Are algae green plants?

Algae and other green plants in the water body that can fix sunlight energy are producers in the ecosystem components.

Introduction to algae plants

(1) Basic characteristics of algae

The concept of algae is different in ancient and modern times. Ancient Chinese books say: "Xiao is an aquatic plant, or an algae." It can be seen that the algae mentioned in ancient my country is a general term for aquatic plants. In modern botany in my country, the word "algae" is still used throughout the names of some higher aquatic plants (such as hornwort, black algae, Trichophyton algae, Myriophyllum algae, etc.), which may also be derived from this. In contrast, people often refer to some small, slimy green plants in water or on wet floors and walls as moss. In fact, these are not what we call moss now, but are mainly algae. According to modern understanding of algae, algae are not a natural taxonomic group, but they have the following unique characteristics:

1. Plants generally do not have true differentiation of roots, stems, and leaves. The shapes and structures of algae plants are very inconsistent, and their sizes are also very different. For example, the well-known Chlorella is spherical in shape and is composed of single cells with a diameter of only a few microns; Macrocystis, which grows in the ocean, has a complex structure and can reach more than 200 meters in length. Although the structures of individual algae plants vary greatly in complexity and size, most of them have no real differentiation of roots, stems, and leaves. Some large algae, such as marine kelp (Laminaria japonica) and freshwater Chara (Chara), although they can be divided into three parts: roots, stems and leaves, they do not have a vascular system in their bodies, so they are not True roots, stems and leaves, therefore, the plant body of algae is mostly called thallus or protophyte.

2． In addition to the same photosynthetic pigments as those of green higher plants, the cells of general algae that can carry out light energy inorganic nutrition also have very special pigments and most of them are not green, so their plastids are specifically called chromoplasts. or chromophore. The nutritional methods of algae are also diverse. For example, some lower single-cell algae can also perform organic phototrophic nutrition, inorganic chemotrophic nutrition, or organic chemotrophic nutrition under certain conditions. But for the vast majority of algae, like higher plants, they can use carbon dioxide and water to synthesize organic matter under light conditions for inorganic photonutrient nutrition.

3. Reproductive organs are mostly composed of single cells. The sporangia that produce spores or the spermatophores and ovipositors that produce gametes in higher plants are generally composed of multiple cells. For example, bryophytes and ferns have a wall of sterile cells outside the egg-producing organ and the spermatozoa that produce sperm. But among algae, except for a few species, their reproductive organs are composed of single cells.

4. The zygote does not develop into an embryo within the mother's body. The zygote (fertilized egg) formed after the fusion of the female and male gametes of higher plants develops into a multi-cell embryo within the mother's body before it separates from the mother's body and continues to develop into a new individual. However, the zygote of algae does not develop into an embryo within the mother's body. Instead, it undergoes cell division and grows into a new individual after it is separated from the mother's body. In zoological terms, higher plants are viviparous, while algae are oviparous.

In short, algae are a large group of plants in the plant kingdom that have no real differentiation of roots, stems, and leaves, live autotrophically by light, and have reproductive organs composed of single cells and no embryonic development.

(2) Classification of Algae

There are many types of algae, and about 30,000 species are currently known. Early botanists mostly classified algae and fungi into one phylum, Phycophyta. With the deepening of people's understanding of algae, especially since the publication of the parallel evolution theory of A. Pascher (1931), it is believed that algae are not a natural taxonomic group, and based on the composition and content of pigments in their vegetative cells and its assimilation products, flagella of motile cells and reproductive methods are divided into several independent phyla. There are also very different opinions on the division of algae into phyla. Chinese phycologists mostly advocate dividing algae into 12 phyla.

