MAIN GROUPS OF PLANTS.
(chlamydomonas, chlorella). Algae propagation. Filamentous algae. The importance of algae in nature and agriculture.
Algae are found ubiquitously in all habitable habitats. Algae are a taxonomically diverse group of organisms that arose and evolved independently of each other. Algae is photosynthetic organisms that secrete oxygen, they live primarily in water. Based on their body structure, algae are divided into unicellular, colonial and multicellular. The body of a multicellular algae is represented thallus or thallus , is not divided into multicellular vegetative organs.
The cells of many algae are similar in structure to plant ones, that is, they have a cell wall, a vacuole with cell sap and chloroplasts, which in algae are called chromatophores. Chromatophores contain pigment systems, which include chlorophylls and carotenoids. Combinations of these pigments determine the color of algal thalli. Some algae have lost the ability to photosynthesize and completely switched to a heterotrophic type of nutrition.
Reproduction in algae can occur in three ways: vegetative, asexual and sexual with the participation of gametes. The sexual process in algae is of three types: isogamy, in which the fusion of motile gametes of the same size and shape occurs; heterogamy, in which motile gametes that have the same shape but differ in size merge; oogamy, when a motionless large female gamete merges - an egg with a small, mobile sperm.
The structure and vital activity of unicellular algae can be considered using the example of Chlamydomonas and Chlorella.
Chlamydomonas- a green algae that lives in puddles and other small bodies of water. The cell shape of this algae resembles a drop. The outside of the Chlamydomonas cell is covered with a cell wall consisting of pectin. The algae moves in water using 2 identical flagella located at the front end of the cell. The largest part is occupied by a cup-shaped chromatophore. Closer to the front end there is a red eye that perceives light. In the chromatophore, the process of photosynthesis occurs and a reserve polysaccharide, starch, is deposited. The cytoplasm of the cell contains a nucleus and two contractile vacuoles. Chlamydomonas does not have a vacuole with cell sap. Reproduction in Chlamydomonas is asexual and sexual. Asexual reproduction carried out using zoospores, which are formed inside the mother cell. The most common formation is 2-4-8 biflagellate zoospores , each of which, after entering the water, grows to the size of an adult. During sexual reproduction, biflagellate gametes are formed under the shell of the mother cell, which fuse in pairs and form zygote . The zygote becomes covered with a thick shell and overwinters. In the spring, the nucleus in it divides meiotically, and as a result, four young haploid chlamydomonas are formed. Thus, most of the life cycle of Chlamydomonas occurs in haploid stage , in diploid only the zygote is present.
Single-celled green algae is found in fresh and salt water bodies, as well as in the soil and on its surface. chlorella. Its cell is spherical in shape and covered with a dense cellulose membrane. The cytoplasm contains a nucleus and a large cup-shaped chromatophore. Chlorella reproduce only asexually using round, immobile aplanospores. Chlorella is a convenient object for scientific research; with its help, many processes occurring in photosynthetic cells are actively studied. It was used on spaceships for air regeneration and disposal of organic residues in closed life support systems.
Representatives of filamentous algae are Ulotrix and Spirogyra.
filamentous green algae ulothrix lives mainly in fresh water bodies and forms a green coating on underwater objects. The ulothrix filament is attached to the substrate using one colorless basal cell (rhizoid). Ulotrix threads do not branch and consist of short identical cells. In the cytoplasm of the cell there is a nucleus and a chromatophore in the form of an open ring. Most of the cell is occupied by a vacuole with cell sap. Ulotrix reproduces vegetatively, asexually and sexually. Four-flagellate zoospores form inside ulothrix cells, enter the water, swim, then attach to underwater objects and begin to divide, forming new filaments. As a result of the first division, the cell forms two cells of different quality: one colorless (rhizoid), the other green. When this cell divides, the thread of the algae's body grows. During sexual reproduction, biflagellate gametes are formed in cells. Having left the mother cell, the gametes fuse in water, forming a four-flagellate zygote, which, after swimming for a certain time, becomes covered with a shell. After a period of rest in the zygote, as a result of meiotic division, 4 haploid zoospores are formed, which, after entering the water, germinate into new filaments, thus, the ulothrix spends most of its life cycle in a haploid state, only its zygote is diploid.
