How do algae reproduce? Types of algae reproduction

Algae are autotrophic organisms that are capable of photosynthesis. To date, more than 30,000 species of algae have been identified. Although they have chlorophyll, like green plants, they lack strong root systems and leaves. Therefore, these are not plants, and therefore the method of reproduction in algae is different.

Algae are not plants, so their reproduction is different from plant reproduction.

The structure of algae can vary from simple unicellular (eg Micromonas) to complex multicellular (eg Kelps) forms. They are found in any habitat: freshwater, marine, marshy, wet soil and on rocks. Based on their characteristic features, there are four main types of algae: cyanobacteria, green, red and brown.

What is algae

Algae are a special group of unicellular or multicellular organisms that live primarily in aquatic environments. This is a fairly large group of lower plants. Their habitat is so large that they can be found everywhere, both in the oceans and in the seas, lakes, rivers, other bodies of water, on moist soil and even the bark of trees.

Algae are both unicellular protozoa and multicellular colonial organisms. The shells of multicellular algae consist of cellulose, which are attached to each other at the end.

They do not have a root system. Instead, algae attach to the surface using special processes called rhizoids.

Algae are the main source of organic matter on the entire Earth. Almost all food chains begin with them. Moreover, they serve as a source of nutrition for many inhabitants of the aquatic environment.

Algae are also suitable for making fertilizers, animal feed, and, of course, can be eaten by humans.

Spore division and generative type

Asexual reproduction also includes division by spores. Usually they contain 2 sets of chromosomes that store information from the parent plant.

There are several types of disputes:

• tetraspores;
• autospores;
• zoospores;
• synzoospores;
• hyprospores;
• alpnospores.

In different types of algae, they can develop inside cells or be independent parts of the body. There are also those that can develop separately from the parent.

During generative reproduction, two adult plants exchange a set of chromosomes to produce offspring that have traits from both parents. The simplest method is conjugation . They appear when two organisms exchange chromosomes and then separate. Fusion (oogamy) in certain species occurs using special tubes.

Many multicellular algae have sex cells called gametes. They merge, after which offspring or spores appear.

Origin of algae

There is still no consensus on the origin of algae and their exact age due to the fact that this type of organism is represented by great diversity. Moreover, not a single example of fossil specimens has been preserved and it is impossible to establish what stages of evolution this type of organism went through.

Biologists around the world are convinced that not a single plant in the world can compare with the healing power of seaweed, since there is a theory about the origin of life in the sea, which means that they contain a unique biological composition.

However, there is an opinion that green and yellow algae appeared on Earth about 3 billion years ago. At first they arose in the form of unicellular organisms and only then colonial ones. And it was the appearance of this type of organism that led to the formation of an oxygen atmosphere and an ozone layer on Earth, which subsequently led to the origin of life. Multicellular complex algae appeared about a billion years ago.

general characteristics

A characteristic feature of all types of algae is the presence of chlorophyll. Other pigments may also be contained. Among them are:

• phycocyan;
• phycoxanthin;
• carotene;
• xanthophyll.

Plant pigmentation depends on them. In addition to green, they can be red, brown or yellow.

Due to the presence of pigments, an autotrophic type of nutrition is ensured. But many species of aquatic plants are capable, under certain conditions, of switching to heterotrophy. There are also known cases of combining such nutrition with photosynthesis.

Scientists now know about 40 thousand species of algae. The classification scheme has not yet been fully developed, since scientists have not yet studied all the forms of these organisms well enough. In Russia, division is carried out by departments. Division often occurs based on the color of the plants. The color, as a rule, coincides with the structural features.

The following structures are distinguished in the structure of the nuclei of eukaryotic algae:

1. Nuclear juice.
2. Nucleoli.
3. Shells.
4. Chromosomes.

The structure of the remaining varieties is characterized by enormous diversity. Evolution has preserved the most promising forms, including those that ultimately allowed the formation of terrestrial species.

For algae to develop well, favorable conditions are necessary:

1. Presence of mineral salts.
2. Sufficient amount of carbon.
3. Light.

The main habitat is water. The life activity of these plants is also influenced by the level of salinity, temperature, etc. Most algae grow in fresh and salt water bodies. Some species inhabit the water column , moving freely in it. This is how phytoplankton is formed. They can also anchor on the seabed, creating phytobenthos. Algae is also present in hot springs. The life cycles of such species occur much faster.

There are also terrestrial algae. In addition, they can live in the snow and ice of the Arctic, as well as calcareous substrate.

Many algae lead a symbiotic lifestyle. They are able to enter into such relationships with other representatives of both the plant and animal world. The most interesting for scientists is the symbiosis with mushrooms. Thanks to him, lichens arise.

