Exam assignments for the cycle of plant development. Plant life cycle: description, stages, diagrams and features

Solving problems on the topic of plant life cycles

It is important not to forget that in animals, during the formation of gametes, first mitosis occurs, and then meiosis. In plants, on the contrary, first meiosis, and then mitosis... During sporogenesis in plants, haploid cells are formed from diploid cells, which then divide by mitosis

№1 What is the chromosomal set of ha-rak-teren for gametes and spores of growing moss ku-kush-ki-na flax? Explains from what cells and in re-zul-ta-te k-go de-leiya they are formed.

Revelation.

Ha-me-you moss ku-kush-ki-na flax ob-ra-zu-yut-sya on ha-me-to-fi-tah from a g-p-lo-id-noy cell by mi-to -per. The set of chromosomes in gametes is the same - n.

Disputes of moss ku-kush-ki-na flax ob-ra-zu-yut-Xia on di-plo-id-spo-ro-fi-te in spo-ran-gi-yah by mei-o-za from di -ploid cells. A set of chro-mo-som in spores is odin-n

№2 What is the chro-mo-som-ny set of ha-rak-te-ren for ha-me-to-fi-ta and gametes of moss sphag-nu-ma? Explains those from which initial cells and in re-zul-ta-te how-to-do-le-ny these cells are formed?

Revelation.

1) Ga-me-to-fit and ha-me-you sphag-nu-ma ha-p-lo-id-ny, and a set of chromium, and the amount of DNA in cells from -we-cha-yut for-mu-le nc.

2) Ga-me-to-fit ob-ra-zu-is from the dispute, which-para-zu-is-Xia in re-zul-ta-te mei-o-za from the fabric -no spo-ro-fi-that.

3) The dispute de-lit-Xia mi-to-zom, forming ga-me-to-fit.

№3 What is the chro-mo-som-ny set of ha-rak-teren for the debate, ha-me-to-fi-ta and spo-ro-fi-ta moss ku-kush-kin flax? From what initial cells and in re-zul-ta-te ka-k-go de-leiya form these stages of development of moss?

Revelation.

1) The dispute and ga-me-to-fit of moss contains a g-p-lo-id-set of chrome-mo-som, and spo-ro-fit is di-plo-i-den.

2) The dispute about-ra-zu-is-Xia in re-zul-ta-te mei-o-za from spo-nasal cells spo-ro-fi-ta,

and ha-me-to-fit ob-ra-zu-is-Xia from the dispute by mi-to-za.

No. 4. What is the chromosomal set of ha-rak-teren for gametes and spores of the bloom club-shaped? Explains from what cells and in re-zul-ta-te k-go de-leiya they are formed.

Revelation.

Ha-me-you lyon is formed on ha-me-to-fi-tah (outgrowths) from a ha-p-lo-id-cell by mi-to-za. The set of chromosomes in gametes is the same - n.

Spores of moss moss are formed on di-plo-id-spo-ro-fi-te ( adult plant) in spore-bearing spikelets by mei-o-za from di-ploid cells. A set of chro-mo-som in spores is odin-n

No. 5. What is the chromosomal set of ha-rak-teren for ha-me-to-fi-ta and fern gametes? Explains those from which initial cells and in re-zul-ta-te how-to-do-le-ny these cells are formed?

Revelation.

1) Ha-me-to-fit (germ) and ha-me-you fern ha-p-lo-id-ny, and a set of chromium, and the amount of DNA in the cells from- ve-cha-yut for-mu-le nc.

2) Ga-me-to-fit ob-ra-zu-is from the dispute, which-para-zu-is-Xia in re-zul-ta-te mei-o-za from the fabric -ne spo-ro-fi-that (an adult plant)

3) The dispute de-lit-Xia mi-to-zom, forming a g-me-to-fit during germination.

№6. What is the chro-mo-som-ny set of ha-rak-te-ren for the dispute, ha-me-to-fi-ta and spo-ro-fi-ta horsetail? From what initial cells and in re-zul-ta-te ka-k-go de-leiya form these stages of development of moss?

Revelation.

1) The spore and ga-me-to-fit (overgrowth) of horsetail contain a g-p-lo-id-set of chromosomes, and spo-ro-fit (adult plant) di-plo- i-den.

2) The dispute is about-ra-zu-is-Xia in re-zul-ta-te mei-o-za from the cells of a spore-bearing spikelet spo-ro-fi-ta, and ha-me-to-fit ob-ra -su-e-xia from the dispute by mi-to-za.

3) Spo-ro-fit ob-ra-zu-is-Xia after payment-acceptance-re-tion from zi-go-you by mi-to-za.

