Transcript 11 plant hormones

Pop-Quiz
•Define a negative feedback system
•Which organ produces the
hormones that are used in regulation
of blood glucose?
•Define Homeostasis?
answer
•A negative feedback system
involves an original stimulus and the
body reacting to return that stimulus
back to a normal level
•Regulation of blood glucose involves
two hormones produced by the
pancreas
Plant
Responses
and
Adaptations
Hormone Action on Plants
A. Plant cells can produce
hormones: which are
chemical messengers that
travel throughout the plant
causing other cells called
target cells to respond.
B. In plants, hormones
control:
Movement
of hormone
Hormoneproducing
cells
Target
cells
1. Plant growth &
development
2. Plant responses to
environment
Cells in one blooming
flower signals other blooms
using hormones to open.
Plant Hormones
Plants are also in an
environment that is
constantly changing.
They need to have a way
to do this. Even though
they do not have a
nervous system plants do
have hormones.
Hormones in plants
are responsible for:
Phototropism
Geotropism
Apical dominance
Ripening of fruit
abscission
Plant cells will send signals
to one another to tell them:
1. When trees to drop their leaves.
2. When to start new growth.
3. When to cause fruit to ripen.
4. When to cause flowers to bloom.
5. When to cause seeds to sprout.
Tree
Budding
Fruit
Ripening
Cactus
Blooming
Leaf Drop
Sprouting
Corn Seeds
Plant hormones
The main groups of
plant hormones are:
Auxins
Gibberellins
Cytokinins
Abscisic acid
ethylene
Auxins
Auxins promote growth of
new shoots, trigger
positive phototropism and
negative geotropism of
shoots and are
responsible for apical
dominance (inhibition of
growth of lower branches)
Eg Indoleacetic Acid
(IAA), it is responsible for
Geotrophism
Gibberellins
Gibberellins (GAs) are
plant hormones that
regulate growth and
influence various
developmental
processes, including
stem elongation,
Initiates seed
germination, dormancy,
flowering, sex
expression, and leaf and
fruit senescence.
Cytokinins
Cytokinins work in
conjunction with
Auxins to stimulate
cell division and
differentiation (cell
reproduction).
Cytokinins are
synthesised in
stems, leaves and
roots
Abscisic acid
Growth inhibiting
hormone with actions
opposite to those of
auxins. Its roles
include abscission of
flowers fruits and
leaves and control of
stomatal movement.
Inhibits growth
Abscisic acid
suppresses cell
growth. It also
promotes leaf
senescence (towards
death) which results in
the colour changes of
leaves in autumn
before they are
dropped from
deciduous plants.
Ethylene causes
Fruit to Ripen
1.Fruit tissues release a
small amount of ethylene
2.Causes fruits to ripen.
3.As fruit become ripe, they
produce more and more
ethylene, accelerating
the ripening process.
Ethylene released
by apples and
tomatoes causes
fruit to age quickly.
Plants responding to
external environments
Plants do not monitor
internal environment but
are sensitive to
environmental stimuli such
as:
Light, gravity, temperature,
touch, water, carbon
dioxide.
We have seen how they
respond to these stimulus
using hormones.
summary
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