Representatives of multicellular green algae. Life activity and structure of algae. Features of the structure of algae. Struggle for existence

>>Multicellular filamentous green algae

§ 80. Multicellular filamentous green algae

In flowing bodies of water you can often see bright green clusters of silky threads attached to underwater rocks and snags. It is a multicellular filamentous green algae called Ulothrix. 168 . Its filaments consist of a number of short cells; in the cytoplasm of each of them are located core and a chromatophore in the form of an open ring. cells divide and the thread grows. Ulotrix feeds in the same way as Chlamydomonas.

At a time favorable for algae life, each cell, except the one with which the thread is attached, can divide into 2 or 4 motile cells with flagella - zoospores. They go out into the water, swim, then attach to some underwater object and divide. This is how new threads of algae are formed.

Under unfavorable conditions for life, numerous small motile gametes with flagella are formed in some algae cells. The gametes enter the water and fuse in pairs.

This is how fertilization occurs. Usually gametes that originate in cells of different threads merge. A zygote is formed. It is covered with a thick shell and can remain dormant for a long time. Under favorable conditions, the zygote divides into 4 spore cells. Each of them, landing on an underwater object, can give rise to a new filamentous algae, ulotrix.

In stagnant or slow-moving waters, slippery bright green lumps often float or settle to the bottom. They look like cotton wool and are formed by clusters of filamentous algae spirogyra. Elongated cylindrical cells are covered with mucus. Inside the cells there are chromatophores in the form of spirally twisted ribbons 169 .

The importance of green algae in nature is great. Forming organic matter, green algae absorb from the water carbon dioxide and like everyone else is green plants, release oxygen, which living organisms living in water breathe. In addition, green algae, especially unicellular and filamentous, serve as food for fish and other animals.

Excessive growth of algae, for example in irrigation canals or fish ponds, can be harmful. To avoid this, canals and reservoirs are periodically cleaned of algae.

1. What are the structural features of ulotrix?
2. How do filamentous green algae feed?
3. How does Ulothrix reproduce?
4. What is the significance of green algae in nature?

Korchagina V. A., Biology: Plants, bacteria, fungi, lichens: Textbook. for 6th grade. avg. school - 24th ed. - M.: Education, 2003. - 256 p.: ill.

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Algae are classified as lower plants. There are more than 30 thousand species. Among them there are both unicellular and multicellular forms. Some algae are very large (several meters in length).

The name “algae” indicates that these plants live in water (fresh and sea). However, algae can be found in many damp places. For example, in the soil and on the bark of trees. Some types of algae are capable, like a number of bacteria, of living on glaciers and hot springs.

Algae are classified as lower plants because they do not have real tissues. Unicellular algae have a body consisting of one cell; some algae form colonies of cells. In multicellular algae, the body is represented by thallus(other name - thallus).

Since algae are classified as plants, they are all autotrophs. In addition to chlorophyll, the cells of many algae contain red, blue, brown, and orange pigments. The pigments are in chromatophores, which have a membrane structure and look like ribbons or plates, etc. A reserve nutrient (starch) is often deposited in chromatophores.

Algae propagation

Algae reproduce both asexually and sexually. Among the types asexual reproduction prevails vegetative. Thus, single-celled algae reproduce by dividing their cells in two. In multicellular forms, fragmentation of the thallus occurs.

However, asexual reproduction in algae can be not only vegetative, but also with the help zoospore, which are formed in zoosporangia. Zoospores are motile cells with flagella. They are capable of active swimming. After some time, the zoospores shed their flagella, become covered with a shell and give rise to algae.

In a number of algae it is observed sexual process, or conjugation. In this case, DNA exchange occurs between cells of different individuals.

At sexual reproduction In multicellular algae, male and female gametes are formed. They are formed in special cells. In this case, gametes of both types or only one (only male or only female) can be formed on one plant. After release, the gametes merge to form a zygote. Most often, the zygote turns into a spore, which remains dormant for some time, thus surviving unfavorable conditions conditions Usually, after wintering, algae spores give rise to new plants.

