Botany - B.Ye. Yakubenko 2017

Part Three. Kingdom Plantae
Chapter VI. Lower Plants
6.1. Group of Divisions Algae

Algae are lower thalloid, or thallus plants that contain Photosynthetic Pigments within their Cells and inhabit primarily aquatic environments. The science that studies algae is known as phycology (or algology). The basic structural unit of an algal thallus is The Cell, which may be naked or enclosed in a pectin, pectin-Cellulose wall, a silica frustule, or other mineralized coverings.

The protoplast of eukaryotic algae is differentiated into Cytoplasm containing Organelles and a nucleus. Cells are predominantly uninucleate, though bi-, tri-, and multinucleate forms also occur. Among the organelles, METABOLISM/14.html">Chloroplasts deserve the greatest attention, consisting of a double membrane, stroma, and non-appressed thylakoids. The chloroplasts of many algae contain pyrenoids, which are proteinaceous bodies responsible for Polysaccharide synthesis.

With the exception of red and certain green algae, most algae are capable of autonomous locomotion or develop motile life stages. Movement is facilitated by the presence of flagella or cilia.

The algal thallus may be unicellular, colonial, coenocytic, or multicellular. Algae exhibit ten principal types of morphological thallus Structure: amoeboid, monad, coccoid, palmeloid, filamentous, heterotrichous, membranous, parenchymatous, siphonous, and charophyte.

The amoeboid structure is characteristic of unicellular algae lacking a rigid Cell wall and a fixed shape. This represents the most primitive structural type, found in phylogenetically ancient forms (such as chrysophytes and xanthophytes).

The monad structure is typical of unicellular algae that possess a rigid cell wall and The ability to move using flagella (found in certain green, euglenoid, and other algae).

The coccoid structure is characteristic of unicellular algae that have a rigid cell wall but lack motile stages (e.g., certain green algae).

The palmeloid structure is a more complex variant of the monad or coccoid type, in which cells aggregate into gelatinous colonies.

The filamentous structure is represented by thalli composed of simple or branched filaments, with cells interacting via plasmodesmata (such as Spirogyra and Ulothrix).

The heterotrichous structure differs from the filamentous type in that the filaments within the thallus are oriented both vertically and horizontally; it is characteristic of highly organized algae.

The membranous (sheet-like) structure forms a thallus resembling blade-like sheets composed of one or more cell layers, occurring in green, brown, and red algae.

The parenchymatous structure represents the highest evolutionary level of algal Organization. The thallus develops through cell divisions in multiple planes and consists of parenchymatous cells differentiated by function—some perform Photosynthesis, while others serve storage, conducting, or mechanical support roles. This structure is typical of highly evolved green, brown, and red algae.

The siphonous structure is typical of non-cellular (coenocytic) algae, whose multinucleate thallus lacks cross-walls (septa); it occurs in certain green and yellow-green algae.

The charophyte structure is characteristic of charophyte algae, whose thalli feature a linearly jointed architecture mimicking the stem of a higher plant, complete with lateral branches and rhizoids at the base.

Algae reproduce via vegetative, asexual, and sexual means. Unicellular algae reproduce vegetatively by Cell Division, whereas multicellular forms reproduce through thallus fragmentation or specialized buds, bulbils, and akinetes (non-motile resting cells). Asexual reproduction occurs via zoospores or spores. Sexual reproduction is highly diverse, encompassing hologamy, autogamy, conjugation, isogamy, heterogamy, and oogamy. Many algae exhibit an alternation of sporophyte and gametophyte generations.

Based on their adaptation to various environmental conditions, algae are categorized into the following ecological groups:

· planktonic — free-floating in the Water Column;

· benthic — attached to the bottom substrates of water bodies;

· periphytic — growing as epibionts on submerged objects or aquatic vascular plants;

· terrestrial — colonizing rock surfaces, stones, tree bark and leaves, as well as walls and roofs of buildings;

· edaphic (soil) — inhabiting the soil surface or subsurface layers;

· hot spring algae, thermophilic algae;

· snow and ice algae (cryophytic algae);

· saline water algae (halophytes);

· symbiotic algae — including nitrogen-fixing algae and those entering into lichen associations.

Algae comprise over 40,000 species, which are divided into ten (to sixteen) divisions, primarily based on their pigmentation and structural features. We will examine only four divisions: diatoms, green, brown, and red algae.

