Fertilization is the process of fusion of male and female reproductive cells (gametes).
Female reproductive cell(gamete) is called egg. The eggs are formed in the ovules of the ovary of the pistil. Pestle- This is the female reproductive organ.
Male reproductive cell(gamete) is called sperm. Sperm are produced in the anthers of the stamens. Stamen- This is the male reproductive organ.
The anthers of the stamens contain pollen.
Pollen consists of pollen grains. Pollen grain- this is one saw blade. A pollen grain contains 2 cells - vegetative and generative.
Vegetative- This is the cell that forms the pollen tube.
Generative- This is a cell that forms two sperm. Sperm- These are male reproductive cells.
During the process of pollination, the pollen grain lands on the stigma of the pistil, germinates and forms a pollen tube. Pollen tube moves through the stigma, style into the ovary. The ovary of the pistil contains the ovules (seed buds). From them the seed will develop. Structure of the ovule: ovule shell, embryo sac, main egg cell with a double set of chromosomes, central egg cell with a single set of chromosomes. Chromosomes contain genes and are responsible for storing and transmitting hereditary information.
The pollen tube carries 2 sperm to the ovules and grows into the ovule through the pollen entrance. Sperm have a single set of chromosomes.
First sperm fertilizes the main egg and the chromosome set becomes double.
As a result, a fertilized egg is formed, which is called - zygote. The embryo of a new plant is formed from the main egg and the first sperm. The structure of the embryo of a new plant: embryonic root, embryonic stalk, embryonic leaves and buds.
Second sperm fertilizes the central egg and the chromosome set becomes triple.
As a result, endosperm is formed. Endosperm- this is a reserve nutrients, which are necessary for the germination of the seed embryo.
From the shells of the ovule the seed coat is formed. From the walls of the ovary The pistil forms a pericarp.
This fertilization of two eggs by two sperm is called double. It was discovered by a Russian scientist Navashin S.G. In 1898. Thus, a fruit is formed, which consists of a seed and a pericarp.
Male reproductive cells - sperm - are formed in pollen grains, which develop in the anthers of flower stamens. Typically, pollen consists of many grains of dust (pollen grains) connected in groups. Sperm - male reproductive cells - are formed in dust particles.
Female reproductive cells - eggs - are formed in the ovules located in the ovary of the pistil of a flower (flowering plants have ovaries with one or more ovules). In order for seeds to develop from all ovules, sperm must be delivered to each ovule to the eggs, since each egg is fertilized by a separate sperm.
The process of fertilization in plants is preceded by pollination. As soon as a speck of dust lands on the stigma of the pistil (either by wind or insects), it begins to germinate. One of its walls extends and forms a pollen tube. At the same time, two sperm are formed in a speck of dust. They move to the tip of the pollen tube. Moving through the tissues of the stigma and style, the pollen tube reaches the ovary and penetrates into the ovule.
By this time, in the ovule, in its middle part, one cell divides and greatly elongates, forming the so-called embryo sac. It contains an egg at one end, and in the center there is a cell with two nuclei, which soon merge to form one - the central nucleus. Having penetrated the ovule, the pollen tube grows into the embryo sac, and there one sperm fuses (joins) with the egg, forming a zygote, from which the embryo of a new plant develops.
Another sperm that enters the embryo sac fuses with the central nucleus. The resulting cell divides very quickly, and soon nutritious tissue - endosperm - is formed from it.
The fusion of sperm in the embryo sac, one with the egg and the other with the central nucleus, is called double fertilization.
The process of double fertilization is a phenomenon characteristic only of flowering plants. Thanks to double fertilization, the embryo of a new plant receives very valuable endosperm with nutrients.
There is also this classification:
13. Structure and functions of a flower.
Flower - organ seed propagation angiosperms. A flower consists of a peduncle, receptacle, perianth, androecium and gynoecium.
Fertile parts of a flower (stamen, pistil).
Sterile parts of the flower (calyx, corolla, perianth).
Functions of a flower.
A flower is a modified shortened shoot adapted for the reproduction of angiosperms (flowering) plants.
The exclusive role of the flower is due to the fact that it combines all the processes of asexual and sexual reproduction, while in lower and many higher plants they are disunited. In a bisexual flower, micro- and megasporogenesis, micro- and megagametogenesis, pollination, fertilization, and the formation of seeds and fruits take place. The structural features of the flower allow the above functions to be carried out with minimal costs plastic substances and energy.