Types of algae

More than 30 thousand species of algae are known to modern biology. However, all of them can be combined into special groups:

1. Euglena or unicellular. The smallest algae.
2. Pyrophytic algae, the membrane of which consists of cellulose.
3. Diatoms. They consist of cells with a so-called double shell.
4. Golden algae. Here you can find both unicellular and multicellular organisms, but they are all freshwater golden or brown-yellow in color.
5. Yellow-green. They are very often combined with the previous group.
6. Green. They can be detected with the naked eye, for example, on the bark of trees.
7. Charovaya algae. These are already multicellular algae, which are often combined with green ones. The height of the stem ranges from 2.5 cm to 10 cm.
8. Red algae. They are so called because of the presence of a special element in their composition - phytoerythrin, which colors them red. These algae live mainly at great depths in the seas.
9. Brown algae. The most perfect look. They live at great depths and are capable of creating thickets, such as, for example, in the Sargasso Sea. Their rhizoids are tightly attached to the surface, so it is almost impossible to tear them off.

Cellular structure of algae

The example below is a schematic representation of Chlamydomonas (transmission electron microscopy). This cell is a single-celled, green, freshwater algae, but multicellular algae cells react in much the same way:

• The cell wall, more or less thick, plays a protective role.
• The cytoplasmic membrane, semipermeable, allows the cell to exchange with the environment.
• The cytoplasm, or plasma membrane, the site of metabolic reactions, looks like a kind of jelly.
• The nucleus is surrounded by a membrane (eukaryotes) and contains DNA.
• The endoplasmic reticulum is responsible for protein synthesis.
• Mitochondria are responsible for the oxidative respiratory chain.
• The dictyosome is also involved in the production of proteins, in particular in their finishing.
• The chromatophore is responsible for photosynthesis.
• Starch grains (not always in the chromatophore) are the cell's reserves.
• The vacuole maintains the internal environment: removal of water, mineral salts and some waste products.
• The stigma (eye) is a structure that informs the cell about the possibility of initiating photosynthesis.
• Pyrenoid of various shapes may contain starch, as well as soluble polysaccharides; its role is not yet very clearly defined. Pyrenoids are not confined to the membrane and are not present in all algal cells.

The structure of Chlamydomonas

Distribution of algae in nature

According to their mode of existence, algae are divided into two large groups: aquatic and those living on land - outside the water.

In turn, water can be divided into several categories:

1. Planktonic. They are suspended in the water. At the same time, they are absolutely adapted to this lifestyle.
2. Benthic. They live at the bottom of reservoirs.
3. Periphyton. They live on underwater rocks and grow on deep-sea objects.
4. Neuston. This type of algae floats in a semi-submerged state. One part is above the surface of the water, the other must be immersed in water.

Algae living on dry land are divided into two subgroups:

1. Aerophyton. Algae that grows on ground objects, fallen objects, stumps.
2. Algae growing on the surface of the soil.

In addition to the above species, there are those that live in salty reservoirs, on snow or ice, and also live in limestone substrate.

Table “Diversity of algae”

In addition to the main groups of algae indicated in the table, there are also:

• diatoms;
• yellow-green;
• golden.

Diatoms are common in seas and fresh water bodies. Their peculiarity is the presence of a shell made of silica. When shells are deposited at the bottom of reservoirs, the rock diatomite is formed.

Rice. 3. Diatom shells under a microscope.

How do algae reproduce?

Let's deal with the main question of the article. In nature, algae reproduce in three ways. Each of them has its own characteristics.

1. Algae reproduce vegetatively. This is a method of reproduction in which an adult is divided in two or, for example, a kidney is separated from the mother's body. The newly formed cells then divide into two and four cells, from which the adult algae subsequently grows.
2. Asexual reproduction. This is a type in which the protoplast divides inside the algae cell, followed by its release to the outside and separation from the mother cell.
3. Algae reproduce by spores that are formed in special organs called sporangia.
4. Sexual reproduction. It consists of the fusion of two cells, gametes, resulting in a zygote, which subsequently grows into a new individual or produces zoospores. Moreover, the zygotes of different algae behave differently after their formation. For some, they enter a period of rest, which can last up to several months. And others germinate immediately into a new layer or thallus.

It is noteworthy that each type of algae reproduces differently. This issue is studied in the school curriculum. And often students hear a question from the teacher: “How do algae reproduce? Describe the reproduction of algae." The answer is simple if you study the material in detail.

Structural features

Speaking about what the body of algae is represented by, we must remember: we are talking about primitive organisms. According to some reports, they are the first to inhabit planet Earth. It is not surprising that such organisms have no division into vegetative organs. Instead, a thallus, or thallus, is present.

The structure of algae

The main feature is the filamentous or lamellar structure. In older organisms, bushy or branched is found. Sizes also greatly depend on the type of organism. The minimum dimensions are a tenth of a millimeter, the maximum are tens of meters.

