In almost every body of water on the entire surface of the globe, you can find such a unique organism that resembles a plant like algae in its composition.
What is algae
Algae is a special group of unicellular or multicellular organisms that live mainly in the aquatic environment. This is a fairly large group of lower plants. Their habitat is so great that it can be found everywhere, both in the oceans and in the seas, lakes, rivers, other bodies of water, on moist soil and even tree bark.
Algae are both unicellular simple organisms and multicellular colonial. Shells of multicellular algae are composed of cellulose, which are attached to each other from the end.
They have no root system. Instead, algae are attached to the surface using special processes - rhizoids.
Algae is the main source of organic matter throughout the world. Almost all food chains begin with them. Moreover, they serve as a source of nutrition for many inhabitants of the aquatic environment.
Also, algae are suitable for the manufacture of fertilizers, animal feed, and, of course, can be eaten by humans.
The origin of algae
There is still no consensus on the origin of algae and their exact age due to the fact that this species of organisms is represented by a great variety. Moreover, not a single example of fossil samples has been preserved, and it is impossible to establish what stages of evolution this species of organisms has passed.
Biologists around the world are convinced that not a single plant in the world can be compared with the healing power of algae, since there is a theory about the origin of life in the sea, which means that they contain a unique biological composition.
However, it is believed that green and yellow algae appeared on Earth about 3 billion years ago. Initially, they arose in the form of unicellular and only then colonial. And it was the appearance of this species of organisms that led to the formation of an oxygen atmosphere and the ozone layer on Earth, which subsequently led to the birth of life. About a billion years ago, multicellular complex algae appeared.
Types of Algae
More than 30 thousand species of algae are known to modern biology. However, all of them can be combined into special groups:
- Euglena or unicellular. The smallest algae.
- Pyrophytes, the membrane of which consists of cellulose.
- Diatoms. They consist of cells with the so-called double-shell.
- Golden seaweed. Here it is possible to meet both unicellular and multicellular, but they are all freshwater golden or brown-yellow.
- Yellow green. They are often combined with the previous group.
- Green. They can be detected with the naked eye, for example, on the bark of trees.
- Harov algae. These are already multicellular algae, which are often combined with green algae. The height of the stem ranges from 2.5 cm to 10 cm.
- Red algae. So called because of the presence in their composition of a special element - phytoerythrin, which stains them in red. These algae live mainly at great depths in the seas.
- Brown algae. The most perfect look. They live at great depths and are able to create thickets, such as, for example, in the Sargasso Sea. Rhizoids are tightly attached to the surface, so it is almost impossible to tear them off.
Algae distribution in nature
According to the mode of existence, algae are divided into two large groups: these are aquatic and those living on land - outside the water.
In turn, water can be divided into several categories:
- Planktonic. They are suspended in water. At the same time, they are absolutely adapted to such a way of life.
- Bentic. They live at the bottom of reservoirs.
- Periphyton. They live on underwater rocks, overgrown with deep objects.
- Neustones. This species of algae floats in a semi-submerged state. One part is located above the surface of the water, the other must be immersed in water.
Land-living algae are divided into two subgroups:
- Aerofiton. Algae that grows on land objects, fallen objects, stumps.
- Algae growing on the surface of the soil.
In addition to the above species, there are those who live in salt bodies of water, on snow or ice, and also live in a limestone substrate.
How do algae breed?
Let's deal with the main question of the article. In nature, algae breed in three ways. Each of them has its own characteristics.
- Algae reproduce vegetatively. This is such a method of reproduction in which an adult individual is divided in two or, for example, the kidney is separated from the mother's body. Then, the newly formed cells are divided into two and four cells, from which adult algae subsequently grows.
- Asexual reproduction. This is the kind in which the protoplast divides inside the algal cell, with its subsequent exit to the outside and separation from the mother cell.
- Algae reproduce by spores, which are formed in special organs - sporangia.
- Sexual reproduction. It consists in the fusion of two cells, gametes, as a result of which a zygote appears, which subsequently grows into a new individual or gives zoospores. Moreover, the zygotes of various algae after their formation behave differently. In some, they fall into a period of rest, which can last up to several months. And others immediately grow into a new layer or thallus.