The central (main) parts of the flower. Most plants have one or more pistils in the center of the flower. Each pistil consists of three parts: the ovary - an expanded base; column - more or less elongated middle part; stigma - the upper part of the pistil. One or more ovules are located inside the ovary. Outside, the ovule is surrounded by integuments through which a narrow channel passes - the pollen passage.
The stamens are located around the pistil (or pistils). Their number in a flower varies among flowering plants: in wild radish - 6, in clover - 10, in cherry - many (about 30). The stamen consists of two anthers and a filament. Pollen develops inside the anther. Individual dust particles are usually very small grains. They are called pollen grains. The largest pollen grains reach 0.5 mm in diameter.
Perianth. In most flowers, the pistils and stamens are surrounded by perianth. In cherries, peas, and buttercups, the perianth consists of a corolla (a set of petals) and a calyx (a set of sepals). This type of perianth is called double. A tulip, lily, or lily of the valley has all the same leaves. Such a perianth is called simple.
Flowers with double perianth
Flowers with a simple perianth
The tepals may grow together or remain free. The tulip and lily have a simple, separate-leaved perianth, while the lily of the valley has a compound-leaved perianth. In flowers with a double perianth, both sepals and petals can also grow together. Primrose flowers, for example, have a fused calyx and a fused corolla. Cherry buttercup flowers have a separate-leaved calyx and a separate-petalled corolla. The bell has a separate-leaved calyx and a fused-petalled corolla.
The flowers of some plants do not have a developed perianth. For example, in willow flowers it resembles scales.
Willow inflorescences and flowers
Flower formula. The structural features of a flower can be noted briefly in the form of a formula. When compiling it, the following abbreviations are used:
Ok - tepals of a simple perianth,
H - sepals, L - petals, T - stamens, P - pistils.
The number of parts of a flower is indicated by numbers in the form of an index (H5 is 5 sepals), with large number flower parts use the sign ∞. If the parts grow together, the number indicating their number is placed in brackets (L(5) - the corolla consists of 5 fused petals). If the parts of the flower of the same name are arranged in several circles, then a + sign is placed between the numbers indicating their number in each circle (T5+5 - 10 stamens in a flower are arranged 5 in two circles). For example, the formula of the lily flower- Ok3+3T3+3P1, bell- Ch5L(5)T5P1.
Receptacle. All parts of the flower (near the flower bed, stamens, pistils) are located on the receptacle - the overgrown axial part of the flower. Most flowers have a pedicel. It extends from the stem and connects it to the flower. In some plants (wheat, clover, plantain) the pedicels are not pronounced. Such flowers are called sessile.
Flowers are bisexual and unisexual. Usually one flower contains both pistil(s) and stamens. Such flowers are called bisexual. Some plants (willow, poplar, corn) have only pistil or stamens in the flower. Such flowers are called unisexual - staminate or pistillate (Fig. 71).
Monoecious and dioecious plants. In birch, corn, and cucumber, unisexual flowers (staminate and pistillate) are located on the same plant. Such plants are called monoecious. In poplar, willow, sea buckthorn, and stinging nettle, some plants have only staminate flowers, while others have pistillate flowers. These are dioecious plants.
The ovary is the empty lower thickened part of the pistil - female organ plant propagation.
It provides protection and fertilization of the ovules (ovules) from which seeds are formed.
The pistil is located in the flower and consists of a stigma that traps pollen, a style that carries pollen inside, and an ovary where the seeds develop. After fertilization, a fetus is formed from it.
In the central part of the ovule (nucellus) there are eggs; in the case of pollination, they are fertilized and seeds develop from them. In the same place, an embryo sac is formed, from which they will feed.
Functions of the ovary
- Inside the ovary, the process of fertilization and seed maturation takes place;
- Protects ovules from external harmful factors environment (temperature changes, drought, eating by insects, rain, etc.);
- Maintains the required level of moisture;
- Provides nutrition to seeds;
- It is the basis of the future fetus.
Types of ovary
According to the number of nests, that is, existing cavities separated by partitions in which the seeds are located, the ovary can be single- or multi-locular.
I - single-locular ovary, II - two-locular ovary, III - five-locular ovary. In all pictures: 1 - wall of the ovary; 2 - socket; a - ovules, 4 - seed carrier.
Another classification of ovaries is based on their location in relation to the receptacle.
The receptacle is the lower part of the flower, that is, its base, on which the petals, sepals, stamens and pistils are located.
