9.3 Reproduction in Angiospermophytes

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9.3 Reproduction in Angiospermophytes
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Dicotyledonous Flower Parts
FLOWER PART FUNCTION
Sepals Protect the developing flower white in the bud
Petals Modified leaves often colourful to attract pollinators
Stamen The male reproductive structure made of anther and filament
Anther Produces and releases pollen
Filament Stalk of stamen that holds up anther
Carpel The female reproductive structure made of ovary, style, and stigma
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Pistil Can refer to a single carpel or a group of fused carpels
Stigma Sticky top of carpel which pollen lands on
Style Supports and holds up the style gives the stigma exposure to pollen
ovary Base of carpel in which the female sex cells develop if fertilization occurs, it will turn into a protective fruit
Ovules Found in the ovary contain female sex cells, eggs
Pollen Contain male sex cells (sperm)
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• Flowers occur in various colours, shapes and
  types reflective of their pollinator
• Complete flowers contain all four basic flower
  parts (sepals, petals, stamen, and carpel)
• Incomplete flowers lack at least one of these
  parts
• Staminate flowers have only stamens
• Carpellate flowers have only carpets

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Pollination

• the process in which pollen (which contains the
  male sex cells sperm) is placed on the female
  stigma.
• Can occur via a variety of vectors
• Wind
• water
• Insects
• Birds
• Bats

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• Angiosperms and their pollinators have coevolved
  (supported by fossil evidence)
• The flowers colours, patterns, odours, shapes and
  even the time of day it blooms are designed to
  attract a specific pollinator
• Often, the flower provides the gift of food to
  the pollinator in exchange for the pollinator
  unintentionally transporting pollen to the stigma

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Examples

• Red flowers pollinated by birds
• Yellow and orange flowers bees
• Heavily scented flowers nocturnal animals
• Inconspicuous, odourless flowers wind

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• Self Pollination when pollen from the anther of
  a plant falls on its own stigma
• A form of inbreeding thus less genetic
  variation
• Cross Pollination pollen lands on the stigma of
  a different plant.
• Increases variation and offspring with different
  fitness

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Fertilization

• When the male and female sex cells unite to form
  a diploid zygote.
• The female sex cells are in the ovules. The sperm
  from the pollen that has attached itself to the
  stigma must make its way to the ovules in the
  ovary.

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• Pollen attaches to stigma and begins to grow a
  pollen tube through the style
• Within the growing pollen tube is the nucleus
  that will produce the sperm.
• The pollen tube completes growing by entering an
  opening at the bottom of the ovary
• The sperm moves from the tube to combine with the
  egg of ovule to form a zygote.

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The Seed and Seed Dispersal

• Once the zygote is formed, it develops with the
  surrounding tissue into the seed
• As the seed is developing, the ovary around the
  ovule mature into a fruit
• Seed dispersal can be aided by water, wind,
  animals

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SEED

• Is the means by which an embryo can be dispersed
  into to distant locations.
• It is a protective structure for the embryo

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Seed Part Function
testa Tough, protective outer coat
cotyledons Seed leaves that function as nutrient storage structures
microphyle Scar of the opening where the pollen tube entered the ovule
Embryo root and embryo shoot Become the new plant when germination occurs
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Pre-Germination

• Once seeds are formed, a maturation process
  follows.
• The seed dehydrates until the water content of
  the seeds is about 10 -15 of its weight.
• At this point, the seed goes into a dormant
  period where there is low metabolism and no
  growth or development.
• Duration is variable for different types of seed
• It is an adaptation to environmental conditions

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FUN FACT

• In 1995, a team of biologists
• found some seeds in a dried-up
• lakebed. The seeds were from a type of lotus
  
• plant. After germinating some of the seeds,
• the biologists found them to be nearly 1300
• years old!!! (They used radiometric dating to
• determine this age.)

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Fun Fact

• In 2005, a 2000 year old Judean Date palm (found
  in the ruins of Herod the Greats palace)was
  germinated

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Germination Conditions

• If conditions become favourable, the seed will
  germinated.
• GERMINATION is the development of the seed into
  a functional plant.
• There are several conditions that must be
  fulfilled for a seed to germinate.