Algae structure diagram

When algae reproduce asexually. Types of asexual reproduction

This is the simplest option. Algae reproduce either asexually or vegetatively only in favorable conditions. This means when the water in a reservoir has a certain temperature and conditions are most conducive to asexual reproduction.

If sudden temperature changes, pollution or overcrowding of inhabitants occur in a reservoir or environment, in this case the algae begin to reproduce sexually.

Asexual reproduction can be divided into several types:

1. Algae reproduce vegetatively - division of vegetative cells occurs.
2. Sporulation. Or, in another way, algae reproduce using special cells. These cells are called spores.

When algae reproduce asexually, there is only one parent from which all existing genomes are inherited. But in the case of mutations, the genetic material can change significantly.

Often, one organism can reproduce both asexually and vegetatively.

Chlorella

Chlorella is a single-celled autotrophic protist. It (Fig. 32) is often found in fresh water bodies, on damp soil, and tree bark.

Structure

Chlorella has a spherical shape. The cell is covered with a dense, smooth membrane. The cytoplasm contains the nucleus, cup-shaped chloroplast and other organelles.

Reproduction

Chlorella reproduces asexually, producing many spores. While still inside the mother cell, the spores are covered with their own membrane and then come out (Fig. 33). The spore subsequently grows into an adult.

Vegetative propagation of algae

Vegetative propagation is characteristic in most cases of brown algae.

With this method of reproduction, parts of the algae (thalli) are separated from the existing ones, without any changes, and the new cells formed inherit part of the maternal shell.

Both unicellular and multicellular algae can reproduce vegetatively. Moreover, in unicellular organisms, the cell is divided into two, and in multicellular organisms, separation occurs in layers or entire thalli, colonies. In filamentous algae, the vegetative method of reproduction occurs by dividing the filaments into their individual fragments.

At the same time, not all algae from the order of colonial representatives can reproduce vegetatively, just as in unicellular species, along with the vegetative method of reproduction, a sexual way can also exist.

Brown algae, as mentioned above, reproduce in this very way, with the help of special brood branches. All types of sargassum in the Sargasso Sea reproduce in a similar way.

Vegetative method of propagation

Algae reproduce in several ways. In vegetative, the DNA of the parental material does not interact with other cells. This method can be quite varied, representing:

1. Cell separation. Some species reproduce by cell division. New binary units begin to develop into a separate organism.
2. Budding. New growths grow on the parent body, which separate after a certain time.
3. Fragmentation. Commonly found in various colonial species. The parent's body splits into several fragments, which become new organisms.

The type of reproduction depends on the specific type of algae and its membership in any group. There are also subtypes of the vegetative method, but they are very rare.

Reproduction by spores

In addition to vegetative propagation, algae reproduce using spores. This is a specific subtype of asexual reproduction.

Spores are formed in special organs, the so-called sporangia or zoosporangia. When the spore disperses, it begins to germinate and then a new adult independent individual is formed.

Motile spores with flagella that are capable of movement are called zoospores.

The option of asexual reproduction by spores can be considered using the example of an algae such as ulothrix. In favorable living conditions for it, its fragments, which contain spores, are separated from the existing maternal thread. They swim in a free state, then, having attached themselves to an underwater object, they begin to actively divide and form a new thread of algae. It should be noted that this type of algae can simultaneously reproduce both asexually and sexually.

It has been noted that it is possible to stimulate the formation of spores in some species of filament algae; for this to happen, there must be an increase in carbon dioxide in the habitat.

The function of asexual reproduction in this case is performed by individuals called sporophytes, that is, they form spores.

Chlamydomonas

Chlamydomonas consists of one cell extended from the anterior end. There are a pair of flagella that provide movement. The cell wall protects Chlamydomonas from external influences. The cell contains a haploid nucleus with a single set of chromosomes, a large cup-shaped plastid (chromatophore), which gives it a green color. At the anterior end there are a pair of contractile vacuoles that remove excess fluid.

Chlamydomonas is able to select more illuminated areas in the water and move towards them. This ability is called positive phototaxis. For such movement, the algae has a light-sensitive eye (stigma) at the base of the flagella.

In the life cycle of Chlamydomonas, there is an alternation of haploid and diploid forms.

Favorable conditions trigger asexual reproduction. Having increased to a certain size, the cell casts off its flagella and takes on a rounded shape. The cell nucleus begins to divide. Then the cell membrane ruptures and several pairs of small cells with flagella come out. These are zoospores. Growing up, they turn into adult Chlamydomonas.

Unfavorable environmental conditions trigger the sexual process. Gametes are formed inside the cells, which, when released into the water, combine to form a zygote. It should be noted that gametes from different parent cells are combined. Next, the zygote is covered with a dense shell, forming a zygocyst, surviving unfavorable conditions in this state. When the surrounding conditions change, meiosis starts in the zygocyst and 4 zoospores emerge, from which adult chlamydomonas grow.

