reproduction spore plants.
Rareproduction is uniqueproperty of any living organism. Reproduction in your own way biological significance significantly different from all other vital functions of the body. Reproduction increases the number of new organisms outwardly similarnyh with the mother. Thanks to reproduction, there are more individuals of any species. In nature, there are 2 forms of reproduction. Sexual and asexual.During sexual reproduction, meiosis produces haploid gametes. At the moment of fertilization, due to the fusion of two haploid cells a diploid zygote develops. Multiple mitotic divisions zygotes and their descendants lead to an increase in the number of diploid cells that build the body of the organism in the process of its development. Upon reaching puberty, the process of formation of haploid gametes resumes.Plants have great property from other organisms, they have an alternation of generations during sexual reproduction.Thus, in the life cycles of organisms that reproduce sexually, two phases are distinguished:haploid and diploid (Fig. 5.11). The relative duration of these phases varies among representatives various groups living beings: in protozoa and fungi, the first prevails, in higher plants and animals - the second.In the evolution of plants there was a transition from haploidy to diploidy.The elongation of the diplophase during evolution is explained by the advantages of the diploid state over the haploid state. Due to heterozygosity and recessiveness in the diploid state, they hide from natural selection, various alleles are stored and accumulated. This increases the amount of genetic information in the gene pools of populations and species, leads to the formation of a reserve of hereditary variability, on which evolutionary prospects depend. At the same time, in heterozygotes, harmful recessive alleles, without affecting the development of the phenotype, do not reduce viability.
It's easy to tell which way is up. This is the male reproductive structure that grows out of the thallus. Identify antheridia, sperm chambers that open onto a flattened upper surface heads. This is a female reproductive structure that grows out of the thallus. Identify an archgonia that is vase shaped and hangs down with their tubular holes facing the ground. Each archgonium contains one egg.
The diploid sporophyte is surrounded by an extended archeogon called the calyptra and depends on the haploid tissue of the archegoniophore for nutrients and water. The sporophyte consists of a foot where it attaches to the gametophyte, a stalk called a bristle, and a large egg-shaped sporangium in which haploid spores are produced through meiosis.
Terminology
sporophyte- diploid multicellular phase in the life cycle of plants and algae, developing from a fertilized egg or zygote and producing spores. It develops from a fertilized egg, or zygote.
Meiosis - reduction division eukaryotic cells, at
where the number of chromosomes in the nucleus is halved.
pay attention to general form and flatness. Look at the top surface of gemmem cups containing gemma, tiny green discs of haploid cells. Since gamma is an asexual distribution, the new gametophytes are genetically identical to the parent gametophyte, meaning they are clones. The archegonium is at the top of the moss and the tubular holes are up. When the egg is fertilized, the sporophyte will develop and grow there.
The tip is surrounded by leaf-shaped scales, forming a cup. When it rains, the semen is empty in the cup and the drops splash them out. Archegonium on female moss indicates sperm production. Living specimens: Mnium, moss. Fruit moss showing the brown stem and sporangium of a mature diploid sporophyte. Note that it grows straight from the tip of the female moss; as in liverworts, the diploid sporophyte is nutritionally dependent on the haploid gametophyte.
Spores (n) are non-sex haploid cells, with the help of
which asexually plants and fungi thrive.A spore is usually a single-celled formation that serves to asexual reproduction and capable of developing into an adult, i.e. independent organisms can develop from spores without merging with each other
All plants produce spores in one form or another. The process of their formation is called , and the cell or organ in which they are formed isName
Green leaf structure - gametophyte. The red-brown structures are soporphytes. When you are studying life cycle plants, fungi and protists, you will come across the term alternation of generations. This alternation of generation refers to the alternation of two phases: a multicellular diploid phase alternating with a multicellular haploid phase. generation are the phases of a plant's reproduction cycle, one of which is sexual and the other is asexual. There are several differences between the gametophyte and sporophyte stages.
Let's look at them to better understand them. This phase in the plant life cycle is the asexual, spore-bearing generation of the plant with diploid cells. This means that plant cells in this generation or phase have two sets of chromosomes in their cells. The zygote or fertilized cell is what leads to the formation of the sporophyte.
