Solving problems on the topic of plant life cycles
It is important not to forget that in animals, during the formation of gametes, mitosis occurs first, 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.
No. 1 What is the chromo-mo-som-ny set of ha-rak-te-ren for gametes and spores of moss races k-kush-ki-na flax? Explain-no-those from which cells and in the re-zul-ta-te ka-ko-go de-le-tion they form.
Clear-no-no.
Ga-me-you moss ku-kush-ki-on flax ob-ra-zu-yut-sya on ha-me-to-fi-tah from ga-p-lo-id-noy cage by mi-to -per. The set of chromosomes in gametes is one-nar-ny - n.
Moss spores ku-kush-ki-on flax are about-ra-zu-ut-sya on di-plo-id-nom spo-ro-fi-te in spo-ran-gi-yah by mei-o-za from di -plo-id-nyh cells. A set of chromo-mo-catfish in spores is one-nar-ny - n
№2 What is the chromo-mo-som-ny set of ha-rak-te-ren for ha-me-to-fi-ta and moss gametes sphag-nu-ma? Explain-those from what source cells and in the result of what de-le-tion about-ra-zu-yut-sya these cells?
Clear-no-no.
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 -ve-cha-yut for-mu-le nc.
2) Ha-me-to-fit ob-ra-zu-et-sya from a dispute, something-paradise ob-ra-zu-et-sya in re-zul-ta-te mei-o-for from fabric -nee spo-ro-fi-ta.
3) Spore de-lit-sya mi-to-zom, ob-ra-zuya ha-me-to-fit.
№3 What chro-mo-som-ny set of ha-rak-te-ren for spores, ha-me-to-fi-ta and spo-ro-fi-ta moss ku-kush-kin len? From what source cells and in the result of what kind of de-le-tion are these stages of development of moss?
Clear-no-no.
1) Spore and ga-me-to-fit moss co-derzhat ha-p-lo-id-ny set of chromo-mo-catfish, and spo-ro-fit di-plo-and-den.
2) The dispute is about-ra-zu-et-sya in re-zul-ta-te mei-o-za from spo-ro-nose cells-tok spo-ro-fi-ta,
and ha-me-to-fit ob-ra-zu-et-sya from a dispute by mi-to-za.
No. 4. What is the chromo-mo-som-ny set of ha-rak-te-ren for gametes and spores of the race of the club club? Explain-no-those from which cells and in the re-zul-ta-te ka-ko-go de-le-tion they form.
Clear-no-no.
Ga-me-you of a club moss-ra-zu-yut-sya on ha-me-to-fi-tah (growths) from ha-p-lo-id-noy cells by mi-to-za. The set of chromosomes in gametes is one-nar-ny - n.
The moss spores of the club moss are formed on the di-plo-id-n spo-ro-fi-te (adult plant) in spore-bearing spikelets by mei-o-za from di-plo-id-nyh cell current. A set of chromo-mo-catfish in spores is one-nar-ny - n
No. 5. What is the chromo-mo-som-ny set of ha-rak-te-ren for ha-me-to-fi-ta and fern gametes? Explain-those from what source cells and in the result of what de-le-tion about-ra-zu-yut-sya these cells?
Clear-no-no.
1) Ga-me-to-fit (growth) and ha-me-you of the ha-p-lo-id-ny fern, and a set of chromium, and the amount of DNA in cells from ve-cha-yut for-mu-le nc.
2) Ha-me-to-fit ob-ra-zu-et-sya from a dispute, something-paradise ob-ra-zu-et-sya in re-zul-ta-te mei-o-for from fabric -ney spo-ro-fi-ta (of an adult plant)
3) Spore de-lit-Xia mi-to-zom, forming ha-me-to-fit during germination.
№6. What is the chromo-mo-som-ny set of ha-rak-te-ren for spores, ha-me-to-fi-ta and spo-ro-fi-ta horsetail? From what source cells and in the result of what kind of de-le-tion are these stages of development of moss?
Clear-no-no.
1) The spore and ga-me-to-fit (growth) of horsetail contain a ha-p-lo-id-ny set of chromo-mo-catfish, and spo-ro-fit (adult plant) is di-plo- i-den.
