Detailed Notes on Sexual Reproduction in Flowering Plants

Flowers and their parts:

• Sepals: Leaf-like structures that enclose and protect the flower bud before it opens. (Ref: NCERT Biology Class 11, Chap. 2)

• Petals: Flower’s colorful and fragrant leaf-like structures that attract pollinators. (Ref: NCERT Biology Class 11, Chap. 2)

• Stamens: Male reproductive organs consisting of anther and filament. The anther produces pollen grains. (Ref: NCERT Biology Class 11, Chap. 2)

• Pistil or Gynoecium: Female reproductive structure comprising the ovary, style, and stigma. (Ref: NCERT Biology Class 11, Chap. 2)

• Ovary: The swollen basal portion of the pistil containing the ovules. (Ref: NCERT Biology Class 11, Chap. 2)

Pollination:

• Self-pollination: Transfer of pollen grains from anther to stigma within the same flower. (Class 11, Chap. 2)

• Geitonogamy: Transfer of pollen grains between different flowers of the same plant. (Class 11, Chap. 2)

• Xenogamy: Transfer of pollen grains between different plants of the same species. Considered more advantageous as it introduces new genetic combinations. (Class 11, Chap. 2)

• Anemophily: Wind-mediated pollination. Often observed in plants with inconspicuous flowers, like grasses. (Class 11, Chap. 2)

• Hydrophily: Pollination through water, seen in aquatic plants like Vallisneria. (Class 11, Chap. 2)

• Entomophily: Transfer of pollen grains by insects like bees, butterflies, etc., who visit flowers for nectar and pollen collection. (Class 11, Chap. 2)

Pollen-pistil interaction:

• Pollen lands on the stigma, followed by the germination of the pollen grain, forming the pollen tube. (Class 11, Chap. 2)

• The pollen tube grows through the style towards the ovary, carrying the male gametes (sperm). (Class 11, Chap. 2)

Fertilization:

• The process where the sperm nuclei fertilize the egg cell (female gamete) to form the zygote. (Class 11, Chap. 2)

• Another fertilization event involving the fusion of one male gamete with the two polar nuclei of the female gametophyte leads to the formation of the primary endosperm nucleus. (Class 11, Chap. 2)

Types of endosperm development:

• Cellular endosperm: Develops through repeated division of the primary endosperm nucleus, resulting in the formation of cellular structures. (Class 11, Chap. 2)

• Free-nuclear endosperm: Primary endosperm nucleus undergoes repeated divisions without cytokinesis, resulting in a multinucleated condition. (Class 11, Chap. 2)

Embryo development and stages:

• Globular stage: Initial zygote undergoes mitotic division to form a globular structure. (Class 11, Chap. 2)

• Heart-shaped stage: Differentiation of cells leads to the formation of two distinct regions, the proembryo and suspensor. (Class 11, Chap. 2)

• Mature embryo: Proembryo develops into an embryo with distinct structures, such as cotyledons, hypocotyls, epicotyls, and the root-shoot axis. (Class 11, Chap. 2)

Apomixis:

• Asexual reproduction in flowering plants without the involvement of fertilization or meiosis. (Class 12, Chap. 2)

• Types: Adventive embryony (embryo develops from somatic cells) and nucellar embryony (embryo develops from nucellus). (Class 12, Chap. 2)

Significance of sexual reproduction in flowering plants:

• Promotes genetic diversity by combining genetic information from different parents. (Class 11, Chap. 2)

• Enhances adaptation to changing environments through the introduction of new genetic combinations. (Class 11, Chap. 2)

• Production of viable seeds, aiding in the dispersal and establishment of new plants. (Class 12, Chap. 2)

Examples and case studies:

• Self-pollinating plants: Wheat, pea, tomato.

• Cross-pollinating plants: Maize, sunflower, rose.

• Wind-pollinated plants: Grasses, birch, ragweed.

• Insect-pollinated plants: Orchids, sunflowers, marigold.

• Water-pollinated plants: Vallisneria, Zostera.

Please note that this is not an exhaustive list, but these details provide valuable insights into the topic for focused preparation. It is crucial to refer to the NCERT Biology textbooks for Class 11 (Chapter 2, “Reproductive Parts of a Flower” and Chapter 5, “Pollination and Fertilization”) and Class 12 (Chapter 2, “Sexual Reproduction in Flowering Plants”).