In almost every body of water on the entire surface of the globe, you can find such a unique organism that resembles a plant in its composition, like an algae.
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 large that they can be found everywhere, both in the oceans and in the seas, lakes, rivers, other bodies of water, on wet soil and even tree bark.
Algae are both unicellular protozoa and multicellular colonial ones. 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 with the help of special processes - rhizoids.
Algae is the main source of organic matter on the whole Earth. Almost all food chains begin with them. Moreover, they serve as a source of food for many inhabitants of the aquatic environment.
Algae are also suitable for making fertilizers, animal feed, and, of course,can be consumed by humans.
Origin of algae
There is still no consensus on the origin of algae and their exact age due to the fact that this type of organism is represented by a wide variety. Moreover, not a single example of fossil specimens has survived and it is impossible to establish what stages of evolution this species of organisms went through.
Biologists around the world are convinced that no plant in the world can compare with the healing power of seaweed, as there is a theory about the origin of life in the sea, which means that they contain a unique biological composition.
However, there is an opinion 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 type of organisms that led to the formation of an oxygen atmosphere and an ozone layer on Earth, which subsequently led to the birth of life. About a billion years ago, multicellular complex algae appeared.
Algae species
Modern biology knows more than 30 thousand species of algae. However, all of them can be combined into special groups:
- Euglenaceae or unicellular. The smallest algae.
- Pyrophyte algae, the membrane of which consists of cellulose.
- Diatoms. They consist of cells with a so-called double shell.
- Golden algae. Here it is possible to meet both unicellular and multicellular, however, they are all freshwater golden or brown-yellow.
- Yellow-green. They are very oftenmerged with the previous group.
- Greens. They can be detected with the naked eye, for example, on the bark of trees.
- Charic algae. These are already multicellular algae, which are often combined with green ones. The height of the stem ranges from 2.5 cm to 10 cm.
- Red algae. They are so called because of the presence in their composition of a special element - phytoerythrin, which colors them 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. Their rhizoids are tightly attached to the surface, so it is almost impossible to tear them off.
Distribution of algae in nature
According to the way of existence, algae are divided into two large groups: they are aquatic and living on land - outside the water.
In turn, water can be divided into several categories:
- Planktonic. They are suspended in the water. At the same time, they are absolutely adapted to this lifestyle.
- Benthic. They live at the bottom of reservoirs.
- Periphytic. They live on underwater rocks, deep-sea objects are overgrown.
- Neuston. This species of algae floats in a semi-submerged state. One part is above the surface of the water, the other must be immersed in water.
Algae living on land are divided into two subgroups:
- Aerophyton. Algae that growground objects, fallen objects, stumps.
- Algae growing on the surface of the soil.
In addition to the above species, there are those that live in s alt water, on snow or ice, and also live in limestone substrate.
How algae reproduce
Let's deal with the main issue of the article. In nature, algae reproduce in three ways. Each of them has its own characteristics.
- Algae reproduce vegetatively. This is a method of reproduction in which an adult is divided in two or, for example, a kidney is separated from the mother's body. Then the newly formed cells divide into two and four cells, from which an adult algae subsequently grows.
- Asexual reproduction. This type, in which the division of the protoplast occurs inside the algae cell, followed by its release 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, resulting in a zygote, 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 dormant period, which can last up to several months. And others germinate immediately into a new layer or thallus.
Remarkably, each species of algae reproduces differently. This question is studied by the school curriculum. And often students hear a question from a teacher:"How do algae reproduce? Describe the reproduction of algae." It is easy to answer if you study the material in detail.
When algae reproduce asexually. Types of asexual reproduction
This is the easiest option. Asexually or vegetatively, algae reproduce mainly only in favorable conditions for them. This means when the water in the reservoir has a certain temperature and conditions are most conducive to asexual reproduction.
If sudden changes in temperature, pollution or overflow of inhabitants occur in a reservoir or environment, in this case the algae begin to reproduce sexually.