№7 What is the chro-mo-som-ny set of ha-rak-te-ren for the cells of the meat-to-ti needles and the sperm of the pine? Explain-no-those from which initial cells and in re-zul-ta-te k-go de-lening these cells are formed

Revelation.

Ele-men-you from-ve-ta:

1) in pine yoke-lok cages, a set of chromosomes - 2n; in the sperm of the pine - n;

2) an adult pine planting develops from zi-go-you (2n);

3) pine sperm develops from ha-p-lo-id micro-spores (n) by mi-to-z

№8 What chromosome set is typical for vegetative, generative cells and sperm of pollen grain flowering plant? Explain from what initial cells and as a result of what division these cells are formed.

Explanation.

1) a set of chromosomes of vegetative and generative cells - n;

2) vegetative and generative pollen cells are formed by mitosis during germination of a haploid spore;

3) chromosome set of sperm - n;

4) sperm are formed from the generative cell by mitosis

№ 9 What is the chromosomal set of ha-rak-teren for the nuclei of cells of the epi-der-mi-sa leaf and eight-nuclei-no-go-ro-d-she-in -th bag se-me-for-chat-ka color-of-th-th plant? Explain-no-those from which initial cells and in re-zul-ta-te k-go de-lening these cells are formed ...

Revelation.

1. Epi-der-mis of the leaf has a di-ploid set of chromosomes. An adult plant is a spo-ro-fi-tom.

2. All cells behind-ro-dy-she-in-th bag are ha-p-lo-id-ny, but in the center there is a di-plo-id-ny nucleus (about -ra-zu-it-Xia in re-zul-ta-te merging of two cores) - this is no longer eight-core, but seven-cell-to-ro- breathe-sack. This is ga-me-to-fit.

3. Spo-ro-fit is formed from cells for-ro-d-sha se-me-ni by mi-to-ti-ti-ti-le-niya. Ga-me-to-fit ob-ra-zu-is-sya by mi-to-ti-ti-ti-le-niya from g-p-lo-id-noy dispute.

No. 10. What a chro-mo-som-ny set of ha-rak-teren for ve-ge-ta-tiv-noy, ge-non-ra-tive-cell-cells and stolen dust th grain color-to-th plant? Explain-no-those from which initial cells and in re-zul-ta-te k-go de-lening these cells are formed ...

Revelation.

1) a set of chromo-som ve-ge-ta-tiv-noy and he-ne-ra-tiv-noy cells - n;

2) ve-ge-ta-tiv-naya and ge-ne-ra-tiv-naya pollen-cells are formed by mi-to-za with pro-growth ha-p-lo-id-noy disputes;

3) chromosomal set of sperms - n;

4) the sperm is formed from the he-ne-ra-tive cell by mi-to-z

The publication uses USE materials from previous years

It can be simple or complex. Chlorella, which reproduces by spores, is an example of a simple cycle. While developing, this green algae becomes a repository of 4-8 autospores, which grow inside the mother's body and are covered with their own shell. But among plants, a complex development cycle is more common, which consists of 2-3 simple ones.

Features of plant life cycles

An important property of all living things is the ability to reproduce. The breeding method is:

• sexual (gametes);
• asexual (by spores);
• vegetative (part of the body).

In complex cycles during sexual reproduction, there are always several distinct phases of the gamete and zygote. Gamete is a mature reproductive cell with a haploid (ordinary) set of chromosomes. A zygote with a diploid (double) set is formed as a result of the union of two gametes. A sporophyte develops from the zygote, which produces haploid spores. Of the spores - gametophyte, which is male and female.

For example, we can take an equal-spore fern, which has two forms of individuals - the fern itself (sporophyte) and its outgrowth (gametophyte). The germ is the offspring of the adult fern. It exists for a very short period, but manages to give birth to a single large-leaved individual. The life cycle of a plant, due to this reproduction feature, consists of an alternation of generations: from an adult fern to an outgrowth and again to an adult fern.

Reproduction methods

Most plants reproduce sexually. In this case, a new organism is formed from the zygote after fertilization and the union of gametes (syngamia). Parthenogenesis - reproduction without fertilization - also refers to the sexual mode: the daughter organism is formed from isogametes, which makes isogametes and spores related. Sexual reproduction is almost always combined with other methods - vegetative or asexual, since it itself is characterized by low productivity.

At the same time, this method and asexual reproduction is found in ferns, and in conjunction with the vegetative variant - in some algae. In seed plants, the formation of a sex cell occurs from one daughter zygote, as a result of which this process is more reminiscent of reproduction rather than reproduction.

During asexual reproduction, zoospores are formed - cells without a cell wall, which in multicellular plants are located in special sporangia, and immobile cells - aplanospores. Independently, this method of reproduction is very rare in nature. Usually it is combined with sexual or vegetative.