Unicellular algae

Chlamydomonas

Chlamydomonas lives in shallow ponds and puddles contaminated with organic matter. Chlamydomonas is a single-celled algae. Its cell is oval in shape, but one of the ends is slightly pointed and has a pair of flagella. The flagella allow them to move quite quickly in water by screwing them in.

The name of this algae comes from the words “chlamys” (the clothing of the ancient Greeks) and “monad” (the simplest organism). The Chlamydomonas cell is covered with a pectin shell, which is transparent and does not adhere tightly to the membrane.

The cytoplasm of Chlamydomonas contains a nucleus, a light-sensitive eye (stigma), a large vacuole containing cell sap, and a pair of small pulsating vacuoles.

Chlamydomonas has the ability to move towards light (due to stigma) and oxygen. Those. it has positive phototaxis and aerotaxis. Therefore, Chlamydomonas usually floats in the upper layers of water bodies.

Chlorophyll is found in a large chromatophore, which has the shape of a bowl. The process of photosynthesis takes place here.

Despite the fact that Chlamydomonas as a plant is capable of photosynthesis, it can also absorb ready-made organic substances present in water. This property is used by humans to purify polluted waters.

Under favorable conditions, Chlamydomonas reproduces asexually. At the same time, its cell discards flagella and divides, forming 4 or 8 new cells. As a result, Chlamydomonas multiplies quite quickly, which leads to the so-called water bloom.

Under unfavorable conditions (cold, drought), Chlamydomonas under its shell forms gametes in the amount of 32 or 64 pieces. The gametes enter the water and fuse in pairs. As a result, zygotes are formed, which are covered with a dense membrane. In this form, Chlamydomonas tolerates unfavorable environmental conditions. When conditions become favorable (spring, rainy season), the zygote divides, forming four Chlamydomonas cells.

Chlorella

The single-celled algae Chlorella lives in fresh water bodies and moist soil. Chlorella has a spherical shape without flagella. It also does not have a light-sensitive eye. Thus, chlorella is immobile.

The chlorella shell is dense and contains cellulose.

The cytoplasm contains a nucleus and a chromatophore with chlorophyll. Photosynthesis occurs very intensively, so chlorella releases a lot of oxygen and produces a lot of organic matter. Just like Chlamydomonas, Chlorella is able to absorb ready-made organic substances present in water.

Chlorella reproduces asexually by division.

Pleurococcus

Pleurococcus forms a green coating on the soil, tree bark, and rocks. It is a unicellular algae.

A pleurococcus cell has a nucleus, a vacuole, and a chromatophore in the form of a plate.

Pleurococcus does not form motile spores. It reproduces by dividing cells in two.

Pleurococcal cells can form small groups (4-6 cells).

Multicellular algae

Ulotrix

Ulothrix is ​​a green multicellular filamentous algae. Usually lives in rivers on surfaces located close to the surface of the water. Ulothrix has a bright green color.

Ulothrix filaments do not branch; at one end they are attached to the substrate. Each filament consists of a number of small cells. The filaments grow due to transverse cell division.

The chromatophore in Ulothrix has the appearance of an open ring.

Under favorable conditions, some cells of the ulothrix filament form zoospores. Spores have 2 or 4 flagella. When a floating zoospore attaches to an object, it begins to divide, forming a thread of algae.

In unfavorable conditions, ulothrix is ​​capable of reproducing sexually. In some cells of its filament, gametes are formed that have two flagella. After leaving the cells, they fuse in pairs, forming zygotes. Subsequently, the zygote will divide into 4 cells, each of which will give rise to a separate thread of algae.

Spirogyra

Spirogyra, like Ulothrix, is a green filamentous algae. In fresh water bodies, it is spirogyra that is most often found. As it accumulates, it forms mud.

Spirogyra filaments do not branch and consist of cylindrical cells. The cells are covered with mucus and have dense cellulose membranes.

The chromatophore of Spirogyra looks like a spirally twisted ribbon.

The Spirogyra nucleus is suspended in the cytoplasm on protoplasmic filaments. The cells also contain a vacuole with cell sap.

Asexual reproduction in Spirogyra is carried out vegetatively: by dividing the thread into fragments.

