Asexual reproduction of plants: division and vegetative reproduction. Propagation of plants Why do many plants reproduce mainly asexually
Lecture 6. Propagation of plants
Reproduction is an integral property of living organisms to reproduce their own kind. Thanks to reproduction, continuity and continuity of life are ensured. There are two main forms of reproduction: asexual and sexual.
Asexual reproduction. Reproduction in which one organism takes part, gametes do not form and merge, genetic material in any form does not merge. This is the most ancient form of reproduction, widespread in all groups of plants, occurs through mitotic division or through spores, a special form of asexual reproduction is vegetative propagation.
Division . Reproduction by division is characteristic of unicellular algae. The division occurs through mitosis, as a result, individuals are formed that are genetically identical to each other and to the mother's body.
Spore propagation . Plant spores - reproductive, unicellular formations that serve to form new individuals. In most algae living in water, spores are mobile, since they have flagella. Such disputes are called zoospores. In terrestrial plants and fungi, they do not have special devices for active movement. Spores are formed in organs of asexual reproduction - sporangia or zoosporangia. In algae, almost any cell can become sporangia, in higher plants sporangia - a multicellular organ. In plants, spores are always haploid. If they arise on a diploid plant, then their formation is preceded by meiosis, if on a haploid plant - mitosis. The spores resulting from meiosis are genetically unequal, the organisms that develop from them are genetically unequal.
The plant on which spores form is called sporophyte. If spores are morphologically indistinguishable, then the plants that form them are called equiporous, heterogeneous plants are plants that form spores, always differing in size and physiological characteristics. Microspores - smaller spores that form in microsporangia, from which they grow male gametophytes (plants forming male gametes ). Megaspores are larger spores that form in megasporangia, from which they grow female gametophytes . Mismatching is more common among higher plants (some plunders, ferns, all gymnosperms and angiosperms).
Reproduction by spores is of great biological importance - as a result of meiosis, recombination of genetic material occurs, new combinations of gene alleles appear in spores that fall under the control of selection; usually, spores are formed in large quantities in plants, which ensures high breeding intensity. Due to its small size and lightness, spores are spread over long distances, ensuring the resettlement of plants; The dense spore membrane provides reliable protection against adverse environmental conditions.
Vegetative propagation of plants - this is an increase in the number of individuals due to the separation of the viable parts of the vegetative body and their subsequent regeneration (recovery to the whole organism). This method of reproduction is widespread in nature. Vegetatively propagate both algae and higher plants.
Vegetative propagation happens natural and artificial . Due to natural vegetative propagation in nature, there is a rapid increase in the number of individuals of the species, their settlement and, as a result, success in the struggle for existence. Natural vegetative propagation occurs in several ways: fragmentation of the maternal individual into two or more daughter ones; the destruction of sections of land-creeping and lodging shoots (crowns, gymnosperms, flowering); with the help of special structures specially designed for vegetative propagation (tubers, bulbs, rhizomes, corms, axillary buds, adnexal buds on leaves or roots, brood bunches of mossy, etc.).
Artificial vegetative propagation is carried out with the participation of humans in the cultivation of cultivated plants. Artificial vegetative propagation has a number of advantages over seed: it provides for the generation of descendants that retain the characteristics of the parent organism, accelerates the generation of descendants, and allows you to get a large number of descendants. In addition, with the help of vegetative propagation, clones of those plants that form non-viable seeds or do not form them at all can be reproduced.
Methods of vegetative propagation.Plants can be propagated by vegetative organs - dividing the whole plant into parts, aboveground and underground shoots, leaves, roots.
Fragmentation they call the division of an individual into two or several parts, each of which regenerates into a new individual (Fig. 34). Such reproduction is characteristic of filamentous and lamellar algae (fragments of threads or part of thallus), some flowering plants (for example, Canadian Elodea). Only female specimens of elodea that were unable to form seeds due to the absence of male plants came to Europe and fragmentation was the only way to reproduce.Division of bushes. Currants, gooseberries, primroses, rhubarb are well propagated by parts of the bushes. The plant is dug up, divided into parts and planted separately from each other. Bushes are usually divided in spring or in the second half of summer.