Class="center">6.1.1. Division Green Algae (Сhlorорhytа)

Green algae are unicellular, colonial, coenocytic, or multicellular lower plants. Their thallus exhibits various types of morphological structures: monadoid, coccoid, palmelloid, filamentous, foliose, or siphonous. The cells are covered by a pectin, pectin-cellulose, or cellulose wall, similar to that of higher plants. The protoplast is differentiated into cytoplasm with organelles and a nucleus. Among the cytoplasmic organelles, the chloroplast with pyrenoids is the most important. Its lamellae contain the same pigments as those in higher plants—chlorophylls a and b, as well as carotenes and xanthophylls. Chlorophylls predominate, giving the thallus a green color. The reserve polysaccharide, as in higher plants, is mostly starch.

Reproduction is vegetative (by fragments of the thallus or bulbils), asexual (via bi- or quadriflagellate zoospores or autospores), and sexual (hologamy, conjugation, isogamy, heterogamy, oogamy).

They are widely distributed mainly in freshwaters, though saltwater, soil, and terrestrial aerophytic algae also exist.

The division includes over 20,000 plant species, which are subdivided into six classes: Prasinophyceae, Chlorophyceae, Trebouxiophyceae, Ulvophyceae, Zygnematophyceae, and Charophyceae. In Ukraine, the most widespread classes are Chlorophyceae, Zygnematophyceae, Ulvophyceae, and Charophyceae, with the latter often classified as a separate division.

Class Chlorophyceae comprises unicellular or colonial forms that are motile in the vegetative state, featuring a monadoid or palmelloid structure. The cells possess two or four flagella, a single nucleus, and Plastids of various shapes: stellate, plate-like, cup-shaped, or granular, mostly with pyrenoids. A contractile vacuole and a red eyespot (stigma) are frequently present within the cell.

Vegetative Reproduction occurs by cell division, asexual reproduction via zoospores, and all types of sexual reproduction are known.

Typical representatives include species from the genera Chlamydomonas, Volvox, and Chlorococcum, which inhabit freshwater bodies and tree bark.

Zygnematoid algae are unicellular, colonial, and multicellular filamentous forms. The cell wall is cellulosic, smooth, or variously ornamented; chloroplasts are plate-like, stellate, or ribbon-shaped with pyrenoids. The most typical Representatives of the class include species from the genera Spirogyra, Cosmarium, and Desmidium, the latter being common in peatlands and Sphagnum bogs.

Ulvophyte algae are characterized by a multicellular thallus of filamentous, foliose, or siphonous structure. The thallus may be attached to a substrate by rhizoidal cells or a holdfast; in filamentous forms, it often forms mats joined into mucous colonies. Representatives include species of the genus Ulothrix—a filamentous macroscopic alga—and Caulerpa, whose thallus reaches up to 50 cm in length and is differentiated into stem-like, rhizoidal, and leaf-like parts with numerous internal cellulose partitions. The genera Cladophora and Valonia possess a multinucleate coenocytic thallus.

Charophytes are macroscopic plants whose thallus reaches 20–200 cm in length; in Ukraine, they are found in the rivers of Polissya and are sometimes harvested by locals as animal feed. In appearance, they resemble horsetails, possessing a so-called stem with nodes and whorled branches, and are attached to the substrate by branched rhizoids. However, detailed examination reveals that each internode of the thallus consists of a single elongated multinucleate cell externally covered by small cortical cells, while the node consists of several small uninucleate cells. The branches attached at the nodes are also single large cells containing numerous granular chloroplasts. Charophytes reproduce vegetatively by means of bulbils formed on the rhizoids or the stem.

The sexual process is oogamy, and the sex Organs—oogonia and antheridia—are multicellular. An oospore enclosed in thick walls develops from the zygote. Following a resting period, the oospore undergoes Meiosis, and one of the haploid cells develops into a new individual.

Most representatives of the division Chlorophyta are constituents of plankton, and less frequently benthos, in fresh or saline waters. During mass reproduction, they may foul water bodies and water intakes. Some are symbionts. Their primary value, however, lies in being a vital link in the food webs of aquatic biocenoses, producing organic matter for aquatic fauna, contributing to sapropel deposits, and purifying water.

Self-Control Questions

1. Name the Characteristic Features of green algae.

2. What Methods of vegetative reproduction do you know for these algae?

3. Name the types of morphological structure found in green algae.

4. Which pigments predominate in the plastids of green algae?

5. What shapes of chloroplasts occur in green algae?

6. What is The structure of charophytes?

7. Why do charophytes occupy a special position in The system of algae?

8. What is THE ECOLOGICAL AND Practical significance of green algae?

9. Name typical representatives of green algae.

6.1.2. Division Red Algae (Rhodophyta)

Red algae, or Rhodophyta, are multicellular, unicellular, or colonial plants whose thallus varies in color from crimson and light pink to purple or olive-green. This coloration is due to the presence of specific pigments: chlorophylls a and d, the red pigment phycoerythrin, the blue pigment phycocyanin, and carotenoids. The concentration of phycoerythrin increases in proportion to the depth of the aquatic environment inhabited by the red algae.