In Spirogyra, the sexual process occurs in the form of conjugation. In this case, two threads are located next to each other, and a channel is formed between their cells. Through this channel, the contents from one cell pass to another. After this, a zygote is formed, which, covered with a dense shell, overwinters. In the spring, a new spirogyra grows from it.

The meaning of algae

Algae actively participate in the cycle of substances in nature. As a result of photosynthesis they produce a large number of oxygen and bind carbon into organic matter that animals feed on.

Algae are involved in the formation of soil and the formation of sedimentary rocks.

Many types of algae are used by humans. So, agar-agar, iodine, bromine, potassium salts, and adhesives are obtained from seaweed.

IN agriculture algae are used as a feed additive in the diet of animals, and also as a potassium fertilizer.

Algae are used to clean polluted water bodies.

Some types of algae are used by humans for food (kelp, porphyry).

Which have no stem, root or foliage. Preferential algae habitat are seas and fresh water bodies.

Green algae department.

Green algae there are unicellular And multicellular and contain chlorophyll. Green algae reproduce sexually and asexually. Green algae live in bodies of water (fresh and salty), in soil, on rocks and stones, and on the bark of trees. The Green Algae department has about 20,000 species and is divided into five classes:

1) Class protococcal- unicellular and multicellular flagellate forms.

2) Volvox class- the simplest unicellular algae that have flagella and are capable of organizing colonies.

3) Heat class- have a structure similar to that of horsetails.

4) Ulothrix class- have a filamentous or lamellar thallus.

5) Siphon class- a class of algae that are similar in appearance to other algae, but consist of a single cell with many nuclei. The size of siphon algae reaches 1 meter.

Department of red algae (purple algae).

Purple fish are found in warm seas at great depths. This department has about 4,000 species. Thallus red algae has a dissected structure; they are attached to the substrate using soles or rhizoid. Red algae plastids contain chlorophylls, carotenoids And phycobilins.

Another feature of red algae is that they reproduce using complex sexual process. Red algae spores and gametes are motionless because they do not have flagella. The fertilization process occurs passively through the transfer of male gametes to the female genitals.

Department of brown algae.

Brown algae- these are multicellular organisms that have a yellowish-brown color due to the concentration of carotene in the surface layers of cells. There are about 1.5 thousand species of brown algae, which have a variety of shapes: bush-like, lamellar, spherical, crust-like, thread-like.

Due to the content of gas bubbles in the thalli of brown algae, most of them are able to maintain a vertical position. Thallus cells have differentiated functions: extinction and photosynthetic. Brown algae do not have a complete conducting system, but in the center of the thallus there are tissues that transport assimilation products. Nutrient minerals are absorbed by the entire surface of the thallus.

Different types of algae reproduce by all types of reproduction:

Sporov;

Sexual (isogamous, monogamous, heterogamous);

Vegetative (occurs when some parts of the thallus are accidentally divided).

The importance of algae for the biosphere.

Algae are the initial link in most food chains of various reservoirs, oceans and seas. Algae also saturate the atmosphere with oxygen.

Seaweed actively are used to obtain various products: polysaccharides agar-agar and carrageenan, used in cooking and cosmetics, are extracted from red algae; alginic acids, also used in the food and cosmetics industries, are extracted from brown algae.

Multicellular green algae

Examples of multicellular green algae are Ulotrix and Spirogyra . Kinds genus, aulothrix They live mainly in fresh water, less often in sea and brackish water bodies, as well as in soil. Algae attach to underwater objects, forming bright green bushes up to 10 cm or more in size.

Unbranched ulothrix filaments, consisting of a single row of cylindrical cells with thick cellulose membranes, are attached to the substrate by a colorless conical basal cell, which performs the functions of a rhizoid. The structure of the chromatophore is characteristic, which has the form of a wall plate forming an open belt or ring (cylinder). All cells, except the basal one, are capable of dividing, causing the continuous growth of the thallus.

Asexual reproduction is carried out in two ways: by disintegrating the filament into short sections, each of which develops into a new filament, or by the formation of four-flagellate zoospores in the cells. They leave the mother cell, shed their flagella one after another, attach sideways to the substrate, become covered with a thin cellulose membrane and grow into a new thread.