Since this book uses a five-kingdom system, in addition to the inclusion of Cyanobacteria in the Prokaryotes kingdom, the characteristics of the nine main phyla are briefly introduced as follows:

1. Chrysophyta is mostly found in fresh water, especially in soft water bodies with low water temperatures. Plants are mostly single cells or groups, and a few are multicellular filaments. Most motile cells have 1-2 flagella. Single-cell or group types usually have 1-2 chromatophores in the cells, with carotene and lutein predominating. The only green pigment is chlorophyll a, so they are mostly golden yellow or golden brown. The main assimilation product is chrysophyllan, also known as chrysophyllose and chrysophyllose. Because it has similar chemical properties to kelpose, it is also called chrysophyllose. In addition, it also contains lipids. The main modes of reproduction are vegetative reproduction and spore reproduction, and sexual reproduction is extremely rare. Common ones include Synospermum and Bellella (see picture).

2． Xanthophyta has very few species of seafood, mainly distributed in fresh water bodies, or growing on wet floors, tree trunks and walls. More in spring when water temperature is lower. Plants are single cells, colonies or multicellular bodies. The pigments and assimilation products contained are basically the same as those of Chrysophyta, but in addition to chlorophyll a, they also contain chlorophyll e, which is mostly yellow-green. The motile cells have two flagella of different lengths and structures, so this group is also called unequal dinoflagellates (Heterocontae). Reproduction methods include vegetative reproduction, spore reproduction and sexual reproduction, but there are also different reproduction methods depending on the species. The most common ones seen with the naked eye are Tribonema and Vauchcria, which have filamentous plants (see picture).

3. Bacillariophyta is widely distributed in seawater and freshwater, and mostly lives in plankton. Plants are composed of single cells or interconnected cells. The cell wall is composed of two petals with patterns on it. Its composition contains pectin and silica, but does not contain cellulose (see picture).

There are one to several golden brown chromatophores in the cells. The chromatophores contain chlorophyll a, c and a large amount of carotene and lutein, and the photosynthetic products are mainly lipids. Diatoms can reproduce vegetatively through cell division, but after several generations they can also form complex megaspores through the conjugation or self-matching of gametes for sexual reproduction (see picture).

4. Pyrrophyta are prolific in the ocean and live plankton. Sometimes they reproduce in large numbers near the coastline, forming red tides. Some species often appear in large numbers in ponds and lakes. Most plants are single-celled, and a few are colonies or filaments. Except for a few species that are bare and wallless, most have cell walls composed of cellulose. The cell wall of a dinoflagellate is called a shell and is made up of many patterned nails connected together. The shell is divided into two parts, the upper shell and the lower shell. There is a transverse groove between these two parts, and there is a longitudinal groove perpendicular to the transverse groove. Where the two grooves meet, two flagella, horizontal and straight, of unequal length, are produced. There are one or more chromatophores, which are yellow-green or brown. In addition to chlorophyll a and c, they also contain a large amount of carotene and lutein. The photosynthetic products of seafood species are mostly lipids, while those of freshwater species are mostly starch. The main mode of reproduction is cell division, or the production of asexual spores in the mother cell for sporulation. Sexual reproduction is only found in a few genera and species. Common Ceralium (see picture) and Peridinium (see picture).

5. Phaeophyta (Phaeophyta) are mostly marine products and live a fixed life. Among more than 1,500 species of brown algae, only about 10 species are produced in fresh water, two of which are found in the Jialing River in Sichuan, my country. Plants are composed of multiple cells and have complex structures. In addition to chlorophyll a and c, the chromatophores also contain a lot of carotene and lutein, so they are mostly brown. The assimilation products are not starch but laminarin and mannitol. The vegetative cells have no flagella, but the zoospores and male gametes have two lateral, unequal-length flagella. There are many ways of reproduction, including sexual reproduction. In the life history, there is often an obvious alternation of generations.

Common and edible species include kelp (Laminaria japonica) and wakame (Undaria pinnalifida) (see picture).