In multicellular algae, which mostly inhabit marine environments, the thallus appears as filaments, small bushes, or flat plates, and is often subdivided into axial organs and branched lateral filaments. These thalli exhibit monopodial, dichotomous, or sympodial branching. Cell Differentiation according to function is frequently observed. The thalli attach to the substrate via rhizoids, holdfast outgrowths, or discs. The cells of red algae vary in shape and possess a two-layered cellulose-pectin cell wall. The inner layer consists of cellulose, while the outer layer is composed of pectic substances, including phycocolloids such as Agar, carrageenan, and agarozoids. In certain species, the cell wall is covered with a protein cuticle. In highly organized forms, the cells are multinucleate, and the chloroplasts are ribbon-like, stellate, or discoid. The reserve polysaccharide produced As a result of photosynthesis is floridean starch, along with various sugars and Lipids.

Red algae reproduce asexually through cell division in unicellular and colonial forms, and via thallus fragmentation in multicellular forms. Asexual reproduction also occurs via monospores, which are produced singly within a cell, or tetraspores, which form in groups of four within a tetrasporangium. Both monospores and tetraspores germinate into gametophytes, which develop gametangia and Gametes. The sexual process is oogamy. Through a series of transformations, a tetrasporophyte develops from the zygote. Thus, red algae exhibit an Morphology/12.html">ALTERNATION OF GENERATIONS, which can be either isomorphic or heteromorphic. Red algae do not form motile stages.

Red algae are typically marine organisms, with only 2% of species occurring in freshwater habitats.

Most red algae are edible, especially in coastal regions along seas and oceans. The phycocolloid deposited in their cell walls is used to produce agar-agar, which is widely applied in the medical, microbiological, and confectionery industries. Meal derived from these algae is also used as a feed additive.

The most typical representatives of red algae include the genera Porphyra (found in the Black Sea), Bangia, Phyllophora, and Polysiphonia, among others.

Self-Check Questions

1. Name the pigments found in the cells of red algae.

2. What is the Structural organization of red algae?

3. What thallus forms are found in these algae?

4. Name the modes of reproduction in red algae.

5. Where are red algae distributed?

6. What is the practical significance of red algae?

7. Name representative genera of red algae.

6.1.3. Division Diatoms (Bacillariophyta)

Diatoms are unicellular, colonial, or filamentous microscopic organisms with a coccoid, or more rarely palmelloid, structure, colored light yellow or brown. Their coloration is due to a set of pigments dominated by lutein, carotene, xanthophyll, and the specific pigments diatomite and diatoxanthin, which mask chlorophylls a and c. A characteristic feature is the presence of a silica frustule surrounding the cell, consisting of two halves fitted together like a box and its lid. The larger outer part is the epitheca, whose edges overlap the smaller inner part, the hypotheca (as seen in Pinnularia). Each half, in turn, consists of a valve with a species-specific structure and a narrower, structureless girdle band. The walls of the frustule are perforated with pores that facilitate Metabolic exchange between the protoplast and the surrounding environment. In motile forms, the valve side features a raphe (slit), along with nodes; cell movement is driven by cytoplasmic streaming and the secretion of mucus through the raphe and the vertical channels running through the nodes.

The cell of a diatom consists of a protoplast enclosed by a cytoplasmic membrane that tightly adheres to the silica frustule (a cellulose cell wall is absent). It contains cytoplasm and a nucleus, while the greater part of the cell volume is occupied by vacuoles filled with cell sap. Chloroplasts are small and granular, lacking pyrenoids, or massive and plate-like with one or several pyrenoids. Reserve nutrients include oil and volutin, and more rarely leucosin, while starch is absent. Most representatives exhibit a photoautotrophic type of Nutrition, though mixotrophs and heterotrophs also occur. Silicon is essential for their nutrition and vital activity, as its absence leads to The formation of malformed cells.

This group of algae is characterized by both Selection/8.html">Asexual and sexual reproduction. Asexual reproduction occurs through vegetative cell division into two halves (the daughter cell receives only one half of the frustule, while the other half—the hypotheca—is synthesized anew) and via specialized cells such as motile spores (specifically zoospores). Sexual reproduction occurs via conjugation and gametogamy (isogamy, heterogamy, and oogamy). Vegetative individuals are diploid, and only the gametes are haploid.

Diatoms comprise approximately 5,000 species, of which over 700 species (about 1,000 infraspecific taxa) have been identified in Ukraine. They are widespread in saline and freshwater bodies, on damp soil, rocks, tree bark, and in bottom silt. The greatest diversity of diatoms is observed in oceanic plankton and freshwater benthos, though they are also prominent components of periphyton on various submerged objects.

