BIOLOGY 11

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BIOLOGY 11

• Plant Reproduction
• and Development

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Introduction

• We saw in earlier units the problems that plants
  faced in evolving to land.
• One major problem was reproduction.
• In the angiosperms, the gametophyte generations
  are very reduced the male is only the pollen
  grain, the female is reduced to embryo sacs
  within the ovule.

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Introduction

• Angiosperms reproduce primarily sexually but have
  a variety of mechanisms for asexual reproduction.
• A. Sexual Reproduction
• The Flower
• The flower is an organ specialized for sexual
  reproduction on land.

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The Flower
2. Incomplete Flowers These lack one or more of
the four flower organs of sepals, petals, stamen,
or carpels Ex. Grass flowers lack petals

• 1. Complete flowers
• Have sepals, petals, stamen, and carpels

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The Flower

• 3. Perfect Flowers
• Contains both sexes
• 4. Imperfect Flowers
• Contain only one sex

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The Flower

• 1. Sepals often photosynthetic, may be brightly
  colored, may protect flower or act as secondary
  petals.
• 2. Petals visual attractant for vector, may have
  specific shape for particular vector.

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The Flower

• 3. The Stamen the male portion of the flower
• Produces the pollen.
• Elevated upon filament for distribution of
  pollen.
• 4. The Carpel (often called the Pistil)
• Female portion produces the egg and eventually,
  the seed and fruit.

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IDENTIFY THESE FLOWERS AS MONOCOT OR DICOT
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Fertilization

• Pollination
• The pollen grain contains three nuclei two
  haploid sperm nuclei, and one diploid tube
  nucleus (directs pollen tube growth).
• Pollen lands on stigma and germinates to grow a
  pollen tube down the style.
• This is pollination (not fertilization).

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Fertilization

• Fertilization occurs when the pollen tube fuses
  with an opening in the ovule called the
  Micropyle.
• The two sperm nuclei enter the ovule.
• One sperm nucleus joins with the egg - this will
  ultimately form the embryo and new plant.
• It also restores the diploid number.

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Fertilization

• The second sperm nucleus joins with two haploid
  polar nuclei (left over from the meiosis that
  formed the egg) to form a Triploid nucleus (3N)
  in a large cell.
• This will divide rapidly to form the endosperm
  which grows rapidly as the embryo grows storing
  food around it.
• This whole process is called Double
  Fertilization.

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Double Fertilization
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Development of the Seed

• Once fertilization is complete events rapidly
  accelerate.
• 1. The zygote rapidly undergoes mitosis to form
  an embryo. It only develops so far then stops.
• 2. The ovule the rapidly growing endosperm fills
  in all the space between the embryo and the ovule
  wall - this will become the seed.

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Development of the Fruit

• 3. The fruit develops from the tissues of the
  ovary which rapidly divide.
• The fruit at first protects the developing seeds
  (thus the name Angiosperm).
• When the seeds are ready for distribution, the
  fruit matures in some fashion to facilitate seed
  dispersal.

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Seed Structure

• Seeds contain three basic structures
• 1. The seed coat formed from the wall of the
  ovule - protection.
• 2. Cotyledon(s) These are food storage sacs
  formed by transfer of food from the endosperm
  (endosperm may be present also).

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Seed Structure

• 3. The embryo made of four parts
• i. The plumule embryonic leaves
• ii. The Epicotyl embryonic stem portion from
  above cotyledon attachment site
• iii. The Hypocotyl stem below the cotyledons
• iv. The Radicle embryonic root

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Seed Structure

• Once the seed is developed, it goes dormant for a
  period of time.
• This is a survival mechanism to withstand winters
  on land (or dry seasons etc).
• Monocot seeds have only one cotyledon (seed
  half) dicots have two.

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Germination

• Dormancy allows a plant to survive seasonal
  hardships.
• This allows plants to significantly extend their
  range and is why the angiosperms are the dominant
  land plants.
• Dormancy can last for years or even much longer
  if the conditions are right.

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Germination

• Dormancy is broken when the dry seed begins to
  absorb water
• (called imbibition).
• This causes the seed to swell and the seed coat
  to burst.
• Imbibition also causes metabolic changes that
  result in the embryo resuming growth.
• This growth is fueled by food stored in the
  cotyledons or endosperm.

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Germination

• In dicots, the first part of the embryo to emerge
  is the radicle (root).
• Next the hypocotyle emerges and pulls the plumule
  (embryonic leaves) to the surface.
• Once the seedling begins photosynthesis, the
  cotyledons shrivel and fall off.
• In monocots, the coleoptile breaks the ground
  first providing a protective sheath for the shoot
  inside.

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Asexual Reproduction

• Most angiosperms are also capable of a form of
  asexual reproduction called Vegetative
  Reproduction which is actually a form of natural
  cloning.

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Bulbs Modified Stem
Tulip bulbs
Gladiolis bulbs
Onion bulbs
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Rhizomes Modified Stem
Bamboo Rhizomes
Iris Rhizomes
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Tubers Modified Stems
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Corms Modified Stems
Crocus corms
Garlic corms
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Monocot vs. Dicot

• You have now seen many differences between these
  two main groups of angiosperms.
• The following slides summarize these differences.

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MONOCOTS OR DICOTS?