6. Rhodophyta Except for a few genera and species, most of them are produced in seawater and live a sessile life. Except for a few genera and species, plants are multicellular, usually filamentous, sheet-like or dendritic. The chromatophores are mostly red or purple, and in addition to chlorophyll, carotene and lutein, they also contain a large amount of phycoerythrin and phycocyanin. The assimilation product is red alginate which is similar to starch. Red algae do not have flagellated motile cells in their life cycle. Sexual reproduction is all egg-type reproduction. The female reproductive organs are fruit cells similar to egg sacs. The fruit cells have trichomes called fertilization filaments. After fertilization, a special spore is produced called a fruit spore. Common ones include Porphyra and Gelidium (see picture).

7. Euglenophyta Euglenophyta, also known as Euglena or Euglena algae, mostly grows in fresh water rich in animal organic matter and lives a planktonic life. When breeding in large numbers, the water often turns green, yellowish brown or red. Except for the genus Colacium, they are all single-cell species with flagella at the top, capable of movement and without a cell wall. In Euglena, except for a few species that are colorless and live heterotrophically, they mostly contain photosynthetic pigments similar to those of green algae, but the storage materials are mainly paramylon and a small amount of lipids. The main mode of reproduction is cell division. Under adverse environmental conditions, thick-walled cysts can also be formed. When environmental conditions improve, the protoplasts break out of the wall to form new individuals. Euglena (see picture) A common genus in the basic phylum.

8． Chlorophyta (Chlorophyta) mostly grows in fresh water, with fewer marine species, living planktonic, sessile or epiphytic life, and a few species are parasitic or paraphytic. Plants can be single cells or groups, or they can be multicellular filaments or sheets. The shape and number of chromatophores often vary with species, and the composition, content and assimilation products of photosynthetic pigments are similar to those of higher plants. Motor cells mostly have 2, 4 or more equal-length, terminal flagella. There are various ways of reproduction, and some species have alternation of generations in their life history. Among green algae, such as single-cell Chlorella (see picture),

Scenedesmus (see picture), which is a colony,

Multicellular filamentous Spirogyra (see picture)

And Cladophora are common species in fresh water.

9. Charophyta are widely distributed in freshwater or brackish water and all live a sessile life. Plants are composed of multi-cells, and have differentiation similar to roots, stems, and leaves. Their appearance is very similar to horsetail and hornwort in higher plants. There is a lot of calcium outside the body, so it is also called stone grass. The composition and storage of photosynthetic pigments are the same as those of green algae, but the structure and life history of reproductive organs are special. Chara do not produce asexual spores during their life cycle, and all sexual reproduction is ovogenetic. The outside of the ovipositor is surrounded by 5 left-handed spiral cells, and the top also has a crown composed of 5 or 10 crown cells. The outside of the sperm storage organ is an outer wall made of 8 (rarely 4) shield cells, and the inside is composed of sperm cyst filaments composed of many sperm sacs and some sterile head cells. In fact, this sperm storage organ is an aggregate composed of many male reproductive organs and sterile cells, so it is also called the spermatheca ball, and its egg storage organ is also called the oocyst ball. Although the structure of the vegetative body and reproductive organs of charophytes is very complex, there is no alternation of generations in the life history. The plants are all haploid, and after the fertilized eggs germinate, they can develop into adults through the protonema stage. Common ones in my country include Chara, Nitella and Tolypella (see picture).

(3) Living habits of algae

Most algae are aquatic, including seaweeds that are produced in the ocean; and there are also freshwater algae that are produced in land and water.

Among aquatic algae, there are planktonic algae that have an enlarged body surface area (such as single cells, colonies, flat, horned or spiny, etc.), store substances with a smaller specific gravity in the body, or have flagella to adapt to planktonic life; Colloidal algae, with holdfasts or rhizoids at the base, are benthic algae that grow on the underwater substrate; there are also ice and snow algae that grow on glaciers and snow; and there are hot spring algae that live in hot springs with water temperatures as high as 80°C or above. There are also many algae whose algae are not completely submerged in water. Some of them are aerial algae with part or all of the algae directly exposed to the atmosphere; some are soil algae that grow on or below the soil surface. In terms of the relationship between algae and the growth of other organisms, there are epiphytic algae that live on the surface of animals and plants; there are also endophytic algae that grow inside animals or plants; and there are also those that feed and live with other organisms. ***Algae. In short, algae have diverse living habits and are highly adaptable to the environment. Algae are found almost everywhere.

