Algae belong to a grouping, not belonging to a systematic taxon, represented by organisms of plant structure, autotrophic, unicellular or multi-cellular, which produce chemical energy by photosynthesis, generating oxygen and which do not present a differentiation in real tissues.
Table of Contents
- 1 Uses
- 2 The “blue algae” and the real algae
- 3 Common characteristics
- 4 Classification
- 5 Morphology
- 6 Unicellular algae
- 7 Multi-cellular algae
- 8 What is the best algae to buy?
- 9 Best Algae Reviews
- 10 Offers and Discounts
- 11 Cheap Algae
- 12 Buy Algae Online
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- 13 Best Algae 2024
- 14 References
Uses
Some algae are used in herbal medicine; among these we can remember the drone, the sea oak and the peacock tail. Some cyanobacteria (spirulina, klamath) with the name of “micro-algae” are also used.
The agar agar, obtained from various species of rhodophytes, is the source of the agarose used for microbiological culture plates.
Many algae are also used in vegan and macrobiotic cuisine; among these are of considerable importance: kombu, arame, dulse, hijiki, nori (the latter used to make the famous sushi), wakame. On the other hand, algae have a long tradition of food consumption also in northern European countries and along the Mediterranean coast. In Italy in particular, the tradition of Zeppolelle di mare, pancakes prepared with green seaweed lettuce, is still alive. Until 20 years ago, in Sicily, in the Catania area, the “mauru” seaweed was collected and sold in special kiosks and eaten raw seasoned with lemon.
Some algae produce dimethyl sulphide, a substance that condenses water vapour particles, causing the formation of clouds and fighting the greenhouse effect.
From the algae fibre it is possible to obtain paper, which can be made without the use of chlorine. The name of this product has been registered as Shiro algae paper.
From brown algae it is possible to extract, through a chemical process of cold micronization, substances able to improve the nutrition of plants known as algal biostimulants.
In the course of time, and in the evolution of the scientific systematization of living beings, within this grouping different systematic groups have been found with congruent characteristics such as very simple and non-differentiated structure in tissues and very often photosynthetic capacity. The only green algae or chlorophytes, together with the embryophytes, or terrestrial plants, constitute the clade of the green plants, or viridiplantae.
Not all algae use chlorophyll a for photosynthesis. They are a very vast and diversified group of simple, unicellular and multi-cellular autotrophic organisms, such as giant kelps growing up to 65 metres in length. Most are photosynthetic like plants, and “simple” because they do not have the cell typical of terrestrial plants and there are no distinct tissue structures.
Although prokaryotes cyanobacteria are informally referred to as blue-green algae, this use is not further correct, algae is a term now limited only to eukaryotes. All real algae must have a nucleus enclosed in a membrane and plastides bound in one or more membranes. Algae therefore form a paraphiletic and polyphiletic group, as not all of them are descended from a common ancestor, although their plastides appear to have a unique origin.
Algae present a wide range of reproductive strategies, from the simplest, asexual cell division to complex forms of sexual reproduction.
Algae do not have the various structures that characterize terrestrial plants, such as the small leaves (phyllites) of bryophytes, the rhizoids of non-vascular plants and the roots, leaves and other organs found in tracheophytes. Many groups are phototrophic, although some contain members that are mixotrophic. Some unicellular species depend entirely on energy sources other than light and have little or no photosynthetic apparatus.
Almost all algae have a photosynthetic apparatus ultimately derived from cyanobacteria, and produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfobacteria. Filamentous fossilized algae from the Vindhya basin were dated 1.6-1.7 billion years ago.
The “blue algae” and the real algae
Despite the ambiguity of the term, in the past also the so-called “cyanoficee” or “blue algae” were considered algae, unicellular organisms (which, however, can unite in colonies) prokaryotes and autotrophs, today more correctly inserted in the taxon of cyanobacteria belonging to the Bacteria kingdom (and domain).
