AP BIOLOGY

Detailed explanation-1: -Pollen tubes serve to deliver sperm cells to the ovule and thus initiate the crucial process of seed development. For successful fertilization, pollen must germinate on the stigma, grow through the style, and find and penetrate the ovule micropyle.

Detailed explanation-2: -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-3: -Due to the spatial separation between male and female pollen grains from the anther of most flowering plants, including orchids, pollens are transported by wind or animals and deposited onto the receptive surface of the stigma of a different plant.

Detailed explanation-4: -In most angiosperms, from pollen landing on the stigma to fertilization inside the ovary, the pollen tube has to traverse an intermediate territory, the style (Figure 1). The pollen tube grows through a stylar canal or a stylar transmitting tissue, and reaches the locule cavity of the ovary where the ovule is located.