Another widespread green filamentous algae is spirogyra forms accumulations of green mud in fresh water bodies. Its threads do not branch and consist of large cylindrical cells covered with a cellulose membrane and mucus. In the center of the cell there is a large vacuole with cell sap, the nucleus. The chromatophore is spirally twisted. Spirogyra reproduces vegetatively (when the filaments break) and sexually. Sexual process: the contents of the vegetative cells of two adjacent filaments merge. The resulting diploid zygote is coated with membranes and becomes a hibernating stage. In the spring, the nucleus undergoes meiotic division, three haploid nuclei die, and only one new haploid filament of Spirogyra grows.
Algae that live in the seas can be unicellular, colonial and multicellular. The largest thalli are brown, red and green algae. Brown algae are multicellular organisms with a yellow-brown color, which is due to the presence of a large number of yellow and brown pigments. The densest thickets of brown algae form to a depth of 15 m, although they can go to a depth of 40-100 (200) m. In the northern and temperate latitudes one of the most common brown algae - kelp, or seaweed, the thallus of which can reach a length of 20 m. Its thallus contains a lot of the amino acid methionine, iodine, carbohydrates, minerals and vitamins, the content of which can exceed many vegetables and forage grasses. In the life cycle of kelp there is an alternation of asexual and sexual generations. This algae is cultivated in the northern seas of Russia and the countries of Southeast Asia.
Red algae, or purple algae, mainly live in the seas. They are called so because of the color of the thallus, which varies depending on the ratio of pigments from dark crimson, pink to bluish-green or yellow. The presence of red pigment allows red algae to live at great depths (up to 200 m). These are the deepest sea algae. Their multicellular thalli look like beautiful, complexly dissected plates, sometimes bushes resembling corals, but some representatives can consist of a single cell or form colonies. In addition to cellulose, the cell wall of red algae contains agar. Many scarlet mushrooms are edible.
The importance of algae in nature and agriculture is diverse . Algae are capable of synthesizing organic substances from inorganic ones through the process of photosynthesis. In aquatic ecosystems, they most often play the role of producers, that is, they perform the same function as green plants on land. This is the initial link in the food chain.
During photosynthesis they release large amounts of oxygen. Oxygen dissolves in water and is used for respiration by other aquatic organisms.
Algae thickets serve as a habitat, shelter and breeding place for many animals, that is, algae form a variety of aquatic biotopes.
When favorable external conditions occur, some algae can develop in large numbers and cause water blooms. Green bloom of water in ditches, puddles and pits is most often caused by the proliferation of euglena algae. Red tides - sea blooms caused by a number of microscopic single-celled algae (hence the name - Red Sea) cause great damage to fisheries. The algae that cause red tides release substances that are toxic to animals and humans.
Soil algae participate in the formation of the soil structure, partially ensure its fertility, saturate the soil with oxygen, and take part in the formation of a number of rocks and sedimentary rocks.
Algae are widely consumed as food (species of the genus Porphyra, Laminaria, Undaria). A number of species are successfully cultivated.
Red algae is used to produce agar, which has gelling properties. Agar is used in the manufacture of jelly, pastille, soufflé, a number of sweets, and products, and in microbiology for the preparation of media on which microorganisms are grown.
Brown algae is the only source of alginates - alginic acid compounds that are used in the food industry.
Algae are used in medicine to treat a number of diseases. In recent years, preparations from algae have been used to remove radionuclides.
Some algae are used as indicator organisms to determine the degree of pollution of water bodies. They are also used for wastewater treatment.
A number of algae serve as objects for scientific research.
Algae are a large group of ancient plants. Their body structure and size are characterized by enormous diversity. There are microscopic unicellular, multicellular and colonial forms (1-2 microns) and large ones, with different structures of the thallus, reaching 30-45 m. Let's look at the general characteristics of algae.
