Reproduction

Sexual Reproduction in Flowering Plants

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• Sexual reproduction is the process by which organisms produce offspring by the fusion of gametes.
• It involves the formation of male and female reproductive structures.
• In flowering plants, sexual reproduction occurs through the formation of flowers.

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Flower structure

• Flowers are the reproductive structures of flowering plants.
• They contain both male and female reproductive organs.
• The main parts of a flower are:
  • Sepals
  • Petals
  • Stamens
  • Pistil (or carpel)

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Sepals

• Sepals are the outermost whorl of the flower.
• They are usually green in color and are leaf-like structures.
• Sepals protect the developing flower bud.

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Petals

• Petals are the second whorl of the flower.
• They are usually brightly colored and attract pollinators.
• Petals are modified leaves that surround the reproductive structures of the flower.

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Stamens

• Stamens are the male reproductive organs of the flower.
• They consist of:
  • Filament: A long stalk that supports the anther.
  • Anther: Contains pollen sacs where pollen grains are produced.

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Pistil (or Carpels)

• Pistil is the female reproductive organ of the flower.
• It consists of:
  • Stigma: The sticky tip of the pistil where pollen grains attach.
  • Style: A slender tube that connects the stigma to the ovary.
  • Ovary: Contains one or more ovules where eggs or female gametes are produced.

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Sexual reproduction process in flowering plants

1. Pollination:

   • Transfer of pollen from the anther to the stigma of a flower.
   • Can be done by wind, water, or animals (insects, birds, etc.).

2. Fertilization:

   • Fusion of the male and female gametes.
   • Occurs within the ovary.

3. Seed formation:

   • After fertilization, the ovule develops into a seed.
   • The ovary develops into a fruit which protects and disperses the seeds.

4. Germination:

   • The process of seed developing into a new plant.

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Types of pollination

• Self-pollination:

  • Transfer of pollen from the anther to the stigma on the same flower or a flower of the same plant.
  • Occurs in plants with perfect flowers.

• Cross-pollination:

  • Transfer of pollen from the anther of one flower to the stigma of another flower of a different plant.
  • Occurs in plants with imperfect flowers or when perfect flowers are not self-compatible.

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Reproduction

Sexual Reproduction in Flowering Plants

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Flower structure

• Flowers are the reproductive structures of flowering plants.
• They contain both male and female reproductive organs.
• The main parts of a flower are:
  • Sepals
  • Petals
  • Stamens
  • Pistil (or carpel)

====

Sepals

• Sepals are the outermost whorl of the flower.
• They are usually green in color and are leaf-like structures.
• Sepals protect the developing flower bud.
• Example: Sepals of a rose flower

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Petals

• Petals are the second whorl of the flower.
• They are usually brightly colored and attract pollinators.
• Petals are modified leaves that surround the reproductive structures of the flower.
• Example: Petals of a sunflower

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Stamens

• Stamens are the male reproductive organs of the flower.
• They consist of:
  • Filament: A long stalk that supports the anther.
  • Anther: Contains pollen sacs where pollen grains are produced.
• Example: Stamens of a lily flower

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Pistil (or Carpels)

• Pistil is the female reproductive organ of the flower.
• It consists of:
  • Stigma: The sticky tip of the pistil where pollen grains attach.
  • Style: A slender tube that connects the stigma to the ovary.
  • Ovary: Contains one or more ovules where eggs or female gametes are produced.
• Example: Pistil of a hibiscus flower

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Sexual reproduction process in flowering plants

1. Pollination:

   • Transfer of pollen from the anther to the stigma of a flower.
   • Can be done by wind, water, or animals (insects, birds, etc.).
   • Example: Bees carrying pollen from flower to flower while collecting nectar.

2. Fertilization:

   • Fusion of the male and female gametes.
   • Occurs within the ovary.
   • Example: Sperm fusing with an egg cell to form a zygote.

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Types of pollination

• Self-pollination:

  • Transfer of pollen from the anther to the stigma on the same flower or a flower of the same plant.
  • Occurs in plants with perfect flowers.
  • Example: Pea plants that have both male and female parts in the same flower.

• Cross-pollination:

  • Transfer of pollen from the anther of one flower to the stigma of another flower of a different plant.
  • Occurs in plants with imperfect flowers or when perfect flowers are not self-compatible.
  • Example: Apple trees that require bees or other insects to transfer pollen between flowers.

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Agents of pollination

• Wind pollination:

  • Pollen grains are light and small, easily carried by the wind.
  • Flowers are often small, inconspicuous, and lack bright colors or strong scents.
  • Example: Grasses and conifer trees.

• Insect pollination:

  • Flowers are large, colorful, and have a sweet scent to attract insects.
  • Pollen grains are sticky or spiky, easily adhering to an insect’s body.
  • Example: Orchids and sunflowers.

• Bird and bat pollination:

  • Flowers are large, brightly colored, and produce copious nectar.
  • Pollen grains are often large and sticky to adhere to the bird or bat.
  • Example: Hummingbird-pollinated flowers and agave plants.

• Water pollination:

  • Flowers are inconspicuous and produce large quantities of pollen.
  • Pollen grains are small, light, and can float on water.
  • Example: Water lilies and eelgrass.