Asexual reproduction can be divided into several types:
- Algae reproduce vegetatively - vegetative cells separate.
- Sporulation. Or in another way, algae reproduce with the help of special cells. These cells are called spores.
When algae reproduce asexually, there is only one parent from which all existing genomes are inherited. But in the case of mutations, the genetic material can change significantly.
Often one organism can reproduce both asexually and vegetatively.
Vegetative propagation of algae
Vegetative reproduction 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 part of the mother's membrane.
Both unicellular and multicellular algae can reproduce vegetatively. Moreover, in unicellular cells, the cell is divided into two, and in multicellular cells, separation occurs in layers or whole thalli, colonies. In filamentous algae, the vegetative mode of reproduction occurs by dividing the threads into their separate fragments.
At the same time, not all algae from the order of colonial representatives can reproduce vegetatively, just like in unicellular, along with the vegetative method of reproduction, there can also be a sexual way.
Brown algae, as mentioned above, reproduce in this way, with the help of special brood twigs. All types of Sargasso breed in the Sargasso Sea in a similar way.
Reproduction by spores
In addition to vegetative propagation, algae reproduce with spores. This is a certain subspecies of asexual reproduction.
Spores are formed in special organs, the so-called sporangia or zoosporangia. When dispersed, the spore begins to germinate and then a new adult independent individual is formed.
Motile spores with flagella capable of locomotion are called zoospores.
The variant of asexual reproduction by spores can be considered on the example of such algae as ulotrix. In conditions of life favorable for her, her fragments are separated from the existing maternal thread, whichcontain controversy. They swim in a free state, then, having attached to an underwater object, they begin to actively divide and form a new thread of algae. It should be noted that this type of algae can simultaneously reproduce both asexually and sexually.
It has been observed that it is possible to stimulate the formation of spores in some types of filamentous algae, for this, an increase in carbon dioxide in the habitat should occur.
The function of asexual reproduction in this case is performed by individuals called sporophytes, that is, those that form spores.
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 that, a zygote is formed, which subsequently becomes the ancestor of a new organism.
Algae have several ways of sexual reproduction:
- Isogamy - implies the fusion of two gametes of the same size and structure.
- Heterogamy. This is the name given to the fusion of two gametes, in which one is larger than the other. Moreover, the one that is larger, 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 two vegetative cells lack flagella.
In primitive algae, the same individual is capable of both sexual and asexual reproduction. The most developed functionperform individuals called gametophytes, that is, forming gametes.
Examples of algae reproduction
Fucus can serve as an example of vegetative propagation of algae. 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 that reproduces both sexually and asexually, with the help of spores (zoospores) that have flagella.
Another example of sexual reproduction is brown algae such as kelp. This species has three modes of sexual reproduction, such as isogamy, heterogamy, oogamy.
Chlorella is a microscopic green algae. It reproduces exclusively asexually, with the help of spores.
Red algae (crimson) reproduce in two ways, one of which is sexual. Its distinctive feature is the formation of male gametes without flagella. At the same time, female gametes remain on the algae, while male gametes are transferred to them with the help of the current.
The importance of algae in nature
Algae are the most numerous and important photosynthetic organisms for the entire planet. Their distribution is so wide that they can be found not only in the seas, oceans, rivers, lakes, but also in small reservoirs, including artificial ones, and even puddles. They can be observed as small greenish spots on the surface of almosteach reservoir. The value of algae in nature is great.
In addition to the fact that they emit a fairly large amount of oxygen, they serve as a habitat for many aquatic animals, participate in the formation of a fertile soil layer. Many algae are eaten, and also serve as the main source in the extraction of special food components. They are also used to prepare various medicines and cosmetics.
Algae are organisms that are unique in their composition and mode of reproduction. They combine several types of reproduction, or rather: sexual, asexual and vegetative. This practically makes them immortal. Moreover, this question is very entertaining, because it is not for nothing that biology teachers around the country are trying to get their students to answer the question: "How do algae reproduce? Describe the reproduction of algae."