Reproduction of the filamentous algae ulothrix: red arrows - asexual reproduction, blue arrows - sexual reproduction.

The sexual process is isogamous. After fertilization, the zygote first floats, then settles to the bottom, loses flagella, develops a dense shell and a mucous stalk, with which it attaches to the substrate. This is a resting sporophyte. After a period of rest, reduction division of the nucleus occurs and the zygote germinates as zoospores.

Thus, in the life cycle of ulothrix there is an alternation of generations, or a change in sexual and asexual forms development: a filamentous multicellular gametophyte (the generation that forms gametes) is replaced by a unicellular sporophyte - a generation that is represented by a kind of zygote on a stalk and is capable of forming spores.

Spirogyra It is common in stagnant and slowly flowing waters, where it often forms large masses of bright green “mud.” It is a thin thread consisting of long cylindrical cells arranged in one row with a clearly visible cell wall. On the outside, the threads are covered with a mucous sheath.

Spirogyra filamentous algae cell

A characteristic feature of spirogyra is a ribbon-shaped, spirally curved chromatophore located in the wall layer of the cytoplasm. In the center of the cell there is a nucleus enclosed in a cytoplasmic sac and suspended on cytoplasmic strands in a large vacuole.

Asexual reproduction is carried out by breaking the thread into short sections, and there is no sporulation. The sexual process is conjugation. In this case, two threads are usually located parallel to each other and grow together with the help of copulation processes or bridges. Their shells dissolve at the point of contact, and a through channel is formed, through which the compressed contents of the cell of one thread moves into the cell of the other and merges with its protoplast. The zygote formed as a result of fertilization germinates after a period of rest. This is preceded by a reduction division of the nucleus: of the four nuclei formed, three die, and one remains the nucleus of a single seedling emerging through a rupture in the outer layers of the zygote shell.

Spirogyra
(Spirogyra)

Spirogyra(Spirogyra Link.) is a green algae from the conjugate group (see Conjugatae), belongs to the Zygnemeae family. The body of Spirogyra is a non-branching thread, consisting of cylindrical cells. The latter contains a chromatophore characteristic of Spirogyra (see): one or several spirally curled, green ribbons. The chromatophores contain colorless bodies around which starch grains, the so-called pyrenoids, are grouped. The nucleus, very clearly visible under a microscope, suspended on protoplasmic filaments, is located in the middle of the cell. Spirogyra grows by intercalary (uniform) cell division. The sexual process of Spirogyra is copulation or conjugation: cells of 2 adjacent filaments are connected by lateral outgrowths; the shells separating these outgrowths are destroyed and, thus, a copulation channel is obtained, through which the entire contents of one cell (male) passes into another (female) and merges with the contents of the latter; the cell in which the fusion occurred (zygote) becomes rounded, separated from the filament and, covered with a thick membrane, turns into a zygospore. The zygospore overwinters and grows into a young thread in the spring. In the zygote, after the fusion of the contents of the male and female cells, the chromatophore of the first cell dies and only the second remains, the nuclei first merge into one, which is then divided into 4 unequal in size (unequal division of the nucleus); Of these, 2 smaller ones diffuse in the surrounding plasma, and 2 larger ones, merging, form the nucleus of the zygote.

The described copulation between cells of different threads (dioecious) is called staircase. In the case when a channel is formed between two neighboring cells of the same thread, copulation (monoecious) is called lateral. In most Spirogyra, during the sexual process, the copulation canal is always developed (subgenus Euspirogyra) and both male and female cells are the same, but in some these cells are unequal in size, and the copulation canal is very poorly developed or completely absent, so that the cells merge with each other directly ( subgenus Sirogonium). Due to the size of Spirogyra cells, reaching up to 0.01 mm in some of its species, due to the clarity of their structure, this algae is one of the best studied and serves as a classic object in the study of the anatomy of the cell and nucleus.

Green algae spirogyra

Spirogyra is one of the most common green algae in fresh waters in all parts of the world; it is also found in brackish waters. Its threads are collected in large green clusters that float on the surface of the water or spread along the bottom and are very often found in the mud of standing and flowing waters, in ponds, swamps, ditches, rivers, streams, pools, etc.