There are 2 types of spores: mitospores, which arise during asexual reproduction, and meiospores, which arise during sexual reproduction. Mitospores appear through mitosis, resulting in a maternal-like specimen. Meiospores are formed by meiosis during germination of a zygote or in sporangia. For most plants, both methods of reproduction are characteristic, due to which two different forms of individuals are obtained.

Vegetative breeding method

With the vegetative reproduction, a division into akineta - thick-walled cells occurs. It consists in separating some part of it from the mother liquor - a brood kidney or a calf. In this way, some, including sargassum, brown, and even flowering plants, such as duckweed, reproduce vegetatively. Some of them develop brood buds that fall to the ground and take root there. Also, buds can branch off and detach from the mother plant. In the angiosperm group of plants, the development of shoots underground from the rhizome is very common.

Plant spread

One of the final stages of reproduction is the spread of plants. In nature, there can be 3 variants of dispersal: by embryos, spores and seeds. In extremely rare cases, distribution can occur with the help of zygotes. Even K. Linnaeus associated seed and spore distribution with secret and phantom plants. The second type included the group of gymnosperms and angiosperms, and the first - all other groups, including algae, moss and ferns.

Plant propagation methods have come a long evolutionary path from vegetative to asexual and sexual. Now the division of plants into spore and seed plants is associated not with distribution, but with reproduction. The seed method stands out in a separate group, since it is considered a combination of reproduction by spores and gametes. Seed reproduction includes several stages: the formation of zygotes, gametes, spores, embryos and seeds, as well as the dispersal of the plant.

Alternation of generations

The life of plants in the form of two different generations can bear different names: a change in developmental forms, alternation of generations, etc. The changeability of a large fern and an outgrowth in the case of an equal-spore fern is an example of alternation of generations, marked by the phases of the adult state of the forms of individuals. These two forms are so different in appearance that it is difficult to recognize the same plant in them. The fern overgrowth is very difficult to see with the naked eye. In angiosperms, the analogue of the germ is the embryonic sac, which is extremely small and hidden in the depths of the flower. Among some groups of algae, these forms of individuals are similar in appearance, but completely differ in biological characteristics. The alternation of generations is found in almost all higher plants and evolutionarily developed algae.

Life Cycles of Higher Plants

The life cycle of higher plants, with the exception of bryophytes, is characterized by the fact that the gametophyte is poorly developed, and in the life cycle a large part is occupied by the sporophyte. differ in that the sporophyte develops inside the female genital organ and is in continuous communication with the gametophyte. In the case of it, it looks like a box of spores growing from the top of the gametophyte.

The rest of the higher plants have pronounced sporophytes, which are large and complex with organs such as foliage, stems and root system... Most of the plants that a person imagines when talking about horsetails, ferns, or other groups are sporophytes.

Life Cycles of Flowering Plants

The most progressive in terms of evolution are flowering plants. The life cycle of flowering plants is characterized by the fact that the embryo is often able to develop from an unfertilized egg cell (apomixis). The predominant form of flowering plants is a multi-spore sporophyte, which is a plant with leaves and stems. The male gametophyte is represented by a pollen grain, and the female gametophyte is represented by the embryonic sac (it develops faster than in gymnosperms). The organ of both sexual and asexual reproduction is a modified shoot - a flower. The seed buds are protected by the walls of the ovary. The life cycle of the development of plants of this group ends after fertilization and the formation of a seed, the embryo in which has a supply of nutrients and does not depend on external factors.

Life cycles of gymnosperms and angiosperms

To the group gymnosperms include representatives conifers and shrubs. Most of them have modified needle-like leaves. The life cycle of gymnosperms is different in that microspores (pollen) are formed in small male cones (anthers), and megaspores - in female ones (ovules). The male gametophyte is formed from the microspores, and the female gametophyte is formed from the megaspore. The life cycle of a plant from this group differs in that fertilization occurs with the help of wind, which delivers pollen to the ovules. After that, an embryo begins to develop inside the ovule, and a seed is formed from it. It lies on the seed scales and is not covered by anything. The seed produces a new sporophyte from which a new plant grows.

Plants are distinguished by the fact that this group has a flower in which spores form and fertilization of gametophytes and development of seeds occurs. The peculiarity of this group is in the protection of seeds, which are hidden inside the fruit and are protected from the effects of the external environment.

The life cycle of spore plants

Spore plants do not bloom, which is why they are also called non-flowering plants. They come in two categories:

• higher (ferns, horsetails, mosses, moss);
• lower (algae, lichens).