According to the type of location, the ovary can be:
- Upper or free - located above the receptacle. It does not grow together with other parts of the flower; the flower is called subpistillate (cereals, ranunculaceae, legumes, etc.);
- The lower one is under the receptacle, the flower is attached to the top of the ovary, therefore it is called suprapistal (Asteraceae, cactaceae, orchids, etc.);
- Semi-inferior - grows together with the flower, but not at the very top; the flower is called semi-pistillate (saxifrage).
Formation of fruits from the ovary
Fruits, depending on the type of formation from the ovary, are divided into several types: 1. Real - formed only by the ovary. Divided into:
- Simple, formed by one pestle (cherry, plum, bird cherry, acacia bean);
- Complex, formed by several fused pistils (raspberries, blackberries)
- Fractional fruits are formed by a multilocular ovary with partitions (forget-me-not, basil, lavender, thyme, etc.);
2. False - formed with the participation of other parts of the flower such as the receptacle and perianth, including petals and sepals.
Please note
It is easy to distinguish false ones from real ones by the remains of parts of the flower (apples, pears).
Causes of damage to the ovary
Damage to the ovary can lead to a lack of further seeds and even fruits. The causes of damage may be:
- Late spring frosts during flowering, during which flowers and set fruits fall off. If the ovaries are partially damaged, then deformed, small, or unsuitable fruits develop from them;
- The absence or small number of pollinators, while some of the flowers remain unfertilized and are therefore discarded;
- Poor soil and lack of watering, when the plant does not have enough substances to grow all the ovaries that appear. In this case, it is necessary to add complex mineral and organic fertilizers and provide watering during drought;
- Pests (codling moth, apple sawfly, flower beetle, etc.). To get rid of them, you do not need to resort to artificial insect repellents, since they will also have a detrimental effect on pollinating insects. It is better to spray the plants with decoctions of herbs that repel pests (nettle, dandelion, garlic, wormwood, etc.)
- Leaf diseases. Healthy leaves are necessary to provide the plant with the necessary substances; without them, the ripening of fruits and seeds is impossible;
- Overload with the number of fruits: with large quantities formed ovaries, the plant cannot feed them all, so it discards some. Timely thinning of flowers will help to avoid this process.
Flowering plants are a large and diverse group that dominate most terrestrial ecosystems. Human existence depends on the main flowering plants cultivated by man. But to flowering plants appeared, they must go through the stage of pollination and fertilization. Read how this happens in this article.
Pollination
This process is carried out by the transfer of pollen from the stamens to the pistil. How does pollination and fertilization occur in flowering plants? This is done in two ways: self-pollination and cross-pollination. In the first case, the transfer of pollen grains to the pistil occurs in the same flower. This is how peas or tulips are pollinated. In cross-pollination, pollen from a flower from one plant is transferred to the pistil of another. most often by insects, in rare cases - by wind (sedge and birch), birds and water.
As a result of pollination by insects, bright, clearly visible flowers with pleasant smell and nectaries that produce a sweet liquid. These plants also produce a lot of pollen. It is food for insects. They are attracted by the bright colors or smell of flowers. When insects extract nectar, they touch the surface of the pollen grains, which stick to their body, and when they fly to a flower of another plant, they remain on the pistil. This is how pollination by insects occurs. Many are pollinated only by certain insects: fragrant tobacco - night butterfly, creeping clover - by a bee, and meadow clover - by a bumblebee.
Cross-pollinated plants are better able to cope with changing conditions environment. But the pollination process in this case depends on a number of factors. And self-pollination does not depend on anything. He is not afraid of weather conditions and the absence of intermediaries.
Fertilization
The pollen grain, falling on the stigma of the pistil, begins to gradually germinate. From the vegetative cell, a long pollen tube develops. Growing up, it reaches the level of the ovary, and then the ovule. At the same time, a pair of sperm is formed, which penetrates the pollen tube. She, in turn, enters the ovule through the pollen passage. Then the tube at the very tip ruptures and releases the male sperm, which are immediately sent to the embryonic membrane, called the sac. This is where the eggs develop.
Next, the egg is fertilized by one sperm and a zygote is formed, from which a small embryo of a completely new organism of plant origin begins to form. At the same time, the second sperm merges with the zygote nucleus or with the polar nuclei. As a result, a triploid cell is formed, from which the endosperm arises. It is called nutrient tissue, which contains reserves necessary substances for the normal development of the embryo of the future plant. This is how the reproductive organs of flowering plants are represented.
When one sperm with an egg, and the other with polar nuclei, merge together, this process is called. It is characteristic only of flowering plants and is unique feature angiosperms. The fertilized ovule grows into a seed. As a result, the ovary of the pistil grows. In flowering plants, the fruit develops from the wall of the ovary.