Spirogyra under a microscope

In total, up to 70 species of Spirogyra are known, differing from each other in the shape and size of cells and zygospores, as well as the shape and number of chromatophore ribbons in them, and belonging, as mentioned above, to 2 divisions - Euspirogyra (the most common: Sp Tenuissima Hass., longata Kg. with one ribbon, Sp. nitida Kg. with several ribbons, Sp. grassa Kg. with very thick cells, etc.) and Sirogonium (Sp. stictica Sm., etc.). For Russia, up to 40 species of Spirogyra are indicated

Ulotrix

It lives in sea and fresh waters, forming green mud on underwater objects. Filamentous type of thallus differentiation. Chloroplast wall in the form of a belt, closed or open, with several pyrenoids. There is only one core, but without painting it is not visible.

The ulothrix thallus is built like a single-row unbranched thread. It is composed of cells similar to each other in structure and function (Table 30, 2). Potentially, all cells are capable of dividing and participating in the growth of a plant, just as all cells can form spores and gametes. Only the cell at the base of the filament differs from the rest: with its help, the thallus is attached to the substrate (in attached forms). Ulothrix cells have significant autonomy. This property is associated with the ability for regeneration and vegetative propagation - individual cells or sections of threads easily break away from the threads and begin independent growth

The order includes more than 16 genera. Despite the fact that all their representatives are constructed as a simple single-row thread, important differences can be found in their organization, on the basis of which the entire order is divided into three groups. In algae of the first group, the thread is a row of cells loosely arranged in a thick mucous sheath. Such are, for example, algae Geminella genus Geminella. It is interesting that all ulothrixes with a similar structure are planktonic organisms.

The second group includes those filamentous algae that vegetate as single cells or as short chains of 2-4 cells, very loosely connected to each other. Their threads are formed rarely and on a short time. An example of such a structure would be genus Stichococcus(Stichococcus, Fig. 216, 2). The algae included in this group lead a terrestrial lifestyle.

The central group of the order is the third group, which includes algae, built as a typical multicellular filament, in which the cells are tightly connected to each other without the help of a mucous sheath. Algae belonging to this group are overwhelmingly attached organisms, at least when young. Their threads are more permanent formations, they no longer fall apart so easily, and they can be distinguished between basal and apical parts. This includes several genera, including the central genus of order - ulothrix(Ulothrix).

Ulothrix species (more than 25 of them are currently known) live mainly in fresh water bodies and only very few enter brackish and sea waters. These algae can also settle on wet surfaces that are periodically wetted by splashes from the surf or waterfalls.

One of the most widespread and well-studied species is ulothrix girdled(Ulothrix zonata).

The thallus of ulotrix consists of unbranched filaments of indefinite length, which at the beginning of growth are attached to the substrate by a basal cell. The filament cells are cylindrical or slightly barrel-shaped, often short. The cell membranes are usually thin, but often they thicken and can become layered. Ulotrix cells, like the cells of all algae of this order, contain a single wall chloroplast with one or more pyrenoids and one nucleus located along the longitudinal axis of the cell. The chloroplast has the shape of a belt that encircles the entire protoplast or only part of it

Vegetative reproduction of ulotrix is ​​carried out by fragmentation: the threads break up into short segments and each segment develops into a new thread. However, ulothrix does not reproduce in this way as often as other algae of the order that have a loose filament structure.

For asexual reproduction, zoospores are used, which are formed in all cells of the filaments except the basal one. The development of zoospores, like gametes, begins at the top of the filament and gradually invades the underlying cells.

Zoospores are ovoid cells with four flagella at the anterior end. They contain a stigma, several contractile vacuoles and a wall chloroplast. Ulotrix girdled has two types of zoospores - macrozoospores and microzoospores. Large macrozoospores have a broadly ovoid shape, often with a pointed posterior end, and a stigma located at the anterior end (. Microzoospores are distinguished by their smaller sizes, rounded posterior end and the location of the stigma in the middle of the spore. The nature of microzoospores remains not entirely clear. Apparently, they represent is a transitional type between macrozoospores and gametes.

