Gymnosperms

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Chapter 25.2

• Gymnosperms

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Gymnosperm Characteristics

• Vascular plants
• Produce seeds on scales of woody stobili (cones)
• Seeds not protected by fruit
• No flowers
• Four phyla
• Cycadophyta
• Ginkgophyta
• Gentophyta
• Coniferophyta

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Gymnosperm Reproduction

• Spores are produced
• Microspores produced by male cone, giving rise
  to male gametophyte, which develops into pollen
  grains
• Megaspores produced by female cone, giving rise
  to female gametophyte, contained within the
  ovule, eventually develop into archegonia with
  eggs

4
Gymnosperm Reproduction

• Pollen (carrying male gametophyte) travels by
  wind to the ovule
• Male gametophyte within pollen grain produces a
  pollen tube that grow into the archegonium
• Provides a way for sperm to reach the egg
• Occurs without water!!

5
Gymnosperm Reproduction

• Fertilized egg zygote embryo
• Embryo organism at early stage of growth and
  development
• Gymnosperm embryos have cotyledons
• Food storage organs that become the plants first
  leaves
• As embryo develops, the tissues of the ovule form
  the food supply and seed coat of the pine seed

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Advantages of Seeds

• Seed an embryo with a food supply enclosed in a
  tough, protective coat
• Advantages
• Food supply
• Protects embryo
• Easy dispersal

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Fertilization without Water

• Spore producing plants are not fully adapted to
  land on Earth because they still require water
  for fertilization
• Male gametophyte develops in a pollen grain that
  includes sperm cells, nutrients and protective
  outer covering
• Female gametophyte develops in an ovule, which
  contains a megaspore cell, one or two layers of
  tissue and a protective covering

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Cycadophyta

• Present at the time dinosaurs existed
• About 100 species left today
• Grow in tropics and subtropics exclusively
• Resemble palm trees, but NOT them

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Ginkgophyta

• Numerous during Jurassic Period (200 mya)
• Most died out 65 mya
• Only one species remains today Ginkgo biloba

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Gnetophyta

• Most found in desert or mountains of Asia, Africa
  or South America
• Contains only three Genera
• Gnetum tropical climate
• Ephedra U.S.
• Welwischia South Africa

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Coniferophyta

• Largest and most diverse phlya within the
  gymnosperm division
• Trees and shrubs with needle or scale-like
  leaves.
• Most produce seeds in woody cones
• Probably emerged around 280 mya

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Coniferophyta

• Adapted to cold climates
• Thick cuticle on leaves retain water
• Bark forms protective covering over stem, also
  reducing water loss
• Most conifers are evergreens
• Retain leaves all year
• Can begin photosynthesis early in Spring

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Coniferophyta

• Some conifers (larches and bald cypress) are
  deciduous
• Lose all their leaves at same time
• Adaptation for reducing water loss
• Tracheids thick-walled non-living cells that
  form the xylem of the vascular systems
• Provide tremendous support
• Wood is made of tissue containing tracheids

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Life Cycle of a Pine

• 1. Adult sporophyte develops male and female
  cones
• 2. Female cones develop ovule
• 3. Male cones develop pollen grains
• 4. Female gametophyte develops within ovule
• 5. Pollination pollen tube penetrates tissue of
  female gametophyte
• 6. Fertilization
• 7. Zygote develops into embryo with many
  cotyledons, mature seed is produced
• 8. Female cone opens, releasing seeds. Seeds
  germinate to form new sporophyte