
along cell walls;
some pass through
the cytoplasm of
root cells.
Transport occurs in
xylem or phloem
PHLOEM
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Sucrose (food) is
transported by the
vascular tissue called
phloem. Unlike
transpiration's one-way
flow of water sap, food
& hormones in phloem
sap can be transported
in any direction
needed.
Phloem
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The bulk-flow mechanism translocates sap from
sugar sources to sugar sinks in the plant. Phloem sap
is mainly water and sucrose, but other sugars,
hormones and amino acids are also transported. The
movement of such substances in the plant is called
translocation. Translocation means the
transportation of photosynthetically produced food
throughout the entire body of the plant through the
phloem cells. Another mechanism that induces the
flow or movement of sap through the phloem of a
plant is the transpiration-condensation-tension
mechanism.
Xylem
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Bulk flow of xylem sap
(water and nutrients
ions) from roots to
leaves occurs within
xylem vessels and
tracheids.
It is driven by
transpiration and
root pressure
Transpiration/ Root pressure
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Transpiration is the
loss of water vapour
from leaves. The
rate of transpiration
depends on factors
that affect the rate
of evaporation:
temperature, wind,
available surface
area and humidity.
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Fluid pressure
generated by the
osmotic uptake of
water accompanying
the active uptake of
mineral salts into
roots contributes to
the movement of
water up the xylem
in plants.
Stomata
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Stomatal movement
is the result of
changes in the
internal fluid
pressure of the
guard cells in
response to
environmental
conditions light,
carbon dioxide and
water in particular
What causes STOMATAL
opening
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The immediate cause is an increase in turgor
pressure - water enters the central vacuole by
osmosis
Turgor pressure increases because of a negative
water potential due to an influx of potassium
ions (K+). The cell becomes hypertonic to its
environment
The reversible uptake of K+ ions takes place
because of the membrane potential created
when H+ are actively pumped out of the cell consuming ATP. The cell's interior becomes
negative compared to the surroundings.
Regulating Stomata
The stoma is closed at night when the large central vacuole is isotonic,
even hypotonic to surrounding fluids. K+ ions are outside of the cell,
and H+ ions by and large remain attached to the weak organic acids
within the cell.
Blue light is absorbed by a membrane protein which somehow causes
an increase in the activity of proton pumps which use ATP to transport
H+ out of the cell.
With H+ on the outside K+ readily diffuse into the cell to compensate
for the negative electrical potential. The hypertonic conditions within
the cell attract water molecules and the stoma opens as turgor pressure
increases.
A cell in a hypertonic
environment is
surrounded by a
higher concentration
of impermeable solute
than exists in the
inside of the cell.
Osmotic pressure
directs a net
movement of water
out of the cell, causing
it to shrink.
The opposite of a
hypertonic environment is
a hypotonic one, where
the net movement of
water is into the cell. If
the cell contains more
impermeable solute than
its surroundings, water
will enter it. In the case of
animal cells, they will
swell until they burst;
plant cells do not burst,
due to the reinforcement
their cell wall provides.
Internal Environment of Plants
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In plants the distinction
between extracellular
fluid and the external
environment is less
clear than it is in
animals and the
composition of
extracellular fluids is not
regulated as precisely
Movement in/out of leaves
During daylight, plants are performing photosynthesis at
a greater rate than cellular respiration (if STOMATA are
open.)
•A - C/R is at constant rate
•B – photosynthesis is unable
to occur or limited by light
(night)
•C – compensation point
•D - light intensity high
(enzymes working at max.
level)
Summary
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Plants need to respond to their external
environment including light, gravity,
touch, day length and temperature.
Plants also need to transport materials
such as water and nutrients around the
plants structure they use the xylem for
water and phloem for nutrients