Reproduction - Sexual Reproduction In Flowering Plants - Flower

• Introduction to sexual reproduction
• Overview of the flower structure
• Function of the flower in sexual reproduction
• Male reproductive structures
  • Stamen
    • Anther
    • Pollen grains
  • Filament
• Female reproductive structures
  • Pistil/Carpel
    • Stigma
    • Style
    • Ovary
      • Ovules
• Pollination
  • Definition and process
  • Types of pollination
    • Self-pollination
    • Cross-pollination
• Fertilization
  • Definition and process
  • Pollen tube growth and entry into ovule
  • Fusion of male and female gametes
• Development of the fruit
  • Ovary wall becomes fruit wall
  • Formation of seeds within the ovary
  • Maturation process
• Seed dispersal methods
  • Wind dispersal
  • Animal dispersal
  • Water dispersal

11. Pollination

• Definition: Pollination is the transfer of pollen from the anther to the stigma of a flower.
• Types of pollination:
  • Self-pollination: Occurs when the pollen from the anther of a flower is transferred to the stigma of the same flower or another flower on the same plant.
  • Cross-pollination: Occurs when the pollen from the anther of a flower is transferred to the stigma of a flower on a different plant of the same species.
• Importance of pollination:
  • It leads to fertilization and the formation of seeds.
  • It promotes genetic variability in plants.
• Examples of pollination:
  • Insect pollination: Bees, butterflies, flies, and beetles are common insect pollinators.
  • Wind pollination: Grasses, maize, and conifers are commonly wind-pollinated plants.

12. Fertilization

• Definition: Fertilization is the fusion of the male gamete (pollen) with the female gamete (egg) to form a zygote.
• Process of fertilization:
  • Pollen grain lands on the stigma of a flower.
  • A pollen tube grows from the pollen grain down through the style into the ovary.
  • The male gamete travels down the pollen tube and reaches the ovule.
  • Fertilization occurs when the male gamete fuses with the egg inside the ovule.
  • Zygote formation marks the beginning of seed development.
• Importance of fertilization:
  • It leads to the formation of a zygote, which develops into an embryo.
  • It ensures genetic recombination and variation in offspring.
• Equation: Pollen + Egg ➜ Zygote

13. Development of the fruit

• After fertilization, the ovary of the flower develops into a fruit.
• The ovary walls thicken and become the fruit walls.
• The seeds formed inside the ovary develop and mature.
• The fruit protects the seeds and aids in their dispersal.
• Examples of fruits: Apple, orange, tomato, and mango.

14. Seed development

• After fertilization, the zygote develops into an embryo.
• The embryo consists of a radicle, plumule, and cotyledons.
• The seed coat forms around the embryo, providing protection.
• Endosperm may be present, providing nutrients for the developing embryo.
• Examples of seeds: Pea, maize, bean, and sunflower.

15. Maturation process

• During maturation, the fruit and seeds undergo changes to become fully developed.
• The fruit ripens and becomes more attractive, facilitating seed dispersal.
• The seeds within the fruit mature and become capable of germination.
• Changes in color, taste, and aroma may occur during maturation.

16. Seed dispersal methods

• Definition: Seed dispersal is the process by which seeds are scattered away from the parent plant.
• Methods of seed dispersal:
  • Wind dispersal: Seeds are light and have structures like wings or hairs to aid in wind dispersal. Examples: Dandelion, maple, and daisy.
  • Animal dispersal: Seeds have adaptations to attract animals, which eat the fruit and disperse the seeds through their droppings. Examples: Apple, cherry, and berries.
  • Water dispersal: Seeds are buoyant and have structures like air pockets or fibrous coverings to aid in water dispersal. Examples: Coconut, mangrove, and water lily.

17. Wind dispersal

• Adaptations for wind dispersal:
  • Lightweight seeds with structures like wings, hairs, or fluffy tufts.
  • Small size to enhance wind-catching ability.
  • Bursting or exploding seed pods to release seeds into the wind.
• Examples: Dandelion seeds with fluffy parachutes, maple seeds with wing-like structures (samaras).

18. Animal dispersal

• Adaptations for animal dispersal:
  • Attractive and nutritious fruits to entice animals.
  • Hooks, spines, or sticky coatings that attach to animal fur or feathers.
  • Hard seed coats that can pass through the digestive system unharmed.
• Examples: Apples eaten by birds, berries consumed by mammals, and burdock seeds that stick to animal fur.

19. Water dispersal

• Adaptations for water dispersal:
  • Buoyant seeds with air pockets or fibrous coverings.
  • Seeds with catchment devices (e.g., floats, spines, or hooks) that aid in floating.
  • Ability to survive soaking in water for extended periods.
• Examples: Coconuts that float in water and mangrove seeds with cork-like coverings.