Sexual reproduction

In addition to the above methods, algae reproduce sexually. It is characterized, first of all, by fertilization, that is, the fusion of two cells - gametes. After this, a zygote is formed, which subsequently becomes the ancestor of a new organism.

Algae have several methods of sexual reproduction:

1. Isogamy - implies the fusion of two gametes of the same size and structure.
2. Heterogamy. This is the name given to the fusion of two gametes, in which one is larger than the other. Moreover, the one that is larger in size is usually female.
3. Oogamy. With this method of reproduction, a sedentary female cell merges with a mobile male gamete.
4. Conjugation. This concept refers to a type of reproduction in which two vegetative cells lacking flagella join together.

In primitive algae, the same individual is capable of both sexual and asexual reproduction. In the most developed ones, the function is performed by individuals called gametophytes, that is, they form gametes.

Green algae department

From an evolutionary point of view, green algae (Chlorophyta) are an extremely important group: some of them not only organized complex differentiated multicellular bodies, but also moved to land, giving rise to embryophytes - true plants. Perhaps because most of the animals and plants we know are terrestrial and multicellular, we do not realize how complex this process was.

True multicellularity among green algae has evolved several times. But the transition to a complex form of organization of the photosynthetic apparatus necessary for life on land was so difficult that it apparently happened only once.

Green algae are extremely evolutionarily plastic. They survive various disasters when most plants die. There are specialized cells in other groups of algae (brown and red), but their metabolism does not tolerate environmental changes. Few of them can live in the soil, in the air, or inside animals, as green algae do.

They can be found in coastal sea waters and in the open ocean in the form of phytoplankton. Individual representatives capable of tolerating extreme salinity conditions are found on the ocean floor in hydrothermal communities and in deserts. Less exotic species settle on the surface of rocks, animal fur and tree bark. Species of Chlorophyta form symbiotic relationships with fungi (resulting in lichens), protozoa, sponges and coelenterates.

Green algae are extremely diverse. By studying them, we understand that the metabolism and organization of angiosperms and humans are not the only successful experiments of evolution in solving biological problems.

The chloroplasts of green algae, like those of higher plants, contain chlorophylls a and b, as well as carotenes and xanthophylls. Their cell wall is formed by a special type of cellulose and pectin substances. The reserve substance is starch, less often oil. Green algae live mainly in fresh water bodies, but marine, terrestrial and soil species are also found.

The most relict and simplest body is a mobile single cell. And today there are many single-celled green algae. But there are also other types of body structure of green algae.

Life cycles of green algae

The type of life cycle of Angiosperms, which is an alternation of heteromorphic (gametophyte and sporophyte) generations, can be traced in other groups of plants up to green algae. In single-celled algae such as Euglena, which do not have sexual processes, the life cycle is a simple cell cycle. Their reproduction is ensured by mitosis and cytokinesis.

With the development of the sexual process in algae, two critical changes occur:

• meiosis appears, releasing a haploid set of chromosomes;
• A sexual process occurs in which two haploid sets of chromosomes are combined into one diploid one.

Not a single multicellular organism on Earth is asexual, and green algae are no exception. Their simplest life cycle looks like this:

• a diploid cell undergoes meiosis;
• Each new haploid cell exists as an independent unicellular organism capable of mitosis. Cell division of unicellular organisms is also their asexual reproduction;
• some of these cells act as gametes. They fuse and produce a diploid zygote, which is also capable of reproducing asexually - using mitosis;
• some of these cells undergo meiosis again.

Gametes, zygotes and algal organisms differ little, since none of them is specialized. Both haploid and diploid cells are capable of growing, dividing and multiplying. This alternation of generations (haploid and diploid stages) is called dibiontic .

Monobiontic species have only one free-living generation. In some monobiont species, the haploid phase is an individual organism, and their only diploid stage is the zygote, which is only capable of meiosis and not reproduction by mitosis and growth. In both multicellular and unicellular organisms, haploid organisms of this type are capable of photosynthesis and growth. In another group of monobionts, the diploid phase is the vegetative growth phase. And their only haploid cells are gametes, which are only capable of syngamy.

In dibiont species of green algae, both stages are multicellular: gametophyte (haploid phase) and sporophyte (diploid phase). Their gametophyte and sporophyte:

• may be very similar to each other ( isomorphy );
• be very different in appearance and structure ( heteromorphy ), which allows them to colonize different ecological niches. They seem to be different organisms and the gametophyte does not compete with the sporophyte.

All sporophytes, both algae and embryophytes, produce spores during meiosis. These spores are diploid and give rise to a new asexual stage of reproduction - the sporophyte. The gametophytes of some algae also produce spores, but through mitosis, they are haploid and develop into a new gametophyte, which is also an asexual stage of the life cycle.

In some cases, algae reproduce by fragmentation, which is similar to the vegetative reproduction of angiosperms. They produce shoots along the edge of the thallus, which, when separated from the mother's body, become independent organisms.