Propagation by overhead shoots.
Mustache . In agricultural practice, mustaches propagate strawberries and strawberries. In the nodes of the mustache, lateral kidneys and additional roots are formed. After drying the internodes, the plants separate. In nature, plants such as creeping buttercup and saxifrage are propagated by the mustache.
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Stem cuttings. The stem stem is a plot of aboveground shoot. The stem cuttings propagate grapes, currants, gooseberries, decorative species of spirea, red pepper, eggplant and others. For propagation, cuttings are taken from 2-3 to 6-8 cm long, consisting of one internode and two nodes. Leaves are left on the top node (if the leaf blades are large, then they are cut halfway). Cuttings are planted in special greenhouses, and after rooting - in open ground.
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a section of bark and wood (peephole) grafted onto another plant is called scion. Rootstock - the plant or its part on which the vaccination is carried out. Vaccination allows the rootstock root system to be used to preserve or propagate a particular variety, replace the variety, produce new varieties, accelerate fruiting, obtain frost-resistant plants, repair or rejuvenate old adult trees.
Many methods of vaccination are known, but all of them can be reduced to two main types: vaccination by rapprochement, when the scion and stock are left on their roots, vaccination by a separate scion, when only the stock has roots.
The most common vaccination methods are as follows (Fig. 38). Split or half-split vaccination. Apply if the scion is thinner than a stock. The cross section of the stock is completely or partially divided and the scion is cut into it, obliquely cut from two sides.
Bark grafting. The graft is also thinner than the stock. A horizontal cut is made on the rootstock under the stem node, the bark is cut in the vertical direction and its edges are carefully turned away. On the scion make a slice in the form of a half-cone, insert it under the bark, clamp it with the lapels of the bark and tie it.
Copulation. It is used if the graft and stock are the same thickness. Oblique sections are made on the scion and rootstock and combine them, ensuring the density of the connection.
Budding. Vaccination of the kidney-eye. A T-shaped incision is made on the rootstock, the edges of the bark are bent, and a kidney with a small area of \u200b\u200bwood is inserted behind the bark and tightly bandaged.
Propagation by underground shoots.
Tuber . Of the agricultural plants propagating by tubers, the most famous are potatoes and Jerusalem artichoke. They can be propagated by planting whole tubers or parts of them with kidney-eyes. Tubers, as a repository of nutrient reserves, are formed in wild plants such as full, weekly.
Rhizome . In agriculture, rhubarb, mint, asparagus, bamboo are propagated by rhizomes, in decorative horticulture - lily of the valley, iris and others. They are easily propagated by dividing the rhizome into parts, each of which should contain a vegetative bud.
A large number of rhizome plants, primarily cereals, live in forests, steppes, and meadows. Rhizome plants include wheatgrass, timothy, whitebird, kupen, sour, horsetail and other wild plants. Many rhizomes branch, and when the old parts die off, new plants become isolated.
Bulb . In agricultural practice, onions propagate onions, garlic, and ornamental plants: tulips, daffodils, hyacinths and others. In nature, many plants multiply with bulbs: tulips, goose onions, bluebills, snowdrops, etc. Vegetative propagation of bulb plants is carried out by overgrown adult bulbs, children, individual scales.
Corm . Spare nutrients of the corm are spent on flowering, but by the end of the season a new corm is formed. In addition, one or more corms can be formed - fleshy kidneys that develop between the old and new corms. Corm plants include gladiolus, crocus.
Root tubers . They are thickening of the lateral roots. In ornamental horticulture, dahlias and sweet potatoes are propagated by root tubers. When propagating dahlias, root tubers must be taken with the base of the stem bearing the kidneys, since the root tubers of the kidneys do not form. Spring tubers propagate root tubers, two-leafed love.Reproduction by root offspring. Root offspring - shoots that arise from the accessory buds on the roots (Fig. 36). Root offspring propagates plants that easily form adnexal buds on the roots: cherry, plum, raspberry, lilac, aspen, sow thistle, field cirsium, etc.
