Brown algae are a numerical group of plants that live mainly in marine waters. To date, only eight species are known that, during evolution, have moved to the freshwater environment.
Division Brown algae: body structure
All representatives of this department have multicellular bodies - colonial and unicellular forms of existence have not been identified. As for the sizes, they can be very different - thalli can be both microscopic and reach several meters in length. Annual marine plants are known , but there are those that live up to 18 years.
If we talk about the shape and structure of thalli, then diversity also reigns here. The body of an algae may consist of threads, plates, sacs, crusts or small bushes. The plant is attached to the substrate either with the sole or with the rhizoid system.
The integument of the body is represented by a cell wall, which, as a rule, consists of two layers (there are also three-layer representatives). The outer, coating layer consists mainly of pectin substances, and also contains sulfated polysaccharides. In the inner layer contains the bulk of cellulose fibers.
Borax algae: cell structure
An important systematic characteristic of the cell is the presence of plastids. In representatives of this group of plants, each cell contains a huge number of small, well-developed chloroplasts. Plastids have four membranes. As a rule, the outer membrane of the chloroplast passes into the membrane of the nucleus or endoplasmic reticulum. As for chlorophyll, here it is represented by forms A, C1 and C2.
In addition, algae plastids contain fucoxanthin, violaxanthin, zeaxanthin and beta-carotene, which is also an important characteristic for plant taxonomy.
The cell nucleus is only one, although several multinucleated species are known. The main reserve product is chrysolaminarin, which is deposited in specialized vacuoles or in the form of cytoplasmic granules.
Brown algae and reproduction
Representatives of this department can reproduce vegetatively, sexually and asexually. In most species, vegetative propagation is carried out by the separation of thallus. But, for example, the ficus on the sole of the body has a group of specialized cells, which, if necessary, can turn into a new thalam.
As for the asexual process, it is most often carried out using zoospores. Only some species reproduce using immovable mono- or tetraspores. By the way, zoospores and gametes are the only flagellate forms of brown algae.
As for the sexual process, it can be:
- Isogamous (sperm and egg cells are the same size).
- Heterogamous (male and female gametes have different gametes).
- Oogamous (male gametes are small and mobile, while female oogonies remain motionless and are large in size).
Around the 80s of the 20th century, certain chemicals were released by the body of algae during sexual development. This is nothing but pheromones, the active study of which continues to this day.
Brown algae and the most famous representatives
One of the most famous species is sugar kelp, or sea kale. The plant has a large dissected thaw, the length of which can be from 1 to 14 meters. A huge amount of laminarine accumulates in the thallus. In addition, seaweed is considered a valuable source of iodine. In some countries, this plant is actively cultivated and used for the preparation of salads and other dishes. From thaloma, drugs are also used that are used to treat thyroid diseases.
The genus Sargassum is also widely known, since it was because of the persistent, long thalli of these plants that the waters of the Sargasso Sea were too dangerous for swimming at one time.