Sex cells in the early stages of evolution were identical ( isogamous ). Later, slight differences between gametes ( anisogamy ) and strong differences ( oogamy ) appeared. Algal gametes are produced in gametangia. Spermatozoa, or microgametes, are formed in microgametangia, and eggs, or macrogametes, are formed in macrogametangia.

Spores are formed in sporangia, depending on the size of the spores, they appear in either megasporangia or microsporangia. The most important difference between algae and real plants is that their gametangia and sporangia have a cellular level of organization. Individual cells develop into gametes or spores inside the cell, and when they leave the cell, there is nothing left but empty chambers.

Unicellular green algae

Most unicellular green algae are characterized by monadic and coccoid morphological structures.

Chlamydomonas is one of the simplest chlorophytes. It is single-celled and, like all green algae, has chlorophyll a and b, carotenoids and xanthophylls. Chlamydomonas starch is formed in chloroplasts in the same way as in real plants. Its mobile pear-shaped cell is covered with a transparent membrane consisting of hemicellulose and pectin substances. Two anterior identical flagella distinguish Chlamydomonas from heterokont motile cells of brown algae.

Most of the Chlamydomonas cell is occupied by the chloroplast, in the recess-cup of which the nucleus is located. In the front part of the cell, in the chloroplast, there is an eye (stigma) with the help of which the alga moves towards the light (positive phototaxis). At the anterior end of the cell there are two pulsating vacuoles that release excess water and regulate the osmotic pressure inside the cell body.

The structure of Chlamydomonas

Chlamydomonas feeds mixotrophically : along with photosynthesis, its cell is able to absorb organic substances dissolved in water, helping to purify polluted waters. This algae lives in shallow fresh water bodies.

Snow chlamydomonas (Chlamydomonas nivalis) from the class Chlorophyceae is found on the surface of snowfields and glaciers, coloring them in reddish shades. This phenomenon is called “red snow”.

Chlamydomonas move quickly in jerks due to the beating of flagella. In unfavorable conditions, when the reservoir dries out, they become immobile, lose their flagella, and their walls become slimy. When conditions change, flagella may reappear.

Like most motile green algae, Chlamydomonas has normal: mitosis, meiosis and fertilization. Its life cycle is simple: a haploid cell resorbs its flagella, divides mitotically, forms 2, 4, 8 or 16 new cells that grow new flagella, each of which floats freely and lives until it meets a compatible cell. Gametes recognize each other by reactions at the tips of their flagella. They undergo plasmogamy and karyogamy, forming a large zygote. In addition to isogamy, different species of Chlamydomonas have hetero- and oogamy.

Life cycle of Chlamydomonas

The zygote sheds four flagella and sinks to the bottom in a calm state. It divides by meiosis and forms four biflagellate haploid individuals. The Chlamydomonas zygote is the only diploid cell in the entire life cycle.

Chlorella (Chlorella vulgaris) is a microscopic planktonic algae that lives in small standing fresh water bodies, puddles, ditches, in moist soil, and on tree trunks. Its cells are spherical, immobile (without flagella), covered with a dense cellulose membrane. The large cup-shaped chloroplast gives chlorella its green color.

Chlorella reproduces only asexually

There is no stigma, the core is small. There is a pyrenoid surrounded by starch grains. It reproduces only asexually with the help of immobile round autospores. It feeds only photoautotrophically, has active photosynthesis and accelerated reproduction. Therefore, it is a convenient object for research. Chlorella has long been recognized as a valuable protein product and is actively cultivated for feed production.

A greenish coating on glass and a film on water in household vessels is caused by another chlorella, Chlorella infusionum.

Mobile colonial species

The cells of the motile colonial lineage of algae strongly resemble Chlamydomonas. But they are formed during the division of the zygote. The cells are held together by a gelatinous matrix. In Gonium, each colony contains only a few cells (4, 8, 16 or 32), and the only sign of their organization is that all the flagella beat in concert.

Pandorina is about the same size as Gonia, made up of 16 squares, but she is a little more complex. Its cells are somewhat differentiated: the anterior ones differ from the posterior ones. The colony swims in one direction.

Volvox is a stunning representative of this lineage: its colonies contain up to 50,000 chlamydomona-like cells, easily visible without a microscope. Their differentiation is expressed in the fact that up to 50 cells in the posterior half of the colony are specialized only for reproduction.

Filamentous multicellular green algae

Representatives of the genus Ulothrix are simple species of filamentous green algae. They have a soft, mostly unbranched thallus, consisting of closely connected cells.

They have a monobiont life cycle, in which only one free-living multicellular generation participates, and it is haploid. The ulotrix consists of one row of fairly identical cells, with the exception of the basal cell, which is modified into a fixative - rhizoidal basal processes or a single cell. With the help of a fixative, ulotrix is ​​attached to the substrate.