2) The dispute is about-ra-zu-et-sya in re-zul-ta-te mei-o-for from the cells of the spore-bearing spikelet spo-ro-fi-ta, and ha-me-to-fit ob-ra -zu-et-sya from the dispute by mi-to-za.
3) Spo-ro-fit about-ra-zu-et-sya after oplo-to-your-re-niya from zi-go-you by mi-to-za.
No. 7 What is a chromo-mo-som-ny set of ha-rak-te-ren for kle-tok my-ko-ti needle-lok and sperm-mi-ev pines? Explain-no-those from which source cells and in re-zul-ta-te ka-ko-go de-le-niya these cells are formed
Clear-no-no.
Ele-men-you from-ve-ta:
1) in the cells of pine needles, a set of chromo-mo-som - 2n; in pine sperm - n;
2) an adult race of pine raz-vi-va-et-sya from zi-go-you (2n);
3) pine sperm-mii raz-vi-va-yut-sya from ha-p-lo-id-ny micro-ro-spores (n) by mi-to-for
№8 What chromosome set is typical for vegetative, generative cells and sperm of the pollen grain of a 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 the germination of haploid spores;
3) chromosome set of sperm - n;
4) sperm are formed from a generative cell by mitosis
No. 9 What is a chromo-mo-som-ny set of ha-rak-te-ren for the nuclei of the cells of the epi-der-mi-sa leaf and eight-mi-nuclei-no-go for-ro-dy-she-vo th bag of se-m-for-chat-ka color-of-the-th-race? Explain-no-those from which source cells and in re-zul-ta-te ka-ko-go de-le-niya these cells are formed .
Clear-no-no.
1. The epidermis of the leaf has a di-plo-id set of chromo-mo-somes. The adult race is yav-la-et-xia spo-ro-fi-tom.
2. All cells are for-ro-dy-she-in-the-th bag ha-p-lo-id-na, but in the center on-ho-di-sya di-plo-id-noe nucleus (about -ra-zu-et-sya as a result of the merger of two nuclei) - this is no longer an eight-nuclear, but a seven-cell-toch-ny for-ro- breathable bag. It's ga-me-to-fit.
3. Spo-ro-fit ob-ra-zu-et-sya from the cell-tok for-ro-dy-sha se-me-no by mi-to-ti-che-sko-go de-le-tion. Ga-me-to-fit ob-ra-zu-et-sya by mi-to-ti-che-sko-go de-le-niya from ha-p-lo-id-noy dispute.
No. 10. What a chromo-mo-som-ny set of ha-rak-te-ren for ve-ge-ta-tiv-noy, gene-non-ra-tive cell-current and sperm-mi-ev dust-tse-vo th grain color-of-th-race-te-niya? Explain-no-those from which source cells and in re-zul-ta-te ka-ko-go de-le-niya these cells are formed .
Clear-no-no.
1) a set of chromo-mo-some ve-ge-ta-tiv-noy and gene-non-ra-tiv-noy cells - n;
2) ve-ge-ta-tiv-naya and gene-non-ra-tiv-naya pollen cells are formed by mi-to-for during pro-ra-ta-nii ha-p-lo-id-noy disputes;
3) hro-mo-som-ny set of sperm-mi-s - n;
4) sperm-mii are about-ra-zu-yut-sya from a gene-non-ra-tiv-noy cell by mi-to-za
The publication uses the materials of the Unified State Examination of previous years
Description of the presentation Cycles of plant development Preparation for the implementation of USE tasks on slides
Cycles of plant development Preparation for the tasks of the Unified State Examination C 5 (application of knowledge to determine the number of chromosomes and DNA in different phases of mitosis and meiosis, in germ and somatic cells of different organisms) © Tikhonova E. N. January 27,
As the results of the exam of previous years showed: Students have poorly formed knowledge about the change in the chromosome set in the cells of the gametophyte and sporophyte of algae, mosses, ferns, gymnosperms and flowering plants; about the formation of spores in plants in the process of meiosis, and germ cells in the process of mitosis, which distinguishes them from animals; the ability to compare spores and germ cells, spores and sporophyte cells; explain and argue the features of the formation of spores, germ cells, gametophyte in plants.
