Add your voice to our December Thunderclap for the new Rainwater Book

Algae

From Appropedia
Jump to: navigation, search

Algae has several applications in sustainability:



Pond scum to the rescue[edit]

More on this soon as J. Craig Ventner is on 'it' and 'on it'. He is working "in the Lab" on this and states that at least ten years are needed for some form of completion of efficient 'manufacturing' and then the harvesting of algal fuel stuffs.

The backbone of the early fact finding section of this Article stems exclusively from the book "The Microbial World : the Fifth Edition" ISBN 0-13-581042-6

by Roger Y. Stanier, John L. Ingraham, Mark L. Wheelis, and Page R. Painter - Authors - 1957 to 1986 - pages 525 to 531 - excerpted below.

Attempts to contact the Publisher and the Authors have been fruitless; I hereby assume the rapp for any flack.

My "verbatum transcription" shows my respect for their Prose [ only just six pages for Algae, two of which contain vastly pertinent and informative micro-photographs ].

Also fruitless is any idea of improving upon their Prose. Enjoy!


THE PROTISTS[edit]

For perspective, 'The Protists' solely occupy Chapter 26 out of the total 33 Chapters in this compendium of microbiology, 'The Microbial World'. { It is only Amazing to Wonder at what those other 32 Chapters enclose - for example Chapter 14 The Archaebacteria }.


'One Step Up' from Bacteria we find The Protists. These are microorganisms with a eukaryotic Cell structure; they perform oxygenic photosynthesis and possess chloroplasts.

Their morphology may be unicellular, filamentous, colonial, or coenocytic, while some may have a plant-like structure. There are numerous transitions between the four types - algae, protozoa, fungi and the slime molds.


The ALGAE[edit]

The primary classification of algae is based upon cellular, not organismal properties: the chemical nature of the wall, if present; the organic reserve materials produced by the Cell; the nature of the photosynthetic pigments; and the nature and arrangement of the flagella borne by motile Cells. In terms of these characters, the algae are arranged in a series of divisions, summarized in Table 26.1.


The Major Groups of Algae[edit]

The Group Names are: Green algae: division Chlorophyta; Euglenids: division Euglenophyta; Dinoflagellates and related forms: division Pyrrophyta; Chrysophytes and diatoms: division Chrysophyta; Brown algae: division Phaeophyta; and Red algae: division Rhodophyta.

The main distinctions are based upon the Pigment systems - the inclusion or not of three chlorophylls, special carotenoids and phycobilins; the composition of the cellulosic Cell wall (Nay, Yay, or double - and with or without algin); and the nature of reserve materials (be they starch, paramylum and fats, starch and oils, leucosin and oils, or laminarin and fats); the number and types of flagella - be there generally two identical flagella per Cell, one two or three flagella per Cell, two flagella dissimilar in form and properties on Cells, two flagella arrangement variable, two flagella of unequal length; or none; and Range of Structure - includes Unicellular, coenocytic, filamentous, and Plant Like Multi-Cellular Forms.


The divisions are not equivalent to one another in terms of the range of organismal structure of their members. For example, the Euglenophyta (euglenid algae) consist entirely of unicellular or simple colonial organisms, while the Phaeophyta (brown algae) consist only of plantlike, multicellular organisms. The largest and most varied group, the Chlorophyta (green algae), from which the higher plants probably originated, spans the full range of organismal diversity, from unicellular organisms to multicellular representatives with a plantlike structure.

The common cellular properties of each algal division suggest that its members, however varied their organismal structure may be, are representatives of a single major evolutionary line. Evolution among the algae thus in general appears to have involved a progressive increase in organismal complexity in the framework of a particular variety of eukaryotic cellular organization. Although it is possible to perceive these evolutionary progressions within each algal division, the relationships between divisions are completely obscure. The primary origin of the algae as a whole is accordingly an unsolved problem.


The Morphology of Algae[edit]

Figure 26.1 : we are presented with a fixed Cell photomicrograph of Euglena gracilis X 1000 [courtesy of G. F. Leedale].

One million nanometers, as well as one thousand microns, total one millimetre. For our purposes the diameter of a small Atom is one Angstrom, or one tenth of a nanometre, across.

This tubular shaped Cell shows as 47 microns in length with a somewhat pointed head end.

Mildly tapering from 10,000 nanometers [nm] to 7,000 nm, it has at its tail end one eyespot [2,000 nm across] and two flagella of unequal length - the longer is a 40 micron long entity - originating within a small cavity of the anterior end of the Cell.

