NEET BIOLOGY

Detailed explanation-1: -When the pollen grain lands on the stigma, chemical communication occurs between the pollen grain and the pistil, helping the pistil recognize the right type of pollen. After acceptance, pollen begins to germinate and the pollen tube develops towards the ovary carrying the male gamete.

Detailed explanation-2: -After pollen lands on the stigma, it initiates pollen tube formation. Pollen tubes are channels which grow down the length of the style to the ovules. After a pollen grain travels down a pollen tube it intercepts an ovule, fertilizes the female germ cells and initiates seed development.

Detailed explanation-3: -When the pollen is transferred from the anther of a flower to the stigma of the same flower or to the stigma of another flower of the same plant, it is called self pollination. Self pollination is also called autogamy.

Detailed explanation-4: -When pollen gran falls on stigma, it germinates on stigma and produce pollen tube which enters into the ovule release 2 male gametes and fuse with the ovule to form a seed.

Detailed explanation-5: -If the pollen and the stigma are compatible, the pollen takes up water (hydrates) and the pollen tube emerges. The pollen tube grows down the style of the carpel toward the micropyle (Figure 20.10). The tube nucleus and the sperm cells are kept at the growing tip by bands of callose (a complex carbohydrate).