Very often, spores are surrounded by a special shell and are able to endure adverse conditions for a long time, such as winter or a period of drought. Since the spores are very light, they are freely carried through the air by wind or other agents and serve to disperse plants. Spores germinate immediately when moisture enters the cell
By meiosis, this sporophyte produces haploid spores. Because spores are formed in this generation, the name given to this phase is the sporophyte. The produced haploid spores then form the next generation of gametophytes, growing into multicellular haploid individuals called gametophytes.
We learned above that the zygote or fertilized cell is diploid; however, the spores they form are haploid. This is due to the reduction division or meiosis that takes place. Meiosis is the process in which the number of chromosomes in each cell is reduced to half, and the next cells formed will have half the number of chromosomes of their parent cells.
Mitosis is a way of dividing eukaryotic cells, as a result
which two cells are formed with exactly the same set
chromosomes, as in the mother.
Gametophyte (n) - the sexual generation of plants, the haploid multicellular phase, develops from spores, it forms
gametes.
Gametes (n) - sex haploid cells, with the help of which
Another alternating phase in the plant's life cycle is gametophyte generation, in which gametes are formed. This is the phase of the plant in which the gametes, i.e. egg and sperm, are haploids having only one set of chromosomes. Thus, the gametophyte phase represents the stage of sexual development of the gamete in the life cycle of the plant.
Spores are actually the first cells of the gametophyte generation. These spores undergo a process of mitosis that produces identical cells with the same number of chromosomes. When these gametes meet, they fuse together, fertilize, and form a zygote that is diploid. This diploid zygote then forms the basis of the next alternating sporophyte birth. It forms the first cell of the diploid generation of sporophytes. This zygote then develops into a sporophyte, which then forms haploid spores in the sporophyte gene, and the cycle continues in the life cycle of the plant.
going on sexual reproduction.
Zygote (2n) is a fertilized egg
Cycle scheme
gametophyte- haploid multicellular phase in the life cycle. It develops from haploid spores.sexualgenerationVvitalcycleplants, developingWithalternationgenerations. ProducesgametesorVconventionalvegetativecellsthallus ( some- ryeseaweed), orVspecialist. bodiessexualbreeding - gametangia, oogonia or archegoniaAndantheridia. StructureGamethophytevaried, WhatconnectedWithdecomppersonaltypesshiftsgenerations
✤ The sporophyte stage is asexual while the gametophyte stage is sexual. ✤ The first cell in the sporophyte gene is a diploid zygote, and the first cell in the gametophyte stage is a haploid spore. The sporophyte phase produces haploid spores and the gametophyte phase produces diploid male and female gametes.
✤ With respect to dominance, in liverworts and mosses, the gametophyte stage is the larger and more familiar plant form, while the sporophyte stage is smaller and found at the gametophyte stage. ✤ In angiosperm phases, the sporophyte is the larger and independent phase, while the gametophyte phase is small and reduced to pollen grains and an eight-celled female gametophyte located inside the egg.
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.
This alternation of generation is very important in plants as it increases the plant's chances of survival in the long run. The next generation is becoming even more adaptable to the environment. The formation of spores from parental cells causes a shuffling of genes conducive to new, different and stronger genetic makeups. Then, at the gametophyte stage, when gametes are formed without reduction division, the formed zygote better adapts to the environment. Thus, both of these generations are indeed significant phases in the life cycle of a plant.
Life cycle green algae
Chlamydomonas can use different ways reproduction, depending on environmental conditions. In warm weather, in a well-heated reservoir, it reproduces asexually. The cell loses flagella. Its content is divided into four parts. At the same time, under cell wall four spores with flagella are formed. They are called "zoospores". The cell membrane then ruptures and the zoospores begin to swim on their own, turning into young algae cells.
And under favorable conditions, reproduction continues again and again.