(4) The significance of algae in human life

my country’s use of algae as food not only has a long history, but also is world-famous for its many types and methods of consumption. According to preliminary statistics, there are at least 50-60 species of large edible algae produced in my country. The edible algae often sold as commodities are mainly marine algae, such as Monostroma nilidum, Ulva lactula, and Laminaria japonica. , Undaria pinnatifida, Porphyra sp., Gelidium amansii, etc. Commercial edible freshwater algae include Nostoc commume and Nostoc commume var.flagelliforme. The "Dao" and "Jie" that are eaten by the Dai compatriots in the Jinghong area of ??Yunnan and exported to Myanmar and other countries are made from Spirogyra and Cladophora, which are freshwater algae. Since single-cell algae are rich in nutrients and have the characteristics of fast reproduction and high yield, large-scale cultivation of single-cell algae as concentrate feed for human consumption or livestock has long attracted people's attention, and some (such as pellets algae, Scenedesmus) have been promoted and utilized at home and abroad.

Algae are also closely related to medicine and agriculture. Some are directly used for medicinal purposes, such as kelp, wakame, and Sargassum fusiforme in brown algae, which all have the effect of preventing and treating goiter. Caloglos-sa leprieurii (Caloglos-sa leprieurii) and Digenea simplex in red algae can be used as special medicines to repel roundworms. Alginic acid extracted from brown algae, mannitol and agar extracted from red algae are also widely used in medicine. For example, alginate can be used as a raw material for making dental molds and hemostatic drugs; mannitol has the effect of eliminating cerebral edema and diuresis. In addition to being used as a laxative to treat constipation, agar can also be used as a base for making ointments, a coating for medicated powder, and a coagulant for bacterial culture media. Soil algae can not only accumulate organic matter, stimulate the activity of soil microorganisms, increase the oxygen content in the soil, prevent the loss of inorganic salts, and reduce soil erosion, some of them can also fix free nitrogen in the air, improving soil fertility. plays an important role. In addition, algae is the basis of the fish food chain. Natural food for fish generally comes directly or indirectly from phytoplankton. Therefore, in freshwater fish farming, algae are mostly fertilized to provide food for fish. However, when phytoplankton blooms and blooms occur, large numbers of fish die due to lack of oxygen in the water or the production of toxic substances.

Products made from algae, especially alginate, have been widely used in industrial production.

For example, in the food industry, agar gum can be used as a coagulant together with sugar to make soft candies, and together with starch to make glutinous rice paper for wrapping sugar. When making bread, adding agar gum can keep the bread soft for a long time, and it can be added to sherbet. It can be made into frozen juice; adding agar gum when canning fish and meat can maintain the original shape of fish and meat and prevent them from falling apart during transportation; in Japan, Europe and the United States, agar gum is also used as a clarifier for brewing wine, vinegar, and soy sauce. agent. In the construction industry, in addition to being used for painting walls, cement reinforcement, coating wood, metal products and machine tools, alginic acid can also be made into substitutes for grid boards and linoleum. In the textile industry, it can be used to modify fabrics, sizing silk, etc. For example, Xiangyun yarn produced in Guangdong, my country is made of seaweed gum as sizing material. Diatoms are also widely used in industry. For example, adding nitroglycerin can prevent explosions and can be used as a raw material for making refractory bricks, filters, and tooth powder.

With the increasing understanding of algae, the scope of utilization is also expanding. Judging from the current preliminary research results, it can be expected that algae can solve the current common problems of food shortage, energy crisis and environmental pollution. will play an important role in other issues.