Cells are cylindrical, mononuclear. In young cells, the length to width ratio is usually greater than in old cells. Chloroplasts are solitary, wall-shaped, belt-shaped, usually lobed, open in young cells, sometimes completely closed in mature cells. There is one pyrenoid, in more mature cells it is surrounded by a thin or thick starch shell; old cells accumulate starch, oil-like and volutin droplets. Asexual reproduction is carried out by four-flagellate zoospores and by fragmentation of filaments. Under unfavorable conditions, thick-walled filaments with akinete-like stages sometimes develop, and rarely true akinetes.

The bulk of cells, through mitosis, produce asexual zoospores with four flagella. They swim freely for a short time. And then they settle and grow into new threads. Some cells produce isogamous biflagellate gametes, similar to Chlamydomonas. They fuse in pairs to form a zygote, which divides by meiosis to form four haploid zoospores. Each zoospore lives independently for some time, then loses its flagella, attaches to the substrate and grows into a new filament.

Ulotrix is ​​a cosmopolitan with a wide ecological amplitude, often found in temperate and cold regions; As a rule, it forms threads collected in bundles or mats several centimeters long.

Spirogyra is a very common freshwater filamentous green algae. It is found in ponds and rivers, where it forms mud. Non-branching filaments are formed by a group of large cylindrical cells covered with a cellulose membrane and mucus. The cells have beautiful spiral-ribbon chloroplasts (chromotophores) located near the walls. The central vacuole occupies most of the cell. The growth of the filament occurs due to transverse cell division.

Spirogyra does not produce motile, floating gametes. Instead, its threads come closer together and mate. Each strand is haploid and is either positive or negative. If compatible threads (+ and -) are opposite each other, then a conjugation tube is formed between its cells, along which protoplasts migrate and merge.

The nuclei unite only 30 days after the start of conjugation . The emerging diploid cell becomes dormant and acquires a thick cell wall that is resistant to external influences. Later it grows into a new thread. Shortly after karyogamy, cells divide meiotically to form haploid spores.

Spiragyra reproduces vegetatively by fragments of thread, and asexually by means of immobile aplanospores, formed one in each cell.

Lamellar types

Ulva is a genus of marine green algae whose thallus imitates a leaf structure. It is much more complex than Ulotrix, but many stages of their life cycle are identical. The four-flagellate haploid zoospore also grows into a filament similar to the ulothrix. Ulva cells divide in two directions and form a leaf-like thallus, then all cells divide in the third plane and the “leaf” becomes two-layered. The cells at the base of the algae form rhizoid-like outgrowths.

Ulva has a dibiontic life cycle with alternating isomorphic generations: its gametophyte and sporophyte look the same. Like flowering plants, Ulva has two types of individuals in one generation. During sexual reproduction, gametophyte cells produce biflagellate anisogametes, with smaller gametes produced on one gametophyte and larger gametes on the other. The zygote grows into a filament and then into a two-layered leaf-like thallus, exactly the same as that of a gametophyte. Many species of Ulva are eaten. They are called "sea salad".

Coenocytic species

The dibiontic life cycle, with alternating heteromorphic (dissimilar) generations, is illustrated by Derbesia , the organism in which it was first discovered. In 1938, P. Kornman managed to obtain zoospores of Derbesia marina

), a branching filamentous algae consisting of giant cells. The zoospores were carefully preserved, but instead of growing into another Derbesia, they gave rise to individuals of a completely different species - Galicystis.

The body of Galicistis is completely different from Derbesia. It consists of one large spherical coenocytic cell attached to the surface using a small holding device. Almost the entire volume of the cell is occupied by a single giant vacuole with a thin layer of protoplasm next to the wall.

In adulthood, Galicystis individuals, which are at the gametophyte stage, produce either male or female anisogametes, which, after undergoing syngamy, form a zygote. After germination, the zygote grows into a Derbezian sporophyte. But it is incorrect to classify even such different life stages as different genera, so the name Halicystis ovalis was excluded from the terminology.

Flowering plants also have alternating heteromorphic generations, but their gametophytes grow inside sporophytes, so the question of their classification is easily resolved.

Parenchymatous species

Several groups of green algae undergo true parenchymal growth, which is the basis of parenchyma in embryophytes. Chlorophytes are divided by a phyplast, which is never found in true plants. Charophytes undergo cell division with the help of phragmoblast, like plant cells.

In chlorophytes, the flagellar root apparatus (attaching the flagella to the cell) consists of four stripes arranged crosswise; no real plant has this type of flagellar apparatus. In charophytes, the flagellated root complex is similar to that of motile cells in true plants: one large band of microtubules extends down into the cytoplasm from the basal body. Characeae are the only algae that have multicellular gametangia.

An interesting example is the chara alga Chara , which has a stem-like body divided into nodes and internodes, with curlicue branches arising at the internodes. The body consists of several cells that make up true parenchymal tissue, obtained as a result of cell division in all three planes. The cells originate from the apical meristem, which contains a prominent apical cell.