You are probably already in contact with disputes. Have you ever walked into your bathroom and noticed a musty smell? And then looked at the green and black icing on the shower curtain? You may remember hearing news stories about the dangers of mold and how it can infect your lungs and cause allergies and other nasty illnesses. But it's not just mold that can hurt you; these are disputes.
Spores are the single-celled reproductive unit of non-flowering plants, bacteria, fungi, and algae. Basically, spores are kids, except they don't need mom and dad. Not all life forms reproduce sexually. Many, such as fungi and bacteria, reproduce without mating at all. Instead, they produce hardy structures known as spores, which are often adapted to disperse from the host plant or fungus. Arguments can go on for a very long time in some unpleasant conditions.
With a cold snap or, conversely, the reservoir begins to dry up from extreme heat. Chlamydomonas begins to multiply in a completely different way - sexually.
Having lost flagella, the cell divides under the shell into many small gametes. These are sex cells. In one chlamydomonas, both female and male gametes.
When the gametes acquire small flagella, they break the membrane of the mother cell and go outside. The gametes fuse in pairs with the gametes of other Chlamydomonas.
Spores are the reproductive structure of "lower plants", plants that do not flower. Fungi, algae, and even some bacteria form spores when they want to pass on their genes. Think of them like seeds, they are grown from a new plant and all they need is the proper environment to thrive.
Disputes - asexual form breeding; a plant or fungus does not need to mate with another plant or fungus to form these particles. The spore is usually a single cell surrounded by a thick cell wall for protection. Once the spores are formed, the organism releases them into the environment to grow and thrive. Spores are often formed through a process called sporogenesis, which means only the production of spores and is carried out through mitosis or cell reproduction.
In this case, a zygote is formed. It is covered with a very dense shell.
In this state, she is able to wait out adverse conditions.
The zygote then germinates, giving rise to new single-celled algae, which begin to divide asexually.
In the life cycle of green algae, the gametophyte (n) predominates, their cells are haploid (n). When unfavorable occurs, 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, upon the onset favorable conditions divides by meiosis with the formation of haploid spores (n), from which new individuals develop (n).
Once a spore arises, she needs to get out into a world where it can grow and prosper. He does this through adaptations of dissipation in spores, which are various functions that allow the spore to move. Some spores are so light that they are picked up by the wind and blown to a new location. Other spores ride along the currents of rivers and streams. Still others are blown into the air by the fungus that creates them, or placed in a fragile container that bursts open when touched.
Spores are very common, and depending on the type of organism that created them, they can look and act very differently. Spores can be classified in many ways based on their structure, where they come from, and how they move around the world.
Tasks
In Chlamydomonas, the dominant generation is the gametophyte. Determine the chromosome set of spores and gametes of Chlamydomonas. Explain from what initial cells and as a result of what division these cells are formed during sexual reproduction.
Answer
1) spore chromosome set - n (haploid);
2) spores are formed from a diploid zygote by meiosis;
Plant spores are produced by organisms that we commonly recognize. The main plant types that produce spores are algae, mosses, and ferns. Algae is the simplest of these plants and can range from tiny, single-veined things to large, multi-celled plants that cover your backyard. The spores from all algae are very tiny, even if the algae plant is huge. In fact, most algae spores are as small as the period at the end of a sentence.
No wonder we can't see them very well! These spores tend to disperse through the water and cluster together in large masses until a good environment. Mosses produce spores that are slightly larger than marine spores. These spores are typically found in areas where mosses are common and are dispersed by being shot into the air, carried by the wind, carried by insects, or sprayed by raindrops.
3) chromosome set of gametes - n (haploid);
Task. 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.
Ferns are probably the best known spore-forming plants. Just look under the long leaves and you will see a lot of brown dots. They are spores just waiting to be sent out into the world. Mushrooms are very complex organisms. Mushrooms that you may know best are mushrooms, but there are many types of mushrooms in the world. These organisms reproduce by spores, and the spores are very complex and differ from fungal species by fungi.
Fungal spores are classified according to their shape and where in the fungus they are produced. We have not met in all varieties of fungal spores, although there are some scientists who spend their lives studying this target or studying fungi. Fungal spores can spread through all sorts of dispersal mechanisms, from floating through the air, to riding the waves, to carrying animals.