Zoospores emerge through holes in the side wall of the cell. They are enclosed in a common mucous membrane, which ruptures a few seconds after release. After a short time, the zoospores settle with their anterior end onto the substrate, become covered with a thin cellulose membrane and germinate. When germinating, the zoospore extends vertically and differentiates into two parts. The lower part, lacking chloroplast, develops into an attachment cell; upper - divides to form vegetative cells. In Ulotrix girdled, however, the zoospores settle at the posterior end and begin to grow laterally rather than vertically.

Quite often, zoospores do not leave the sporangia, but secrete a thin membrane and turn into aplanospores. The latter are released as a result of the destruction of the thread, but sometimes they can begin to germinate while in sporangia.

During sexual reproduction, gametes are formed in threads in exactly the same way as zoospores. As a rule, they develop in the same threads as zoospores, or in similar ones. Most often, the transition to sexual reproduction is associated with the end of active growth and the onset of unfavorable conditions. Unlike zoospores, gametes bear two flagella. The sexual process is isogamous. Fusion occurs between gametes of the same or different strands. The zygote remains mobile for a short time, then settles, loses its flagella, becomes covered with a thick membrane and turns into a single-celled sporophyte. It enters a period of rest, during which reserve substances accumulate. The shape of the sporophyte is varied; it is usually spherical with a smooth shell; in some marine species it becomes ovoid and sits on a mucous stalk.

BROWN ALGAE,

Brown algae (Phaeophyta), a type of spore plants, including 240 genera (1500 species), of which 3 are freshwater, the rest are marine. Thallus is olive-green to dark brown in color due to the presence in the chromatophores of a special brown pigment, fucoxanthin (C40H56O6), which masks other pigments (chlorophyll a, chlorophyll c, xanthophyll and beta-carotene). Brown algae vary in shape and size (from microscopic branched filaments to 40-meter plants). In higher brown algae (for example, kelp), tissue differentiation and the appearance of conductive elements are observed. Brown algae are characterized by multicellular hairs with a basal growth zone, which are absent in other algae. Cell membranes contain cellulose and specific substances - algin and fucoidin. Usually each cell has one nucleus. Chromatophores are mostly small and disc-shaped. Some species of brown algae have pyrenoids that are not very similar to the pyrenoids of other algae. In the cell around the core, colorless bubbles containing fucosan, which has many tannin properties, accumulate. As reserve products, mannitol (polyhydric alcohol) and laminarin (polysaccharide), and less often oil, accumulate in the tissues of brown algae. Brown algae reproduce sexually and asexually, rarely vegetatively. Brown algae usually have a sporophyte and a gametophyte; in the higher ones (Laminariaceae, Desmarestiaceae, etc.) they strictly alternate; in Cyclosporans, gametophytes develop on sporophytes; in primitive species (ectocarpaceae, chordariaceae, cutleriaceae, etc.), the gametophyte or sporophyte may drop out of the development cycle or appear once every few generations. The reproductive organs are unilocular or multilocular sporangia. A multilocular sporangium, which more often functions as a gametangium, is formed in the form of a single cell or a series of cells divided by septa into chambers containing one gamete or spore inside. Meiosis usually occurs in unilocular sporangia, and in dictyotes - in tetrasporangia. The sexual process is isogamy, heterogamy or oogamy. Pear-shaped spores and gametes usually have an eye and have two flagella on the side, one directed forward, the other backward. Brown algae are divided into 3 classes: Aplanosporophyceae (only dictyotes), Phaeosporophyceae (heterogenerate and isogenerate, excluding dictyotes) and Cyclosporophyceae (cyclosporans). brown algae are common in all seas, especially in cold ones, where they form large thickets. They are used to produce alginic acids and their salts - alginates, as well as feed flour and powder used in medicine, containing iodine and other trace elements. Some brown algae are used as food.

