Most plant species are characterized by the presence of both sexual and asexual reproduction. Each type of breeding has its own advantages. In different groups of plants, in the process of evolution, various organs and forms of sexual reproduction have been formed.
The material was prepared together with a teacher. Experience as a biology teacher over 19 years.
Sexual reproduction of angiosperms
The highest group of plants are angiosperms or flowering plants. Consider which parts of the plant are involved in sexual reproduction.
Sex cells (gametes) develop in a flower:
- male – in stamens (anthers);
- female – in the ovary of the pistil (in the ovule).
In order for the fertilization process (gamete joining) to take place, the pollen containing the male gametes must be transferred to the pistil. This can be facilitated by wind, insects, water, and even humans.
Inside the pistil, there is a fusion of two sperm with two cells (ovum and central cell):
- 1 sperm + egg = zygote (future embryo);
- 2 sperm + central cell = endosperm (nutrient tissue).
The type of reproduction of flowering plants is called double fertilization.
After the formation of the zygote and endosperm, the process of turning the flower into a fruit begins, which contains seeds – the rudiments of a new generation of plants.
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Gymnosperms and spore plants are characterized by the alternation of sexual and spore generation.
From the zygote, a sporophyte grows a generation in which spores develop.
A gametophyte, also called an outgrowth, grows from the spore. This is a sexual generation with special organs – gametangia. Sex cells develop in gametangia. After leaving the gametangia, male gametes merge with female ones, forming a zygote.
In gymnosperms, the sexual process takes place inside the cones and does not depend on the availability of water. In spore plants, gametes are combined only in water; therefore, spore plants are dependent on the moisture factor.
The gametophyte of gymnosperms is highly reduced and consists of only a few cells of the pollen grain. It develops in male and female bumps. The wind carries pollen from the male cone to the female, where fertilization and seed development takes place.
For spore plants, a different ratio of sporophyte and outgrowth in the life cycle is characteristic. So, in fern-like outgrowths are small, asexual generation-sporophyte prevails.
In mosses, on the contrary, the gametophyte dominates over the sporophyte. Mosses have male and female plants.
Algae are characterized by various forms of sexual reproduction.
Some multicellular algae have special cells in which gametes develop. Gametes go out into the water and form a zygote, from which a new organism grows.
There is a special type of sexual reproduction in which there is no increase in the number of organisms. This is conjugation, a temporary connection of algal cells for the exchange of genetic material.
The essence of sexual reproduction is the unification of the genetic information of parental individuals in the hereditary material of a new generation.
A number of unicellular species are characterized by cell fusion. It occurs under unfavorable conditions. After fusion, the cell is covered with a protective membrane and stops moving.
Under normal conditions, the cell divides into 4 new-generation motile cells.
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Sexual reproduction of plants takes place in various forms. The reproductive organ of flowering plants is the flower. Gymnosperms and spore plants are characterized by a change of generations that reproduce sexually and asexually. The advantage of sexual reproduction over asexual is the receipt of new combinations of genes, which increases the vitality of organisms.