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. 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).
Bacterial spores are a little different from other spores we've looked at. While plant and fungal spores are exclusively designed to reproduce, bacteria can use the spores to reproduce or to survive in harsh environments. Certain groups of bacteria will cause spores when they are exposed to very hot, very cold or very dry environments.
These disputes protect inner work bacteria and can remain dormant for many, many years. The bacterial spore is a very hardy cell and allows bacterial cell survive in the adverse conditions. Spores are single-celled reproductive units produced by many various organisms including plants, fungi and bacteria. Spores are primarily used for asexual reproduction, although some bacterial groups use spores to survive harsh environments.
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). On male plants(n) antheridia are formed (n) with spermatozoa (n), on female (n) - archegonia (n) with eggs (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. 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. What chromosome set is typical 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.
Task. What chromosome set is typical for the leaves of the cuckoo flax moss and its spores? Explain from what initial cells and as a result of what division these cells are formed.
Answer
Cuckoo flax spores are formed on the sporophyte by meiosis, they have a haploid set of chromosomes. The moss gametophyte, a plant with a stem and leaves, develops from the spore by mitosis. All gametophyte cells are haploid.
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).
Task. 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.
Thank you for your attention.
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 of meiosis. Meiosis occurs during the formation of haploid cells - spores or gametes. 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 homologues, but by 1 chromosome. 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.
In other organisms, the ratio of the diploid and haploid phases of the cycle may be different. Different organisms show a wide variety of life cycles, but in all of them 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 (on the left) only gametes are haploid, in plants (in the middle) there is a diploid generation (sporophyte) and a haploid generation (gametophyte), and in many unicellular organisms the haploid phase predominates, and the zygote after fertilization divides by meiosis, resulting in again haploid cells.
The ratio of haploid and diploid stages in the life cycle different organisms may be different. As we have already seen, in animals the only stage is diploid, and only gametes are haploid. In some organisms, on the contrary, the only stage is haploid, and only the zygote is diploid, which immediately after the sexual process enters meiosis. We can observe such a situation, for example, in chlamydomonas. In most plants, both phases are present. In mosses, the green plants familiar to us are haploid. They form organs of sexual reproduction: antheridia, in which spermatozoa are formed, and archegonia, each of which contains one egg. The resulting gametes after fertilization give a diploid stage, which develops directly on the haploid. It is a thin long thread with an extension at the end. It is brown because it does not contain chlorophyll, is incapable of photosynthesis and lives off the haploid part of the plant. Inside an extension called the boll, many cells divide by meiosis to form haploid spores. Spores give rise to green haploid plants. Thus, the main stage in mosses is haploid.
The main life stage in ferns is 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 - the outgrowth. 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 of pollen grains, but at this time no noticeable vital processes occur in it. After fertilization from a zygote, a new diploid organism also passes the first stages of development inside maternal organism.
Systematic position
Kingdom: plants
higher spore plants
Superdivision: bryophytes
Department: bryophytes, or real mosses
Class: leafy, or real, mosses
Class: sphagnum mosses
Department: liver mosses
Department: anthocerot mosses
Bryology- the science of bryophytes.
The main characteristic of the Bryophytes department
- Small sizes.
- Wet habitats.
- Absence of roots, there are rhizoids.
- No conductive tissue.
- For sexual reproduction, the presence of droplet liquid moisture is necessary for the movement of spermatozoa.
- In the life cycle, alternation of generations with a predominance of the haploid gametophyte (!).
Division Bryophytes
CLASS LEAF-STEMULAR MOSSES
Kukushkin flax (Fig. 1)
Widely distributed in temperate rain forests. Its brownish stem, reaching a length of 30 cm, contains dead elongated cells, performing the function of conducting and accumulating water. Simple leaflets consist of several layers of green cells and do not have veins. In the lower part of the stem of young moss, unicellular outgrowths are formed - rhizoids, which perform the function of absorbing water and mineral salts. Usually cuckoo flax grows in the form of curtains, which contain several hundred individuals. Green moss plants are the haploid stage, or gametophyte. Moss cuckoo flax is a dioecious, or dioecious, plant. At the top of some plants are formed female organs, called archegonia (Fig. 2).