Life stages of plants Sporophyte Gametophyte literally - bearing spores all cells contain a diploid set of chromosomes (2 n) forms spores (n) verbatim - bearing gametes all cells contain a haploid set of chromosomes (n) forms gametes (n)
Generations Asexual Sexual 2 n develops from sporophyte sporophyte spore (n) (MEIOSIS) n develops from spore gametophyte gamete (n) (MITOSIS)
Spores (n) - why then are they asexual cells, and gametes (n) are sexual? 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; gametes are formed from them. Each haploid gamete does not form a new organism. Only after the stage of fertilization with another gamete (after the combination of the genetic material of (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
Task 1. "Department of Bryophytes" 1. In the life cycle of Bryophytes, (_) prevails. 2. Bryophytes breed (_). 3. Asexual reproduction occurs with the help of (_). 4. Spores, like in all higher plants, are formed (_), and have (_) a set of chromosomes. 5. The moss sporophyte is represented by (_). 6. The moss gametophyte is represented by (_). 7. Gametophytes are called dioecious if (_). 8. Antheridia and archegonia in mosses are formed on (_). 9. For the fusion of germ cells, (_) is necessary. 10. After fertilization, (_) develops from the zygote. 11. Moss spore develops (_). 12. When does meiosis occur in the moss development cycle (_)
Task 2. “Department of Ferns” 1. The sporophyte of ferns is represented by (_), the gametophyte - (_). 2. Strobili in ferns (_). 3. Antheridia and archegonia in the male thyroid gland are formed on (_). 4. The spores of the male shield are formed on the lower part of the leaf in (_), covered with a veil - (_). 5. What is the asexual generation of ferns? Explain the answer. 6. How is the sexual generation represented in ferns? Explain the answer. 7. Where are gametes formed in a fern? 8. How does sexual reproduction occur in ferns? 9. Where do fern spores form? 10. How does asexual reproduction occur in ferns? 11. Where is the embryo of a new plant formed in a fern?
Task 3. "Department of Gymnosperms" 1. What is the sporophyte of gymnosperms? 2. What is the male gametophyte of gymnosperms? 3. What is the female gametophyte of gymnosperms? 4. What are the main aromorphoses that led to the emergence of gymnosperms? 5. What are microsporangia of gymnosperms? 6. What are the megasporangia of gymnosperms? 7. What are the gametangia of gymnosperms? 8. When does meiosis occur in the life cycle of gymnosperms? What develops from microspores and megaspores of gymnosperms?
Task 4. "Department Gymnosperms" 1. What features does pine pollen have? 2. What is the male gametophyte that forms germ cells? 3. What is the female gametophyte that forms germ cells? 4. Is water necessary for the fertilization of gymnosperms? Why? 5. Where is the embryo of a new plant formed in a pine tree?
Task 7. “Department of Gymnosperms” 1. In the spring, on each scale of a pine tree, reddish cones are formed by .... 2. Megasporangium of gymnosperms is represented by .... 3. In the nucellus, the megasporocyte undergoes meiosis, three megaspores die, and the nucleus of the fourth .... 4. On the scales of greenish-yellow cones that form at the base of young shoots, ... are formed. 5. Microsporocytes meiotically divide and form ..., each of which, as a result of mitotic divisions, forms .... 6. Several cells are distinguished in a pollen grain: .... 7. Fertilization in pine occurs after ... after pollination. 8. One of the sperm merges with the egg, and the second .... 9. The second archegonium of the female gametophyte also .... 10. Pine seeds ripen only through ... after pollination. 11. From a fertilized egg, a zygote, ... is formed. 12. Endosperm in gymnosperms .... 13. For fertilization of gymnosperms water .... 14. Unlike a spore, a pine seed has ....
Megaspore (n) Female gametophyte (embryo sac) (n) Micro spore (n) Male gametophyte (pollen grain) (n)
Task 5. "Department of Angiosperms" 1. What is the flowering sporophyte? 2. What is the male gametophyte of flowering plants? 3. What is the female gametophyte of flowering plants? 4. What are the main aromorphoses that led to the appearance of flowering plants? 5. What are flowering microsporangia represented by? 6. What are flowering megasporangia represented by? 7. What are flowering gametangia? 8. When does meiosis occur in the life cycle of flowering plants - during the formation of gametes or spores? 9. What develops from microspores and megaspores of flowering plants?
