We all studied the general characteristics of algae in the 7th grade biology course. In our article, we will recall the features of the habitat, structure and classification of these plants.
General characteristics of algae
This group of plants is the most ancient. Systematics number about 30 thousand modern species of these organisms. All of them are lower plants. This means that their body is not differentiated into tissues and organs. It is called the thallus, or thallus. Attachment to the substrate is carried out with the help of rhizoids. These are filamentous structures that consist of individual cells. They do not form tissues, which is how they differ from roots.
The presence of a cellulose membrane of cell walls and chloroplasts of various shapes also belong to the general characteristics of algae. For example, in chlamydomonas, it looks like a horseshoe, and in spirogyra, it looks like a spirally twisted thread. There are other pigments in algae cells. They can be red, brown, golden or yellow-green in color. But this does not mean that chlorophyll is absent in the cells of such algae. He's just well disguised.
Distribution
Aquatic habitat is another aspect of the general characteristic of algae. They can be attached to the substrate at the bottom or move freely in the thickness. The depth of algae spread is determined by the degree of penetration of sunlight.
These organisms are also found on the surface of the underwater parts of rocks, other plants, hydraulic structures. The inhabitants of the land are also widely known. They settle on the bark of trees and in the upper layers of the soil.
Green Algae
This department is the most numerous. Among its representatives there are unicellular species. These are chlamydomonas and chlorella. The first lives in fresh water or on wet land. Chlamydomonas cells are pear-shaped and have two flagella. They serve as organelles for locomotion.
Permanent cellular structures of this representative are two types of vacuoles. The first are called contractions. They bring out excess water with s alts dissolved in it. Thus, the regulation of osmotic pressure occurs. The second type of vacuoles are reservoirs with cell sap - a supply of water and nutrients. The cytoplasm also contains a light-sensitive eye, a horseshoe-shaped chloroplast and a pyrenoid - a place of accumulation of organic substances in the cell.
Green algae, the general characteristics of which we are considering, are represented by both multicellular species and colonies. The latter consist of many cells surrounded by a common membrane. Thema typical representative is a Volvox colony.
Methods of reproduction
The general characteristics of algae (Grade 7 studies this topic in the botany course) includes several types of their reproduction. Consider them on the example of chlamydomonas. The main way is asexual. In this case, the cell loses flagella, and the cytoplasm and nucleus are divided into a multiple number of parts, which are called spores. They leave the shell of the mother cell into the water. Within a day, they can divide on their own, giving rise to new algae.
Sexual reproduction of algae is both a way of reproduction and an adaptation to experiencing adverse environmental conditions. This may be a lack of moisture or a sharp drop in water temperature. In this case, the formation of germ cells occurs. They also fall into the water and merge in pairs. This creates a new cell called a zygote. It is covered with a strong shell that reliably protects the contents of the cell from moisture loss and freezing. When environmental conditions become favorable again, zygote cleavage occurs with the formation of motile spores.
Multicellular algae reproduce vegetatively. The essence of this method is the splitting of a multicellular part from the whole organism. For example, the green alga ulotrix reproduces by scraps of threads.
Brown and red algae
Widespread in nature and other departments of algae. Sargassum, cystoseira,kelp, in addition to chlorophyll, contain brown pigments in cells. These are predominantly marine plants. Their sizes vary widely: from a few centimeters to tens of meters. Thus, the macrocystis thallus grows up to 60 m.
Now consider the general characteristics of the department of algae, which have a red, yellow or greenish-blue color. They are also called scarlet. All of them are exclusively multicellular species that prefer s alty water bodies. Red pigments not only determine the color of the purple thallus. They have a unique ability to capture light. This allows them to live at considerable depths - up to 250 meters.
Value in nature and economic activity
The value of algae is largely determined by their habitat. These plants oxygenate the water and the air above it, serve as food for many animals. Diatom shells are the basis of sedimentary rocks of diatomite and limestone. Algae living on the soil increase its fertility. Organic sludge is widely used as a fertilizer. It is formed at the bottom of reservoirs as a result of the settling of dead thalli.
For humans, algae are a source of important chemical elements. Agar-agar is obtained from filophora, on the basis of which marmalade and marshmallow are made. In the chemical industry, algae are used to produce dyes, adhesives, organic acids, alcohols, and drugs.
Some species have a uniqueability to absorb harmful substances from water. Therefore, algae are used in the biological method of cleaning polluted water bodies.
So, the general characteristics of algae include the following characteristics:
- Habitats are fresh and s alt water, soil, wet land.
- Absence of tissues and organs.
- The body is represented by a thallus (thallus), the attachment function is performed by filamentous structures - rhizoids.
- Among algae, there are unicellular, multicellular, and also colonial forms.