Three other structures are the eukaryotic Cell nucleus at 2,500 nm in diameter, the (single) mitochondrion at 5,000 nm in diameter, and the chloroplasts - which are a tubular 2.5 X 8 microns in dimension - there are upwards of fifteen of them situated along the internal space of the Cell membrane.

For comparison, a model Human Cell is 10 microns [or100,000 Atoms] in diameter.


The Photosynthetic Flagellates[edit]

In many algal divisions, the simplest representatives are motile, unicellular organisms, known collectively as flagellates. The Cell of a typical flagellate, illustrated by Euglena (Figure 26.1 - Euglena gracilis), has a very marked polarity: it is elongated and leaf-shaped, the flagella usually being inserted at the anterior end. In the Euglenophyta, to which Euglena belongs, there are two flagella of unequal length, which originate from a small cavity at the anterior end of the Cell. Many chloroplasts and mitochondria are dispersed throughout the cytoplasm. Near the base of the flagellar apparatus is a specialized organelle, the eyespot, which is red, owing to its content of special carotenoid pigments; the eyespot serves as a photoreceptor to govern the direction and intensity of illumination. The Cell of Euglena, unlike that of many other flagellates, is not enclosed within a rigid wall; its outer layer is an elastic pellicle, which permits considerable changes in shape. Cell division occurs by longitudinal fission [Figure 26.2(a)]. About the time of the onset of mitosis, there is a duplication of the organelles of the Cell, including the flagella and their basal apparatus; cleavage subsequently occurs through the long axis, so that the duplicated organelles are equally partitioned between the two daughter Cells. This mode of Cell division is characteristic of all flagellates except those belonging to the Chlorophyta, such as Chlamydomonas, where each Cell undergoes two or more multiple fissions to produce four smaller daughter Cells, liberated by rupture of the parental Cell wall [Figure 26.2(b)]. Even in such cases, however, the internal divisions take place in the longitudinal plane. As we shall see in a subsequent section, longitudinal division also occurs in the nonphotosynthetic flagellate protozoa and is one of the primary characters that distinguish these organisms from the other major group of protozoa that possess flagellalike locomotor organisms, the ciliates.

Most multicellular algae are immotile in the mature state. However, their reproduction frequently involves the formation and liberation of motile Cells, either asexual reproductive Cells (zoospores) or gametes. Figure 26.3 shows the liberation of zoospores from a Cell of a filamentous member of the Chlorophyta, Ulothrix; it can be seen that these zoospores have a structure very similar to that of the Chlorogonium Cell, illustrated in Figure 26.2(c). The structure of the motile reproductive Cells of multicellular algae thus often reveals their relationship to a particular group of unicellular flagellates.


The Nonflagellate Unicellular Algae[edit]

By no means are all unicellular algae flagellates; several algal divisions also contain unicellular members that are either immotile or possess other means of movement. Many of these unicellular and nonflagellate algae possess strikingly specialized and elaborate Cells, which may be illustrated by considering two groups, the desmids and the diatoms.


The desmids, members of Chlorophyta, have flattened, relatively large Cells, with a characteristic bilateral symmetry (Figure 26.4). Asexual reproduction involves the systhesis of two new half-Cells in the equitorial plane, followed by cleavage between the new half-Cells to produce two bilaterally symmetrical daughters, each of which has a Cell consisting of an"old" and a "new" half.

The diatoms (Figure 26.5), members of the Chrysophyta, have organic walls impregnated with silica. The architecture of the diatom wall is exceedingly complex; it always consists of two overlapping halves, like the halves of a petri dish. Division is longitudinal, each daughter Cell retaining half of the old wall and synthesizing a new half.

Although devoid of flagella, some desmids and diatoms can move slowly over solid substrates. The mechanism of desmid locomotion is not known. The locomotion of diatoms is accomplished by a special modification of ameboid movement. In motile diatoms, there is a narrow longitudinal slot in the wall, known as a raphe, through which the protoplast can make direct contact with the substrate. Movement is brought about by directed cytoplasmic streaming in the canal of the raphe, which pushes the Cell over the substrate.

Many fossil diatoms are known, because the siliceous skeleton of the wall (Figure 26.6) is practically indestructible, and as diatoms are one of the major groups of algae in the Oceans, large fossil deposits of diatom walls have accumulated in many areas. These deposits, known as diatomaceous Earth, have industrial uses as abrasives and filtering agents.