Brown algae: 1 - kelp; 2 - dictyota; 3 - ectocarpus; 4 - lessonia; 5 - nereocystis; 6 - alaria; 7 - cystoseira; 8—elachista bushes on the stem of another algae; 9 - fucus; 10 - dictyosiphon; 11 - sargassum (all except 3 and 8, greatly reduced; 3 - view under a microscope, magnified approximately 40 times).

As beautiful and amazing as the underwater world is, it is just as mysterious. Until now, scientists are discovering some completely new, unusual species of animals, exploring the incredible properties of plants, and expanding their areas of application.

The flora of the oceans, seas, rivers, lakes and swamps is not as diverse as the terrestrial one, but it is also unique and beautiful. Let's try to figure out what these amazing algae are, what is the structure of algae and their significance in the life of humans and other living beings.

Systematic position in the system of the organic world

By generally accepted standards, algae are considered a group of lower plants. They are part of the Cellular Empire and the Lower Plants sub-kingdom. In fact, this division is based precisely on the structural features of these representatives.

They got their name because they are able to grow and live under water. Latin name - Algae. Hence the name of the science that deals with the detailed study of these organisms, their economic significance and structure - algology.

Classification of algae

Modern data make it possible to include all available information about different types representatives to ten departments. The division is based on the structure and vital activity of algae.

1. Blue-green single-celled, or cyanobacteria. Representatives: cyanea, shotgun, microcystis and others.
2. Diatoms. These include pinnularia, navicula, pleurosigma, melosira, gomphonema, sinedra and others.
3. Golden. Representatives: chrysodendron, chromulina, primnesium and others.
4. Porphyritic. These include porphyry.
5. Brown. Cystoseira and others.
6. Yellow-green. This includes classes such as Xanthopodaceae, Xanthococcaceae, and Xanthomonadaceae.
7. Reds. Gracillaria, ahnfeltia, scarlet flowers.
8. Green. Chlamydomonas, Volvox, Chlorella and others.
9. Evshenovye. These include the most primitive representatives of the greens.
10. as the main representative.

This classification does not reflect the structure of algae, but only shows their ability to photosynthesize at different depths, exhibiting pigmentation of one color or another. That is, the color of a plant is the sign by which it is assigned to one or another department.

Algae: structural features

Their main distinguishing feature is that the body is not differentiated into parts. That is, algae, like higher plants, do not have a clear division into a shoot, consisting of a stem, leaves and a flower, and a root system. The body structure of algae is represented by a thallus, or thallus.

In addition, the root system is also missing. Instead, there are special translucent thin thread-like processes called rhizoids. They perform the function of attaching to the substrate, acting like suction cups.

The thallus itself can be of very varied shapes and colors. Sometimes in some representatives it strongly resembles a shoot of higher plants. Thus, the structure of algae is very specific for each department, so in the future it will be discussed in more detail using examples of the corresponding representatives.

Types of thalli

The thallus is the main distinguishing feature of any multicellular algae. The structural features of this organ are that the thallus can be of different types.

1. Amoeboid.
2. Monadic.
3. Capsular.
4. Coccoid.
5. Filamentous, or trichal.
6. Sarcinoid.
7. False tissue.
8. Siphon.
9. Pseudoparenchymatous.

The first three are most typical for colonial and unicellular forms, the rest for more advanced, multicellular, complex in organization.

This classification is only approximate, since each type has transitional variants, and then it is almost impossible to distinguish one from the other. The line of differentiation is erased.

Algae cell, its structure

The peculiarity of these plants lies initially in the structure of their cells. It is somewhat different from that of the higher representatives. There are several main points by which cells are distinguished.

1. In some individuals they contain specialized structures of animal origin - locomotion organelles (flagella).
2. Sometimes there is stigma.
3. The membranes are not exactly the same as those of a regular plant cell. They are often equipped with additional carbohydrate or lipid layers.
4. The pigments are enclosed in a specialized organ - the chromatophore.

Otherwise, the structure of the algae cell obeys general rules that of higher plants. They also have:

• nucleus and chromatin;
• chloroplasts, chromoplasts and other pigment-containing structures;
• vacuoles with cell sap;
• cell wall;
• mitochondria, lysosomes, ribosomes;
• Golgi apparatus, and other elements.

