Understanding Angiosperm Flower Anatomy and Reproduction

Angiosperms: The Flower

1. Floral Peduncle: The peduncle is the stalk that connects the flower to the plant.

2. Floral Receptacle: The receptacle is the expanded end of the peduncle where the floral parts (whorls) are attached. These include the calyx, corolla, androecium, and gynoecium.

Calyx

3. Sepals: The calyx consists of sepals, which are modified leaves that protect the developing flower bud.

Gynoecium (Female Reproductive System)

4. Ovary: The ovary contains one or more ovules (seminal primordia). Each ovule is attached to the ovary wall by a short stalk called the funiculus. The region where the ovule is inserted is called the placenta.

5. Carpels: The gynoecium is composed of one or more carpels, which are fused, bottle-shaped structures. Each carpel features a widened basal part (the ovary), a neck-like extension called the style, and an opening at the top called the stigma, where pollen grains are deposited.

6. Ovule Structure: Each ovule is protected by two integuments (primary and secondary), which surround the ovule almost completely, except for a small opening called the micropyle. The nucellus, or macrosporangium, forms the main body of the ovule, containing the embryo sac mother cell.

7. Embryo Sac Development: The embryo sac mother cell undergoes meiosis, resulting in four haploid daughter cells arranged in a row. Three of these cells degenerate, and the cell closest to the micropyle develops into the embryo sac. The nucleus of the embryo sac undergoes three successive mitotic divisions, resulting in an eight-nucleate haploid cell.

8. Ovule Apparatus: Three of these nuclei migrate to the micropylar end and become organized as cells, forming the ovule apparatus. This apparatus consists of the oosphere (egg cell) in the center and two synergids on either side.

9. Antipodal Cells and Secondary Nucleus: The other three nuclei migrate to the opposite end of the embryo sac and become organized as antipodal cells. The remaining two nuclei fuse together in the center of the embryo sac, forming a diploid secondary nucleus.

Androecium (Male Reproductive System)

4. Androecium: The androecium is the male reproductive system, consisting of stamens. Each stamen has a filament that widens at its end to form the anther.

Corolla

5. Corolla: The corolla is composed of petals, which are often brightly colored to attract pollinators. Together with the calyx, the corolla forms the perianth.

Anther

6. Anther Structure: The anther is divided into two lobes (thecae), each containing two microsporangia or pollen sacs, where the pollen mother cells are located.

7. Microspore Formation: Each pollen mother cell undergoes meiosis, resulting in four microspores. Each microspore develops a double-layered wall: an external, thick, and resistant layer (exine) and an internal, fine, and delicate layer (intine).

8. Pollen Grain Development: The nucleus of the microspore undergoes mitosis, resulting in a vegetative nucleus and a generative nucleus. The generative nucleus then divides again by mitosis into two sperm nuclei. The resulting pollen grain contains three haploid nuclei: the vegetative nucleus and two sperm nuclei.