We all studied the general characteristics of algae in a class 7 biology course. In our article we recall the features of the habitat, structure and classification of these plants.
General characteristics of algae
This group of plants is the oldest. 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 using rhizoids. These are threadlike structures that are made up of individual cells. They do not form tissue, which is why they differ from the roots.
The general characteristic of algae also includes the presence of a cellulose membrane of cell walls and chloroplasts of various shapes. For example, in chlamydomonas, it looks like a horseshoe, and in spirogyra it looks like a spirally twisted thread. There are other pigments in the cells of algae. They can have a red, brown, golden or yellow-green color. But this does not mean that chlorophyll is absent in the cells of such algae. He is just well disguised.
Spread
Aquatic habitat is another aspect of the general characteristics of algae. They can attach to the substrate at the bottom or move freely in the thickness. The depth of distribution of algae 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, and hydraulic structures. The inhabitants of sushi 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 in humid land. The chlamydomonas cell has a pear-shaped and two flagella. They serve as organelles of movement.
The permanent cellular structures of this representative are two types of vacuoles. The first are called contractile. They bring out an excess of water with salts dissolved in it. Thus, the regulation of osmotic pressure occurs. The second type of vacuole is a reservoir with cellular juice - a supply of water and nutrients. The cytoplasm also contains a photosensitive 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. Their typical representative is the volvox colony.
Breeding methods
The general characteristics of algae (Grade 7 studies this topic in the course of botany) includes several types of their reproduction. Consider them with the example of chlamydomonas. The main way is asexual. In this case, the cell loses its flagella, and the cytoplasm and nucleus are divided into a multiple of the parts, which are called spores. They exit the maternal cell membrane into the water. In a day they can independently share, giving rise to new algae.
Sexual reproduction of algae is both a method 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 forms a new cell called a zygote. It is covered with a durable shell that reliably protects the contents of the cell from moisture loss and freezing. When environmental conditions again become favorable, zygote is crushed to form motile spores.
Multicellular algae reproduce vegetatively. The essence of this method is to split the multicellular part from the whole organism. For example, the green algae Ulotrix propagates by scraps of thread.
Brown and red algae
Widespread in nature and other departments of algae. Sargassum, cystoseira, kelp, in addition to chlorophyll, contain brown pigments in the cells. These are mainly marine plants. Their sizes vary significantly: from a few centimeters to tens of meters. So, the thallus of macrocystis grows to 60 m.
Now consider the general characteristics of the department of algae having a red, yellow or greenish-blue color. They are also called scarlet. All of them are exclusively multicellular species that prefer salty water bodies. Red pigments not only determine the color of the thallus of scarlet. They have a unique ability to capture light. This allows them to dwell at considerable depths - up to 250 meters.
Significance in nature and economic activity
The importance of algae in many respects determines their habitat. These plants saturate oxygen with water and air above it, serve as food for many animals. The shells of diatoms are the basis of sedimentary rocks of diatomite and limestone. Algae living on the soil increase its fertility. Organic fertilizer is widely used as fertilizer. It is formed at the bottom of reservoirs as a result of subsidence of dead thalli.
For humans, algae are a source of important chemical elements. Agar-agar substance is obtained from phylophores, on the basis of which marmalade and pastille are made. In the chemical industry, algae is used to produce dyes, adhesives, organic acids, alcohols, and drugs.
Some species have a unique ability to absorb harmful substances from water. Therefore, algae is used in the biological method of cleaning contaminated water bodies.
So, the general characteristics of algae include the following characteristics:
- The habitat is fresh and salty water, soil, wet land.
- Lack of tissues and organs.
- The body is represented by a thallus (thallus), the function of attachment is performed by filamentary structures - rhizoids.
- Among algae there are single, multicellular, as well as colonial forms.