Life Cycle of Flowering Plants

Life Cycle of Flowering Plants

• Haploid and Diploid Stages: Flowering plants exhibit alternating haploid (gametophyte) and diploid (sporophyte) phases, with the haploid stage significantly reduced.
• Flower Structure: Flowers are specialized organs for sexual reproduction, harboring male and female gametes.
• Male Gametes: Produced in pollen grains within anthers.
• Female Gametes: Generated in embryo sacs located inside ovules within the ovaries.
• Pollination Mechanism: Pollen is transferred to the stigma, often facilitated by animals (insects, birds) or wind, ensuring cross-pollination.
• Fertilization Process: Upon pollen germination, a tube grows down the style, leading to the ovule where a diploid zygote is formed from the fertilization of the egg cell. The ovule subsequently develops into a seed.

Plant Growth Substances

• Chemical Signaling: Plants utilize chemicals for communication and regulation, typically synthesized near action sites rather than in endocrine glands.
• Key Plant Hormones:
  • Auxins: Stimulate cell elongation and regulate growth.
  • Gibberellins: Promote stem growth and seed germination.
  • Cytokinins: Encourage cell division.
  • Abscisic Acid: Inhibits growth and seed germination.
  • Ethylene: Triggers fruit ripening.

Seed Banks

• Definition: A seed bank refers to a reserve of dormant seeds in the soil, allowing rapid regrowth after environmental disturbances (e.g., fire, drought).

Asexual Reproduction in Plants

• Complementary Reproductive Strategies: Many plants utilize both sexual and asexual methods, each providing distinct advantages.
• Variation and Adaptation: Sexual reproduction introduces genetic variation, beneficial for adapting to evolving environmental pressures.
• Rapid Cloning: Asexual reproduction allows well-suited plants to quickly clone themselves, maintaining stability in established environments.

Types of Asexual Reproduction

• Rhizomes: Underground stems that produce new plants through nodal shoots.
• Tubers: Enlarged underground stems, such as potatoes, capable of breaking apart for vegetative reproduction.
• Bulbs: Underground buds with fleshy leaves, forming new plants like lilies and onions.
• Stolons: Horizontal, above-ground stems that can create new plants at their nodes.

Gametophyte Development

• Male Gametophyte: The pollen grain serves as the male gametophyte, initially functioning independently for a brief period after formation.
• Female Gametophyte: Made up of the embryo sac, containing a megaspore that becomes the egg cell and polar nuclei for future nourishment.

Pollination and Fertilization

• Pollination Explanation: The transfer of pollen from anther to stigma initiates the union of male and female gametophytes.
• Double Fertilization: Characteristic of angiosperms, includes one sperm fusing with the egg to create a zygote and another sperm merging with polar nuclei to form endosperm, essential for seed development.

Explore the fascinating life cycle of flowering plants, focusing on the haploid and diploid stages. Understand the structure of flowers, the role of male and female gametes, and the processes of pollination and fertilization. Dive into the chemical signaling involved in plant growth and reproduction.