1. What is indicated in the figure by numbers 1 - 6? 2. When does meiosis occur - during the formation of spores, or during the formation of gametes?
Task 6. "Double fertilization of flowering plants" 1. The male gametophyte of flowering plants is represented by (_). 2. The pollen grain on the stigma of the style swells and forms (_). 3. The generative cell divides and forms (_). 4. The ovule is protected from the outside (_), between which there is a hole - (_). 5. The female gametophyte of flowering plants is represented by (_). 6. Inside the ovule develops (_), consisting of seven cells. 7. One sperm merges with (_), the second - (_), that is, two fertilizations occur. 8. Double fertilization was discovered by a Russian scientist (_). 9. The germ of the seed develops from (_). 10. Endosperm is formed from (_). 11. Perisperm is formed from (_). 12. The seed coat is formed from (_) 13. 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 the cells of the ovule before meiosis, at the end of meiosis telophase 1 and meiosis telophase 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, doubling of DNA molecules occurs, therefore the number of DNA molecules is 56 molecules (4 s). 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) - from 14 chromosomes, the number of DNA molecules is 2 s (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 (1 s).
The chromosome set of wheat somatic cells is 28. Determine the chromosome set and the number of DNA molecules in one of the cells of the ovule before meiosis, in meiosis anaphase I and meiosis anaphase II. Explain what processes take place during these periods and how they affect the change in the number of DNA and chromosomes. 1) before the start 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 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 the same 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.
The endosperm cells of lily seeds have 21 chromosomes. How will the number of chromosomes and DNA molecules change at the end of the telophase of meiosis 1 and meiosis 2 compared to 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, DNA molecules are doubled, so the number of DNA molecules is 28 (4 s). 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 (2 s). 3) In the second division of meiosis, the chromatids diverge, therefore, at the end of telophase 2 of meiosis, the chromosome set in the cells is single (n)-7 chromosomes, the number of DNA molecules is one-7 (1 s).
What chromosome set is typical 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 seed embryo, the diploid set of chromosomes is 2 n, since the embryo develops from a zygote - a fertilized egg; 2) in the cells of the endosperm of the seed, the triploid set of chromosomes is 3 n, since it is formed by the fusion of two nuclei of the central cell of the ovule (2 n) and one sperm (n); 3) cells of the leaves of a flowering plant have a diploid set of chromosomes - 2 n, since an adult plant develops from an embryo.
What chromosome set is typical for pine pollen grain and sperm cells? Explain from what initial cells and as a result of what division these cells are formed. 1) Pine pollen and sperm cells have a haploid set of chromosomes. 2) Pine pollen cells develop from haploid spores by mitosis. 3) Pine sperm cells develop from pollen grain cells (generative cells) by mitosis.
What chromosome set is typical for sperm and endosperm cells of the seed of a flowering plant? Explain from what cells and as a result of what division these cells are formed. 1) In sperm cells, the set of chromosomes is haploid, and in the cells of the endosperm of the seed, it is triploid. 2) Sperm is formed from a haploid spore (generative cell of the male gametophyte) as a result of mitosis. 3) The 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 typical for the cells of the epidermis and the eight-nuclear 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 part of the sporophyte of a flowering plant whose cells are diploid (2 n). An eight-nuclear embryo sac is an immature female gametophyte of a flowering plant whose cells are haploid (n) 2) Leaf cells are formed during the mitotic division of the educational tissue (including the cells of the leaf epidermis). 3) The cells of the eight-nuclear embryo sac are formed during the 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 which cells and as a result of what division they are formed. 1) Cuckoo flax moss gametes are formed on gametophytes from a haploid cell by mitosis. 2) The set of chromosomes in gametes is single - n. 3) Cuckoo flax moss spores 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 gametophyte and sphagnum moss gametes? Explain from what initial cells and as a result of what division these cells are formed? 1) The gametophyte and gametes of sphagnum are haploid, and the set of chromosomes and the amount of DNA in the cells correspond to the formula nc. 2) The gametophyte is formed from a spore, which is formed as a result of meiosis from the tissues of the sporophyte. 3) The spore divides by mitosis, forming a gametophyte.
