Govt. Exams
Entrance Exams
In Polygonum type (typical angiosperm), the functional megaspore undergoes three successive mitotic divisions producing eight nuclei in seven cells. The three degenerate megaspores are absorbed.
The fibrous thickening of endothecial cells creates differential drying patterns that generate mechanical stress, causing anther rupture and pollen dehiscence.
Heterospory (production of two types of spores) is a characteristic of advanced groups including most gymnosperms and all angiosperms, where microspores develop into male gametophytes and megaspores into female gametophytes.
The tapetum is derived from the innermost layer of the anther wall, which develops from the middle layers. It undergoes mitotic divisions to form the nutritive tissue for pollen development.
The endosperm is triploid (3n) because it develops from the primary endosperm nucleus, which is formed by fusion of two polar nuclei (2n) and one sperm nucleus (n).
The generative nucleus lies within the vegetative (or tube) cell in mature pollen. The vegetative cell also contains a large vacuole.
The fusion of two polar nuclei (2n) with one sperm nucleus (n) produces the primary endosperm nucleus (3n), which develops into the endosperm tissue.
The nucellus is the nutritive tissue surrounding the megasporangium that provides nutrients to the developing megaspore and female gametophyte.
Apomixis is asexual reproduction through seeds where the embryo develops from an unfertilized egg cell (apomeiotic parthenogenesis) or other cells without meiosis or fertilization.
The tapetum is a nutritive tissue layer that provides nutrients to developing microspores and pollen grains through absorption and transfer.
