Question

In angiosperms, endomitosis occurs in
A. Ovule
B. Tapetum
C. Endothecium
D. Leaf tip

Answer 1

Endomitosis is the replication of the nuclear genome without the process of nuclear or cell division leading to polyploidy conditions i.e., elevated nuclear genome content. The replication of the genome takes place in the S phase of the cell cycle and hence, in endomitosis the S-G cycles are repeated which generates multiple copies of the nuclear genome followed by the initiation of mitosis but some processes of mitosis are missing.

Complete answer:
Option (A) is incorrect. Ovule, in angiosperms, is present inside the ovary which gives rise to female reproductive cells. In ovules, megaspore mother cells (MMCs) are present that are diploid and thus each MMC undergoes meiotic division to produce four haploid megaspores.
Option (B) is correct. Tapetum, being composed of nutritive cells, is a specialized layer within the anther of angiosperms. It is meant for providing nutrition to the pollen grains produced inside the anther. This layer is produced by the process of endomitosis which generates elevated nuclear genome content that helps in providing nutrients and regulatory molecules to the developing pollen grains.

Structure of anther showing the layer of tapetum.
Option (C) is incorrect. Endothecium is a layer just beneath the epidermis of the wall of the anther. Thus, the ploidy (number of chromosomes) in the endothelium is ‘2n’.
Option (D) is incorrect. Leaf tip in angiosperms possesses a ‘2n’ number of chromosomes as the leaves are derived from the zygote (2n). So, each cell of the leaf tip will be in a diploid condition indicating that endomitosis has not occurred in the leaf tip of angiosperms.

Hence, the correct option is (B).

Note: Tapetum is the innermost layer in the anther that has its role in providing nutrients and enzymes for the process of microsporogenesis or formation of pollen grains and the maturation of pollen grains. In Tapetum, polyploidy condition exists due to the replication of the nuclear genome without the nuclear division, and this process is known as endomitosis.