The haploid set of pea chromosomes is 7. How many chromosomes are contained in the cells of the leaves, the seed embryo and the cotyledons of the seed. Explain the answer. 1. Leaf is a vegetative organ of a plant, cells contain 2 n 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 (2 n = 14) substance, they are formed as a result of the fusion of sperm (n) and the central cell of the ovule (2 n) and have a triple set of chromosomes (3 n = 21)
The role of sexual reproduction in wildlife.
During sexual reproduction, new combinations of genes are constantly created, which increases the genetic diversity of offspring and, accordingly, the chances of adapting to changing environmental conditions. The creation of new combinations of genes occurs in the process meiosis. Meiosis occurs during the formation of haploid cells (spores or gametes) from diploid cells. At the same time, the chromosomes inherited from the mother and father cease to exist as a whole - as a result of crossing over, new variants of chromosomes are formed, combined from paternal and maternal ones. Thus, the chromosomes of children, as a rule, are not identical to the chromosomes of their parents - they contain other combinations of alleles (gene variants).
During meiosis, the chromosome set is reduced - the formation of 4 haploid cells (n) from a diploid cell, in which each chromosome is no longer represented by a pair of sister chromatids, but by 1 chromatid. In humans, sex cells (gametes) are formed by meiosis, each of them carries 23 chromosomes.
The diploidy of cells in the life cycle is restored during fertilization - the fusion of gametes. In this case, two different sets of chromosomes from two different genomes (the genome of the mother and the genome of the father) are combined.
Types of life cycles.
Different organisms show a wide variety of life cycles, however, in all types of life cycles, it is possible to distinguish diploid phase, or diplophase(from fertilization to meiosis) and haploid phase, or haplophase(from meiosis to the next fertilization).
For example, in animals (in the figure on the left) only gametes are haploid, in plants (in the figure in the center) there is a diploid generation ( sporophyte) and haploid generation ( gametophyte), while in many unicellular organisms the haploid phase predominates, and the zygote after fertilization divides by meiosis, resulting in haploid cells again.
Life cycles of plants.
In lower plants, all of the above types of life cycles are found. Thus, the predominance of the diplophase is characteristic of fucus (brown algae), diatoms and some green algae (codium, cladophora). Gametophyte and sporophyte are present, for example, in porphyry (red algae), kelp (brown algae), ulva (green algae). Finally, in Chlamydomonas, Chara, and Spirogyra, the haplophase predominates, and the zygote is the only diploid stage in the life cycle.
In higher plants, both the gametophyte and the sporophyte are present in the life cycle. In mosses, the green plants familiar to us are haploid. Organs of sexual reproduction are formed on them: antheridia, in which numerous spermatozoa are formed, and archegonia each containing one egg. The resulting gametes after fertilization give rise to the diploid stage, which develops directly on the haploid. The moss sporophyte consists of haustoria by which it attaches itself to the gametophyte, legs and boxes. The moss sporophyte is incapable of photosynthesis and lives off the haploid part of the plant, so it usually has a brown color. Inside the box, many cells divide by meiosis, forming haploid spores. The spores give rise to new green haploid plants. Thus, the predominant stage in the life cycle of mosses is haploid.
The main life stage in vascular plants (mosses, horsetails, ferns, seeds) - diploid. On the leaves of ferns or in special structures in horsetails and club mosses, sporangia are formed, in which, as a result of meiosis, small unicellular spores are formed. Scattering and falling into suitable conditions, they give rise to the haploid stage - overgrowth. Antheridia and archegonia are formed on the growths, gametes are formed, fertilization occurs, and a diploid plant develops from the zygote.
In seed plants, there is no independent haploid stage; it is represented by groups of cells that develop in special organs of diploid parent organisms. For some time, only the male gametophyte exists separately in the form pollen grain, but no noticeable vital processes take place in it at this time. The female gametophyte of gymnosperms is primary endosperm, in flowering plants, the reduced female gametophyte is embryo sac. After fertilization, a new diploid organism that has developed from the zygote goes through the first stages of development also under the protection of the mother's organism.