Life Cycles spore plants, depending on the species, can be either sexual or asexual. They are not able to reproduce sexually without the participation of the aquatic environment. For sexual reproduction, a gametophyte is used, and for asexual reproduction, a sporophyte. There are two subgroups of spore plants: haploid and diploid. The haploid subgroup includes mosses, horsetails and ferns, in which the gametophyte is more developed, and the sporophyte is formed in the form of an overgrowth. The haploid subgroup differs in that the sporophyte has a subordinate status in it.

Plant life cycles: diagrams

Mosses are representatives of a primitive species of higher plants. They have a very conditional division of the organism into stem and leaves, instead of roots - filamentous rhizoids. They grow in marshy, wet places and evaporate moisture very strongly. They reproduce sexually, the sporophyte depends on the gametophyte, the spores are formed in a special capsule, which is located above the gametophyte and is associated with it.

Ferns have large feathery leaves (sporangia are located on the underside). The plant has a pronounced root system, and the leaf is actually a system of branches, which is called a frond or pre-shoot. The life cycle of ferns consists of two phases: sexual and asexual.

The sexual phase occurs with the participation of gametes, and the asexual phase occurs with the participation of spores. The asexual generation begins with a diploid zygote, and the sexual generation begins with a haploid spore. The changeability of these phases is the major part of the cycle.

As shown by the exam results of past years:

Students are poorly formed

Knowledge about changes in the chromosome set in the cells of the gametophyte and sporophyte of algae, mosses, ferns, gymnosperms and flowering plants;

On the formation of spores in plants during meiosis, and germ cells during mitosis, which distinguishes them from animals;

Ability to compare spores and germ cells, spores and sporophyte cells;

Explain and argue the peculiarities of the formation of spores, germ cells, gametophyte in plants.

The presentation is intended to conduct a lesson to prepare students for solving the tasks of part C5 (cytology).

There is a slide for repeating the stages of meiosis.

Understands the difference between gametophyte and sporophyte, spores from gametes.

A complete analysis of the development cycles of algae, bryophytes, ferns, gymnosperms and angiosperms is carried out.

At the end of the lesson, time is allocated for solving problems. (The solutions are built-in, but hidden from students - they can be used when checking the solution).

Good luck in job!

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Cycles of plant development Preparation for completing the tasks of the USE C5 (application of knowledge to determine the number of chromosomes and DNA in different phases of mitosis and meiosis, in the reproductive and somatic cells of different organisms) © Tikhonova E.N. January 6, 2015

As the results of the past exam have shown: Students have poorly formed knowledge about changes in the chromosome set in the cells of the gametophyte and sporophyte of algae, mosses, ferns, gymnosperms and flowering plants; on the formation of spores in plants during meiosis, and germ cells during mitosis, which distinguishes them from animals; the ability to compare spores and germ cells, spores and sporophyte cells; explain and argue the peculiarities of the formation of spores, germ cells, gametophyte in plants.

Life stages of plants Sporophyte Gametophyte literally - spore-bearing all cells contain a diploid set of chromosomes (2n) forms spores (n) literally - gamete-carrying all cells contain a haploid set of chromosomes (n) form gametes (n)

Dictionary (Reimers N.F.) Sporophyte is a representative of asexual generation or a stage of a plant life cycle from zygote to spore formation Gametophyte is a representative of a sexual generation or a stage of a plant life cycle from spore to zygote formation

Dictionary (Reimers N.F.) Sporangia organ of asexual reproduction of plants and fungi, in which spores are formed Gametangium genital organ of plants, fungi, in which gametes are formed

Generations Asexual Sexual 2n develops from the zygote spore spore (n) (MEIOSIS) n develops from the spore gametophyte gamete (n) (MITOSIS)

Disputes (n) - why, then, are these asexual cells, and gametes (n) are reproductive ?! Let's figure it out! A haploid spore (one) without merging with any other cell forms a new organism (or rather another life stage) genetically identical to this one spore. the spore, being a product of the sporophyte, itself forms the future gametophyte> asexual reproduction. The tissues of the gametophyte are haploid, of which the gametes are formed. Each haploid gamete does not form a new organism. Only after the stage of fertilization it with another gamete (after combining the genetic material (n) ♀ and (n) ♂ gametes, a diploid (2 n) zygote is formed). That. gametes, being a product of a haploid gametophyte, only merging in pairs male and female will ensure the further development of a new organism> sexual reproduction

Asexual generation Sexual generation meiosis Disputes n n n 2n mitosis x Zygote 2n ♂ ♀ n n n mitosis

Sporophytes Gametophytes

Development cycle of leafy moss (cuckoo flax)