Moreover, the cellular structure of unicellular algae corresponds to that of prokaryotic creatures. That is, the nucleus, chloroplasts, mitochondria and some other structures are also absent.

The cellular structure of multicellular algae completely corresponds to that of higher land plants, with the exception of some specific features.

Green algae department: structure

This department includes the following types:

• unicellular;
• multicellular;
• colonial.

In total there are more than thirteen thousand species. Main classes:

• Volvoxaceae.
• Conjugates.
• Ulotrix.
• Siphon.
• Protococcal.

The structural features of unicellular organisms are that the outside of the cell is often covered with an additional membrane that functions as a kind of skeleton - a pellicle. This allows it to be protected from external influences, keep a certain shape, and also, over time, form beautiful and amazing patterns of metal ions and salts on the surface.

As a rule, the structure of green algae of the unicellular type necessarily includes some kind of locomotion organelle, most often a flagellum at the posterior end of the body. The reserve nutrient is starch, oil or flour. Main representatives: chlorella, chlamydomonas, volvox, chlorococcus, protococcus.

Representatives of siphonaceae such as Caulerpa, Codium, and Acetobularia are very interesting. Their thallus is not a filamentous or lamellar type, but one giant cell that performs all the basic functions of life.

Multicellular organisms can have a lamellar or filamentous structure. If we are talking about plate forms, then they are often multi-layered, and not just single-layered. Often the structure of this type of algae is very similar to the shoots of higher land plants. The more the thallus branches, the stronger the similarity.

The main representatives are the following classes:

• Ulotrix - ulothrix, ulva, monostroma.
• Couples, or conjugates - zygonema, spirogyra, muzhozia.

Colonial forms are special. The structure of green algae of this type consists in the close interaction among themselves of a large accumulation of unicellular representatives, united, as a rule, by mucus in external environment. The main representatives can be considered Volvox and Protococcal.

Features of life

The main habitats are fresh water bodies and seas, oceans. They often cause the so-called bloom of water, covering its entire surface. Chlorella is widely used in cattle breeding, as it purifies and enriches water with oxygen, and is used as livestock feed.

Single-celled green algae can be used in spacecraft to produce oxygen through photosynthesis without changing their structure or dying. In terms of time, this particular department is the oldest in the history of underwater plants.

Department Red algae

Another name for the department is Bagryanka. It appeared due to the special color of representatives of this group of plants. It's all about the pigments. The structure of red algae as a whole satisfies all the basic structural features of lower plants. They can also be unicellular or multicellular and have a thallus various types. There are both large and extremely small representatives.

However, their color is due to certain features - along with chlorophyll, these algae have a number of other pigments:

• carotenoids;
• phycobilins.

They mask the main green pigment, so the color of plants can vary from yellow to bright red and crimson. This happens due to the absorption of almost all wavelengths of visible light. The main representatives: ahnfeltia, phyllophora, gracilaria, porphyra and others.

Meaning and lifestyle

They are able to live in fresh waters, but the majority are still marine representatives. The structure of red algae, and specifically the ability to produce a special substance agar-agar, allows it to be widely used in everyday life. This is especially true for the food confectionery industry. Also, a significant part of individuals is used in medicine and directly consumed by people as food.

Department Brown algae: structure

Often within school curriculum studying lower plants, their different departments, the teacher asks the students: “List the structural features. The answer will be this: the thallus has the most complex structure of all known individuals of lower plants; inside the thallus, which is often impressive in size, there are conductive vessels; the thallus itself has a multi-layered structure, because of which it resembles the tissue type of structure of higher land plants.

The cells of representatives of these algae produce special mucus, so the outside is always covered with a peculiar layer. Spares nutrients are:

• carbohydrate laminarite;
• oils (various types of fats);
• alcohol mannitol.

This is what you need to say if you are asked: “List the structural features of brown algae.” There are actually a lot of them, and they are unique compared to other representatives of underwater plants.

Farm use and distribution

Brown algae are the main source of organic compounds not only for marine herbivores, but also for people living in the coastal zone. Their consumption is widespread among different nations peace. They are made from medicines, obtain flour and minerals, alginic acids.