CBSE Class 12 Biology Chapter 2: Sexual Reproduction in Flowering Plants NCERT Solutions

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, also known as the embryo sac, takes place within the ovule, originating from a functional megaspore within the nucellus.

Solution:

Microsporogenesis and megasporogenesis are distinct processes in the formation of gametophytes in flowering plants:

• Microsporogenesis: This is the process of the formation of microspores (which develop into male gametophytes) from a microspore mother cell. It occurs within the pollen sac of the anther.
• Megasporogenesis: This is the process of the formation of megaspores (which develop into the female gametophyte) from a megaspore mother cell. It occurs within the ovule, in the region of the nucellus.

The type of cell division that occurs during both microsporogenesis and megasporogenesis is meiosis (reductional division). This ensures that the resulting spores, and subsequently the gametes, are haploid.

At the end of microsporogenesis, haploid microspores are formed, typically in a tetrad. At the end of megasporogenesis, usually, one functional haploid megaspore is formed from a tetrad of megaspores, with the other three degenerating.

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

1. Sporogenous tissue: This diploid tissue within the microsporangium contains cells that will give rise to microspores.
2. Pollen mother cell: Each cell of the sporogenous tissue differentiates into a diploid pollen mother cell (microspore mother cell).
3. Microspore tetrad: The pollen mother cell undergoes meiosis to form a tetrad of four haploid microspores.
4. Pollen grain: Each microspore in the tetrad develops into a haploid pollen grain.
5. Male gametes: The pollen grain matures and divides to form male gametes.

Therefore, the sequence is: Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes.

Solution:

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

• Funicle: The stalk that attaches the ovule to the placenta in the ovary wall.
• Hilum: The point where the funicle is attached to the main body of the ovule.
• Integuments: Protective outer layers that surround the nucellus. Typically, there are one (unitegmic) or two (bitegmic) integuments.
• Nucellus: The main part of the ovule, consisting of a mass of parenchymatous cells, which contains the megasporocyte (megaspore mother cell). It provides nourishment to the developing embryo sac.
• Embryo sac (Female gametophyte): Located within the nucellus, this is a small sac containing the female gamete (egg cell) and other nuclei. It develops from the functional megaspore.
• Micropyle: A small opening or pore in the integuments through which the pollen tube usually enters during fertilization.
• Chalaza: The basal part of the ovule opposite to the micropyle, representing the base of the nucellus.
• Micropylar pole: The end of the ovule containing the micropyle.
• Chalazal pole: The end of the ovule containing the chalaza.

(Note: A diagram would typically be included here to visually represent these parts.)