The real algae are therefore the eukaryotic algae, which traditionally belong to the protists’ kingdom and can be both unicellular and multi-cellular. However, this grouping is certainly paraphyletic or polyphyletic: the algae have therefore recently been separated into various groups of eukaryotes, although this taxonomy is still very uncertain and varies considerably from author to author.
Common characteristics
In general it can be said that an algae represents a degree, rather than a grouping with taxonomic value. Generally algae do not have the typical structures of terrestrial plants such as rhizoids in non-vascular plants and leaves, roots and other organs that are typical of tracheophytes and have only pseudotextiles (thalli), instead of real distinct tissues formed by cells separated by transverse septa.
Algae are usually photosynthetic, although there are both autotrophic and heterotropic forms and some algae now included in the Archaeplastida clade, such as Chlamydomonas, have sometimes been included among the protozoa. Some unicellular algae depend solely on external energy sources and have a limited or absent photosynthetic apparatus.
The photosynthetic structures of algae derive primarily or secondarily from cyanobacteria and thus produce oxygen from photosynthesis, unlike photosynthetic bacteria such as sulphurous bacteria.
Algae are structurally very simple organisms. In most cases they have a haploid life cycle, others are haplo-diplonti – with an alternation of haploid (sporophyte) and diploid (gametophyte) generations – and only the more evolved algae (such as Bacillariophyta) have a diploid cycle.
In algae the embryo is not protected by cells of maternal origin.
Classification
Algae are widespread in all seas and freshwater locations. Before the appearance of phylogenetic classifications, they were divided into nine Divisions (suffix -phyta) depending on the conformation and the type of photosynthetic pigment used:
- Kingdom: Chromista
- Euglenophyta (euglenoids)
- Chrysophyta (yellow-brown algae)
- Dinophyta (dinoflagellate)
- Bacillariophyta (diatom)
- Phaeophyta (brown algae)
- Cryptophyta
- Kingdom: Plantae
- Chlorophyta (green algae)
- Rhodophyta (red algae)
- Glaucophyta
- Charophyta
Morphology
In algae the morphology varies from single to multi-cellular organisms. They can be presented as:
- flagellated, consisting of a single flagellated cell (e.g. Euglena) or in colony (e.g. Eudorine);
- rhizopodial, consisting of a single cell, without rigid walls, moves by emitting pseudopods;
- capsals, constituted by motionless cells, without wall, aggregated in small colonies wrapped by gelatinous material;
- coccali, formed by only one cell, uninucleated, without scourges, with rigid wall;
siphonal or cenocytic, formed by a single cell, with wall, plurinucleated even of remarkable dimensions; - trichal, pluricellular, formed by uninuclear cells, with simple or branched thallus;
siphonocladali, pluricellular, with plurinuclear cells; - pseudoparenchimatic, with laminar thallus originating from the division of cells into a plane, with one or two layers of cells (e.g. Ulva lactuca).
Unicellular algae
They are located near the surface of the expanses of water, where the light is most abundant. They consist of a single cell, completely self-sufficient. They are part of the phytoplankton, therefore they have a basic role as producers in the food chains, on which the life of aquatic animals depends. They also supply the atmosphere with large quantities of oxygen.
Multi-cellular algae
They generally live in shallow water. They are characterized by particular shapes and different colours due to the accessory pigments, thanks to which they use the whole spectrum of light. The water acts as a filter for the various radiations of the visible spectrum. Green algae are located closer to the surface of the water, absorbing red-orange light that has longer wavelengths and is stopped first. At greater depths there are brown algae that absorb blue-green rays (more penetrating). Even lower down is the habitat of red algae that absorb the faint blue light, which can penetrate even deeper. Multi-cellular algae are aquatic organisms that have poorly differentiated cells that form a tissue, called thallus, without roots, stem, leaves. The algae do not need roots, nor conductive vessels, because they live immersed in water. Each cell can absorb on its own all the nourishment it needs.
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