MP Board · Class 12 · Biology · Sexual Reproduction in Flowering PlantsExplain the structure of a typical anatropous ovule with the help of a well-described anatomical breakdown. Discuss its various parts and their respective functions.

Introduction to Anatropous Ovule\nThe ovule, also known as the megasporangium, is the structure that gives rise to and contains the female reproductive cells. In angiosperms, the most common type of ovule is the anatropous ovule, in which the body of the ovule becomes completely inverted during development, placing the micropyle close to the funicle.

Detailed Structure and Parts of an Anatropous Ovule

• Funicle: It is the stalk by which the ovule is attached to the placenta of the ovary. It provides structural support and vascular connection for nutrient transport.
• Hilum: It represents the junction between the ovule and the funicle. After detachment of the seed, the hilum remains as a scar on the seed coat.
• Raphe: In an anatropous ovule, the funicle is fused with the main body of the ovule along one side, forming a longitudinal ridge called the raphe.
• Integuments: These are protective envelopes or coverings that surround the nucellus entirely, except for a small opening at the tip called the micropyle. Typically, there are two integuments: an outer integument and an inner integument.
• Micropyle: A tiny pore or opening left by the integuments at the distal end. It serves as the entry point for the pollen tube during fertilization and allows the absorption of water during seed germination.
• Chalaza: The basal part of the ovule located opposite to the micropylar end. It represents the region where the nucellus, integuments, and funicle merge.
• Nucellus: The central mass of parenchymatous tissue enclosed within the integuments. It provides nutrition to the developing embryo sac. In some seeds, residual nucellus is retained as perisperm (e.g., black pepper, beet).
• Embryo Sac (Female Gametophyte): Located inside the nucellus, it typically contains a 7-celled and 8-nucleate structure comprising an egg apparatus (one egg cell and two synergids), three antipodal cells, and a central cell with two polar nuclei.

Significance\nThe complex yet organized structure of the anatropous ovule ensures efficient pollination, protection of the female gametophyte, successful double fertilization, and subsequent transformation into a well-protected seed capable of surviving adverse environmental conditions.