It can be simple or complex. An example of a simple cycle is chlorella, which reproduces by spores. Developing, this green alga becomes a receptacle for 4-8 autospores, which grow inside the mother's body and become 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 method of reproduction is:
- sexual (gametes);
- asexual (spores);
- vegetative (part of the body).
In complex cycles during sexual reproduction, there are always several separate phases of the gamete and zygote. A gamete is a mature sex 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. The zygote develops into a sporophyte that produces haploid spores. Of the spores - the gametophyte, which is male and female.
For example, we can take an isosporous fern, which has two forms of individuals - the fern itself (sporophyte) and its growth (gametophyte). A sprout is the offspring of adult ferns. It exists for a very short period, but manages to give birth to a single large-leaved individual. Due to this feature of reproduction, the life cycle of a plant consists of an alternation of generations: from an adult fern to a growth 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 (syngamy). Parthenogenesis - reproduction without fertilization - also refers to the sexual method: the daughter organism is formed from an isogamete, 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 are found in ferns, and in conjunction with the vegetative variant, in some algae. In seed plants, the formation of the germ cell occurs from one daughter zygote, as a result of which this process is more reminiscent of not reproduction, but 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 occur during asexual reproduction, and meiospores, which arise during sexual reproduction. Mitospores appear by mitosis, resulting in an individual similar to the mother. Meiospores are formed by meiosis during the germination of the zygote or in sporangia. For most plants, both methods of reproduction are characteristic, due to which two different forms of individuals are obtained.
Vegetative propagation method
With the vegetative variant of reproduction, a division into akinetes occurs - thick-walled cells. It consists in separating some part of it from the mother liquor - a brood bud or body. In this way, some reproduce, including sargassum, brown, and even flowering plants, such as duckweed, reproduce vegetatively. Some of them form brood buds that fall to the ground and take root there. Also, the buds can branch off and separate from the mother plant. In the angiospermous group of plants, the development of shoots underground from the rhizome is very common.
plant propagation
One of the final stages of reproduction is the spread of plants. In nature, there can be 3 options for settling: embryos, spores and seeds. In extremely rare cases, spread can occur with the help of zygotes. Even K. Linnaeus associated seed and spore distribution with cryptogamous and phenogamous plants. The second type included a group of gymnosperms and angiosperms, and the first type included 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 plant dispersal.
Generation alternation
The life of plants in the form of two different generations can have different names: change of forms of development, alternation of generations, etc. The succession of a large fern and a growth in the case of an isosporous fern is an example of alternation of generations, marked by the phases of the adult state of individual forms. These two forms are so different in appearance that it is difficult to recognize the same plant in them. Fern growth is very difficult to see with the naked eye. In angiosperms, the analog of the outgrowth is the embryo 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 occurs 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 the sporophyte occupies most of the life cycle. differ in that the sporophyte develops inside the female genital organ and is in continuous connection with the gametophyte. In the case of c, it looks like a spore box 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 systems. Most of the plants that people think of when they talk 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 often the embryo is able to develop from an unfertilized egg (apomixis). The predominant form of flowering plants is the heterosporous sporophyte, which is a plant with leaves and a stem. The male gametophyte is represented by a pollen grain, and the female gametophyte by the embryo sac (it develops faster than in gymnosperms). The organ of both sexual and asexual reproduction is a modified shoot - a flower. The rudiments of seeds 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
The group of gymnosperms includes representatives of coniferous trees and shrubs. Most of them have modified needle-like leaves. The life cycle of gymnosperms differs in that microspores (pollen) are formed in small male cones (anthers), and megaspores in female (ovules). The microspores form the male gametophyte, while the megaspores form the female gametophyte. 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 differ in that this group has a flower in which spores are formed and fertilization of gametophytes and seed development occur. The peculiarity of this group is in the protection of seeds, which are hidden inside the fruit and protected from the effects of the external environment.
Life cycle of spore plants
Spore plants do not flower, which is why they are also called non-flowering plants. They are of two categories:
- higher (ferns, horsetails, mosses, club mosses);
- lower (algae, lichens).