Exercise 1 . "Department of Bryophytes" In the life cycle of bryophytes prevails (_). Bryophytes reproduce (_). Asexual reproduction occurs with (_). Spores, like all higher plants, are formed (_), and have (_) a set of chromosomes. The sporophyte of mosses is represented by (_). The gametophyte of mosses is represented by (_). Gametophytes are called dioecious if (_). Antheridia and archegonia in mosses are formed on (_). For the fusion of germ cells, (_) is required. After fertilization, (_) develops from the zygote. From the moss spore (_) develops. When does meiosis occur in the moss cycle (_)

Task 2. "Division Fern" Fern sporophyte is represented by (_), gametophyte - (_). Ferns strobili (_). Antheridia and archegonia in the male shieldworm are formed on (_). The spores in the male shield bush are formed on the lower part of the leaf in (_), covered with a veil - (_). What is the representation of asexual generation in ferns? Explain the answer. What is the sexual generation of ferns represented by? Explain the answer. Where do fern gametes form? How does ferns reproduce? Where do fern spores form? How does asexual reproduction take place in ferns? Where does a fern embryo a new plant?

Pine development cycle

Task 3. "Division of gymnosperms" How is the sporophyte of gymnosperms represented? How is the male gametophyte of gymnosperms represented? How is the female gametophyte of gymnosperms represented? The main aromorphoses that led to the appearance of gymnosperms? What are the microsporangia of gymnosperms? What are the megasporangia of gymnosperms represented by? What are the gametangia of gymnosperms? When does meiosis occur in the life cycle of gymnosperms? What develops from microspores and megaspores of gymnosperms?

Task 4. "Division of gymnosperms" What features does pine pollen have? How is the male gametophyte that forms the sex cells represented? What is the female gametophyte that forms sex cells represented by? Do you need water to fertilize gymnosperms? Why? Where does the embryo of a new plant form in a pine?

Task 7. "Department of Gymnosperms" In the spring of a pine on each scale of reddish cones formed by…. The megasporangium of gymnosperms is represented by…. In nucellus, the megasporocyte undergoes meiosis, three megaspores die off, and the nucleus of the fourth…. On the scales of greenish-yellow cones formed at the base of young shoots,… are formed. Microsporocytes meiotically divide and form ..., each of which forms ... as a result of mitotic divisions. Several cells are distinguished in a pollen grain:…. Fertilization in pine occurs later ... after pollination. One of the sperm fuses with the egg, and the second…. The second archegonium of the female gametophyte is also…. Pine seeds ripen only after ... after pollination. From a fertilized egg, a zygote, ... is formed. Endosperm in gymnosperms…. For fertilization of gymnosperms water…. Unlike the spore, the pine seed has….

Megaspore (n) Female gametophyte (embryonic sac) (n) Microspore (n) Male gametophyte (pollen grain) (n)

Sexual generation n gamete mitosis n fertilization zygote 2 n asexual generation 2 n meiosis spores n

Task 5. "Angiosperms Department" What is the flowering sporophyte? What represents the male gametophyte of flowering plants? What represents the female gametophyte of flowering plants? The main aromorphoses that led to the appearance of flowering? How are flowering microsporangia represented? What are the flowering megasporangia? What are flowering gametangia? When does meiosis occur in the life cycle of flowering plants - during the formation of gametes or spores? What develops from flowering microspores and megaspores?

What is indicated in the figure by numbers 1 - 6? When does meiosis occur - during the formation of spores, or during the formation of gametes?

Task 6. "Double fertilization of flowering plants" The male gametophyte of flowering plants is represented by (_). The pollen grain on the stigma of the column swells and forms (_). The generative cell divides and forms (_). The ovule is protected from the outside (_), between which there is a hole - (_). The female gametophyte of flowering plants is represented by (_). Inside the ovule develops (_), consisting of seven cells. One sperm merges with (_), the second - (_), that is, two fertilizations occur. Double fertilization was discovered by a Russian scientist (_). The seed embryo develops from (_). Endosperm is formed from (_). Perisperm is formed from (_). The seed coat is formed from (_) The pericarp is formed from (_).

The chromosome set of wheat somatic cells is 28. Determine the chromosome set and the number of DNA molecules in ovule cells before the onset of meiosis, at the end of the telophase of meiosis 1 and telophase of meiosis 2. Explain what processes occur during these periods and how they affect changes in the number of DNA and chromosomes ... 1) Before the onset of meiosis, the chromosome set in the cells of double (2 n) -28 chromosomes, in the interphase there is a doubling of DNA molecules, therefore the number of DNA molecules is 56 molecules (4c). 2) In the first division of meiosis, homologous chromosomes, consisting of two chromatids, diverge, therefore, at the end of the telophase of meiosis, 1 chromosome set in cells is single (n) - of 14 chromosomes, the number of DNA molecules is 2c (28 DNA molecules). 3) In the second division of meiosis, chromatids diverge, therefore, at the end of telophase 2 of meiosis, the chromosome set in cells is single (n) -14 chromosomes, the number of DNA molecules is 14 molecules (1c).

