AP BIOLOGY

Detailed explanation-1: -A pollen grain on the stigma grows a tiny tube, all the way down the style to the ovary. This pollen tube carries a male gamete to meet a female gamete in an ovule.

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: -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).

Detailed explanation-4: -After a pollen grain lands on a receptive stigma of a pistil, a pollen tube germinates from the hydrated pollen grain and delivers the immotile sperm cells over a long distance toward the ovule. A pollen tube is a tip-growing cell that grows surprisingly fast.

Detailed explanation-5: -The pollen grain fallen on stigma starts germinating pollen tube to rich ovules.