A common property of all algae is the presence of chlorophyll. In addition to chlorophyll, algae may also contain other pigments (phycocyan, phycoerythrin, carotene, xanthophyll, phycoxanthin). These pigments give the algae a red, brown, yellow-green color, masking the main green color.
general characteristics
Nutrition. The presence of pigments in algal cells provides an autotrophic type of nutrition. However, many algae have the ability, under certain conditions, to switch to heterotrophic nutrition (euglena - in the dark) or combine it with photosynthesis.
Classification of algae. The number of algae species exceeds 40 thousand. However, their classification is not complete, since not all forms have been studied well enough. In our country, it is customary to divide algae into 10 divisions: blue-green, pyrophyte, golden, diatom, yellow-green, brown, red, euglenophyte, green, charophyte. The largest number of species are green (13-20 thousand) and diatoms (10 thousand).
The division of algae into sections usually coincides with their color, which is usually associated with the structural features of the cells and thallus.
The structure of algae cells. Algae are the only group of organisms among which prokaryotes (blue-green) and eukaryotes (all others) are found. In the nuclei of eukaryotic algae, all the structures characteristic of the nuclei of other eukaryotes are revealed: membranes, nuclear juice, nucleoli, chromosomes.
The structure, composition and properties of the remaining cellular components of algae are characterized by great diversity. In the process of evolution, natural selection has preserved the most promising forms, including a type of cellular organization that allowed plants to transition to a terrestrial lifestyle.
Algae propagation It can be vegetative, asexual (using spores) and sexual. For the same species, depending on the conditions and time of year, the methods of reproduction are different. In this case, a change in nuclear phases is observed - haploid and diploid.
Living conditions and habitats of algae. Favorable conditions for the existence of algae are: the presence of light, carbon sources and mineral salts, and the main habitat for them is water. The life of algae is greatly influenced by temperature, water salinity, etc.
Most algae are inhabitants of fresh and marine waters. They can inhabit the water column, swim freely in it, forming phytoplankton, or settle on the bottom, attaching to a variety of objects, living and dead organisms, forming phytobenthos. They inhabit algae and hot springs, as well as water bodies with high salinity.
Until about the middle of the 20th century, all plants were divided into inferior And higher. TO to the lowest plants were attributed bacteria, fungi, slime mold, algae, lichens. Representatives of these groups are extremely heterogeneous, but they are characterized by some common features: the absence of tissues and differentiation of the body into root, stem, leaf (i.e., absence of organs).
Currently bacteria And mushrooms separated into independent kingdoms of living organisms, and slime mold And lichens are considered as separate groups (divisions) in the kingdom mushrooms.
Plants are characterized by the following characteristics:
– aerobic photosynthesis;
– presence of chloroplasts in cells;
– reserve substance – starch;
– dense cellulose cell membrane;
– relative immobility.
According to one classification, the kingdom Plants divided into three subkingdoms: Bagryanka(red algae), Real seaweed And Higher plants.
Vegetative body scarlet And real algae not divided into organs and tissues. They are often called in the old way lower plants. However now scarlet And real seaweed belong to the kingdom Protista.
Higher plants, in contrast to the lower ones, they are complex, multicellular organisms differentiated into organs and tissues, adapted to living in a terrestrial environment.
Seaweed - a collective group of predominantly aquatic photosynthetic protists. They arose in the Proterozoic ~800–900 million years ago.
The concept of “algae” suffers from great uncertainty in scientific terms. The word “algae” itself means only that they are the simplest organisms living in water. However, seed plants can also be found in water ( water lily, duckweed), higher spores (moss fontinalis, horsetail river, lake poloshnik, fern salvinia) secondary aquatic plants. In addition, photosynthetic bacteria also live in water bodies ( cyanobacteria), which are not plants or protists, but are capable of aerobic photosynthesis (often called blue-green algae). On the other hand, a significant number of microscopic algae also grow on land (unlike “aquatic” algae, these “land” algae easily tolerate drying out and very quickly come to life at the slightest moisture).