The chromosome set of wheat somatic cells is 28. Determine the chromosome set and the number of DNA molecules in one of the ovule cells before the onset of meiosis, in meiosis anaphase I and meiosis anaphase II. Explain what processes occur during these periods and how they affect the change in the number of DNA and chromosomes. 1) before the onset of meiosis, the number of DNA molecules is 56, since they double, and the number of chromosomes does not change - there are 28 of them; 2) in the anaphase of meiosis I, the number of DNA molecules is 56, the number of chromosomes is 28, homologous chromosomes diverge to the poles of the cell; 3) in the anaphase of meiosis II, the number of chromosomes is 28, sister chromatids diverge to the poles of the cell and become independent chromosomes (but they are all in one cell), the number of DNA molecules is 28, after the first division, DNA doubling does not occur, therefore the number of DNA decreased by 2 times.

In the cells of the endosperm of lily seeds there are 21 chromosomes. How will the number of chromosomes and DNA molecules change at the end of the telophase of meiosis 1 and meiosis 2 in comparison with the interphase in this organism? Explain the answer. 1) The endosperm of flowering plants has a triploid set of chromosomes (3 n), which means that the number of chromosomes in a single set (n) is 7 chromosomes. Before the onset of meiosis, the chromosome set in cells is double (2 n) of 14 chromosomes, in the interphase there is a doubling of DNA molecules, therefore the number of DNA molecules is 28 (4c). 2) In the first division of meiosis, homologous chromosomes, consisting of two chromatids, diverge, therefore, at the end of the telophase of meiosis, 1 chromosome set in cells is single (n) of 7 chromosomes, the number of DNA molecules is 14 (2c). 3) In the second division of meiosis, chromatids diverge, therefore, at the end of telophase 2 of meiosis, the chromosome set in cells is single (n) -7 chromosomes, the number of DNA molecules is equal to one-7 (1c).

What chromosomal set is characteristic for the cells of the embryo and endosperm of the seed, leaves of a flowering plant. Explain the result in each case. 1) in the cells of the embryo of the seed there is a diploid set of chromosomes - 2n, since the embryo develops from a zygote - a fertilized egg; 2) in the cells of the endosperm of the seed there is a triploid set of chromosomes - 3n, since the ovule (2n) and one sperm (n) are formed by the fusion of two nuclei of the central cell; 3) the cells of the leaves of a flowering plant have a diploid set of chromosomes - 2n, since an adult plant develops from an embryo.

What chromosome set is typical for the cells of the pollen grain and sperm cells of the pine? Explain from what initial cells and as a result of what division these cells are formed. 1) The cells of the pollen grain of pine and sperm have a haploid set of chromosomes. 2) Pine pollen grain cells develop from haploid spores by mitosis. 3) Pine sperm develop from pollen grain cells (generative cells) by mitosis.

What chromosomal set is typical for sperm and endosperm cells of the seed of a flowering plant? Explain from which cells and as a result of what division these cells are formed. 1) In the sperm, the set of chromosomes is haploid, the cells of the endosperm of the seed are triploid. 2) Sperm will form from a haploid spore (the generative cell of the male gametophyte) as a result of mitosis. 3) Endosperm is formed by the fusion of two haploid nuclei of the central cell of the embryo sac (2 n) and one sperm (n).

What chromosome set is characteristic of the cells of the epidermis and the eight-nucleated embryo sac of the ovule of a flowering plant? Explain from what initial cells and as a result of what division these cells are formed. 1) The leaf is a part of a sporophyte of a flowering plant whose cells are diploid (2n). Eight-nucleated embryo sac is an immature female gametophyte of a flowering plant whose cells are haploid (n) 2) Leaf cells are formed during mitotic division of educational tissue (including the cells of the leaf epidermis). 3) The cells of the eight-nucleated embryo sac are formed during mitotic division of the megaspore from which the female gametophyte of the flowering plant is formed.

What chromosome set is typical for gametes and spores of the cuckoo flax moss plant? Explain from what cells and as a result of what division they are formed. Gametes of cuckoo flax moss are formed on gametophytes from a haploid cell by mitosis. 2) The set of chromosomes in gametes is single - n. 3) Spores of cuckoo flax moss are formed on a diploid sporophyte in sporangia by meiosis from diploid cells. The set of chromosomes in spores is single - n

What chromosome set is typical for the gametophyte and gametes of sphagnum moss? Explain from what initial cells and as a result of what division these cells are formed? 1) The gametophyte and sphagnum gametes are haploid, and the set of chromosomes and the amount of DNA in the cells correspond to the nc formula. 2) The gametophyte is formed from the spore, which is formed as a result of meiosis from the tissues of the sporophyte. 3) The spore is divided by mitosis, forming a gametophyte.

