Sexual Reproduction In Plants

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Sexual Reproduction In Plants

• Meeting the Challenge

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Making New Plants

• Many plants reproduce successfully through
  asexual reproduction.
• Others use sexual reproduction to pass on their
  genetic material.
• This is challenging because most plants do not
  move.

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Meeting the Challenge

• In animals the product of sexual reproduction is
  the zygote.
• In plants the product of sexual reproduction is
  the seed.
• The seed contains an embryo, a food supply and a
  seed coat (protects seed from dehydration).
• Plants can be classified into two groups based on
  their seed type.

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Angiosperms

• Flowering plants
• The seeds form inside the flowers.
• When mature the seeds are enclosed in a case,
  such as a pod or a shell.
• Look at page 60 - which are angiosperms?
• Can you name other angiosperms

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Gymnosperms

• Gymnosperms do not produce flowers.
• Seeds are produced inside cones.
• Their seeds have a coat but they are not enclosed
  in a case.
• Look at page 60 - which are gymnosperms?
• Can you name other gymnosperms?

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Others ??

• Not all plants fall into these two categories.
• Ferns and mosses are neither angiosperm nor
  gymnosperm.
• They reproduce sexually without seeds.
• Look on Page 60 - which do not produce seeds.

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Sexual Reproduction in Angiosperms

• More than one half of all known plants are
  angiosperms.
• Some produce large, showy flowers (lily,
  tulip,etc,)
• Some have very small, easily missed flowers
  (grasses)
• Big or small, all flowers have the same function.

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Purpose of Flowers

• All of the plants reproductive organs are
  contained in the flower.
• Female reproductive organ is called the pistil.
• Male reproductive organ is called the stamen

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Reproductive Organs In Angiosperms
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Pollination and Fertilization in Angiosperms

• Before seeds can develop inside the flower pollen
  grains from the anther must reach the stigma of
  the pistil.
• Some plants self-pollinate - both male and female
  gametes come from the same plant.
• What might be some of the advantages to this type
  of sexual reproduction?

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Pollination and Fertilization in Angiosperms

• Most angiosperms cross-pollinate.
• Pollen from one plant is transferred to another
  plant.
• Most common way to cross pollinate is to use the
  wind or insects.
• Which type of pollination would produce the most
  seeds?

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Development of a Pollen Tube
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Seed Development in Angiosperms

• While pollen tube is growing, cells inside ovule
  prepare for its arrival.
• Once the sperm cell meets the egg, a zygote is
  formed.
• Other cells in the ovule develop into the
  cotyledon which contains food.
• Zygote now goes through mitosis to form an embryo.

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• In Angiosperm the developing seed is surrounded
  by the walls of the ovary.
• As the ovary matures it becomes the fruit.

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Seed Dispersal in Angiosperms

• The fruit of an angiosperm aids in its dispersal.
• Dispersal is the transport of the seed away from
  the parent.
• Some launch their own fruits
• Some need help from outside agents
• Wind, animals, water

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Germination and Growth

• Germination - the process in which a seed begins
  to grow,
• Some seeds can lay dormant for years.
• Look at page 68 in text to see the germination of
  a bean plant.
• What process is going on at the cellular level?

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Sexual Reproduction of Gymnosperms

• The life cycle is similar to angiosperms.
• Gymnosperms do not bear flowers.
• These plants are called conifers.
• Usually male and female cones are produced in the
  same trees.
• Seeds contain an embryo, food supply, and a coat
  - but no fruit.

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