Reproduction of Seed Plants

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Reproduction of Seed Plants

• Chapter 24
• Unit VI

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Alternation of Generations

• All plants have a life cycle in which a diploid
  sporophyte generation alternates with a haploid
  gametophyte generation
• Gametophyte plants produce male and female
  gametes (sperm and eggs)
• When the gametes join, they form a zygote that
  begins the next sporophyte generation
• The sporophyte is what we recognize as the plant
  and the gametophyte is hidden deep within tissues
  of the sporophyte plant (inside cones or flowers)

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Alternation of Generations

• An important trend in plant evolution is the
  reduction of the gametophyte and the increasing
  size of the sporophyte

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Life Cycle of Gymnosperms

• Reproduction in gymnosperms takes place in cones,
  which are produced by a mature sporophyte plant
• Pollen cones are the male cones which produce the
  male gametophyte pollen (sperm)
• Seed cones are the female cones which produce
  female gametophytes (eggs)
• The gymnosperm life cycle takes 2 years to
  complete
• It begins in the spring when the male cones
  release pollen carried by wind to fertilize the
  female eggs

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Pollen Cones and Seed Cones
pollen cone (male)
seed cone (female)
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Life Cycle of Gymnosperms
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Structure of Flowers

• Flowers are reproductive organs that are composed
  of four kinds of specialized leaves
• Sepals
• Petals
• Stamens
• Carples

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Sepals and Petals

• The outermost circle of floral parts contains the
  sepals, which in many plants are green and
  closely resemble ordinary leaves
• Sepals enclose the bud before it opens and
  protect the flower while it is developing
• Petals, often brightly colored, are used to
  attract insects and other pollinators

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Stamens and Carpels

• Within the ring of petals are the structures that
  produce male and female gametophytes
• The male parts consist of an anther and a
  filament that together make up the stamen
• The filament is a stalk that supports the anther,
  which produces pollen grains
• The innermost floral parts are carpels, each of
  which forms an ovary (containing eggs)

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Stamens Carpels
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Life Cycle of Angiosperms

• Reproduction in angiosperms takes place within
  the flower
• Following pollination and fertilization, the
  seeds develop inside protective structures

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Life Cycle of Angiosperms
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Pollination

• Most gymnosperms and some angiosperms are wind
  pollinated, whereas most angiosperms are
  pollinated by animals

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Seed and Fruit Development

• As angiosperms seeds mature, the ovary walls
  thicken to form a fruit that encloses the
  developing seed
• A fruit is a ripened ovary that contains
  angiosperm seeds

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Seed Dispersal

• Seeds dispersed by animals are typically
  contained in fleshy, nutritious fruits
• Seeds dispersed by wind or water are typically
  lightweight, allowing them to be carried in the
  air or to float on the surface of the water

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Seed Dormancy

• Many seeds enter a period of dormancy when they
  first mature during which the embryo is alive but
  not growing
• Environmental factors such as temperature and
  moisture can cause a seed to end dormancy
• Seed dormancy can allow seeds to germinate under
  ideal growth conditions (most seeds germinate in
  spring)

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Seed Germination

• Seed germination is the early growth stage of the
  plant embryo