RED ALGAE: CHARACTERISTICS, TAXONOMY, REPRODUCTION, NUTRITION - BIOLOGY - 2024

The red algae or Rhodophytas are a phylum of organisms belonging to the kingdom Protista are characterized by a reddish color due to the presence in their cells of the pigment phycoerythrin.

It was described in 1901 by the Austrian botanist Richard Von Wettstein. It is a phylum that includes a total of two subphiles: Cyanidiophyna and Rhodophytina. The first comprises one class, while the second groups six.

Red algae. Source: By Budhiargomiko, from Wikimedia Commons

They prefer marine habitats, even playing an important role in the formation of coral reefs. Some develop taking as a substrate other algae or the shells of animals such as gastropods (snails) or bivalves (mussels, oysters).

The group of red algae is one of the most studied, as it provides a large number of benefits for humans: in the area of ​​health, cosmetics and biotechnology research.

Taxonomy

Domain: Eukarya

Kingdom: Protista

Edge: Rhodophyte

General characteristics

The phylum Rhodophyta constitutes a fairly large and diverse group of organisms that sometimes have dissimilar characteristics from one another.

From a morphological point of view, these organisms can have different appearances: tree-like branching, cylinder-shaped, or broad laminae. AND

Among the algae's own structures we can mention the thallus, which is the body of the algae itself, and the rhizoid, which is a structure analogous to the roots of plants.

Likewise, some have structures known as tendrils, which allow them to attach to various elements of the habitat or to other algae.

-Cell structure

Regarding its cellular structure, in this edge can be found from unicellular organisms (formed by a single cell), to multicellular organisms (formed by more than two cells).

From this it can be deduced that among the red algae there are some that are microscopic and others that are extremely large. So much so that they even reach a length that exceeds one meter

Cellular wall

The cells of this type of algae are similar to those of plants, since they have an internal structure known as the cell wall. This is made up of a biopolymer known by the name of cellulose.

Likewise, cells have an outer layer, above the cell wall, which is made up of mucilaginous carbohydrates. The function of these within cells is that the tissues are compact.

These cells are not isolated from each other, but because in certain sectors the cell wall of each cell is not fully developed, this causes communication to be established between cells, through which there may be exchange of various substances. This is a differential characteristic of this group.

Chloroplasts

Similarly, among the cellular organelles found in their cells, we can mention chloroplasts, which in the case of red algae have a double membrane and whose thylakoids are not grouped, as in all plants in which they are found. they group together forming structures known as granas.

Centrioles

Likewise, within cells, the significant absence of an important organelle in the mitosis process in other living beings is observed: the centrioles.

Regarding the typical cellular structure, the cells of the Rhodophyas can present a single nucleus, as well as be multinucleated.

Pigments

As is known, different pigments are located within chloroplasts, the best known being chlorophyll. Chlorophyll type a can be found in the chloroplasts that cells of this type of algae have, as well as carotenoids and other accessory pigments such as xanthophylls, phycoerythrin and phycocyanin.

The characteristic reddish color of these algae is due to the green of the chlorophyll being masked by phycoerythrin and phycocyanin, because these pigments absorb blue light, which has greater penetration in water.

Reserve substance

The cells of these algae store a substance known as florid starch, which is unique and exclusive to members of the phylum Rodhophyta.

This carbohydrate is a product of the photosynthesis process and remains stored in your cells. Storage occurs in granules arranged in the cytoplasm, in the vicinity of the chloroplasts.

Mobility

Rhodhophytas are sessile and immobile organisms. They do not present flagella in any of the phases of their life cycle.

Habitat

Most species of red algae are found in marine ecosystems. However, there are a few unique to freshwater ecosystems. They are particularly abundant in temperate and warm waters.

There are species that have the ability to bind calcium carbonate, which makes them essential members of coral reefs.

Nutrition

Members of the phylum Rodhophyta are autotrophs. This means that they are capable of synthesizing their own nutrients, specifically through the process of photosynthesis.

Red algae carry out oxygenic photosynthesis, where water is the main electron donor, thus releasing oxygen as a by-product. This type of photosynthesis is made up of two well differentiated stages: the photochemical and the biosynthetic.

Photochemical stage

The substrates that are required for this phase to take place are water, ADP (Adenosine diphosphate) and NADP (Nicotinamine diphosphate). During this stage the first thing that happens is the absorption of sunlight by chlorophyll molecules.

Product of the energy that is released there, the water molecule is separated, the oxygen being released. It also donates 2 e ^- which after passing through the electron transport chain generate NADPH + H ⁺.

Biosynthetic stage

The substrates that are needed for this stage to occur are: carbon dioxide (CO2), ATP and NADPH. It is also known as the Calvim Cycle or the Pentoses Cycle.

This is a cyclical process that CO2 enters, as well as ATP and NADP obtained from the phosotynthetic stage. In this cycle, through a series of reactions, the reserve substance of the red algae, the floridian starch, NADP ⁺ and ADP is generated.

Reproduction

Red algae have two types of reproduction: asexual and sexual. Regarding asexual reproduction, it can be through two processes: sporulation or thallus fragmentation.

Asexual reproduction

In the case of sporulation, monospores are produced in each cell of certain branches. Each spore is capable of creating a new living being.

Likewise, in algae that reproduce asexually by fragmentation of the thallus (body of the algae), a part of the algae separates from the body and from this a fully functional adult organism can be generated.

Asexual reproduction is a process in which a parent produces descendants exactly like him, from a physical and genetic point of view.