Each archegonium contains one egg. On male plants, antheridia develop - organs that are sacs in which spermatozoa are formed. Since the plant is haploid, the formation of gametes does not require meiosis. For fertilization, mosses need water through which spermatozoa could swim across to female plant and penetrate the archegonium. For this, rain or abundant dew is enough, drops of which will fall on the tops of plants. After fertilization, the resulting zygote develops into a diploid sporophyte. It grows on a haploid green plant and uses the substances formed by it. It does not contain chlorophyll and does not photosynthesize. It looks like a long brown thread called a leg. At one end it is attached to the top of the gametophyte, and at the other end an extension is formed, which is a sporangium. In this expansion, spore mother cells are formed, which divide by meiosis to form many unicellular spores. A mature sporangium consists of a capsule and an operculum. The lid comes off, and the spores spill out and are carried by the wind over long distances. A thin branching thread grows from spores that have fallen into a moist, lit place. (protonema). Buds form at its ends, giving rise to new haploid plants.
CLASS Sphagnum mosses
Moss Sphagnum
An important group of mosses are sphagnum mosses (Fig. 3). They are widespread and form the so-called sphagnum, or raised, swamps. The tops of sphagnum have light green leaves. As the moss grows, its lower part is under the thickness of younger leaves, dies off and begins to decompose. Moss fabrics contain carbolic acid, which has a powerful bactericidal action. The decomposition of moss occurs without access to air and under conditions of almost total absence microorganisms. Moss practically does not rot and turns into peat. Peat, like a sponge, retains moisture, waterlogging occurs forests.
Sphagnum does not have rhizoids. It absorbs water with its entire surface. Small light green leaves covering the stem and branches consist of two types of cells that are clearly distinguishable under a microscope. Narrow green photosynthetic cells form a mesh structure in which movement occurs. organic matter. Between them are large transparent dead cells, of which only membranes remain (Fig. 4). These cells serve as a reservoir for water. Through the pores in them cell walls water is replenished from the surrounding air.
Sphagnum is a monoecious plant. Archegonia (female organs of sexual reproduction) and antheridia ( male organs sexual reproduction) are located on the same plant. Spermatozoa (n) drop by drop of water reach the eggs (n), fertilization occurs. A zygote (2n) is formed, from which a sporangium grows. There, meiosis occurs and haploid (n) spores are formed, giving rise to a thin filament-pregrowth - protoneme(n). A bud is formed on it, germinating into a new gametophyte (n).
ORDER LIVER MOSSES
Small tender plants, the body of which is most often represented by a thallus in the form of a plate irregular shape. In some, the thallus bears scales corresponding to the leaves. There are numerous rhizoids. The protonema is poorly developed.
Reproduction is sexual (like other mosses) and asexual (with the help of special buds).
A common representative of hepatic mosses is marchantia (Fig. 5).
Rice. 5
ORDER ANTOCEROTIC MOSSES (FIG. 6)
Lamellar thallus.
common for the most part in the tropics.
Sporophytes ( sporogony) horn-shaped.
At the base of the sporangium stem is a meristem, so the stem is constantly growing. The formation and maturation of spores takes a long time.
Most are monogamous. Cross-pollination (female and male gametophytes mature in different time).
The meaning of mosses
- Peat formation.
- Water supply of ecosystems.
- Species that form ecosystems.
- Contains antibiotics.
Systematic position
Kingdom: plants
higher spore plants
Supersection: ferns
Department: ferns
Department: Lycopsoid
Department: horsetail
General characteristics of ferns
- They originated in the Devonian. They reached their biological flowering in the Carboniferous, becoming the main forest-forming group. The remains of the forests have formed vast deposits of coal.
- The largest number of species in the tropical zone.
- They prefer moist habitats, because male gametes are mobile, and moisture is needed to move the sperm to the egg.
- There are tissues and organs.