More than 40,000 species of algae are known, which were previously grouped into 9 divisions: red, diatomaceous, green, brown, pyrophytic, yellow-green, golden, charophytic, euglenic. At present, the question of the number and composition of algal divisions, as representatives of the kingdom Protista, has not been finally resolved. What algae have in common is their ability to have an autotrophic method of nutrition due to the presence of a photosynthetic apparatus (however, some algae have heterotrophic nutrition along with autotrophic nutrition). Different groups of algae differ in the set of pigments, the structure of chloroplasts, photosynthetic products, and the number and structure of flagella. It is believed that the divisions of algae originated from different groups of single-celled organisms, i.e. are not directly related to each other. Terrestrial chlorophyll-bearing plants probably originate from them.
The science that studies algae is algology(from lat. algae- seaweed).
Cell structure. The organization of the cell of most algae differs little from the organization of typical plant cells, but it also has its own characteristics (Fig. 4.7.).
The cell of most algae is covered with dense shell, consisting mainly of cellulose and pectin substances.
The algae shell is layered (heterogeneous, 2-3 layers). As a rule, the inner layers are cellulose, and the outer ones are pectin, which protects the cell from the harmful effects of acids and other reagents.
In many algae, additional components are deposited in the shell: calcium carbonate ( characeae), alginic acid ( brown), iron ( red, volvox). U diatoms Instead of cellulose, the cell membrane contains silicon(it strengthens the shell matrix, creating a shell-like structure).
Only a few algae are “naked” (i.e. without a shell, surrounded only by the plasmalemma); more often they are covered pellicle – dense elastic protein layer ( Euglena)
and are able to easily change the shape of their body.
WITH
Rice. 4.7.
The structure of an algae cell. A - chlamydomonas; B – spirogyra(part of the thread).
Under the shell there is a protoplast, which includes cytoplasm And core(kernels). In most algae, the cytoplasm is located in a thin wall layer, surrounding a large central vacuole with cell sap.
Most algae have only 1 nucleus per cell, but, for example, cladophores there are several dozen of them, and water mesh (hydrodiction) – several hundred. Cells with a large number of nuclei are called coenocytic.
Algae cells contain all organoids typical for plant cells: endoplasmic reticulum, ribosomes, Golgi complex, mitochondria, chloroplasts and others.
However, chloroplasts algae ( chromatophores) differ from plant chloroplasts in a huge variety of shapes, location in the cell, and a set of pigments.
They can be cup-shaped in shape ( chlamydomonas), spiral ( spirogyra), lamellar ( melosira), cylindrical ( ulothrix), stellate ( zygnema) etc. (Fig. 4.7., 4.8.).
IN 
chloroplasts there are various pigments: chlorophylls a, b, c, d; carotenoids(orange), fucoxanthin(brown), phycocyanin(blue), phycoerythrin(red).
IN
Rice. 4.8.
Some forms algae chloroplasts. 1 – star-shaped zygnema; 2 – cylindrical ulotrix; 3 – lamellar Melosirs.
Unicellular algae also have a photosensitive red eye - stigma(catches and transforms light, necessary for orientation in space) , pulsating vacuoles(remove excess water from the cell, perform an excretory function) And flagella(used for movement) . Almost all algae, except red, can form motile cells.
Body structure. Algae may be unicellular (Chlamydomonas, Chlorella), colonial (water mesh, Volvox, Pandorina) And multicellular(filamentous - spirogyra, cladophora; lamellar – fucus, kelp; charophytic – hara, nitella). Their sizes range from microscopic (1 micron – chlorella) to giant (up to 60 m in length - macrocystis giantis).
The body of a multicellular algae is represented thallus, or thallus, does not have real tissues and organs (leaves, stems and roots), although some have externally similar parts (Fig. 4.9.).