Sexual reproduction

Sexual reproduction occurs through a process known as oogamy. This consists of the fertilization of a female gamete that is not mobile, by a mobile male gamete.

As can be expected, as this is a process of sexual reproduction, the exchange of genetic material between both gametes occurs.

The female gamete of Rodhophytas is large and immobile, while the male gamete is small and moves carried by the water current, since it does not have a flagellum.

The male gamete, known as spermatium, reaches the female gametangium and fertilizes it. It has a male gamete receptor filament called trichogyny.

Lifecycle

To understand the life cycle of red algae (one of the most complex in nature), it is necessary to know and understand two terms:

• Gametophyte: it is the haploid sexual generation (with half the genetic load of the species)
• Sporophyte: it is the diploid phase (with the complete genetic load of the species) multicellular of algae and plants that have cycles with alternating generations.

Once this is established, it can be said that Rodhophytas can have two types of biological cycles: digenetic and trigenetic. This depends on the complexity of the species.

Digestive cycle

It is presented, for example, by the species Phophyra linearis, a type of red algae. In this type of cycle there are two generations that occur: gametophyte and sporophyte. The first is the dominant.

The gametophyte produces gametes, female and male. When fertilization occurs, the sporophyte is generated. This in turn will produce spores from which, in time, new gametophytes will germinate.

It is important to clarify that both the gametophyte and the spores are haploid, while the sporophyte is a diploid structure.

Trigenetic cycle

In this type of cycle there are three generations: carposporophyte, tetraspores and a gametophyte. The carcosporophyte is diploid and the tetraspores and gametophyte are haploid.

The tetrasporphyte, through the meiosis process, produces spores, which are grouped four by four (tetraspores). Each spore produces a gametophyte.

As expected, each gametophyte generates immobile female gametes and mobile male gametes. These are released, while the female remain in the gametophyte.

Life cycle of a red alga (Chondrus crispus). Source: Chondrus at en.wikipedia, from Wikimedia Commons

Once fertilization occurs, a diploid zygote is generated, known as carposporophyte, which develops on the female gametophyte. This structure produces spores known as cascospores, which germinate and originate the first generation of the cycle, the tetrasporophyte.

Applications

Red algae have been used by humans for hundreds of years, due to the many benefits and uses they have.

They are source of agar

Agar is a gelatinous substance that is used in various fields. In microbiology it is used as a culture medium, in the gastronomic area as a gelling agent and in molecular biology it is used in the agarose gel electrophoresis process and in molecular exclusion chromatography.

Red algae contain a large amount of mucilage. These are the basis for the production of agar.

The process for obtaining the agar is quite simple. First of all, they must be dried in the sun. Subsequently submerged in hot water with some alkaline solution. Then they are washed very well with cold water and sulfuric acid is added to make them lose alkalinity and sodium hypochlorite to whiten them.

They are cooked for two hours, at the end of which the product is extracted. This is subjected to a filtering process. Once the filtrate is obtained, the gelling process is carried out, cooling it to different temperatures. It is then pressed and dried using hot air. Finally it is ground and sifted to be packed.

Health benefits

Red algae are a source of numerous compounds that are very useful in the pharmaceutical industry.

First of all, they are a recognized source of iodine. This is an element that has been used for years to treat conditions of the thyroid gland such as goiter.

Similarly, red algae have proven antioxidant and antiviral effects. In the first place, they are capable of reducing the negative effect of free radicals in cells, in addition to stimulating the production of interferon in order to fight against viral agents that enter the body.

Recent studies have shown that red algae have a certain degree of participation in blocking an enzyme that intervenes in the process of arterial hypertension, thus managing to control this pathology.

Likewise, red algae are rich in calcium and vitamin K. Calcium is an important supplement in the prevention of a disease that affects more people every day: osteoporosis. Vitamin K has important properties that have to do with the blood clotting process and thus prevent bleeding.

Cosmetic industry

Red algae are widely used in the cosmetic industry due to its components and the potential benefits of these.

For example, the algae of the Chondrus crispus species are used in the production of moisturizing, protective and emollient products. Likewise, another species, Gracilaria verrucosa, is very rich in agar, which is used in the production of various beauty products.

Similarly, Asparagopsis armata, another species of red algae, is widely used in the production of moisturizing and regenerating products, as well as in products for sensitive skin and products for children.

References

1. Adl, SM et al. 2012. The revised classification of eukaryotes. Journal of Eukaryotic Microbiology, 59 (5), 429-514
2. Freshwater, W. (2009). Rhodophyta. Red algae. Retrieved from: tolweb.org/Rhodophyta
3. Mouritsen, O. (2013). The science of red seaweeds. Retrieved from: americanscientist.org/article/the-science-of-seaweeds.
4. Quitral, V., Morales, C., Sepúlveda, M. and Shwartz M. (2012). Nutritional and healthy properties of seaweed and its potential as a functional ingredient. Chilean nutrition magazine. 39 (4). 196-202
5. Souza B, Cerqueira MA, Martins JT, Quintas MAC, Ferreira AC, Teixeira JA, Vicente AA. Antioxidant potential of two red seaweeds from Brazilian coasts. J Agric Food Chem 2011; 59: 5589-94.
6. Yoon, Hwan Su, KM Müller, RG Sheath, FD Ott, and D. Bhattacharya. (2006). Defining the major lineages of red algae (Rhodophyta). J. Phycol. 42: 482-492