Video Transcript
What is the correct sequence of structures through which a pollen tube grows? (A) Stigma, style, integuments, ovule. (B) Style, filament, micropyle, ovule. (C) Stigma, style, micropyle, ovule. (D) Stigma, filament, micropyle, ovule. Or (E) style, stigma, micropyle, ovule.
Pollen is a powdery substance that contains the male gamete of angiosperms, which are otherwise known as flowering plants. The function of the male gamete is to reach and fertilize an egg cell, which is the female gamete of an angiosperm. It does this by forming a structure called a pollen tube. Let’s take a look at an overview of how the male gamete reaches the egg cell.
This diagram shows the basic structure of the female reproductive organs in an angiosperm’s flower. They consist of a sticky structure at the top called a stigma, which is connected by a structure called the style to the ovary. The ovary contains one or sometimes more ovules, which in turn each contain one egg cell, the female gamete, when they are fully mature. The ovules are surrounded by a layer of integuments, in this case two integuments. But this number will vary between different plant species.
When a pollen grain that contains the male gamete first lands on the female part of a flower in pollination, it makes contact with the stigma. Next, a structure called a pollen tube begins to grow down from the stigma and through the style. The pollen tube grows toward the ovary, which contains the ovule and therefore the egg cell. The male nuclei travel along the pollen tube. There is a small gap in the integuments that surround the ovule called the micropyle. The pollen tube and the male nuclei within it can then enter the micropyle. Once the pollen tube has entered the ovule, it stops its growth, but it provides an entrance point for the male nuclei to enter the female ovule and fertilize the egg cell.
The sequence of structures through which a pollen tube grows is therefore (C): stigma, style, micropyle, ovule.