The division is divided into two classes: Centrales (centric) and Pennales (pennate). Cells of pennate diatoms possess axial Symmetry and are common in both fresh and saline waters. Examples include genera such as Tabellaria, Navicula, and Pinnularia. Centric diatoms comprise predominantly marine species whose cells exhibit radial symmetry. These include genera such as Melosira and Chaetoceros.

Diatoms are a relatively young and isolated group of algae with no direct phylogenetic links to other divisions.

In aquatic biocenoses, they serve as food for hydrobionts. In heavily polluted waters, they contribute to water purification to some extent; however, when proliferating in massive numbers, they clog water intake systems, and their frustules form deposits on water pipe walls as well as entering The Human Body via drinking water. Dead diatoms form sedimentary deposits known as diatomite, which is utilized in various industrial sectors.

Self-Check Questions

1. What are the Structural Features of a diatom cell?

2. What types of pigments do chloroplasts contain?

3. How do diatoms reproduce?

4. What type of sexual process do they exhibit?

5. Where are diatoms distributed?

6. What is The Role of diatoms in nature?

7. Name representatives of pennate algae.

8. Name representatives of centric algae.

6.1.4. Division Brown Algae (Phaeophyta)

Brown algae are eukaryotic, multicellular, predominantly macroscopic (up to 60 m) marine benthic plants with a yellowish-brown coloration. The thallus form can be filamentous, platelike, shrubby, crustose, etc. The thalli of some species possess air bladders, or pneumatocysts, which keep the thallus branches in a vertical position. All brown algae attach to the bottom of a water body or to other aquatic plants using rhizoids or basal holdfasts.

In some brown algae, cellular Differentiation of the thallus is observed according to Functions: There is a cortical layer containing chloroplasts that perform photosynthesis, and a medullar layer consisting of colorless storage cells. The cells of brown algae have a two-layered wall: the outer layer is pectic, and the inner layer is cellulosic. They possess a single nucleus, and chloroplasts shaped like ribbons, disks, or grains with very small pyrenoids. Their composition includes pigments such as chlorophylls a and c, carotenes, and xanthophylls, among which the brown pigment fucoxanthin predominates. In addition to standard organelles, the cells of brown algae contain small vacuoles called physodes, which store Tannins. The reserve nutrient is the polysaccharide laminarin, the six-carbon sugar alcohol mannitol with a sweet taste, and oil.

Brown algae reproduce vegetatively by fragmentation of the thallus or through specialized buds. Asexual reproduction is carried out by zoospores or non-motile spores—tetraspores or monospores. The sexual process is mostly oogamous. In most algae, Various Forms of alternation of the sporophyte and gametophyte occur. The life cycle of most brown algae proceeds through the following stages:

1. On the diploid sporophyte, haploid zoospores or spores are formed within zoosporangia or sporangia.

2. Gametophytes grow from zoospores or spores, upon which gametes—eggs and spermatozoa—are formed. Gametophytes can be either unisexual (female or male) or bisexual.

3. Fertilization takes place on the gametophyte, and the asexual generation—the sporophyte—develops from the diploid zygote.

The dominant generation in the reproduction cycle can be either the sporophyte or the gametophyte in heteromorphic algae, or the gametophyte and sporophyte may be indistinguishable from one another, as in isomorphic algae. However, there are some species of algae that lack alternation of generations and are represented exclusively by gametophytes (for example, Fucus and Sargassum).

Almost all brown algae are part of the benthos of seas and oceans, occasionally forming underwater "forests." A significant number of representatives have a perennial thallus and exhibit clearly defined seasonal vegetation patterns in temperate latitudes.

There are about 1,500 species of brown algae, divided into two classes: Phaeosporeae and Cyclosporeae.

Representatives of the class Phaeosporeae are characterized by independently developed sporophytes and gametophytes. The most common genera of this class include Ectocarpus, Sphacelaria, Cladostephus, Dictyota, Macrocystis, and Laminaria (kelp). Cyclosporeae include algae that lack alternation of generations, undergoing only nuclear phase changes, with asexual reproduction entirely absent. A typical representative is the genus Fucus.

Brown algae are an important source of organic matter produced by the World Ocean. Through Processing, they yield alginates, mannitol, iodine, bromine, microelements, and fertilizers. Alginates are used to stabilize solutions and Dyes, improve the quality of food products (marmalade, marshmallows), and find application in many industries such as food, chemical, medical, paint and varnish, paper, and explosives manufacturing. Brown algae are consumed as food; they are capable of binding and removing heavy metal salts and radioactive substances from the body.