THE

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THE EVOLUTION OF SEED PLANTS

• Packet 71
• Chapters 29, 30 38

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THE EVOLUTION OF PLANT ORGANS
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EVOLUTION OF ROOTS

• The evolution of roots allowed plants to become
  anchored and helped enable them to absorb water
  and nutrients from the soil
• Roots allow the shoot system to grow taller and
  contain lignified vascular tissue.

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EVOLUTION OF LEAVES

• See Pages 584-586
• Chapter 29

• Figure 29.13
• Page 586

• Leaves increase the surface area of vascular
  plants.
• Leaves can be classified as microphylls or
  megaphylls
• All lycophytes (club mosses) have small, usually
  spine-shaped leaves with a single vein
• Microphylls
• Leaves of other modern vascular plants are
  known as megaphylls
• The larger sized leaves are possible due to the
  highly branched vascular system which supports
  greater photosynthetic activity.

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THE EVOLUTION OF SEED

• The evolution of seed facilitated reproduction on
  land
• Plants that produce seeds may be placed into two
  categories
• Gymnosperms
• Angiosperms
• A seed consists of a plant embryo packaged with a
  food supply in a protective coat
• The first vascular plant, according to the theory
  of evolution, originated about 360 MYBP in the
  Devonian Period.
• Those seeds were not enclosed in any special
  chambers.
• These plants evolved into the gymnosperms
• The Naked Seeds

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THE EVOLUTION OF FLOWERS

• According to the theory of evolution, flowers
  evolved in the Cretaceous Period about 130 MYBP
• Led to further plant diversity
• A flower is a complex structure that bears seeds
  within a protective chamber called an ovary.
• Most modern day flowering plants are known as
  angiosperms.

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APICAL MERISTEMS

• Recall, plants cannot move.
• The elongation of their shoots and roots
  maximizes their exposure to environmental
  resources.
• Growth occurs throughout the life of the plant
  via cell division in the apical meristematic
  tissue found at the tips of roots and shoots.
• Cells produced by meristematic tissue can
  differentiate into various plant tissues.

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INTRODUCTION TO THE SEED AND SEED BEARING PLANTS
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INTRODUCTION TO SEED BEARING PLANTS

• Seed plants are vascular plants that produce
  seeds.
• After fertilization in seed plants, an ovule
  (megasporangium) and its enclosed structures
  develop into a seed
• Earliest fossilized seeds are gymnosperms.
• 360 MYBP
• Seed plants dominate modern landscapes and are a
  large component of plant diversity.
• Seed bearing plants have important reproductive
  adaptations -
• Continued reproduction of the gametophyte
• The advent of the seed
• The evolution of pollen

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INTRODUCTION II

• The gametophytes of seed plants are even smaller
  than those of the seedless vascular plant and are
  protected in the ovules and pollen grains,
• Miniature female gametophytes develop from spores
  that are retained within the parental sporophyte.

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COMPARISON OF SEEDS VS. SPORES

• Seeds are the primary means of reproduction and
  dispersal of flowering plants.
• Seeds are reproductively superior to spores.
• Embryonic development is further advanced in
  seeds
• Seeds contain an abundant food supply
• Each seed has a protective coat.

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SEEDS, DISPERSAL ADAPTATION

• Seed dispersal becomes important in adaptations
• Seed is a resistant structure that is
  multicellular and complex.
• Seed consists of a sporophyte embryo packaged
  with food in a protective coat
• Seeds can be dispersed by wind, water and animals.

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SEED BEARING PLANTS

• All seed bearing plants are heterosporous
• These plants have different types of sporangia
  that produce two types of spores.
• Megasporangium
• Microsporangium

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HETEROSPOROUS SPORE PRODUCTION

• Mega. vs. Micro.

• Diagram on Page 586

• Megasporangia
• Produce megaspores
• Retained in the parent sporophyte
• Formed within the megasporangium
• Enveloped with tissue called integumens
• Entire structure is called the ovule
• Microsporangia
• Produce microspores
• Develop into male (sperm containing)
  gametophytes.
• The development of pollen reduced the need for
  water for fertilization.

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MEGASPORES

• Develop into female (egg containing)
  gametophytes.
• In the female gametophyte, there is the
  production of one or more egg cells
• If egg is fertilized by sperm, the zygote
  develops into a sporophyte embryo
• The ovule, that contains the fertilized egg,
  develops into a seed.
• Seed may be viable for days, months or years.

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MICROSPORES

• Microspores develop into pollen grains
• Pollen grains mature to become the gametophytes
  of seed plants
• The most common gymnosperms, and all angiosperms
  sperm, lack flagella.
• Pollen can be transferred by wind and animals.

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POLLINATION

• The transfer of pollen to ovules
• Self Pollination
• Cross Pollination

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REVIEW
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REVIEW

• Students
• List potential examination questions and/or here,
  and on following slides, based on the packet.