Sexual reproduction - this is a type in which new individuals are formed as a result of the sexual process. The sexual process consists of the fusion of two sex cells - gametes - and the formation of a zygote. The fusion of gametes is called fertilization.
Biological role the sexual process is that it ensures the emergence of genetically diverse offspring, combining and varying combinations individual characteristics maternal and paternal organisms. The offspring are more vital, more adapted to external conditions.
There are 4 types of sexual process in plants: isogamy, heterogamy, oogamy and conjugation.
In progress isogamy a union of two mobile and morphologically identical gametes occurs. This is the most primitive type of sexual reproduction, widespread in many algae and fungi. In heterogamy, the gametes are mobile, but the male gametes are small and the female gametes are larger. , it is observed in green and brown algae. In oogamy, gametes differ in shape and size. The female gamete is immobile, large (ovum); male - small, mobile (sperm), in conifers and angiosperms it loses mobility and is called sperm. Sex gametes are formed in gametangia. In lower plants the gametangia are unicellular, in higher plants they are multicellular. In lower plants, the gametangia in which eggs are formed are called oogonia; in higher plants, they are called archegonia. Male gametangia are called antheridia. During conjugation, gametes are not formed, but the contents of two vegetative cells merge.
That period or phase in the life cycle which is associated with the formation of organs asexual reproduction- spore, called asexual generation, or sporophyte. The phase associated with the formation of reproductive organs and sexual gametes is called the sexual generation, or gametophyte. In other words, sporophyte and gametophyte are two interconnected phases in the plant development cycle that reproduce each other. A gametophyte includes everything that develops from a spore to a zygote, and a sporophyte includes everything that develops from a zygote to a spore.
Spores are haploid formations, and from them the haploid gametophyte develops. Sex cells - gametes - are also haploid. During the sexual process, male and female gametes fuse to form a diploid zygote. From the zygote an organism develops, each cell of which also has a diploid set of chromosomes. Consequently, the sporophyte contains a diploid set of chromosomes in the nuclei of its cells, but haploid cells - spores - are formed in the sporophyte. Thanks to the alternation of generations, plants produce abundant and different-quality offspring.
Everyone has multicellular organisms Haploid and diploid phases necessarily alternate, and reproduction occurs sexually. Plants have a diploid stage life cycle — sporophyte (from spore and Greek phyton- plant). At this stage, meiosis occurs, resulting in the formation of haploid spores, from which, under favorable conditions, sprouts gametophyte (from gamete And fiton)- haploid stage. It is at this stage that gametes are formed through mitosis. In the process of plant evolution, the diploid stage became increasingly important. In flowering plants, unlike ferns or mosses, the gametophyte has simply become part of the sporophyte.
Male gametophyte of flowering plants - pollen grains. This is where sperm are formed (Fig. 10). They are formed in anthers, where in large quantities contains pollen mother cells. It is these cells that undergo meiosis, turning into notebooks, some, in fact, form pollen grains. At first, pollen grains are single-celled. After the first mitotic division they become bicellular. One cell, called a vegetative cell, stops dividing. A pollen tube is formed from it. In the second cell - the generative one - another mitosis occurs; two nuclei are formed in it. As a result, a mature pollen grain is formed, consisting of two cells, one of which is binucleate.
The female sporophyte develops into ovule, where are the mother cells located? macrospores (Fig. 11). From each of them four are formed by meiosis macrospores, three of whom die. The remaining macrospore, called embryo sac, and is the female gametophyte. It goes through three mitoses. As a result, eight nuclei are formed in the embryo sac. They gather in three groups: two polar, containing three nuclei (one of them contains the egg), and a central one, consisting of two central nuclei, which, merging, give a diploid central body .Material from the site
Flower - organ of seed reproduction. It is a shortened modified shoot that performs the following functions: the formation of spores, female and male shoots, gametes, as well as pollination, fertilization, formation of seeds and fruits.
Bisexual flower - a flower containing both stamens and pistils (apple, potato, rye).
Staminate flower - a flower that has only stamens (cucumber, corn, poplar).
a flower that has only pistils (cucumber,
Pistillate flower.- a flower that has only pistils (cucumber,
corn, poplar).
Monoecious plant - plant with dioecious flowers
(cucumber, corn).
Dioecious plants - plants of the same species, in which
staminate and pistillate flowers are on different individuals(poplar,
sea buckthorn, hemp, mulberry).
Pedicel - the axial part of a flower between the flower and the bract.
Receptacle - the expanded part of the peduncle on which the sepals, petals, stamens, and pistils are located.