Thallus algae are distinguished by a wide variety of morphological structures, reflecting the main stages of their evolution. The following main morphological structures of algae are distinguished:
– amoeboid – this is the primary and most primitive morphological structure characteristic of unicellular organisms and is characterized by the absence of a permanent cell shape, membrane and flagella. These algae, like amoebas, move with the help of pseudopods ( golden And yellow-green);
– monadic structure - characteristic of unicellular organisms and is characterized by the presence in such cells of one, two or several flagella, thanks to which they move ( pyrophytic, golden, euglenic); in more highly organized ones, cells serving for asexual and sexual reproduction have a monad structure;
– coccoid – characterized by immobile cells with a dense cell wall, solitary or connected in colonies ( green, golden, at diatoms – this is the only structure);
– palmeloid – is a union of many coccoid cells immersed in common mucus, but without plasmatic connections ( green);
– filamentous – connection by means of cytoplasmic strands of immobile cells into filaments, which can be simple and branching, free-living and attached, often united in mucous colonies (green, yellow-green and etc.);
–
heterogeneous - this is a complicated filamentous structure, consisting of threads creeping along the substrate and vertical threads extending from them ( green, golden, red, brown);
– lamellar – characterized by multicellular thalli in the form of plates consisting of one, two or more layers of cells ( green, brown, red);
– siphonal – the thallus is characterized by the absence of cellular partitions and a large number of nuclei; it is mainly seaweed ( green, yellow-green)
– charophytic – a large multicellular thallus of a linear-segmented structure, where the main “shoot”, “leaves” and rhizoids are distinguished ( characeae).
Reproduction. Algae multiply asexual And sexual way.
Asexual reproduction occurs vegetatively or disputes.
Vegetative Reproduction in unicellular organisms is carried out by cell division (mitosis), in colonial and filamentous organisms - by parts of the thallus, or by special organs (for example, nodules in characeae algae).
In some filamentous algae ( Spirogira) the thread (body, thallus) splits in a strictly defined way along, and at the same time two new threads are formed - fragmentation.
In a number of filamentous algae (for example, ulothrix) individual cells become rounded, accumulate a large amount of reserve nutrients and pigments, and their membranes thicken. Such cells are called akinetes. They are able to survive unfavorable conditions under which ordinary vegetative algae cells die and their threads are destroyed. When favorable conditions occur Akinetes sprout into threads.
Spore reproduction is carried out using aplanospore(fixed spores) or zoospore(mobile - in most algae)), formed by dividing the protoplast of ordinary cells or in special cells - sporangia.
Sexual reproduction is carried out using germ cells - gametes (gametogamy), after their fusion it is formed zygote, which produces a new individual or zoospores. Gametes are formed in cells that do not differ from vegetative ones, or in special cells - gametangia(female gametangium - oogonium, male – antheridium). Only characeae algae gametangia are multicellular. Main types of sexual reproduction – iso-, hetero- And oogamy. Also found in algae conjugation – fusion of protoplasts of unspecialized nonmotile cells ( spirogyra) And hologamy – fusion of two adult single-celled motile organisms (some volvox).
In primitive algae (for example, chlamydomonas) each individual is capable of forming both spores and gametes depending on the time of year and external conditions (for example, temperature). In others, the functions of asexual and sexual reproduction are performed by different individuals - sporophytes(form spores) and gametophytes(form gametes). In a number of algae there is a strict alternation of generations - haploid gametophyte and diploid sporophyte.
Environmental groups. Majority algae lives in freshwater reservoirs and seas. However, there are also terrestrial, soil and other ecological groups of algae.
