To date, green algae is considered the most extensive group, which has about 20 thousand species. This includes both unicellular organisms and colonial forms, as well as plants with large multicellular thallus. There are representatives that live in water (marine and fresh), as well as organisms adapted to survive on land in high humidity.
Division Green algae: a brief description
The main distinguishing feature of representatives of this group is their color - all species are characterized by green or green-yellow color. This is due to the main pigment of the cells - chlorophyll.
As already mentioned, the department brings together completely different representatives. There are unicellular and colonial forms, as well as multicellular organisms with a large, differentiated thallus. Some unicellular representatives move with the help of flagella, multicellular, as a rule, attach to the bottom or live in the water column.
Although organisms with bare cells are found, most representatives have a cell wall. The main structural component of the cell membrane is cellulose, which, incidentally, is considered an important systematic characteristic.
The number, size and shape of chloroplasts in a cell can be different depending on the type of plant. The main pigment is chlorophyll, in particular, a and b forms. As for carotenoids, plastids contain mainly beta-carotene and lutein, as well as small amounts of neosanthin, zeaxanthin and violaxanthin. Interestingly, the cells of some organisms have an intense yellow or even orange color - this is due to the accumulation of carotenes outside the chloroplast.
Some unicellular green algae have a specific structure - the eye, which responds to the light of the blue and green spectrum.
The main storage product is starch, the granules of which are contained mainly in plastids. Only some representatives of the order reserve substances are deposited in the cytoplasm.
Division Green algae: reproduction methods
In fact, almost all possible methods of reproduction are characteristic of representatives of this order. Vegetative propagation can occur by cell division (unicellular representatives without a cell membrane), fragmentation of thallus (this method is characteristic of multicellular and colonial forms). In some species, specific nodules form.
Asexual reproduction is represented by the following forms:
- zoospores - cells with flagella, capable of active movement;
- aplanospores - such spores do not have a flagellar apparatus, but contractile vacuoles are well developed ; cells are not capable of active movement;
- autospores - this type of dispute is primarily associated with adaptation to the external environment. In this form, the body can wait out for dry conditions and other adverse conditions.
Sexual reproduction can also be diverse - this is oogamy, and heterogamy, and hologamia, as well as isogamy and conjugation.
Order Green algae: characteristics of some representatives
This group includes many famous representatives of the plant world. For example, unicellular algae spirogyra and chlorella are also included in the order.
Chlamydomonas is a fairly well-known genus of green algae, which is of great practical importance. This group includes unicellular organisms with a red eye and a large chromatophore that contains pigments. It is chlamydomonas that causes the "bloom" of ponds, puddles and aquariums. In the presence of sunlight, organic matter is produced by photosynthesis. But this organism can absorb substances from the external environment. Therefore, chlamydomonas are often used to purify water.