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WATER

• Required to rehydrate the dried seed tissues
• Makes the seed swell
• As a result the seed coat will crack and
  hydrolytic enzymes are activated- they will start
  to catabolize large molecules (storage
  polysaccharides such as starch is converted into
  maltose) for cellular respiration.

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OXYGEN

• Required for the break down of those sugars in
  cellular respiration

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TEMPERATURE

• Appropriate temperature is required, that is
  varied among plants depending on their natural
  environment.
• Ex. Period of low temperature followed by high
  temps ensures that the seed does not geminate
  until the winter has passed.
• Temperature is important for enzyme activity

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• Many plants have specific conditions other than
  these that must be met in order to germinate.
• ExLodgepole Pine

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• The emerging seedling is fragile and will be
  exposed to hard weather, parasites, predators,
  and other hazards.
• Many seeds will not produce a functional plant
  because of these threats
• To compensate, plants produce a large number of
  seeds

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Metabolic Processes during Germination of a
Starchy Seed

• Seed absorbs water (which leads to many metabolic
  changes)
• Gibberellin is released after the uptake of water
• Gibberellin plant growth hormone

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• Gibberellin triggers the release of the enzyme
  amylase
• Amylase causes the hydrolysis of the starch into
  maltose
• Maltose is hydrolysed into glucose which can be
  used for cellular respiration or converted into
  cellulose to build cell walls for new cells

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• Stored proteins and lipids will also be
  hydrolyzed to make proteins/enzymes and
  phospholipids and energy metabolism.
• Germination uses the food stored in cotyledons to
  grown until it reaches light when it starts to
  photosynthesize

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Control of Flowering

• Light important factor for growth and development
• Plants are able to detect the presence of light,
  its direction, wavelength, intensity
• PHOTOPERIODISM the plants response to light
  involving the relative lengths of day and night.

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• To ensure continued existence in an area, a
  plant must flower when pollinators are available
  and when necessary resources are plentiful

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PLANT TYPE FLOWERING AND LIGHT EXAMPLES
LONG-DAY PLANTS Bloom when days are longest and nights the shortest (midsummer) - Require Pfr Radishes, spinach, lettuce
SHORT-DAY PLANTS Bloom in spring, late summer, and autumn when days are shorter - Inhibited by Pfr Poinsettias, chrysanthemums, asters
DAY-NEUTRAL PLANTS Flower without regard to day length Roses, dandelions, tomatoes
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• It is actually the length of night that controls
  the flowering process.
• The control is brought about by a special
  blue-green pigment called phytochrome.

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Phytochrome

• Phytochrome is a photoreceptor and a pigment
• It absorbs light
• There are 2 forms of phytochrome
• Pr absorbs red light
• Pfr absorbs far-red light/darkness

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Far-Red Light

• Wavelengths between 700-800nm
• At the far end of the visible light spectrum
• (Between red light and infrared light)

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• During the day, when there is light, red light
  (wavelength of 660nm) is present
• Pr absorbs red light and is rapidly converted
  into Pfr
• At the end of the day, after many hours of light,
  plants will have most of their phytochrome in the
  form of Pfr

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• During the night, when there isnt light
  (therefore no red light), Pfr is slowly converted
  back into Pr
• By morning, most of the phytochrome will be Pr
  again
• If there is even a flash of light interrupting
  the darkness during the night, it will disrupt
  the process of Pfr turning into Pr

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• Pr Pfr
  
• __________________________________________________
  ___________
• Pfr
  Pr

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• Long-day plants, require Pfr to flower
• Long day short night!
• At the end of a short night, there will still be
  lots of Pfr remaining.
• The remaining Pfr at the end of a short night
  stimulates the plant to flower.

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• In short-day plants, the Pfr acts as an
  inhibitor for flowering.
• So after a short night, the remaining Pfr will
  prevent the plant from flowering.
• If it was a long night, all the phytochrome will
  be in the form of Pr (there will be no Pfr) so
  flowering CAN occur.