The haploid set of chromosomes of a pea is 7. How many chromosomes are contained in the cells of leaves, embryo of a seed and cotyledons of a seed. Explain the answer. 1. Sheet- vegetative organ plants, cells contain 2n chromosomes, therefore, they contain 14 chromosomes 2. The seed embryo is formed as a result of fertilization, therefore, they have a diploid set of chromosomes (2n = 14) 3. The cotyledons of pea seed contain a reserve nutrient, they are formed as a result of sperm fusion (n) and the central ovule cell (2n) and has a triple set of chromosomes (3 n = 21)

The life cycle of higher plants consists of two rhythmically alternating phases, or “generations” (Fig. 1), sexual (gametophyte) and asexual (sporophyte). The genitals develop on the gametophyte. The gametophyte can be bisexual. In this case, both antheridia and archegonia develop on it. But in the vast majority of higher plants (including all gymnosperms and flowering plants), it is unisexual and carries either only antheridia (male gametophyte) or only archegonia (female gametophyte). As a result of fertilization, that is, the fusion of the male gamete with the female, a new cell is formed with a double set of chromosomes (paternal and maternal), called a zygote.

In higher plants, in contrast to lower ones, the zygote gives rise to a multicellular embryo. As a result of the growth and differentiation of the embryo, a sporophyte develops. Like the zygote, all the cells of the embryo and the sporophyte developing from it are characterized by a doubled number of chromosomes.

On the sporophyte, sporangia are formed, in which spores develop - very small, usually barely distinguishable with the naked eye, unicellular formations that serve for asexual reproduction. With the formation of spores, the number of chromosomes as a result of meiosis is halved, and therefore each spore in relation to the cells of the sporophyte is haploid.

In many higher plants, for example, in most ferns, each spore gives rise to a bisexual gametophyte, on which both antheridia and archegonia develop. However, most higher plants have two types of sporangia: microsporangia, in which smaller microspores are formed, and megasporangia, in which larger megaspores develop. Each microspore gives rise to one male gametophyte, and from each megaspore one female gametophyte is formed. Therefore, some authors, for example B. M. Kozo - Polyansky, call microspores "male disputes", and megaspores - "female disputes." Only antheridia develop on the male gametophyte, and only archegonia develop on the female gametophyte.

Both sexual and asexual reproduction have definite biological advantages. With sexual reproduction, a combination of the hereditary material of the parental forms is achieved. An individual formed during sexual reproduction is not genetically identical to any of its parents. The sexual process provides for the recombinant genetic variability of organisms from generation to generation, so sexual reproduction provides the species with the advantages that are realized with natural selection.

With asexual reproduction, hereditary features are transmitted without changes and can easily be fixed in a number of generations, while the hereditary material of the parent individual is, as it were, "replicated" and a rapid increase in numbers is possible. However, most often in plants, it is precisely the alternation of sexual and asexual generations that takes place.

In all higher plants, except for bryophytes, the sporophyte predominates in the life cycle, the gametophyte is less developed and relatively short-lived. Sporophytes are large multicellular organisms with a complex anatomical structure and dismemberment of the body into organs - stems, leaves, roots (real or adventitious).

Thus, the complete life cycle of a higher plant from zygote to zygote consists of gametophase (gametophyte) and sporophase (sporophyte). Due to this, a kind of "dual individuality" appears in the life cycle of a higher plant, and, moreover, in two different forms... In many higher plants (moss, horsetails, and ferns), these phases are, as it were, separate physiologically independent creatures. In mosses, and especially in seed plants, one of the two generations is subordinate to the other and, in physiological terms, is, as it were, reduced to its organ. But although physiologically they ceased to be here separate generations (independent creatures), in their origin they fully correspond to them, and the terms "gametophyte" and "sporophyte" can be applied to them.

The concept of the life cycle of plants

In the life cycle of plants, there is an alternation of asexual and sexual reproduction and the associated alternation of generations.

A haploid (n) plant organism that forms gametes is called a gametophyte (n). He represents the sex generation. Gametes are formed in the genitals by mitosis: sperm (n) - in antheridia (n), eggs (n) - in archegonia (n).

Gametophytes are bisexual (antheridia and archegonia develop on it) and dioecious (antheridia and archegonia develop on different plants).