Reproduction
Any plant, having reached a certain size and having gone through the appropriate stages of development, begins to reproduce organisms of a similar species. This is reproduction, which is a necessary property of life. All organisms thus prolong the existence of the species itself. There are sexual and those that occur with the participation of one individual. When plants develop specialized cells called spores, the organisms begin to reproduce.
Mosses, algae, ferns, mosses and horsetails. Spores are special small cells with a nucleus and cytoplasm that are covered with a membrane. They are capable long time endure bad conditions. But when they find themselves in a favorable environment, they quickly germinate and begin to form daughter plants, the properties of which do not differ from those of the mother.
During sexual reproduction, female and male reproductive cells merge, resulting in the formation of daughter organisms that are qualitatively different from the parent ones. Parental organisms of the feminine and masculine principles are already taking part here.
The macrosporangium plays a dominant role in the composition of the ovule. It is in it that the laying of one mother cell occurs, from which macrospores are formed. The three pieces begin to die off and eventually collapse. The fourth macrospore, the female principle, lengthens and its nucleus divides. Then the daughter nuclei move to different poles of the elongated cell. Each nucleus formed further divides twice.
Cells located near different poles form four nuclei. This is called the embryo sac, which contains eight haploid nuclei. Then, from each four nuclei, one of them moves to the center of the embryo sac. There they merge, as a result of which they form a secondary nucleus - diploid.
Then, in the embryo sac, in the cytoplasm, partitions are formed between the nuclei at the cellular level. The bag becomes seven cells. Near one of its poles is the egg apparatus, which includes a large egg and two auxiliary cells. At the other pole there are antipodal cells, there are three in total. So, there are now six in the bag and one is diploid, with a secondary nucleus. It is located in the center of the embryo sac.
What is an ovary?
It is called the lower thickened part of the pistil with a cavity closed inside in which the ovules are located. Pollen falls from the stigma of the pistil into the ovule, which is protected from unfavorable conditions internal damp cavity. In the ovule, the development of female germ cells - eggs - occurs.
What types of ovaries are there?
The types of ovaries of flowering plants are:
- Upper. It is attached to the receptacle freely, without merging with other parts of the flower. The walls of the ovary are formed from carpels. In flowering plants, the fruit develops from the wall of the ovary. Examples are buttercups and cereal plants. These flowers are called subpistillate or circumpistillate.
- The inferior ovary is always located under the receptacle. It is formed with the participation of other parts of the flower: the base of the sepals and stamens with petals, which in many flowers are attached to the top of the ovary. In flowering plants, a fruit develops from the wall of the ovary. Examples are Asteraceae, cactus and orchid plants. The flower is called suprapistal.
- Semiinferior ovary. Its top does not grow together with other parts, so it is free. Flowers of this type are called semi-supristal. These are the types of ovaries of flowering plants.
Flowering plants
They are the most progressive group of plants, numbering two hundred and fifty thousand species, distributed throughout planet Earth. The smallest plant is duckweed, with a diameter of one millimeter. She lives in the water. The largest flowering plants are trees, reaching a height of one hundred meters or more.
The appearance of flowering plants occurs due to the development of a special reproductive organ - the flower. In some plants it is colored bright colors, others smell wonderful. The flowers are small and inconspicuous in plants that look like grass. Despite the huge variety of flowering plants, they all fit harmoniously into our lives: they decorate gardens and parks, and give us the joy of communicating with them.
Flower structure
The flower is complex system organs that ensure the propagation of plants by seeds. Its appearance led to the widespread distribution of angiosperms (flowering) plants on Earth. The flower has many functions. With its participation, stamens with pollen grains and pistils with ovules are formed. He's playing main role in pollination, fertilization, formation of seeds and fruits.
The flower is a shortened, modified shoot of limited growth, bearing a perianth, pistils and stamens. All have flowers similar in structure and different in shape. This is how adaptation to pollination occurs in various ways.
The main or lateral stems may end in flowers, the bare part of which under the flower itself is called the peduncle. It is greatly shortened or completely absent in sessile flowers. The peduncle turns into a receptacle, which can be elongated, convex, concave or flat. All parts of the flower are placed on it. These are sepals with petals, stamens with a pistil, in the lower part of which the ovary is formed, which contains the ovules or ovules. A flower with such an ovary has a concave receptacle. If the ovary forms at the top of the pistil, the receptacle will be convex or flat.