External structure of chara algae

Although these features correspond to those of flowering plants, virtually all similarities are spurious, since the earliest vascular land plants did not have any nodes, internodes, or branches. If the Chara are the sister group of the embryophytes, then the only characters that may be homologous rather than analogous are the parenchymal body and the growth of the apical meristem.

Simple bodies of parenchymatous cells are also found in members of Coleochaete, another group of charophytes that are being studied as possible close relatives of land plants.

The reproduction of Hara is of great importance. Like embryophytes, it has multicellular reproductive structures with sterile cells, and based on this, Chara would be classified as a plant rather than an algae. Its sperm are produced in a multicellular gametangium, the outer cells of which are sterile; only the inner cells turn into sperm. At adulthood, the outer cells separate slightly and the motile sperm swim away. The egg cell is formed as the terminal cell of a short filament of three cells, but the subterminal cell divides and these cells grow upward and surround the macrogamete.

After fertilization, the sterile cells surrounding the fertilized egg deposit thickenings on their inner walls adjacent to the zygote. Thus, the resting structure consists not only of a thick-walled zygote, but also of protective sterile cells. When a quiescent cell germinates, it becomes a haploid filament, which soon forms an apical meristem and exhibits parenchymal growth.

Sources:

1. Algae: Cyanobacteria, red, green and charophytic algae: educational method. manual / A. G. Paukov, A. Yu. Teptina, N. A. Kutlunina, A. S. Shakhmatov, E. V. Pavlovsky; [under general ed. A. G. Paukova] ; Ministry of Education and Science of Russia. Federation, Ural. federal univ. - Ekaterinburg: Ural Publishing House. University, 2021.
2. Agafonova I.B. Biology of plants, fungi, lichens, grades 10-11: school. allowance M: Bustard, 2008.
3. Andreeva I.I., Rodman L.S. Botany. — 2nd ed. reworked and additional - M.: KolosS, 2002.
4. James D. Mauseth, PhD University of Texas at Austin SIXTH EDITION

Examples of algae reproduction

An example of vegetative propagation of algae is fucus. On its main thallus, additional thalli of similar structure are formed, which subsequently give rise to a new organism.

Asexual reproduction, that is, division into two cells, can be observed in euglena.

Chlamydomonas is an algae that reproduces both sexually and asexually, using spores (zoospores) that have flagella.

Another example of sexual reproduction is in brown algae such as kelp. This species has three modes of sexual reproduction, such as isogamy, hetogamy, and oogamy.

Chlorella is a microscopic green algae. It reproduces exclusively asexually, using spores.

Red algae (purple algae) reproduce in two ways, one of which is sexual. Its distinctive feature is the formation of male gametes without flagella. In this case, female gametes remain on the algae, and male gametes are transferred to them using the current.

Systematics of algae

In accordance with modern ideas, green and charophyte algae, along with true terrestrial plants, form the subkingdom Green Plants (Viridiplantae), which, in turn, together with red algae and glaucophytes (together forming the subkingdom of algae Biliphyta) forms a separate branch in the phylogenetic tree - kingdom Plants (Archaeplastidae, or Plantae).

The Chromalvelolata branch, or the kingdom Chromista, includes the Ochrophyta department, which includes brown, yellow-green, golden, sinurous and some other classes of algae. Diatoms, cryptophytes and haptophytes are divided into special divisions within the kingdom. Among non-photosynthetic organisms, they are related to opalines, labyrinthulids and oomycetes.

The kingdom Chromista also includes dinophyte algae, which, together with ciliates, apicomplexans and colpodellids, are included in the department Alveolata (Miozoa, or Alveolata). The department Euglenophyta, united by many researchers in Excavata, belongs to the kingdom Protozoa and includes euglenophytes, as well as parasitic and free-living flagellates, such as kinetoplastids, diplonemids, etc.

Representatives of the Chromist kingdom. Author: Alison R. Taylor (University of North Carolina Wilmington Microscopy Facility); Professor Gordon T. Taylor, Stony Brook University; Keisotyo; Daniel Vaulot, CNRS, Station Biologique de Roscoff; Shane Anderson; CC BY-SA 3.0

Chlorarachniophytes are the only autotrophs among the group Rhizaria (Rhizopods). These are organisms characterized by the development of usually quite long outgrowths - pseudopods. Heterotrophic organisms related to chlorarachniophytes are cercomonas and philous testate amoebae (eugliphids), some sunfishes and radiolarians, as well as parasitic organisms - plasmodiophores and haplosporidia. According to other ideas, rhizomes called Cercozoa belong to the kingdom Chromista along with Bacillariophyta, Cryptophyta, Miozoa and Ochrophyta.

