Lecture: Sexual Reproduction in Flowering Plants

Key Concepts

• Angiosperms: Also known as flowering plants.
• Life Cycle of Angiosperms
  • Two generations: Sporophyte and Gametophyte
  • Sporophyte: Diploid generation that reproduces asexually by means of spores.
  • Gametophyte: Haploid generation that reproduces sexually by forming gametes.

Alternation of Generations

• Sporophyte gives rise to Gametophyte and vice versa.
• Dominant generation in angiosperms is the sporophyte.

Types of Spores

• Heterosporous: Two types of spores; large female spores called Megaspores and smaller male spores called Microspores.
• Angiosperms are heterosporous.

Reproductive Structures

• Sporophylls: Leaf-like structures concerned with spore production.
  • Megasporophyll: Represented by carpels (female structure).
  • Microsporophyll: Represented by stamens (male structure).

Megasporangium and Microsporangium

• Megasporangium: Inside the ovule; produces megaspores.
• Microsporangium: Represented by pollen sacs in stamens; produces microspores.

Gametophytes

• Male Gametophyte: Also called pollen (single cell that becomes multicellular).
• Female Gametophyte: Also known as embryosac.
• Both gametophytes are haploid.

Pollination and Fertilization

• Pollination: Transfer of pollen grains from male to female flowers.
• Siphonogamy: Fertilization through the formation of a pollen tube.
• Zygote Formation: Fusion of male and female gametes to form a diploid zygote.

Meiosis and Mitosis in Reproduction

• Sporic Meiosis: Meiosis occurring at the time of spore formation.
• Gamete Formation: Haploid cells are formed through mitosis from the gametophyte.

Structure of the Stamen

• Anther: Typically bilobed, containing four pollen sacs (microsporangia).
• Layers: Epidermis (outermost), Endothecium, and Middle Layers.
  • Tapetum: Innermost layer providing nutrition, forming exine of pollen grains and pollen kit for sticking to insects.

Microsporogenesis

• Process of Microsporogenesis: Formation of microspores through meiosis.
• Each microspore mother cell undergoes meiosis to form four haploid microspores.

Pollen Grain Structure

• Exine: Outer layer, made of sporopollenin, highly resistant to biological degradation.
• Intine: Inner layer, made of pecto-cellulosic material.
• Germ Pores: Areas where exine is absent to allow for germination.

Important Terms

• Tectum: Outer covering of exine with species-specific patterns.
• Dehiscence: Opening of the anther to release pollen.
• Tetrad: Group of four microspores formed after meiosis.