The following are distinguished: environmental groups algae:
– aquatic: – phytoplankton – a collection of predominantly small, passively floating algae in the water column ( Volvox, Pandorina, Fragilaria, Euglena, Chlamydomonas); – phytobenthos – a collection of algae living at the bottom of reservoirs or overgrowing various aquatic objects, as well as green cotton wool-like accumulations floating on the surface of the water, called mud(chara, nitella, cladophora, ulotrix, spirogyra, pinnularia, novicula, kelp, fucus);
– ground(aerophytic, several hundred species) – algae that form differently colored plaques and films on trees ( pleurococcus, chlorococcus, chlorella, trentepoly), rocks, damp earth, roofs and walls of houses (cosmarium, pinnularia), on fences, etc.;
– soil – algae living on the soil surface or in its uppermost horizons (in the Republic of Belarus there are ~200 species: diatoms, green, yellow-green: Chlamydomonas, Chlorella, Chlorococcus, Navicula, Pinnularia);
– cryophyton – algae of ice and snow (~350 differently colored species; the phenomenon of “red snow” is an accumulation of unicellular algae chlamydomonas snowy; green color of snow - raphidonema snowy; brown color of snow and ice - ancylonema nordenskiöld);
and etc.
1. Meaning. In water bodies they are the main source of organic matter -
producers.
Current estimates suggest that the ocean accounts for at least half of the world's primary production in terms of fixed carbon.
Algae (primarily phytoplankton) are a very important link in aquatic ecosystems; most food chains begin with them.
They enrich the hydrosphere and atmosphere with oxygen, with algae releasing ~50% of all oxygen into the atmosphere. Carbon dioxide is fixed. Participate in the Ca and Si cycle.
3. Participate in soil formation.
4. They enter into symbiosis with other organisms.
5. They participate in the process of natural self-purification of waste and polluted waters, air regeneration in closed systems (during space flights, scuba diving), and can be used to purify water contaminated with radionuclides ( chlorella capable of accumulating radionuclides).
6. They are indicators of environmental pollution and salinity.
7. Used by humans as food products ( kelp, alaria, ulva, porphyra), fertilizers and feed additives for animals, a source of vitamins (A, B 1, B 2, B 12, C and D) and biostimulants.
Apparently, almost all algae can be eaten, since there are no poisonous forms among them. For example, on the Sandwich Islands, out of 115 available species of algae, the local population eats about 60.
Red algae is especially rich in vitamins purple. The most famous as a therapeutic and prophylactic remedy is seaweed ( sugar kelp), used against some gastrointestinal disorders, sclerosis, goiter, rickets and other diseases.
8. They are raw materials for industry.
Agar-agar (from red), algin (from brown) obtained from algae are used in the food industry (in the production of marmalade, marshmallows, ice cream, etc.; as an additive to bread - it does not go stale so quickly), paper (gives density and gloss), pharmaceutical industry (for the production of creams, ointments) , in scientific research (solid medium for the cultivation of microorganisms).
Diatomine(accumulations of dead diatoms) is used in almost 50 industries. Their valuable qualities are high porosity and low specific gravity. A large amount of diatoms is used to prepare light bricks; used as an additive to cement. But it is most widely used as a filter material in the production of oils, fats, in the sugar and chemical industries.
Some substances are used in perfumery, to produce glue (alginic acids), etc. They are used to produce organic acids, alcohols, varnishes, etc.
From brown algae receive iodine and bromine.
9. Together with bacteria, they cause “blooming” of water.
“Blooming” is observed in fairly warm weather, when there is a lot of nutrients in the water (this situation is very often artificially created by man, when industrial waste is discharged into the water or when fertilizers from fields enter rivers and lakes). As a result, an explosive reproduction of the primary producers begins, and they, in violation of all laws of nature, begin to die off before they have time to be eaten. With the subsequent decomposition of the residues, an equally intense proliferation of aerobic bacteria (decomposers) occurs and the water is completely deprived of oxygen. As a result, fish and other animals and plants begin to die. Toxins produced during water blooms, especially during the proliferation of cyanobacteria (blue-green algae), increase the death of animals.
Hi all! It's time for a new post, the topic of which will be the general characteristics of algae. From what you read below, you will learn their structure, how they reproduce and what algae actually are, what is it?
General characteristics of algae.
