Sexual Reproduction in Flowering Plants MCQs

Xenogamy... This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.

The ears you see are nothing but the stigma and style which wave in the wind.

In Vallisneria, the female flower reach the surface of water... pollen grains are released on to the surface of water.

In... seagrasses, female flowers remain submerged in water and the pollen grains are released inside the water.

A typical microsporangium is surrounded by four wall layers: the epidermis, endothecium, middle layers, and tapetum. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen. The innermost layer is the tapetum which nourishes the developing pollen grains.

The wall layers from outside to inside are epidermis, endothecium, middle layers, and tapetum. The center is occupied by sporogenous tissue.

The cells of the sporogenous tissue (PMCs) are diploid (2n) and undergo meiosis to form microspore tetrads, which are haploid (n).

The hard outer layer called the exine is made up of sporopollenin, which is one of the most resistant organic materials known. It withstands high temperatures, strong acids, and alkalis, allowing pollen to be preserved as fossils.

In over 60 percent of angiosperms, pollen grains are shed at the 2-celled stage, comprising a large vegetative cell and a small generative cell. In the remaining species, the generative cell divides to form two male gametes before shedding (3-celled stage).

The vegetative cell is bigger, has abundant food reserve, and a large irregularly shaped nucleus. The generative cell is small, spindle-shaped, and floats in the cytoplasm of the vegetative cell.