After the fusion of gametes (n), a zygote with a diploid set of chromosomes (2n) is formed, and from it an asexual generation develops through mitosis - a sporophyte (2n). In special organs - sporangia (2n) of the sporophyte (2n), after meiosis, haploid spores (n) are formed, during the division of which new gametophytes (n) develop by mitosis.

Life cycle of green algae

In the life cycle of green algae, gametophyte (n) predominates, that is, the cells of their thallus are haploid (n). With the onset of unfavorable conditions (cold snap, drying out of the reservoir), sexual reproduction occurs - gametes (n) are formed, which merge in pairs into a zygote (2n). The zygote (2n), covered with a membrane, hibernates, after which, when favorable conditions occur, it divides by meiosis with the formation of haploid spores (n), from which new individuals develop (n).

Life cycle of mosses (cuckoo flax)

In mosses, the sexual generation (n) predominates in the development cycle. Leafy mosses are dioecious gametophytes (n). On male plants (n), antheridia (n) with sperm (n) are formed, on female (n) - archegonia (n) with eggs (n). With the help of water (during rain), sperm (n) get to the eggs (n), fertilization occurs, a zygote (2n) appears. The zygote is located on the female gametophyte (n), it divides by mitosis and develops a sporophyte (2n) - a capsule on a leg. Thus, the sporophyte (2n) in mosses lives off the female gametophyte (n).

In the sporophyte capsule (2n), spores (n) are formed by meiosis. Mosses are heterogeneous plants; there are microspores - male and macrospores - female. From spores (n), by mitosis, first progrowths develop, and then adult plants (n).

Fern life cycle

In ferns (also horsetails, lycopods), the sporophyte (2n) predominates in the life cycle. On the underside of the leaves of the plant (2n), sporangia (2n) develop, in which spores (n) are formed by meiosis. From the spore (n), which has fallen into moist soil, an outgrowth (n) grows - a bisexual gametophyte. On its lower side, antheridia (n) and archegonia (n) develop, and in them, by mitosis, spermatozoa (n) and eggs (n) are formed. With droplets of dew or rainwater, the sperm (n) get to the eggs (n), a zygote (2n) is formed, and from it the embryo of a new plant (2n).

On the scales of female cones, ovules are located - megasporangia (2n), in which 4 megaspores (n) are formed by meiosis, 3 of them die, and from the remainder, a female gametophyte develops - endosperm (n) with two archegonia (n). In archegonia, 2 eggs (n) are formed, one dies.

On scales male cones there are pollen sacs - microsporangia (2n), in which microspores (n) are formed by meiosis, from which male gametophytes develop - pollen grains (n), consisting of two haploid cells (vegetative and generative) and two air chambers.

Pollen grains (n) (pollen) are carried by the wind to female cones, where by mitosis from the generative cell (n) 2 sperm (n) are formed, and from the vegetative (n) - the pollen tube (n), which grows into the ovule and delivers the sperm (n) to the ovum (n). One sperm dies, and the second participates in fertilization, a zygote (2n) is formed, from which a plant embryo (2n) is formed by mitosis.

As a result, a seed is formed from the ovule, covered with a skin and containing an embryo (2n) and endosperm (n) inside.

Life cycle of angiosperms

Angiosperms are sporophytes (2n). The organ of their sexual reproduction is a flower.

In the ovary of the flower pistils there are ovules - megasporangia (2n), where meiosis occurs and 4 megaspores (n) are formed, 3 of them die, and from the remaining, a female gametophyte develops - an embryonic sac of 8 cells (n), one of them is an egg (n), and two merge into one - a large (central) cell with a diploid set of chromosomes (2n).

In microsporangia (2n) of anthers of stamens, microspores (n) are formed by meiosis, from which male gametophytes develop - pollen grains (n), consisting of two haploid cells (vegetative and generative).

After pollination, 2 sperm (n) are formed from the generative cell (n), and from the vegetative (n) - the pollen tube (n), which grows into the ovule and delivers the sperm (n) to the ovum (n) and the central cell (2n). One sperm (n) fuses with the egg (n) and forms a zygote (2n), from which a plant embryo (2n) is formed by mitosis. The second sperm (n) is fused by the central cell (2n) to form the triploid endosperm (3n). Such fertilization in angiosperms is called double fertilization.

As a result, a seed is formed from the ovule, covered with a skin and containing an embryo (2n) and an endosperm (3n) inside.

General conclusions

1. In the process of plant evolution, there was a gradual reduction of the gametophyte and the development of the sporophyte.

2. In gametes of plants there is a haploid set (n) of chromosomes, they are formed by mitosis.

3. In plant spores there is a haploid set (n) of chromosomes, they are formed by meiosis.