Root cuttings. The root stalk is part of the root. They breed species on the roots of which the accessory buds easily develop: horseradish, raspberry, cherry, roses. Root cuttings are harvested in the fall, less often in the spring. For this, lateral roots of the first order at the age of 2-3 years are used. The length of the cuttings is up to 10-15 cm, the diameter is 0.6-1.5 cm. Cuttings are planted in the soil to a depth of 2-3 cm. Many wild plants propagate by cuttings: willow, poplar, aspen, dandelion
Reproduction by leaves.
Whole leaves. Many flowering plants are propagated by leaves, for example, senpolia, begonia. It is enough to put a leaf in water, adventitious roots and accessory buds appear, after a while the plant is transplanted into the soil.
Leafy cuttings. Sometimes even a part of the leaf is enough for vegetative propagation. At the royal begonia, a part of the leaf with a large vein is cut out, the sansevier leaf can be cut into several leaf cuttings and put into water.
The adnexal buds on the leaves, children . In bryophyllum, adnexal buds are formed on the leaves, similar to small plants. Falling, they become independent plants.
Tissue culture. Tissue culture is the growth of cereals of plant cells on artificial media. Plant cells have the property totipotency - A single cell can develop into a normal plant when using certain phytohormones. The tissue culture method allows to obtain clones some higher plants. Cloning - obtaining a set of individuals from one maternal vegetative way. Cloning is used to propagate valuable plant varieties and to improve planting stock.
Sexual reproduction. Sexual reproduction is associated with the formation by plants of a special type of cells - gametes. The plant on which the formation of gametes occurs is called gametophyte. The process of formation of gametes is called gametogenesis. It happens in special organs - gametangia. In equiporous plants, the gametophyte is usually bisexual: it carries both female and male gametangia. In heterogeneous plants, the gametophyte with male gametangia develops from microspores, and the gametophyte with female gametangia develops from megaspores. Plant gametes are formed mitotically; meiosis occurs after the formation of a zygote ( zygotic reduction) - many algae, or during the formation of spores ( sporic reduction) - in diploid algae and higher plants. In animals, meiosis occurs with the formation of gametes ( gametic reduction).
Sexual reproduction has several advantages compared to asexual. Firstly, when gametes merge, an organism is formed with a unique double set of alleles of genes received from parents with different genotypes, an organism with a unique genotype is formed. As a result of selection, individuals whose genotype allows them to adapt to these environmental conditions will survive, even if these conditions change.
Secondly, mutations that change genes are often recessive and harmful in these environmental conditions. The diploid set of genes allows the recessive alleles that have arisen to survive due to the presence of dominant alleles of these genes. Each diploid organism contains hundreds, thousands of genes in a recessive state, both the sponge is saturated with water and the genotype is saturated with them, they are transmitted to the next generation and gradually spread throughout the population. A mutation will occur if both gametes carry a given recessive allele of the gene, and by this time the environment may change, and this mutation may be useful. This is the accumulation and spread of mutations.
Gametes are always haploid. When the male and female gametes merge, a diploid zygote forms, from which a new organism develops. Gamete fusion process is called fertilization. The essence of the sexual process is the same for all living organisms, and its forms are diverse. The following types of sexual process are distinguished: chologamia, conjugation, isogamy, heterogamy and oogamy (Fig. 39).
Hologamia . Hologamia - the fusion of haploid unicellular, apparently indistinguishable organisms with each other. This type of reproductive process is characteristic of some unicellular algae. In this case, not gametes merge, but whole organisms acting as gametes. The resulting diploid zygote usually immediately meiotic divides ( zygotic reduction) and 4 daughter haploid unicellular organisms are formed.
Conjugation. A special form of the sexual process is conjugation, characteristic of some filamentous algae. Individual haploid cells of threadlike thalli located close to each other begin to form outgrowths. They grow towards each other, connect, the partitions at the junction dissolve, and the contents of one cell (male) passes into another (female). As a result of conjugation, a diploid zygote is formed.
Isogamy. With isogamy, gametes are morphologically similar to each other, that is, they are identical in shape and size, but physiologically they are of different quality. This sexual process is characteristic of many algae and some fungi. Isogamy occurs only in water, for the movement in which gametes are equipped with flagella. They are very similar to zoospores, but they are smaller.
Heterogamy. With heterogamy, the fusion of motile germ cells occurs, similar in shape but different in size. The female gamete is several times larger than the male one and less mobile. Heterogamy is characteristic of the same groups of organisms as isogamy, and also occurs in water.Oogamy. It is characteristic of some algae and all higher plants. The female gamete - the egg - is large and motionless. In lower plants, it forms in unicellular gametangia - oogonyin higher plants (excluding angiosperms) - in multicellular archegonies. The male gamete (sperm) is small and mobile, it is formed in fungi and algae in unicellular organisms, and in higher plants (excluding angiosperms) - in multicellular gametangia - anteridia. Sperm cells can only move in water. Therefore, the presence of water is a prerequisite for fertilization in all plants, except for seed. In most seed plants, male gametes have lost flagella and are called sperm.
Key terms and concepts
1. Asexual reproduction. 2. Spores of plants. 3. Zoospores. 4. Sporophyte. 5. Male and female gametophytes. 6. Microspores and megaspores. 7. Vegetative reproduction. 8. Privoy. 9. Rootstock. 10. Gametangia. 11. Zygotic reduction. 12. Sporic reduction. 13. Gametic reduction. 14. Hologamia. 15. Isogamy. 16. Heterogamy. 17. Oogamy. 18. Conjugation. 19. Oogonia. 20. Archegonia. 21. Anteridia. 22. Typeotency.
Key questions to repeat
1. Propagation of plants by division.
2. Reproduction by spores.
3. Natural vegetative propagation.
4. Reproduction by fragmentation and division of bushes.
5. Propagation by aerial shoots (mustache, layering, stem cuttings).
6. The main methods and features of reproduction by vaccination.
7. The main methods of propagation by ground shoots.
8. The main methods of root propagation.
9. The main methods of plant propagation by leaves.
10. Reproduction by tissue culture.
11. Benefits of sexual reproduction.
12. Characterization of the main types of sexual processes (hologamia, conjugation, isogamy, heterogamy, oogamy).
With asexual reproduction of plants, division of the parent individual and vegetative reproduction is possible.
Asexual reproduction is widespread in all groups of plants. In the simplest form, with this type of reproduction, the parent individual is divided into two parts, each of which develops into an independent organism. This method of reproduction, called division, is found, as a rule, only in unicellular organisms. The cell at the same time is divided by mitosis.
Many multicellular organisms are also able to multiply successfully by separating viable areas of the vegetative body, from which full-fledged daughter individuals are formed. This type of asexual reproduction in the plant world is often called vegetative. The ability to vegetative propagation is very characteristic for plants and fungi at all levels of their organization, as well as for some lower groups of animals. Such reproduction is characterized by the restoration of the whole organism from its part, called regeneration.
Often, plants reproduce in fragments or parts of thallus, mycelium, or parts of vegetative organs. Many filamentous and lamellar algae, mycelium of fungi, and thalli of lichens freely disintegrate into parts, each of which easily becomes an independent organism. So can some flowering plants that live in the water. An example of a plant that propagates exclusively vegetatively in Europe is the dioecious Canadian Elodea (Elodea canadensis), which came here from North America. At the same time, only female specimens that were unable to form seeds in the absence of male plants were introduced into Europe. Despite the lack of seed renewal, the plant reproduces extremely rapidly and rapidly develops new habitats.
In agricultural practice, many methods have been developed for the artificial vegetative propagation of cultivated plants belonging to a variety of life forms. So, many shrubs and perennial grasses multiply by dividing the bush, rhizomes and root offspring. Onions, garlic, lilies, tulips, hyacinths, crocuses, gladioluses, etc. successfully propagate by bulbs and tuber-onions, separating daughter bulbs, or "babies," from mother plants. In gardening, forms of vegetative propagation with the help of cuttings and grafting are especially widespread.
A cut is a segment of a vegetative organ that serves for artificial vegetative propagation. Cuttings can be stem, or shoot, however, some plants can also propagate leafy (begonia, lily) or root (raspberry) cuttings. A variety of cuttings is the propagation of trees and shrubs by layering. In this case, part of the shoot is first specially pressed to the soil for rooting and only then cut off. Layers are found in nature, when lodging branches of fir, linden, bird cherry and other species that can root in this way. Cuttings propagate many fruit, woody and herbaceous ornamental plants in open and closed ground. When grafting, all the properties of the maternal cultivated plant are preserved, which is very important, since during seed propagation, many traits specially selected by selection are easily lost.
Vaccination is very widely used in horticulture, when a stalk or just a vegetative bud of a plant with the desired properties, the so-called scion, merges with a more powerful and unpretentious plant or stock. Vaccination allows you to quickly propagate valuable plants and ensures their accelerated development, while fully maintaining the necessary qualities. At the same time, the grafted plant receives such valuable stock properties as frost resistance, resistance to fungal diseases and unpretentiousness to soil fertility. More than 100 vaccination methods have been developed. Many varietal plants that do not form seeds propagate exclusively by vaccination.
Asexual reproduction - this is the reproduction of organisms in which there is no participation of another individual, and reproduction of their own kind occurs by separating several or one cell from the mother's body. In this process, a single parent takes part. cells are fully consistent with the original maternal.
Asexual reproduction is extremely simple. This is due to the fact that the organization of the structure of unicellular organisms is also relatively simple. Organisms with this method of reproduction reproduce their own kind very quickly. In favorable conditions, the number of such cells doubles every hour. Such a process can continue indefinitely until a random change in the so-called mutation occurs.
In nature, such reproduction occurs in both plants and
Asexual reproduction of organisms
Simple division is observed in animals, for example, in ciliates, amoebas, and some algae. First, the nucleus in the cell is divided through mitosis in half, and then a constriction is formed, and the parent individual is divided into two parts, which are daughter organisms.
In animals, asexual reproduction persisted only in some forms: sponges, intestinal, tunicates. In these organisms, a new individual is obtained as a result of budding or division, after which the part separated from the parent organism is extended to the whole. In some cases, parts of the body have the ability to develop into a separate organism in animals. A whole hydra, for example, can develop from a two hundredth part. With asexual reproduction, newly created individuals come from several cells or one through mitotic divisions, receiving the same hereditary information that the cell of the mother's body possessed.
Asexual reproduction of plants
Widespread this way of reproduction in the plant world. There are a number of plants that multiply well by tubers, layering, cuttings, and even leaves, which makes it possible to use the vegetative organs of the parent plant to grow new organisms. This type of asexual reproduction is called vegetative, and it is inherent in highly organized plants. An example of such a breeding can be considered one that occurs with a mustache, for example, in strawberries.
Spore formation is asexual reproduction occurring in many plants, for example, algae, ferns, mosses, mushrooms at some stage of development. In this case, special cells take part in the multiplication mechanism, often covered with a dense shell, which protects them from the adverse effects of the external environment: overheating, cold, and drying. As soon as favorable conditions arise, the spore membrane bursts, the cell begins to divide many times, giving life to a new organism.
Budding is a method of reproduction, when a small part of the body is separated from the parent individual, from which the daughter organism is later formed.
The totality of individuals that descended from one common ancestor using this type of reproduction is called clones in biology.
Asexual reproduction is widely used in agriculture in order to obtain plants with a set of necessary traits that are useful for human life. Long "mustache", shoots spread strawberries, and trees - cuttings. Scientists are exploring the mechanisms of reproduction in order to learn how to control and manage their development. The necessary hereditary information is first propagated, and then the necessary whole plant is grown from them.
Breeding - this is the reproduction of similar organisms, an important property of the living. Sooner or later, organisms die: some from old age, others from disease, others become victims of predators. However, with the death of each organism, the life of species on Earth does not stop. Thanks to reproduction, new generations of organisms appear to replace dying and dying individuals.
When propagating, an increase in the number of individuals occurs, organisms settle in new places. Reproduction is associated with growth - an increase in mass and size and development - internal and external changes that occur from the moment of formation to the death of the body.
There are asexual and sexual reproduction. The most ancient and simplest method of reproduction is asexual. It is carried out by division, spores and autonomic organs. Only one organism is involved in asexual reproduction. With this method of reproduction, the greatest similarity of the offspring with the parents is preserved.
Male and female individuals participate in sexual reproduction, fertilization occurs - the fusion of male and female germ cells. Therefore, during sexual reproduction, each organism inherits the properties of both parents.
Plant propagation. Widespread in plants vegetative propagation. It occurs due to the separation of the vegetative organs or their parts from the mother's body and the development of new, daughter plants from them (Fig. 62). During vegetative propagation, a new individual is formed from a part of the body of the mother’s body, so it inherits all of its signs.
Fig. 62. Vegetative propagation of flowering plants
In flowering plants, vegetative propagation in nature occurs with the help of all the organs on which the buds are formed - future shoots. Vegetative propagation allows plants to settle faster and occupy new areas.
Many weeds, such as dandelion, wheat grass, sow thistle, reproduce vegetatively. It is very difficult to fight them. Pulling a dandelion from the soil, you will surely leave in it part of the root from which a new plant will grow.
Some forest herbs reproduce with the help of long rhizomes, since seed reproduction is difficult due to the lack of pollinators, lack of light, etc. Lily of the valley refers to such plants.
Plots of filaments, separation of a part of the body at the place of attachment to the soil can reproduce algae. In mosses and ferns, young shoots can grow and separate from each other.
Some plants: algae, mosses, ferns - reproduce using spores. A spore is one cell with a thick shell that protects it from drying out and mechanical damage.
Usually a lot of controversy is formed. They are very small and light, so they are carried by the wind over long distances. Of the vast amount of spores, only a few fall into favorable conditions and germinate, giving rise to a new organism. A significant part of them die. Therefore, the formation by plants or fungi of a large number of spores is an adaptation to the survival and preservation of the species.
Answer the questions
- What is breeding?
- What are the features of asexual reproduction?
- Why do many plants reproduce in a predominantly asexual way?
New concepts
Reproduction. Asexual reproduction. Vegetative propagation.
Think
Why do many cultivated plants propagate vegetatively?
My lab
Vegetative propagation is used for landscaping cities, in agriculture. For example, gooseberries, currants, phloxes, daisies are propagated by dividing the bush; strawberries - mustache, potatoes - tubers.
Often cuttings are used for propagation - part of the stem, leaf, root, which develop into a new shoot. With stem stalks, currants, tradescantia, and pelargonium are propagated; root cuttings - wild rose, raspberries; leafy cuttings - begonia.
You can propagate indoor plants ficus, comus, etc. by cuttings. To do this, cut the cuttings with 3-4 leaves. Cut the bottom two sheets (explain why). Place the cuttings in a box with soil covered with moistened sand, inclined at an angle of 45 °. Cover the cuttings with a glass jar to reduce the evaporation of water. After two to three weeks, roots form on the bottom of the cuttings planted in the soil. Transplant young plants into pots and care for them.
Recently, another method of vegetative propagation has received widespread use in the national economy - from a single cell or piece of tissue. This is the so-called tissue culture method (Fig. 63). It allows for a relatively short time in small areas, even in vitro, to receive numerous offspring of a particular plant.
Fig. 63. Tissue culture method
Using the tissue culture method, it was possible to establish industrial production of such a rare and valuable medicinal plant as ginseng. If in natural conditions only by the age of 50 the mass of ginseng root is about 50 g, then in artificial conditions this mass is obtained in about six to seven weeks.
Asexual reproduction is also characteristic of animals. In this case, the offspring produces one parent. The simplest form of asexual reproduction of animals is division. It is characteristic of unicellular and some multicellular animals.
Asexual reproduction of freshwater hydra is budding. Under favorable conditions, kidneys form on the hydra body, which grow and after some time separate from the mother's body, turning into young hydras (Fig. 64).
Fig. 64. Asexual reproduction of freshwater hydra by budding
REMEMBER
Question 1. How do plants reproduce?
All types of reproduction can be divided into two main groups - vegetative reproduction and generative. About vegetative propagation, it is enough to say only that this is propagation by lateral shoots, buds, roots, tubers, that is, a young plant is separated from an adult plant. Generative reproduction is divided in turn into sexual, asexual and seed. Asexual reproduction, that is, spore reproduction is characteristic of ferns and mosses, as well as algae. Other higher plants reproduce sexually, that is, they have special organs in which fertilization, pollination occurs, that is, the fusion of male and female germ cells. A type of sexual reproduction is seed propagation, when a seed is formed, from which a new plant subsequently grows.