The life cycles of 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. The gametophyte is used for sexual reproduction, and the sporophyte is used for asexual reproduction. 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 a growth. The haploid subgroup differs in that the sporophyte has a subordinate status in it.
Life cycles of plants: schemes
Mosses are representatives of a primitive species of higher plants. They have a very conditional division of the body into a stem and leaves, instead of roots - filamentous rhizoids. They grow in marshy, damp places and evaporate moisture very strongly. They reproduce sexually, the sporophyte depends on the gametophyte, spores are formed in a special box, which is located above the gametophyte and is associated with it.
Representatives of ferns have large feathery leaves (sporangia are located on the underside). The plant has a pronounced root system, and the leaf is actually a branch system called a frond or preshoot. 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 spores. The asexual generation begins with a diploid zygote, and the sexual generation begins with a haploid spore. The change of these phases makes up most of the cycle.
Solving the problems of the Unified State Examination on the life cycle of plants
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 alternation of generations associated with this.
A haploid (n) plant organism that produces gametes is called a gametophyte (n). He represents the gender generation. Gametes are formed in the genital organs by mitosis: spermatozoa (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 an asexual generation develops from it by 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, the gametophyte (n) predominates, that is, the cells of their thallus are haploid (n). When adverse conditions occur (cooling, drying up of the reservoir), sexual reproduction occurs - gametes (n) are formed, which merge in pairs into a zygote (2n). The zygote (2n), covered with a shell, hibernates, after which, when favorable conditions occur, it divides by meiosis with the formation of haploid spores (n), from which new individuals (n) develop.
Task 1. What set of chromosomes is typical for the cells of the ulotrix thallus and for its gametes? Explain from which initial cells and as a result of what division they are formed.
Answer:
1. Thallus cells have a haploid set of chromosomes (n), they develop from a spore with a haploid set of chromosomes (n) by mitosis.
2. Gametes have a haploid set of chromosomes (n), they are formed from thallus cells with a haploid set of chromosomes (n) by mitosis.
Task 2. What set of chromosomes is typical for the zygote and spores of green algae? Explain from what initial cells and how they are formed.
Answer:
1. The zygote has a diploid set of chromosomes (2n), it is formed by the fusion of gametes with a haploid set of chromosomes (n).
2. Spores have a haploid set of chromosomes (n), they are formed from a zygote with a diploid set of chromosomes (2n) by meiosis.
Life cycle of mosses (cuckoo flax)
In mosses, the sexual generation (n) predominates in the development cycle. Leafy moss plants are dioecious gametophytes (n). Antheridia (n) with spermatozoa (n) are formed on male plants (n), archegonia (n) with eggs (n) are formed on female plants (n). With the help of water (during rain), spermatozoa (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 box on a leg. Thus, the sporophyte (2n) in mosses lives off the female gametophyte (n).
In the sporophyte box (2n), spores (n) are formed by meiosis. Mosses are heterospore plants, distinguish between microspores - male and macrospores - female. From spores (n), by mitosis, first pre-germs develop, and then adult plants (n).
Task 3. What chromosome set is typical for gametes and spores of cuckoo flax? Explain from which initial cells and as a result of what division they are formed.
Answer:
1. The gametes of the cuckoo flax moss have a haploid set of chromosomes (n), they are formed from antheridia (n) and archegonia (n) of male and female gametophytes with a haploid set of chromosomes (n) by mitosis.
2. Spores have a haploid set of chromosomes (n), they are formed from sporophyte cells - pedunculated boxes with a diploid set of chromosomes (2n) by meiosis.
Task 4. What chromosome set is characteristic for the cells of the leaves and the pod on the leg of the cuckoo flax? Explain from which initial cells and as a result of what division they are formed.
Answer:
1. Cuckoo flax leaf cells have a haploid set of chromosomes (n), they, like the whole plant, develop from a spore with a haploid set of chromosomes (n) by mitosis.
2. In the cells of the box on the stem there is a diploid set of chromosomes (2n), it develops from a zygote with a diploid set of chromosomes (2n) by mitosis.
