CBSE Class 12 Biology NCERT Solutions: Sexual Reproduction in Flowering Plants

Solution: The development of the male gametophyte, which is the pollen grain, occurs within the anther, specifically inside the pollen chamber. The development of the female gametophyte, known as the embryo sac, takes place inside the ovule, originating from a functional megaspore within the nucellus.

Solution:

Microsporogenesis and megasporogenesis are distinct processes in plant reproduction:

Feature	Microsporogenesis	Megasporogenesis
Process	Formation of microspores (pollen grains) from a microspore mother cell.	Formation of megaspores from a megaspore mother cell.
Location	Occurs inside the pollen sac of the anther.	Occurs inside the ovule, within the nucellus.
Cell Division	Involves meiosis (reductional division).	Involves meiosis (reductional division).
Structure Formed	Forms a tetrad of haploid microspores from a diploid microspore mother cell.	Forms four haploid megaspores from a diploid megaspore mother cell. Typically, one megaspore is functional.

The type of cell division that occurs during both microsporogenesis and megasporogenesis is meiosis. This reductional division is crucial for producing haploid microspores and megaspores from diploid mother cells, which are essential for sexual reproduction.

Solution: The correct developmental sequence for the formation of male gametes in angiosperms is as follows:

1. Sporogenous tissue: This is the initial tissue within the microsporangium responsible for producing microspores.
2. Pollen mother cell: Cells derived from the sporogenous tissue that undergo meiosis.
3. Microspore tetrad: A group of four haploid microspores formed after meiosis of a single pollen mother cell.
4. Pollen grain: Each microspore develops into a pollen grain, which is the immature male gametophyte.
5. Male gametes: The pollen grain matures and divides to form two male gametes.

This sequence illustrates the process from undifferentiated cells to the functional male gametes required for fertilization.

Solution:

An ovule, also known as a megasporangium, is the structure within the ovary of a flowering plant that contains the female gamete (egg cell). It develops into a seed after fertilization. A typical angiosperm ovule has the following parts:

• Funicle: The stalk that attaches the ovule to the placenta within the ovary.
• Hilum: The point where the funicle is attached to the main body of the ovule.
• Integuments: Protective outer layers that surround the nucellus, except at the micropyle. Typically, there are one (unitegmic) or two (bitegmic) integuments.
• Nucellus: The main body of the ovule, consisting of parenchymatous cells rich in stored food reserves. It contains the embryo sac.
• Micropyle: A small opening or pore at the tip of the ovule, through which the pollen tube usually enters during fertilization.
• Chalaza: The basal part of the ovule, opposite to the micropyle, where the integuments and nucellus merge.
• Embryo sac (Female Gametophyte): Located within the nucellus, this is a multicellular structure containing the egg cell and other nuclei essential for fertilization.

The diagram below illustrates these parts: