Transcript Plant Hormones

Plant Ecology
Section 1: Interactions Between Plants and
Their Environment
Tropisms
All living organism have the ability
to respond to their environment.
Tropism: a directional growth to an
environmental stimulus
• Phototropism: response to light
– Stems grow toward light
– How is phototropism
beneficial to the plant.
Tropisms
• Gravitropism: response to gravity
– Roots always grow with the force of gravity
– Stems always grow against the force of gravity.
• Thigmotropism: Response to touch
– Vines and climbing plants grow
around anything that they touch.
Plant Hormones
• Hormone: chemical signals
produced by living organisms
that affect growth and
development as well as
respond to the environment.
• Hormone are usually created
in one part of an organism
and travel to different cells
and tissues.
Plant Hormones
• Charles Darwin and his son wanted to find out what causes
phototropism.
– Describe Darwin’s experiment?
– What did Darwin learn from the experiment?
Auxins
• The substance in Darwin’s
seedlings was identified as
auxin.
• Produced in the apical
meristem of the stem.
• The effects of auxin.
– Cause cell elongation
(cells on the shaded side
of the plant grow faster,
causing phototropism)
– Promotes the growth of
new roots.
Auxins
The effects of Auxin (cont.)
• Auxin inhibits the growth of
buds near the apical meristem.
– Apical Dominance – the side
branches closest to the apical
meristem grow more slowly.
– Why does this happen?
– If you remove the apical
meristem, the side branches
will grow more quickly?
– Why does this happen?
Cytokinins
• Produced in the roots of the
plant
• Effects in the plant
– Promotes cell division.
– Promotes the growth of
new stems
– Inhibits cell elongation
• The opposite of Auxins
– Auxins are produced in the top of the plant and
move down
– Cytokinins are produced at the bottom of the plant
and move up.
Ethylene
• The only hormone that exist as a gas.
• Produced in fruit tissues and aging leaves and flowers.
• Effects of Ethylene
– Causes unneeded plant parts to fall off
(leaves in autumn, and flower petals after pollination)
– Speeds up the ripening of fruit.
– Ripe or wounded fruits
produce more ethylene
than unripe fruits
– “One rotten apple spoils
the whole bunch”
Gibberellins
• Produced in the meristems of the
stems, roots and seeds.
• Effects of Gibberellins
– Promote plant growth (especially
in stems and fruits)
– Promote dormant seeds to
germinate.
Abscisic Acid
• Abscisic acid (ABA)
has the opposite
effects of gibberellins.
• Produced by the seeds
• Effects of ABA
– Promote seed dormancy (rain may wash away the
ABA from the seed and cause it to germinate)
– Closes the stomata during drought
– Prevents plant growth.
Section 2: Interactions Between
Plants and Other Organisms
Symbiosis
Symbiosis: a close relationship where 2 different species
live closely together.
• Mutualism: both organisms benefit in the relationship.
Ex: Fungi help almost
all plants absorb
minerals from the soil.
The plant provides the
fungus with
carbohydrates.
Symbiosis
• Commensalism: one organism benefits and the other
is not affected.
Ex: Epiphytes are plants that grow on larger plants
Explain how the epiphyte is benefited by growing on a
larger plant.
Symbiosis
Parasitism: one organism benefits
(parasite) and the other organism
is harmed (host)
Ex: Mistletoe grow directly on a
host tree. Its roots insert into the
tree’s vascular tissue and it steals
water and nutrients.
• Explain the difference between an
epiphyte and a parasite.
Predation
• Predation: the consumption of one
organism (the prey) by another (predator)
• One organism is benefited and the other
is harmed.
• Coevolution: predators evolve to be
better at catching prey and prey evolve to
be better at escaping predators.
– Ex: Milkweed evolved toxins that are
poisonous to almost all animals.
Overtime, monarchs caterpillars
evolved a tolerance to milkweed
toxins.
Predation
• Carnivorous Plants: plants that
have specialized leaves to trap and
digest insects.
– Plants do not get energy from
digesting insects
– Trapping insects is an adaptation
evolved for growing in mineral
poor soils.
Ex: Venus Flytrap – Insects land
on a hinged leaf and touch the
trigger hairs, which cause the
leaf to suddenly close
Competition
Competition occurs when 2 or more individual
simultaneously require a single resource that is in limited
supply
• Plant compete for water, light, minerals and space.
• Competition harms both species that use a limited resource.
Section 3: Interactions Between Plants
and Humans
Agriculture
• Humans have been on Earth for 2 million years, but have
for only farmed for the last 10,000 years
– 6 plant species provide 80% of human calories
Wheat, rice, corn, potato, sweet potato, cassava
• Domesticated plants have been change to meet our needs.
– Domesticated plants appear
considerably different they
did in nature.
– Domesticated plants are
completely dependent on
humans for their survival.
Agriculture
• How have humans domesticated plants
1. Selective Breeding: allowing only
plants with desired traits to reproduce.
– Hybridization: using cross-pollination
to breed different plant together to get
the best of both plants.
– Indbreeding: using self-pollination to
produce plants that have the same
traits as the parent plant.
– How are were humans able to use
selective breeding to change teosinte
into modern corn?
Agriculture
– Selective breeding requires traits already exists in a
population – we can not make new traits.
2. Genetically Modified (GM) Crops: genes from other
organisms have been inserted into the DNA of the crop
plant.
– Ex: Bt Corn has a
bacteria gene that
produces a toxin
that is harmless to
humans but kills
insects.
Agriculture
Pros of GM Crops
• Farmers use less pesticides.
• Produce more food in less
space
Cons of GM Crops
• The spread GM pollen
grains cannot be controlled
Ex: Some weeds
inherented genes that make
them immune to
pesticides.
• The long-term effects GM
crops have not been
studied.
Loss of Biodiversity
Monocultures: the practice of growing
a single species over a wide area.
Advantages
– Allows higher crop yields
– improves harvesting efficiency.
• Disadvantages
– Removes more nutrients from
soil. (Forces farmers to use
chemical fertilizers)
– Pest and disease spread very
rapidly. (Forcers farmers to use
chemical pesticides)
What is
biodiversity?
Loss of Biodiversity
Invasive Species: introduction
of foreign species to new
environments which out
compete native species for
resources.
• Example:
Loss of Biodiversity
Habitat Destruction
• Deforestation: loss of forest
– Forest hold soil in place
– Some forest never grow back
because of soil erosion
• Acid Rain: Air pollutants
combine with water vapor in the
atmosphere to form nitric and
sulfuric aid.
– How does acid affect plants?
Ecological Succession
Plants (and their habitats) will recover if they are just left alone.
Ecological Succession: changes in an ecosystem over time
(especially after disturbances).
• Primary Succession: begins with no remnants of an older
community.
– Begins after a volcanic explosion or a retreating glacier.
– Leaves only bare rock
Ecological Succession
•
Secondary Succession: begins after a natural disturbance
that leaves soil behind.
– Begins after a forest fire, deforestation and farming
– Occurs much faster than primary succession.
– Climax Community – fairly stable, dominant
community established after succession.