Systematically, algae are divided into many independent divisions, differing in color, depending on the set of pigments, cell organization and thalli structure. Below is a generalized taxonomy of photosynthetic organisms.

Kingdom Plantae (Archaeplastida) Subkingdom Viridiplantae Division Chlorophyta - Green algae Division Charophyta - Charophyta Division Tracheophyta Division - Higher plants Subkingdom Biliphyta Division Glaucophyta - Glaucophyte algae Division Rhodophyta - Red algae Kingdom Chromista Division Ochrophyta Class Chrysophyceae - Golden algae Class Synurophyceae - Sinura algae Class X anthophyceae — Yellow-green algae Class Phaeophyceae — Brown algae Class Raphydophyceae — Raphidophyte algae Class Bolidophyceae — Bolidophycean algae Class Dictyochophyceae — Dictyochophycean algae Class Pelagophyceae — Pelagophycean algae Class Phaeothamniophyceae — Pheotamnia algae Division Bacillariophyta — Diatoms Division Cryptophy ta - Cryptophyte algae Division Haptophyta - Haptophyte algae Division Miozoa (Alveolata) Class Dinophyceae - Dinoflagellates Division Cercozoa (Rhizaria) Class Chlorarachniophyceae - Chlorarachniophytes Kingdom Protozoa Excavata Division Euglenophyta - Euglena algae

The importance of algae in nature

Algae are the most numerous and important photosynthetic organisms for the entire planet. Their distribution is so wide that they can be found not only in seas, oceans, rivers, lakes, but also in small bodies of water, including artificial ones, and even puddles. They can be observed in the form of small greenish spots on the surface of almost every body of water. The importance of algae in nature is great.

In addition to the fact that they emit quite a large amount of oxygen, they serve as a habitat for many aquatic animals and participate in the formation of a fertile soil layer. Many algae are used as food and also serve as the main source of special food components. They are also used to prepare various medicines and cosmetics.

Algae are organisms unique in their composition and method of reproduction. They combine several types of reproduction, or more precisely: sexual, asexual and vegetative. This practically makes them immortal. Moreover, this question is very interesting, because it is not for nothing that biology teachers across the country are trying to get their students to answer the question: “How do algae reproduce? Describe the reproduction of algae."

Department of brown algae

Department of brown algae

The brown algae (Phaeophyta) department includes about 1,500 species. These are exclusively marine multicellular algae. Most of them are attached to the substrate. Sizes range from a few millimeters to 60 m in length. Brown algae are the largest algae in size. The cells have a highly mucous cell wall, which consists of an inner cellulose layer and an outer pectin layer, one nucleus, one or many vacuoles, granular brown chloroplasts. Different shades of brown color are due to the fact that in addition to chlorophyll (a and c) there are brown and yellow (fucoxanthin, carotene, xanthophyll) pigments. Especially high in fucoxanthin. The main reserve substance is laminarin , which is deposited in the cytoplasm. In addition, hexahydric alcohol mannitol and fats are stored.

In most brown algae, the thallus consists of several layers of cells that divide in three mutually perpendicular directions. In multinucleated thalli, specialization of cells with the formation of tissues is observed. There is a cortex, consisting of intensely colored cells with chloroplasts, and a core, consisting of colorless large cells of the same size. The core provides transport of photosynthetic products and performs a mechanical function.

They reproduce sexually and asexually. Characteristic is alternation of generations with a predominance of sporophyte. Vegetative propagation occurs using parts of the thallus. Asexual - with the help of haploid zoospores that germinate into gametophytes. Sex organs are formed on gametophytes. The sexual process is isogamous, heterogamous and oogamous. The zygote, without a dormant period, grows into a diploid plant - sporophyte.

Representatives of brown algae

The most famous representatives are kelp (sea kale), fucus, cystoseira, macrocystis , etc. Representatives of brown algae can be found, in particular, in the Black and Azov seas.

Brown algae is used to produce alginates (salts of alginic acid, an analogue of gelatin), which are used in various sectors of the economy. They are used to produce glue for textile production, paper sizing, and cement bonding. Sodium alginate films are applied to metals, concrete structures, etc. to protect them from corrosion, destruction, and rotting. Alginates are used in the production of canned food, fruit juices, and dyes.

Kelp

This is the most famous brown algae. Attached to the surface of the substrate by branched rhizoids. It has a so-called “stem” and an elongated plate. The gametophyte does not live long; the main life form is the sporophyte. Two species are common in the northern seas - sugar and palmate . They are industrial types and are used for animal feed, production of various food products and medicines (iodine, mannitol, etc.). Mannitol is used in medicine as a blood substitute during surgical operations.

Sargassum

They look like small bushes (0.5-2 m). They grow at the bottom of shallow seas, some float at the surface thanks to bubbles filled with air. This brown algae, east of Florida and south of Bermuda, thanks to a circular current, forms the Sargasso Sea in the middle of the ocean.