Botany and Plant Science

The movement of pollen tube towards embryosac though style is chemotactic as it secrets pectinases and other hydrolytic enzymes to create a passage for its entry into style .

In porogamy, filiform apparatus of synergids secretes, some chemotropically active sunstances, which direct the pollen tube towards micropyle of ovule.

The pollen grain wall consists of an outer exine (sporopollenin) and an inner intine. The intine is composed of pecto-cellulose.

This type of tapetum can be seen easily in Alisma, Butomus, Tradescantia, and Typha, etc. The tapetal cells fuse among themselves for forming a tapetal plasmodium. The protoplast of the fused tapetal cells then moves into the locule, where they surround the pollen mother cells or pollen grains. This protoplast movement into the locule is taking place during meiotic prophase. 

Thus the correct answer is option D.

The pollen wall actually is the multi-layered structure that includes an intine, which is composed mainly of polysaccharide, and an exine, which consists mainly of sporopollenin. The exine can be further divided into the sexine and nexine. Sexine is the single layer of bacula which is covered by a layer of the tectum.

So the correct answer is C.

The anther is responsible for the production of microspores (pollen grains), the production of Ubisch bodies (which contribute to exine formation), and the protection/storage of developing pollen.

In the development of the ovule, the archesporial cell typically differentiates from the nucellar tissue in the hypodermal region at the micropylar end.

Abundant occurrence and preservation of the fossil pollen grains result from the extremely resistant nature of the outer wall of the pollen grains. This wall is the exine and composed of a compound commonly known as sporopollenin. It originates from the polymerization of carotenoids and carotenoid esters.

Thus the correct answer is B. 

Antipodal cells are part of the mature embryo sac and are haploid (n). The egg cell is also haploid (n). Nucellus and megaspore mother cells are diploid (2n).

A pollen grain is the male gametophyte in seed plants. At the time of release, it is considered an immature male gametophyte.

Nucellus, embryo sac, and micropyle are all parts of the ovule. A pollen grain is a separate structure (the male gametophyte) that is not part of the ovule itself.

Asphodelus is known to have a tritegmic ovule, meaning it has three integuments. Most angiosperms are bitegmic or unitegmic.

The pollen is having two layers. The tough outer layer is referred to as the exine. This sophisticated and complex outer layer is having a compound known as sporopollenin. It is waterproof, resistant to the deterioration and very stiff as well. This shell is actually one of nature's most advanced polymers. It ensures that the tender cells must have a strong chance of survival.

Thus the correct answer is option D.

A crassinucellate ovule is characterized by a well-developed nucellus, where the primary parietal cell divides to form a layer of parietal tissue between the epidermis and the megaspore mother cell.

Each microsporocyte (microspore mother cell) undergoes meiosis to produce 4 microspores (pollen grains). Therefore, 4 microsporocytes produce 4 * 4 = 16 pollen grains.