Question 2. What do you know about animal reproduction?
Multicellular animals reproduce predominantly through sexual contact, but there are groups (especially among the lower invertebrates) that reproduce very successfully asexually.
Asexual multiplication of multicellular organisms is an increase in the number of individuals formed from somatic (non-asexual) cells. Among animals, it is completely absent in primary cavity worms and mollusks. In arthropods, vertebrates, asexual reproduction can include polyembryony, that is, asexual reproduction at the stages of embryonic development.
Sexual reproduction in animals exists in several forms. First, bisexual reproduction, which exists in the form of dioecious and hermaphroditism, can be distinguished, and secondly, virgin reproduction, or parthenogenesis.
Question 1. What is reproduction?
Reproduction is the reproduction of similar organisms, an important property of the living.
Question 2. What are the features of asexual reproduction?
The most ancient and simplest method of reproduction is asexual. It is carried out by division, spores and autonomic organs. Only one organism is involved in asexual reproduction. With this method of reproduction, the greatest similarity of the offspring with the parents is preserved.
Question 3. Why do many plants reproduce mainly asexually?
In plants, vegetative propagation is widespread. It occurs due to the separation of the autonomic organs or their parts from the mother's body and the development of new, daughter plants from them. During vegetative propagation, a new individual is formed from a part of the body of the mother’s body, so it inherits all of its signs.
1. Consider Figure 81 and plan the story of the vegetative propagation of flowering plants. Pick some examples.
1. Methods of vegetative propagation and their diversity
2. Reproduction by individual parts of the body
3. What plants propagate vegetatively?
2. Using online sources, non-fiction magazines, books, textbook text, prepare a message on the topic "Reproduction through spores."
Propagation of plants is a physiological process of reproducing similar organisms, ensuring the continuity of the existence of the species and its distribution in the environment.
Asexual reproduction in a number of plants (algae, mosses, ferns) is carried out using spores. A spore is one cell protected by a thick membrane from drying out and mechanical damage. Disputes are formed in special formations - sporangia. Being very light, spores are carried far away by the wind. Under favorable conditions, spores germinate and form new organisms. Usually plants form a huge amount of spores, but not all plants develop new ones. Many disputes fall into adverse conditions and die.
In the process of evolution, about 400 million years ago, rhinophytes emerged from multicellular green algae - the first higher plants that reproduce by spores, which gave rise to all modern higher spore and seed plants. This is an extinct group of plants. In the life cycle of higher spore plants, as in some algae, individuals of asexual and sexual generations alternate, which multiply, respectively, asexually and sexually. In the full life cycle, which ensures the continuity of the life of organisms, there is an alternation of the gametophyte (sexual) and sporophyte (asexual generation). On sporophyte, organs of asexual reproduction are formed, on gametophyte - sexual.
After emergence on land, higher spore plants underwent metamorphoses in two directions during evolution. Thus, two large evolutionary groups were formed - haploid and diploid. The first branch includes mosses, in which the gametophyte is better developed, and the sporophyte occupies a subordinate position. Ferns, horsetails and lice belong to the diploid branch. Their gametophyte is reduced, and looks like a seedling.
Of the spores that form individuals of the asexual generation, individuals of the sexual generation grow. They have special male and female genital organs, in which male and female reproductive cells (gametes) develop - mobile spermatozoa and fixed eggs. For fertilization, the sperm must enter the external environment and fertilize the egg, which is located inside the female genital organ. Water is needed to move the sperm. An embryo is formed from a fertilized egg. It sprouts and turns into an individual of the asexual generation, which multiplies by spores.
THINK!
Why do many cultivated plants propagate vegetatively?
With vegetative propagation, the properties of the mother plant are fully preserved. Here, neither pollination can affect, nor methods of pruning, fertilizing, etc. Whereas sowing seeds from a cultivated plant gives a whole fan of differences from the original plant.