It is noteworthy that each species of algae multiplies differently. This question is being studied by the school curriculum. And often the students hear a question from the teacher: "How do algae breed? Describe the propagation of algae." It is easy to answer it if you study the material in detail.
When algae reproduces asexually. Types of Asexual Reproduction
This is the easiest option. Asexually or vegetatively, algae reproduce mainly only in conditions favorable to them. This means when the water in the pond has a certain temperature and conditions maximize asexual reproduction.
If sharp changes in temperature, pollution or overfilling by inhabitants occur in a reservoir or environment, in this case, algae begins sexual reproduction.
Asexual reproduction can be divided into several types:
- Algae reproduce vegetatively - there is a separation of vegetative cells.
- Sporulation. Or in another way, algae reproduce using special cells. These cells are called spores.
When algae reproduces asexually, there is only one parent from which all existing genomes are inherited. But in the case of mutations, genetic material can change significantly.
Often, one organism can reproduce both asexually and vegetatively.
Vegetative propagation of algae
Vegetative propagation is typical in most cases for brown algae.
With this method of reproduction, parts of the algae (thalli) are separated from the existing ones without any changes, and the formed new cells inherit a part of the maternal membrane.
Vegetatively, both unicellular and multicellular algae can reproduce. Moreover, in unicellular cells, the cell is divided into two, and in multicellular separation occurs by layers or whole thalli, colonies. In filamentous algae, the vegetative propagation method occurs by separating the filaments into their individual fragments.
At the same time, not all algae from the detachment of colonial representatives can reproduce vegetatively, just as in unicellular organisms, along with the vegetative method of reproduction, the genital tract can also exist.
Brown algae, as mentioned above, reproduce in this way, using special brood branches. In a similar way, all types of Sargasso breed in the Sargasso Sea.
Spore propagation
In addition to vegetative propagation, algae reproduce using spores. This is a specific subspecies of asexual reproduction.
Spores are formed in special organs, the so-called sporangia or zoosporangia. When the spore is dispersed, it begins to germinate and then a new adult independent individual forms.
Movable spores with flagella capable of movement are called zoospores.
The option of asexual reproduction by spores can be considered on the example of such algae as ulotrix. In conditions favorable for her, her fragments that contain spores are separated from the existing mother thread. They float in a free state, then, having attached to an underwater object, begin to actively divide and form a new thread of algae. It should be noted that this species of algae can simultaneously reproduce both asexually and sexually.
It has been noted that spore formation can be stimulated in some types of filamentous algae; for this, an increase in carbon dioxide should occur in the habitat.
The asexual reproduction function in this case is performed by individuals called sporophytes, that is, spores forming.
Sexual reproduction
In addition to the above methods, algae reproduce sexually. It is characterized, first of all, by fertilization, that is, by the fusion of two cells - gametes. After this, a zygote is formed, which subsequently becomes the ancestor of a new organism.
Algae has several methods of sexual reproduction:
- Isogamy - implies a fusion of two gametes of the same size and structure.
- Heterogamy. So called the merger of two gametes, in which one is larger than the other. Moreover, the one that is larger in size, as a rule, is female.
- Oogamy. With this method of reproduction, a sedentary female cell merges with a mobile male gamete.
- Conjugation. By this concept is meant a type of reproduction in which there is a connection of two vegetative cells devoid of flagella.
In primitive algae, the same individual is capable of both sexual and asexual reproduction. In the most developed, the function is performed by individuals called gametophytes, that is, gamete-forming.
Algae propagation examples
An example of vegetative propagation of algae is Fucus. On its main thallus, additional thalli similar in structure are formed, which subsequently give rise to a new organism.
Asexual reproduction, that is, division into two cells, can be observed in euglena.
Chlamydomonas is an algae, the reproduction of which occurs both sexually and asexually, using spores (zoospores) with flagella.
Another example of sexual reproduction is brown algae, such as kelp. This species has three methods of sexual reproduction, such as isogamy, heterogamy, and oogamy.
Chlorella is a microscopic green alga. Propagated exclusively asexually by means of spores.
Red algae (scarlet) breed in two ways, one of which is sexual. A distinctive feature of it is the formation of male gametes without flagella. At the same time, female gametes remain on the algae, and male ones are transferred to them by the flow.