Lecture
Life cycle of ferns
In ferns (also horsetails, club mosses) 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 a spore (n) that has fallen into moist soil, a growth (n) germinates - a bisexual gametophyte. Antheridia (n) and archegonia (n) develop on its lower side, and spermatozoa (n) and eggs (n) are formed in them by mitosis. With drops of dew or rainwater, spermatozoa (n) get to the eggs (n), a zygote (2n) is formed, and from it - the embryo of a new plant (2n). (slide show).
Scheme 3. The life cycle of ferns
Workshop
Task 5. What chromosome set is typical for leaves (wai) and fern growth? Explain from what initial cells and as a result of what division these cells are formed.
Answer:
1. Fern leaf cells have a diploid set of chromosomes (2n), so they, like the whole plant, develop from a zygote with a diploid set of chromosomes (2n) by mitosis.
2. In the cells of the outgrowth there is a haploid set of chromosomes (n), since the outgrowth is formed from a haploid spore (n) by mitosis.
Lecture
Life cycle of gymnosperms (pine)
The leafy plant of gymnosperms is a sporophyte (2n), on which female and male cones (2n) develop.
On the scales of female cones there are ovules - megasporangia (2n), in which 4 megaspores (n) are formed by meiosis, 3 of them die, and from the rest a female gametophyte develops - endosperm (n) with two archegonia (n). In archegonia, 2 eggs (n) are formed, one dies.
On the scales of 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 mitosis from a generative cell (n) produces 2 sperm (n), and from a vegetative cell (n) a pollen tube (n) grows inside the ovule and delivers sperm (n ) to the egg (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 peel and containing an embryo (2n) and an endosperm (n) inside.
Scheme 4. Life cycle of gymnosperms (pine)
Workshop
Task 6. What chromosome set is typical for pine pollen grain and sperm cells? Explain from what initial cells and as a result of what division these cells are formed.
Answer:
1. In the cells of a pollen grain, a haploid set of chromosomes (n), since it is formed from a haploid microspore (n) by mitosis.
2. Sperms have a haploid set of chromosomes (n), since they are formed from a generative cell of a pollen grain with a haploid set of chromosomes (n) by mitosis.
Task 7. What chromosome set is typical for pine megaspore and endosperm cells? Explain from what initial cells and as a result of what division these cells are formed.
Answer:
1. Megaspores have a haploid set of chromosomes (n), since they are formed from ovule cells (megasporangia) with a diploid set of chromosomes (2n) by meiosis.
2. Endosperm cells have a haploid set of chromosomes (n), since the endosperm is formed from haploid megaspores (n) by mitosis.
Life cycle of angiosperms
Angiosperms are sporophytes (2n). The organ of their sexual reproduction is a flower.
In the ovary of the pistils of the flower there are ovules - megasporangia (2n), where meiosis occurs and 4 megaspores (n) are formed, 3 of them die, and from the rest a female gametophyte develops - an embryo 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 stamen anthers, 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 cell (n), a pollen tube (n) grows inside the ovule and delivers the sperm (n) to the egg (n) and the central cell (2n). One sperm (n) merges with the egg (n) and a zygote (2n) is formed, from which the plant embryo (2n) is formed by mitosis. The second sperm (n) fuses with the central cell (2n) to form a triploid endosperm (3n). Such fertilization in angiosperms is called double fertilization.
As a result, a seed is formed from the ovule, covered with a peel and containing an embryo (2n) and an endosperm (3n) inside.
Scheme 5. Life cycle of angiosperms
Task 8. What chromosome set is typical for the microspore, which is formed in the anther, and the endosperm cells of the seed of a flowering plant? Explain from what initial cells and how they are formed.
Answer:
1. Microspores have a haploid set of chromosomes (n), since they are formed from microsporangial cells with a diploid set of chromosomes (2n) by meiosis.
2. Endosperm cells have a triploid set of chromosomes (3n), since the endosperm is formed by the fusion of a haploid sperm (n) with a diploid central cell (2n).
General conclusions
1. In the process of plant evolution, a gradual reduction of the gametophyte and the development of the sporophyte took place.
2. Plant gametes have a haploid set (n) of chromosomes; they are formed by mitosis.
3. Plant spores have a haploid set (n) of chromosomes, they are formed by meiosis.
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