The Natural Distribution of Algae[edit]

Most algae are aquatic organisms that inhabit either fresh water or the Oceans. These aquatic forms are principally free-living, yet certain unicellular marine algae have established durable symbiotic relationships with specific marine invertebrate animals (e.g., sponges, corals, various groups of marine worms) and grow within the Cells of the host Animal. Some terrestrial algae grow in soil or on the bark of trees. Others have established symbiotic relationships with fungi, to produce the curious, two-membered natural associations termed lichens, which form slowly growing colonies in many arid and inhospitable environments, notably on the surface of rocks.

The marine algae play a very important role in the cycles of matter on Earth, since their total mass (and consequently their gross photosynthetic activity) is equal to that of all land plants and is probably much greater. This role is by no means evident, because the most conspicuous of marine algae, the seaweeds, occupy a very limited area of the Oceans, being attached to rocks in the intertidal zone and the shallow coastal waters of the continental shelves. The great bulk of marine algae are uniCellular floating (planktonic) organisms, predominantly diatoms and dinoflagellates, distributed through the surface waters of the Oceans. Although they sometimes become abundant enough to impart a definite brown or red color to local areas of the sea, their density is usually so low that there is no gross sign of their presence. It is the enormous total volume of the Earth's Oceans which makes them the most abundant of all photosynthetic organisms.


The Nutritional Versatility of Algae[edit]

The ability to perform photosynthesis confers on many algae very simple nutrient requirements, in the light they can grow in a completely inorganic medium. However, many algae have specific vitamin requirements, a requirement for Vitamin B12 being particularly common. In Nature the source of these vitamins is probably bacteria that inhabit the same environment. The ability to perform Photosynthesis does not necessarily preclude the utilization of organic compounds as the principal source of carbon and energy, and many algae have a mixotrophic metabolism.

Even when growing in light, certain algae (e.g., the green alga Chlamydobotrys) cannot use CO2 as their principal source of carbon and are therefore dependent on the presence of acetate or some other suitable organic compound to fulfill their carbon requirements. This is caused by a defective photosynthetic machinery: although these algae can obtain energy from their photosynthetic activity, they cannot obtain the reducing power to convert CO2 to organic Cell materials.

Many algae that perform normal photosynthesis in the light, using CO2 as the carbon source, can grow well in the dark at the expense of a variety of organic compounds; such forms can thus shift from photosynthetic to respiratory metabolism, the shift being determined primarily by the presence or absence of light. Algae completely enclosed by Cell walls are osmotrophic and dependent on dissolved organic substrates as energy sources for dark growth. However, a considerable number of unicellular algae that lack a Cell wall, or are not completely enclosed by it, can phagocytize bacteria or other smaller microorganisms and thus employ a phagotrophic mode of nutrition as well. It is not correct, accordingly, to regard the algae as an exclusively photosynthetic group; on the contrary, many of their unicellular members possess and can use the nutritional capacities characteristic of the two major subgroups of nonphotosynthetic eukaryotic protists, the protozoa and fungi.


The Leucophytic Algae[edit]

Loss of the chloroplast from a eukaryotic Cell is an irreversible event, which results in a permanent loss of photosynthetic ability. Such a change appears to have taken place many times among unicellular algal groups with a mixotrophic nutrition, to yield nonpigmented counterparts, which can be clearly recognized on the basis of other Cellular characters as nonphotosynthetic derivatives of algae. Such organisms, known collectively as leucophytes, exist in many flagellate groups, in diatoms, and in nonmotile groups among the green algae. The recognition of leucophytes is often easy, since they may have preserved a virtually complete structural identity with a particular photosynthetic counterpart. In some case, this structural near-identity may include the preservation of vestigial, nonpigmented chloroplasts, as well as a pigmented eyespot. There can be little doubt accordingly that these non-photosynthetic organisms are the close relatives of their structural counterparts among the algae and have arisen from them by a loss of photosynthetic ability in the recent evolutionary past. Indeed, the transition can be demonstrated experimentally in certain strains of Euglena, which yield stable, colorless races when treated with the antibiotic streptomycin or when exposed to small doses of ultraviolet irradiation or to high temperatures (Figure 26.7). These colorless races cannot be distinguished from the naturally occurring nonphotosynthetic euglenid flagellates of the genus Astasia.

The classification of the leucophytes raises a difficult problem. In terms of the Cell structure, they can be easily assigned to a particular division of algae, as nonphotosynthetic representatives, and this classification is no doubt the most satisfactory one. However, since they are nonphotosynthetic unicellular eukaryotic protists, they can alternatively be regarded as protozoa by zoologists. The leucophytes accordingly provide the first and by far the most striking case of a group, or rather a whole series of groups, which are clearly transitional between two major assemblages among the protists.