Plant Ecology:
Section 1: Plant responses to their Environment
1) How do plants respond to their environment?
a) All living organism respond to their environment.
b) Plants respond to their envirnemtn in 2 ways:
i) Tropisms – the way plants grow and move in response to their envirnment
ii) Hormones – chemiocals plants release in response to their envirnment
2) What are different tropisms?
a) Phototropism – plants growing in response to light
i) Stems always try to grow toward light to maximize photosynthesis
b) Gravitropism - plants growing in response gravity
i) Roots always grow with the force of gravity
ii) Stems always grow against the force of gravity.
(1) Gravotropism insures that roots stay in the ground where they can get water and nutrients and
leaves grow out of the grown where they can absorb light
c) Thigmotropism- plants growing in response to touch
i) Vines and climbing plants grow around anything that they touch.
ii) Most plants respond negatively to touch which helps them grow away from neighbor plants and
compete less fro resources
iii) Some carnivorous plants (vines fly traps) close in response to touch to capture prey
3) What are different plant Hormons?
a) Most organism create hormones in response to environmental changes
b) Hormone are usually created in one part of an organism and travel to different cells and tissues.
4) What is auxin.
a) Production:
i) Auxen is a plant hormone that is produced in the apical meristem
b) What causes it
i) Produced in response to shade
c) Effect:
i) Cause cell elongation and root growth
(1) cells on the shaded side of the plant grow faster slanting stem towards a light source
(2) Auxin causes phototropism
ii) Auxin inhibits the growth of buds near the apical meristem.
(1) This causes plants to grow up and not out
(2) Apical Dominance – the side branches closest to the apical meristem grow more slowly.
5) Cytokinin
a) Production
i) Produced in the roots of the plant
b) What causes it
i) Lack of auxen
c) Effects in the plant
i) Inhibits cell elongation.
(1) Promotes the growth of buds and thus causes the plant to grow out not up
(2) The opposite of Auxins
6) Auxins are produced in the top of the plant and move down
7) Cytokinins are produced at the bottom of the plant and move up.
8) Ethene
a) Ethane is the only hormone that exist as a gas.
b) Where is it produced:
i) Produced in fruit tissues as well as aging leaves and flowers.
c) What causes it:
i) Plant cell injury and death
d) Effects of Ethylene:
i) Causes unneeded plant parts to die and fall off
(1) I.e: leaves in autumn, and flower petals after pollination
ii) Speeds up the ripening of fruit.
9) Effects of Gibberellins
a) Where is it produced:
i) In seeds (and most of the rest of the plant)
b) What causes it to be produced:
i) Exposure to water (if you’re a seed)
c) Effects of Gibberellins
i) Promote plant growth (especially in stems and fruits)
ii) Promote dormant seeds to germinate.
10) Abscisic acid
a) Where its produced:
i) Seeds
b) What causes its production
i) Clemet changing to colder temperatures
c) Effects of adscicic acid
i) Inhibits plant growth
ii) Helps seeds stay dormant (rain may wash away the ABA from the seed and cause it to germinate)
iii) (ABA) has the opposite effects of gibberellins.
Section 2: Interactions Between Plants and Other Organisms
11) Symbiosis- a close relationship where 2 different species live closely together.
a) There are 4 main symbiotic relationships:
i) Mutualism
ii) Commensalism
iii) Parasitism
iv) Predation
v) competition
b) Mutualism - both organisms benefit in the relationship.
i) Ex: Fungi help almost all plants absorb minerals from the soil. The plant provides the fungus with
carbohydrates.
c) Commensalism- one organism benefits and the other is not affected.
i)
Ex: Epiphytes are plants that grow on larger plants
d) Parasitism- one organism benefits (parasite) and the other organism is harmed (host)
i) Ex: Mistletoe grow directly on a host tree. Its roots insert into the tree’s vascular tissue and it steals
water and nutrients.
e) Predation- the consumption of one organism (the prey) by another (predator)
i) One organism is benefited and the other is killed (not harmed)
ii) Predators and prey coevoed
(1) predators evolve to be better at catching prey and prey evolve to be better at escaping
predators.
(2) Ex: Milkweed evolved toxins that are poisonous to almost all animals. Overtime, monarchs
caterpillars evolved a tolerance to milkweed toxins.
f)
Competition- occurs when 2 or more individual simultaneously require the same resource
i) Plant compete for water, light, minerals and space.
ii) Competition harms both species that use a limited resource.
Section 3: Interactions between Plants and Humans
12) Humans have been on Earth for 2 million years, but have for only farmed for the last 10,000 years
a) 6 plant species provide 80% of human calories (Wheat, rice, corn, potato, sweet potato, cassava)
b) The more humans farm the more they directly and indirectly interfere with natural plant evolution
c) There are 3 main ways that humans interfere with natural plant evolution
i) Selective breeding
ii) Monocultures
iii) Introduction of invasive species
13) Selectively breeding plants interferes with natural plant evolution
a) Selective Breeding-allowing only plants with desired traits to reproduce.
i) Hybridization - using cross-pollination to breed different plant together to get the best of both plants.
(1) Hybridization is a form of sexual reproduction
ii) Inbreeding - using self-pollination to produce plants that have the same traits as the parent plant.
(1) Hybridization is a form of asexual reproduction
iii) Genetically Modified (GM) Crops - genes from other organisms (usually bacteria that produces
insecticides) have been inserted into the DNA of the crop plant.
(1) Ex: Bt Corn has a bacteria gene that produces a toxin that is harmless to humans but kills insects.
(2) There are many pros and cons to GM crops
(a) Pros of GM Crops
(i) Farmers use less pesticides.
(ii) Produce more food in less space
(b) Cons of GM Crops
(i) The spread GM pollen grains cannot be controlled
1. Ex: Some weeds inherited genes that make them immune to roundup.
(ii) The long-term effects GM crops have not been studied, and are not known
1. I.E – Hive collapse
14) Monoculturing crops interferes with natural plant evolution
a) Monocultures- the practice of growing a single species over a wide area.
i) Advantages
ii)
(1) Allows higher crop yields
(2) Improves harvesting efficiency and lowers cost
Disadvantages
(1) Removes more nutrients from soil. (Forces farmers to use chemical fertilizers)
(2) Pest and disease spread very rapidly. (Forcers farmers to use chemical pesticides and
herbicides)
15) The introduction of invasive plant interferes with natural plant evolution
a) Invasive Species - introduction of foreign species to new environments which out compete native
species for resources.
i) Example: Hogweed and the ash borer
Section 4: Habitat Destruction & Recovery
16) Habitat destruction happens as a result of an excess negative human interaction with an environment
a) Deforestation is an example of habitat loss
b) Deforestation - loss of forest
i) A living forest holds soil in place, so some forests never grow back because of soil erosion
ii) Humans cause deforestation in a number of ways:
(1) Humans causing forest fires
(2) Humans preventing forest fires for too long causing a build up of fuel and 1 massive fire
(3) Logging
(4) Clear cutting
17) Plants (and their habitats) will recover if they are just left alone.
a) Ecological Succession - changes in an ecosystem over time (especially after disturbances).
i) Primary Succession- begins with no remnants of an older community.
(1) Begins after a volcanic explosion or a retreating glacier.
(2) Leaves only bare rock
ii) Secondary Succession - begins after a natural disturbance that leaves soil behind.
(1) Begins after a forest fire, deforestation and farming
(2) Occurs much faster than primary succession.
(3) Climax Community – fairly stable, dominant community established after succession.