20. Summary

• Sexual reproduction in flowering plants involves the flower, which has male and female reproductive structures.
• Pollination is the transfer of pollen from the anther to the stigma of a flower.
• Fertilization occurs when the male gamete fuses with the egg inside the ovule.
• After fertilization, the ovary develops into a fruit, and the seeds mature within it.
• Seed dispersal methods include wind, animal, and water dispersal.
• These processes ensure the survival and reproduction of flowering plants in various environments.

21. Importance of Sexual Reproduction in Flowering Plants

• Genetic variation leads to increased biodiversity and adaptability.
• Increases the chances of survival in changing environments.
• Allows for the formation of seeds and propagation of new plants.
• Ensures genetic recombination and avoids inbreeding.

22. Sexual Reproduction vs Asexual Reproduction

• Sexual Reproduction:
  • Involves the fusion of male and female gametes.
  • Increases genetic variation.
  • Requires the presence of compatible individuals.
• Asexual Reproduction:
  • Involves the production of offspring without the fusion of gametes.
  • Produces genetically identical offspring.
  • Can occur through various methods such as budding or fragmentation.

23. Advantages of Sexual Reproduction

• Genetic Variation:
  • Increases the chances of adaptation and survival.
  • Enables plants to evolve and better compete for resources.
• Increased Genetic Fitness:
  • Offspring inherit a combination of traits from both parents.
  • Allows for natural selection to act upon a wider range of genetic possibilities.
• Recombination of Traits:
  • Allows for the formation of new combinations of alleles.
  • Can lead to the development of advantageous traits.

24. Disadvantages of Sexual Reproduction

• Costly and Time-Consuming:
  • Requires energy for the production of flowers, pollen, and nectar.
  • Pollination and fertilization processes take time.
• Dependent on External Factors:
  • Requires the presence of compatible individuals for successful reproduction.
  • Dependence on pollinators and environmental conditions for pollination.

25. Heterostyly in Plants

• Definition: Heterostyly is a floral polymorphism that involves the presence of different flower types within a species.
• Types of Heterostyly:
  • Pin-Homostyly: Flowers with long styles and short stamens.
  • Thrum-Homostyly: Flowers with short styles and long stamens.
  • Pin and Thrum flowers are reciprocally placed in different individuals within a population.
• Advantages of Heterostyly:
  • Promotes outcrossing and prevents self-pollination.
  • Enhances genetic diversity in the population.
• Examples: Primrose, Cowslip, and Fuchsia.

26. Double Fertilization in Flowering Plants

• Definition: Double fertilization is a unique reproductive mechanism found in flowering plants.
• Process:
  • One male gamete fuses with the egg to form the zygote (2n).
  • The other male gamete fuses with two polar nuclei to form the endosperm (3n).
• Importance of Double Fertilization:
  • Ensures the formation of both zygote (embryo) and nutritive endosperm.
  • Endosperm provides nutrients for the growing embryo.
• Examples: Wheat, Maize, and Mango.

27. Growth and Development of the Embryo

• Embryogenesis:
  • Zygote undergoes repeated mitotic divisions.
  • Forms an embryo with a root (radicle), shoot (plumule), and cotyledons.
  • Protective seed coat develops around the embryo.
• Types of Embryos:
  • Monocotyledonous (monocot) embryos have a single cotyledon.
  • Dicotyledonous (dicot) embryos have two cotyledons.
• Examples: Monocot - Grass, Dicot - Bean.

28. Germination of Seeds

• Definition: Germination is the process by which a seed develops into a new plant.
• Conditions Required for Germination:
  • Water availability for metabolic processes.
  • Suitable temperature for optimal enzyme activity.
  • Oxygen for respiration.
• Steps in Germination:
  1. Imbibition: Absorption of water by the seed.
  2. Activation of enzymes that break down stored food.
  3. Growth of the embryo and emergence of the radicle and plumule.
  4. Development of roots and shoots.

29. Seed Dormancy

• Definition: Seed dormancy is a state of inhibited germination, even under favorable conditions.
• Causes of Seed Dormancy:
  • Unfavorable external conditions (e.g., temperature, light, or moisture).
  • Presence of seed coat impermeable to water and gases.
  • Inhibition by chemicals present in the seed.
• Overcoming Seed Dormancy:
  • Scarification: Mechanical or chemical treatment to break the seed coat.
  • Stratification: Simulating the natural cold and warm periods to initiate germination.
  • Hormonal treatments or exposure to smoke or fire.

30. Significance of Seed Dispersal

• Avoids Competition:
  • Seeds are dispersed away from the parent, reducing competition for resources.
  • Helps in the colonization of new habitats.
• Prevents Inbreeding:
  • Dispersal enhances outcrossing, reducing the chances of inbreeding.
  • Prevents detrimental effects of genetic variability.
• Expands Species Range:
  • Seed dispersal aids in plant population expansion to new areas.
  • Increases biodiversity and plant communities.