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Slide 21

Types of fertilization

• External fertilization:

  • Occurs in aquatic organisms.
  • Eggs are released into the water where they fuse with sperm.
  • Example: Fish and frogs.

• Internal fertilization:

  • Occurs in land-dwelling organisms.
  • Eggs are fertilized inside the female’s body.
  • Example: Mammals and birds.

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Slide 22

Life cycle of flowering plants

• The life cycle of a flowering plant consists of two phases: the sporophyte and the gametophyte.

• Sporophyte phase:

  • It starts from a fertilized egg and develops into a mature plant.
  • It produces spores through meiosis.
  • Example: The dominant phase of most plants.

• Gametophyte phase:

  • It starts from a spore and develops into a plant that produces gametes.
  • Gametes fuse to form a zygote which develops into a sporophyte.
  • Example: Mosses and ferns.

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Slide 23

Asexual reproduction in plants

• Asexual reproduction is the production of offspring without the involvement of gametes.

• Types of asexual reproduction in plants:

  • Vegetative propagation: New plants develop from vegetative parts (stems, roots, or leaves).
  • Apomixis: Seeds develop without fertilization.
  • Fragmentation: Parent plant breaks into fragments, each growing into a new plant.

• Advantages of asexual reproduction:

  • Rapid reproduction.
  • Offspring are genetically identical to the parent plant.

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Slide 24

Sexual and asexual reproduction comparison

Sexual reproduction	Asexual reproduction
Involves fusion of gametes	No gamete fusion
Genetic variation	No genetic variation
Requires pollinators or other agents in plants	No external agents required
Slow reproduction process	Rapid reproduction process
Examples: Flowers, fruits	Examples: Runners, bulbs

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Slide 25

Factors affecting reproduction

• Environmental conditions:

  • Temperature, humidity, and photoperiod can affect the growth and reproduction of plants.
  • Example: Some plants require specific day lengths to flower (long-day or short-day plants).

• Pollinators:

  • Availability of pollinators can affect the success of sexual reproduction in plants.
  • Decline in pollinator populations can lead to reduced fruit and seed production.
  • Example: Bees are important pollinators for many crop plants.

• Competition:

  • Intense competition for resources can limit the reproductive success of plants.
  • Example: Overcrowding of plants in a dense forest.

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Slide 26

Importance of sexual reproduction in plants

• Genetic variation:

  • Sexual reproduction leads to the formation of new combinations of genes, increasing genetic diversity.
  • This allows plants to adapt to changing environments and increases their chances of survival.

• Evolutionary advantage:

  • Sexual reproduction allows for the elimination of harmful mutations and the spread of beneficial traits.

• Seed dispersal:

  • Sexual reproduction produces seeds, which can be dispersed over a wide range, colonizing new habitats.

• Recombination of traits:

  • Sexual reproduction allows for the recombination of traits from two parents, leading to offspring with unique characteristics.

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Slide 27

Disorders of reproductive system

• Polycystic ovary syndrome (PCOS):

  • Hormonal disorder in women leading to multiple cysts in the ovaries.
  • Causes irregular periods, fertility issues, and increased risk of diabetes and heart disease.

• Erectile dysfunction (ED):

  • Inability to maintain an erection during sexual intercourse.
  • Can be caused by physical or psychological factors.

• Endometriosis:

  • Condition where the tissue lining the uterus grows outside the uterus.
  • Causes pain, heavy periods, and fertility problems in women.

• Prostate cancer:

  • Cancer that develops in the prostate gland, a part of the male reproductive system.
  • Common in older men and can cause urinary problems.

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Slide 28

Reproductive technologies

• In vitro fertilization (IVF):

  • Eggs and sperm are collected and fertilized in a lab.
  • Embryos are then transferred to the woman’s uterus for implantation.

• Surrogacy:

  • A woman carries a pregnancy for another person or couple who cannot conceive.
  • Can be traditional (using the surrogate’s egg) or gestational (using IVF with donor eggs).

• Artificial insemination:

  • Sperm is artificially introduced into a woman’s uterus to facilitate fertilization.
  • Can be done with partner’s sperm or donor sperm.

• Preimplantation genetic diagnosis (PGD):

  • Testing embryos for genetic diseases or abnormalities before implantation.
  • Allows for the selection of healthy embryos and reduces the risk of genetic disorders in offspring.

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Slide 29

Ethical considerations in reproductive technologies

• Access and affordability:

  • Reproductive technologies can be expensive, limiting access for some individuals or couples.

• Genetic manipulation:

  • Technologies like PGD raise ethical questions about selecting certain traits and altering the genetic makeup of offspring.

• Surrogacy:

  • Surrogacy arrangements can sometimes exploit vulnerable individuals or create complex legal and emotional situations.

• Consent and autonomy:

  • Reproductive technologies require informed consent and consideration of the rights and autonomy of all parties involved.

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Slide 30

Summary

• Sexual reproduction in flowering plants involves the formation of flowers and the fusion of male and female gametes.
• Pollination, fertilization, seed formation, and germination are essential processes in sexual reproduction.
• Different types of pollination and agents of pollination facilitate the transfer of pollen.
• Asexual reproduction in plants allows for rapid reproduction without gamete fusion, but lacks genetic variation.
• Factors like environmental conditions, pollinators, and competition can affect plant reproduction.
• Reproductive disorders and technologies have significant impacts on human fertility and reproductive health.