Algae are lower semi-aquatic or aquatic plants that live in oceans, lakes, streams and ponds, or on moist land areas. Together with animals, they form ocean plankton and are the main source of food for fish.
Some algae are huge and complex in structure, while others are single-celled organisms that are no more than 0.01 mm in diameter. Some of the seaweed species reach 100 m in length.
Algae are a fairly diverse group of plants that are classified according to characteristics such as cell wall composition and pigmentation.
In total, there are about 20 thousand algae in the world. They find shelter in hot springs, in which the water is boiling water, and in polar ice, in salty brine, and in hard water.
Structure.
All algal cells have chromatophores that contain various pigments. Green chlorophyll – the most important of these, it is present in chromatophores called chloroplasts. Different algae have different numbers and shapes of chloroplasts.
For example, chlorella has one single chloroplast, similar to a calyx. Spirogyra has numerous chloroplasts, which are connected into long spiral ribbons. And in other algae they are in the shape of stars or saucers.
Each group of algae has its own range of pigments in a special combination. Thanks to this, there are groups of blue-green, brown, red and green algae. Some of the species form lichens in symbiosis with.
Unicellular algae like chlorella consist of just one cell, where inside the shell there is a carrier of genetic material - DNA (nucleus) - and chloroplasts containing chlorophyll.
Some unicellular algae can move using flagella. Multicellular algae consist of many threads that form thalli of different shapes, this is clearly seen in the example of seaweed.
Reproduction.
Algae reproduce in various ways. Some reproduce vegetatively (fragments of the thallus fall off and continue to grow on their own). Unicellular algae They usually reproduce in the same way as some - by division.
Asexual reproduction of higher algae occurs with the help of spores that are formed from the mother cell. Some spores have flagella (zoospores), which give them motility.
Same as with bacteria conjugation also occurs. In a more sophisticated way, sexual reproduction occurs in more complex algae (like fucus). The female and male reproductive organs of most fucus species appear on different plants, but sometimes they are found on the same plant.
The female (oogonium) and male (antheridium) reproductive organs, which appear in the spring, throw their cells into the water when they are covered by a tidal wave. With the help of flagella, male gametes approach and merge with immobile eggs.
Initially, the fertilized egg is enveloped in a cell wall, and later it germinates and gives rise to a new plant.
I hope that the general characteristics of algae helped you understand everything. 😉
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 classify all available information about different types of representatives into ten departments. The division is based on the structure and vital activity of algae.
- Blue-green single-celled, or cyanobacteria. Representatives: cyanea, shotgun, microcystis and others.
- Diatoms. These include pinnularia, navicula, pleurosigma, melosira, gomphonema, sinedra and others.
- Golden. Representatives: chrysodendron, chromulina, primnesium and others.
- Porphyritic. These include porphyry.
- Brown. Cystoseira and others.
- Yellow-green. This includes classes such as Xanthopodaceae, Xanthococcaceae, and Xanthomonadaceae.
- Reds. Gracillaria, ahnfeltia, scarlet flowers.
- Green. Chlamydomonas, Volvox, Chlorella and others.
- Evshenovye. These include the most primitive representatives of the greens.
- 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.
- Amoeboid.
- Monadic.
- Capsular.
- Coccoid.
- Filamentous, or trichal.
- Sarcinoid.
- False tissue.
- Siphon.
- 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.
- In some individuals they contain specialized structures of animal origin - locomotion organelles (flagella).
- Sometimes there is stigma.
- The membranes are not exactly the same as those of a regular plant cell. They are often equipped with additional carbohydrate or lipid layers.
- The pigments are enclosed in a specialized organ - the chromatophore.
Otherwise, the structure of the algae cell follows the general rules of 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 between a large accumulation of unicellular representatives, united, as a rule, by mucus in the 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 of 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, as part of a school program for studying lower plants and their different departments, the teacher asks 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 conducting vessels; The thallus has a multilayer structure, which is why 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. Spare 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 as food is widespread among different peoples of the world. Medicines are made from them, flour and minerals, and alginic acids are obtained.