Perianth - the covering of a flower that protects the stamens and pistils and also promotes pollination.
A simple perianth. - a collection of identical leaves
not divided into a calyx and corolla: green - calyx-shaped perianth (beet, quinoa); white or colored corolla-shaped perianth (tulip).
Double perianth - combination of calyx and corolla
(apple tree, peas).
Calyx - the outer tepals, usually green, herbaceous, called sepals.
Whisk - inner tepals, usually bright
colored or white, called petals.
Stamen - part of a flower consisting of a filament and anther, in which small spores are formed and then
pollen.
Minor disputes - haploid cells that form
inside the anther as a result of meiosis. From them is formed
pollen.
Pollen - male prothallus (gametophyte) flowering plant; consists of two cells with a haploid set of chromosomes - vegetative and generative, covered with a double shell.
Vegetative cell - haploid cell, from which, when a pollen grain germinates, forms a pollen tube. It penetrates inside the ovary, enters the ovule through the pollen duct, and two sperm move along it to the egg.
Generative cell - a haploid cell from which, when a pollen grain germinates, two sperm are formed - male
gametes without flagella.
Pollination - transfer of pollen from the anthers to the stigma.
Self-pollination - transfer of pollen on the stigma of the pistil within one flower; usually occurs before the bud opens (peas,
wheat).
Cross pollination - transfer of pollen to the stigma of another flower (rye, corn, sunflower).
Natural pollination - pollen transfer by wind (cereals, birch, hazel); insects (apple tree, cucumber), birds.
Artificial pollination - transfer of pollen on the stigma of a pistil by humans for breeding purposes or in the absence of the possibility of natural pollination (greenhouse crop, calm weather).
Pestle - the central part of the flower; consists of from ovary, style and stigma; the stigma catches the pollen, the style carries it out
the stigma, the ovary protects the ovules and forms the fruit.
Ovule (ovule) - a modified sporangium of seed plants, in which large spores, female prothalla are formed and fertilization occurs. A seed is formed from the ovule.
Major disputes - haploid cells that are formed inside the ovule as a result of meiosis. Of the four spores, three die, one remains and divides three times mitotically. As a result, an embryo sac is formed.
Embryo sac - female prothallus of a flowering plant. It is one large cell with 8 haploid nuclei. By the time of fertilization, the nuclei are grouped in threes at the poles and two remain in the center. Nuclei are usually called cells.
Ovum - female gamete located at the pole of the embryo sac on the side of the pollen opening. On either side of it lie two satellite cells.
Central core - diploid nucleus formed in the center of the embryo sac from two fused polar nuclei.
Antipodes - three haploid cells lying at the pole of the embryo sac opposite the pollen opening.
Double fertilization- The sexual process in flowering plants, discovered in 1898 by S. G. Navashi, consists in the fact that one of the two sperm fuses with the egg, and the second with the central nucleus of the embryo sac.
Seed - the reproductive organ of a flowering plant, which is formed as a result of double fertilization from the ovule. The obligatory parts of the seed are the embryo and the peel; many plants have endosperm (cereals, nightshades, buckwheat,
poppy).
Seed embryo - a new generation formed as a result of the development of the zygote and having a diploid set of chromosomes. Consists of embryonic organs - root, stalk and bud. The first leaves of the embryo are cotyledons (cotyledons). Monocots have one cotyledon, dicots have two.
Endosperm of the seed - triploid nutritional tissue, which is formed as a result of double fertilization from triploid-
noy cells (central nucleus and sperm).
Fruit - the receptacle for the seeds of a flowering plant, formed from the ovary of a flower as a result of fertilization. Serves for preserving and distributing seeds. The pericarp is formed from the wall of the ovary, which is dry and juicy.
Simple fruit - a fruit that develops from one pistil in a flower (cherry drupe, pea bean, tomato berry).
Complex fruit - fruit developing from several or many pistils of one flower (collective strawberry achene, collection
raspberry drupe).
"False fruits" - obsolete name for fruits, in education
which, in addition to the ovary, take part in the overgrown receptacle, the bases of the stamens, petals, sepals (apple, pear, rowan; collective strawberry achene).
Infertility - a fruit formed from the fused pistils of several flowers (fruit of beet, mulberry, pineapple).
Inflorescence - a specialized flowering shoot that bears flowers and modified leaves. Simple inflorescences have one axis (tassel, spadix, head, basket, umbrella), complex inflorescences have a branching axis (panicle, complex umbrella, complex spike). Biological significance inflorescences - an adaptation to pollination.