Plant biology and ecology

Biology

Blake

The Features and Functions of Seeds seed can be simply defined as the propagule that seed plants produce, with this propagule helping to protect, nourish, and disperse the offspring of the plant. This is a simple definition that effectively describes the function of the seed, but the biology is a little more complex.

A seed is produced by a megasporangium. The megasporangium produces a megaspore. The megaspore develops into a female gametophyte and is fertilized. An sporophyte embryo also develops. These are all enclosed within an integument. This entire structure of the seed is often referred to as the ovule. Overall then, a seed is made up of a megagametophyte, which is the female gametophyte, and a sporophyte embryo, enclosed by an integument. Functionally, the integument protects the female gametophyte. The sporophyte embryo provides nourishment. The seed also allows for dispersal, both because the female gametophyte is fertilized, protected, and nourished, and because the male gametophyte is dispersed as pollen. The explanation of how the seed and pollen allows for dispersal can be explained by considering how it solves the problem of terrestrial life for plants.

The seed solved the problem of terrestrial life in several ways. Firstly, it is important to note that as well the female part, which is the seed, a male part is also needed for reproduction. The male parts are in the form of pollen grains, with these produced from microspores. Like the female part, the male part is also fertilized. This means that the distance over which the male part can travel is not limited by the distance that a sperm can travel. This partially solves the problem of terrestrial life for plants.

The next important point is that the development of the new plant does not depend on fertilization. Instead, it depends on pollination. Pollination refers to the process where the male gametophyte, in the form of pollen, travels to the female gametophyte, in the form of the seed. The pollen can travel over a much greater distance than sperm. This ability to disperse is important and reduces the requirement for water. In saying this, it must be noted that when the male part is in the form of sperm, it requires water. This is partly because the sperm does not have any vascular tissue. This is also because the sperm's only form of movement is swimming, which clearly requires water. For terrestrial plants then, not having water is a major problem. Having a seed and pollen solves this problem and makes dispersal without water possible.

Pollination then occurs when a pollen grain reaches a seed and passes through its micropyle, a tiny hole in the seed covering present exactly for this purpose. The male and female parts then meet and a new plant is produced. Most importantly, there is no requirement for water for this process to occur, making terrestrial plant life feasible.