The theme: "Why are flowering plants called fertilization double" are studied in the sixth grade of the school. However, not every adult person will be able to explain the subtleties of this process.
Plants, like all living things, multiply, using three main methods. The first is vegetative, that is, a new plant appears from any part of its "parent" - the root, stem, leaf, even a single cell. The second one is called asexually, because the plants appear from the spores and look like maternal. So mushrooms and some algae breed. The most perfect is the fertilization of plants by the sexual method.
In the plant world, this process occurs through the fusion of gametes, which may be the same in size (isogamy), different in size (heterogamy) and fundamentally different from each other (oogamy). We can say that fertilization is the process of combining the male (sperm) and female (egg) gametes, as a result of which a cell with a doubled set of chromosomes (zygote) is formed, from which a new plant will appear.
Why do flowering plants call fertilization double? Here there is a special organ of reproduction - a flower. Its constituent parts are: stamens on filaments with anther (contains pollen), ovary, column, pestle (with stigma), a pollen tube that reaches the embryo sac where the ovule is located. From the course of school biology, many remember something about the pistil and stamen and may think: that's why in flowering plants fertilization is called double. But this is not so.
In the anther, as already mentioned, pollen is formed, which consists of two cells - a large vegetative and smaller in size, generative. When the anther expands, these elements are spread by wind or insects. Once on the pestle (directly on the stigma), the pollen cells germinate so that the vegetative part becomes a pollen tube attached to the embryo sac. Through it a generative cage enters the sac, which during its penetration is divided into two sperm. One of them reaches the ovum, merges with it, forming a zygote, and the second joins the secondary nucleus. This process is the reason why in flowering plants fertilization is called double.
Some modern plants successfully combine different ways of reproduction, which increases the survival rate of the species. And at a time when this process was just beginning, this way of reproduction was a very important, evolutionary process. This is due to the fact that the body, created through the fusion of cells with different sets of chromosomes, had greater variability and adaptability to the environment. Modern physico-chemical studies have shown how sexual reproduction of plants is complex in nature. For example, it was found that the pollen and stigma of the pistil have different pH levels, different levels of the isoelectric point of proteins, different enzyme and amino acid composition, which, however, contributes to the optimal course of physiological processes when these cells are combined.