- The life cycle is dominated by the diploid sporophyte.
- Reproduction is sexual and asexual (sporulation).
- The organs of sexual reproduction are multicellular.
Division Ferns
Currently, the department has approximately 12,000 species.
Life forms: grasses, trees (Fig. 1) and creepers (several tropical species). There are water forms (Salvinia floating (Fig. 2)).
Rice. 1 Fig. 2
fern leaves - fronds- whole or complexly dissected with a well-developed conduction system. The development of the leaf comes from the "snail" (Fig. 3).
Leaves can be differentiated into sterile and fertile (leaf grass (Fig. 4)), or simultaneously perform both functions (most ferns (Fig. 5)). The fertile leaves of the ostrich do not photosynthesize (Fig. 6).
Rice. 3 Fig. 4 Fig. 5
Most ferns have an underground rhizome and well-developed adventitious roots (Fig. 7).
Rice. 6 Fig. 7
The life cycle of ferns includes the alternation of a haploid gametophyte and a diploid sporophyte with a predominance of the sporophyte. In the life cycle, there is an alternation of sexual and asexual reproduction (Fig. 8).
During asexual reproduction, paired outgrowths are formed on the underside of the leaf - sori(Fig. 9). The sorus is a stem and a veil that covers the bottom of the spherical sporangia (Fig. 10), extending from the base of the stem. In sporangia, spore mother cells are formed, which divide by meiosis to form haploid cells that become spores. In dry weather, the edges of the spathe are folded back, and the sporangium shell bursts due to uneven thickening of the walls of the cells that form it.
Rice. 9 Fig. 10
From spores that have fallen into a moist, lit place, a haploid fern gametophyte develops - sprout- in the form of a heart-shaped plate with numerous rhizoids. On its lower side, antheridia with spermatozoa and archegonia with eggs are formed. Like mosses, ferns need water to thrive. On it, polyflagellated fern spermatozoa swim to archegoniums. There, the sperm fuse with the egg, forming a diploid zygote. A new diploid plant grows from it.
In the forests of the temperate zone, the most common are the male boletus, the female boletus, and the bracken.
Department of Lycopods
- The shoot is creeping, dichotomously branching.
- leaflets (phylloids)small simple with one central vein.
- Reproduction is sexual and asexual (sporulation).
- The life cycle is dominated by the diploid sporophyte.
The representative of the club mosses, often found in our country, is the club moss (Fig. 11).
In the life cycle of club mosses, like all ferns, there is an alternation of sexual and asexual reproduction (Fig. 12). At the ends of the shoots of the club moss, erect spore-bearing spikelets- strobili. Spore-bearing spikelets are covered with modified scaly leaves - sporophylls- on which sporangia are formed. In sporangia, meiosis produces haploid spores. Mature spores spill out, and a haploid outgrowth develops from them. In many species of club moss, the growth develops underground for several years, feeding heterotrophically, mainly due to symbiosis with the fungus. On a mature gametophyte, archegonia with eggs and antheridia with spermatozoa are formed. After fertilization, the zygote develops into a diploid sporophyte, which feeds on the gametophyte until it reaches the ground, where it begins to photosynthesize.
Horsetail department
An ancient group of vascular plants, currently represented by about 30 species.
The stems are hollow, consisting of individual segments and performing the function of photosynthesis (Fig. 13). To increase strength, bundles of sclerenchyma fibers pass under the epidermis, forming ribs on the surface of the stem. In addition, small crystals of silicon oxide are deposited in the stems of horsetails, which increase their rigidity.
Under the ground, horsetail forms a dense network of rhizomes that serve for vegetative reproduction and winter survival.
In the spring, spore-bearing shoots grow out of the ground. They have Brown color, since they do not contain chlorophyll and live off the reserves of nutrients accumulated last year. On their sporophylls, as a result of meiosis, haploid spores are formed, which have special filamentous outgrowths that change shape depending on humidity. This allows them to leave the sporangium more easily and spread more widely. They give rise to a haploid outgrowth. The life cycle of horsetails is similar to the life cycle of ferns (Fig. 14).
